afl-fuzz.c源码阅读笔记

写在前面

经历过面试以后，开始怀疑自己并不是真的懂fuzzing，所以花了小半个月把afl的源码从头读了一遍，然后直接在源码里写满了注释。

原作者用的都是/**/风格的注释，我用的都是//，所以不会混淆

未来空闲了考虑重新整理一下吧

直接看注释吧

/*
  Copyright 2013 Google LLC All rights reserved.

  Licensed under the Apache License, Version 2.0 (the "License");
  you may not use this file except in compliance with the License.
  You may obtain a copy of the License at:

    http://www.apache.org/licenses/LICENSE-2.0

  Unless required by applicable law or agreed to in writing, software
  distributed under the License is distributed on an "AS IS" BASIS,
  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  See the License for the specific language governing permissions and
  limitations under the License.
*/

/*
   american fuzzy lop - fuzzer code
   --------------------------------

   Written and maintained by Michal Zalewski <lcamtuf@google.com>

   Forkserver design by Jann Horn <jannhorn@googlemail.com>

   This is the real deal: the program takes an instrumented binary and
   attempts a variety of basic fuzzing tricks, paying close attention to
   how they affect the execution path.

*/

#define AFL_MAIN
#include "android-ashmem.h"
#define MESSAGES_TO_STDOUT

#ifndef _GNU_SOURCE
#define _GNU_SOURCE
#endif
#define _FILE_OFFSET_BITS 64

#include "config.h"
#include "types.h"
#include "debug.h"
#include "alloc-inl.h"
#include "hash.h"

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <errno.h>
#include <signal.h>
#include <dirent.h>
#include <ctype.h>
#include <fcntl.h>
#include <termios.h>
#include <dlfcn.h>
#include <sched.h>

#include <sys/wait.h>
#include <sys/time.h>
#include <sys/shm.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/resource.h>
#include <sys/mman.h>
#include <sys/ioctl.h>
#include <sys/file.h>

#if defined(__APPLE__) || defined(__FreeBSD__) || defined (__OpenBSD__)
#  include <sys/sysctl.h>
#endif /* __APPLE__ || __FreeBSD__ || __OpenBSD__ */

/* For systems that have sched_setaffinity; right now just Linux, but one
   can hope... */

#ifdef __linux__
#  define HAVE_AFFINITY 1
#endif /* __linux__ */

/* A toggle to export some variables when building as a library. Not very
   useful for the general public. */

#ifdef AFL_LIB
#  define EXP_ST
#else
#  define EXP_ST static
#endif /* ^AFL_LIB */

/* Lots of globals, but mostly for the status UI and other things where it
   really makes no sense to haul them around as function parameters. */


EXP_ST u8 *in_dir,                    /* Input directory with test cases  */
          *out_file,                  /* File to fuzz, if any             */
          *out_dir,                   /* Working & output directory       */
          *sync_dir,                  /* Synchronization directory        */
          *sync_id,                   /* Fuzzer ID                        */
          *use_banner,                /* Display banner                   */
          *in_bitmap,                 /* Input bitmap                     */
          *doc_path,                  /* Path to documentation dir        */
          *target_path,               /* Path to target binary            */
          *orig_cmdline;              /* Original command line            */

EXP_ST u32 exec_tmout = EXEC_TIMEOUT; /* Configurable exec timeout (ms)   */
static u32 hang_tmout = EXEC_TIMEOUT; /* Timeout used for hang det (ms)   */

EXP_ST u64 mem_limit  = MEM_LIMIT;    /* Memory cap for child (MB)        */

EXP_ST u32 cpu_to_bind = 0;           /* id of free CPU core to bind      */

static u32 stats_update_freq = 1;     /* Stats update frequency (execs)   */

EXP_ST u8  skip_deterministic,        /* Skip deterministic stages?       */
           force_deterministic,       /* Force deterministic stages?      */
           use_splicing,              /* Recombine input files?           */
           dumb_mode,                 /* Run in non-instrumented mode?    */
           score_changed,             /* Scoring for favorites changed?   */
           kill_signal,               /* Signal that killed the child     */
           resuming_fuzz,             /* Resuming an older fuzzing job?   */
           timeout_given,             /* Specific timeout given?          */
           cpu_to_bind_given,         /* Specified cpu_to_bind given?     */
           not_on_tty,                /* stdout is not a tty              */
           term_too_small,            /* terminal dimensions too small    */
           uses_asan,                 /* Target uses ASAN?                */
           no_forkserver,             /* Disable forkserver?              */
           crash_mode,                /* Crash mode! Yeah!                */
           in_place_resume,           /* Attempt in-place resume?         */
           auto_changed,              /* Auto-generated tokens changed?   */
           no_cpu_meter_red,          /* Feng shui on the status screen   */
           no_arith,                  /* Skip most arithmetic ops         */
           shuffle_queue,             /* Shuffle input queue?             */
           bitmap_changed = 1,        /* Time to update bitmap?           */
           qemu_mode,                 /* Running in QEMU mode?            */
           skip_requested,            /* Skip request, via SIGUSR1        */
           run_over10m,               /* Run time over 10 minutes?        */
           persistent_mode,           /* Running in persistent mode?      */
           deferred_mode,             /* Deferred forkserver mode?        */
           fast_cal;                  /* Try to calibrate faster?         */

static s32 out_fd,                    /* Persistent fd for out_file       */
           dev_urandom_fd = -1,       /* Persistent fd for /dev/urandom   */
           dev_null_fd = -1,          /* Persistent fd for /dev/null      */
           fsrv_ctl_fd,               /* Fork server control pipe (write) */
           fsrv_st_fd;                /* Fork server status pipe (read)   */

static s32 forksrv_pid,               /* PID of the fork server           */
           child_pid = -1,            /* PID of the fuzzed program        */
           out_dir_fd = -1;           /* FD of the lock file              */

EXP_ST u8* trace_bits;                /* SHM with instrumentation bitmap  */

EXP_ST u8  virgin_bits[MAP_SIZE],     /* Regions yet untouched by fuzzing */
           virgin_tmout[MAP_SIZE],    /* Bits we haven't seen in tmouts   */
           virgin_crash[MAP_SIZE];    /* Bits we haven't seen in crashes  */

static u8  var_bytes[MAP_SIZE];       /* Bytes that appear to be variable */

static s32 shm_id;                    /* ID of the SHM region             */

static volatile u8 stop_soon,         /* Ctrl-C pressed?                  */
                   clear_screen = 1,  /* Window resized?                  */
                   child_timed_out;   /* Traced process timed out?        */

EXP_ST u32 queued_paths,              /* Total number of queued testcases */
           queued_variable,           /* Testcases with variable behavior */
           queued_at_start,           /* Total number of initial inputs   */
           queued_discovered,         /* Items discovered during this run */
           queued_imported,           /* Items imported via -S            */
           queued_favored,            /* Paths deemed favorable           */
           queued_with_cov,           /* Paths with new coverage bytes    */
           pending_not_fuzzed,        /* Queued but not done yet          */
           pending_favored,           /* Pending favored paths            */
           cur_skipped_paths,         /* Abandoned inputs in cur cycle    */
           cur_depth,                 /* Current path depth               */
           max_depth,                 /* Max path depth                   */
           useless_at_start,          /* Number of useless starting paths */
           var_byte_count,            /* Bitmap bytes with var behavior   */
           current_entry,             /* Current queue entry ID           */
           havoc_div = 1;             /* Cycle count divisor for havoc    */

EXP_ST u64 total_crashes,             /* Total number of crashes          */
           unique_crashes,            /* Crashes with unique signatures   */
           total_tmouts,              /* Total number of timeouts         */
           unique_tmouts,             /* Timeouts with unique signatures  */
           unique_hangs,              /* Hangs with unique signatures     */
           total_execs,               /* Total execve() calls             */
           slowest_exec_ms,           /* Slowest testcase non hang in ms  */
           start_time,                /* Unix start time (ms)             */
           last_path_time,            /* Time for most recent path (ms)   */
           last_crash_time,           /* Time for most recent crash (ms)  */
           last_hang_time,            /* Time for most recent hang (ms)   */
           last_crash_execs,          /* Exec counter at last crash       */
           queue_cycle,               /* Queue round counter              */
           cycles_wo_finds,           /* Cycles without any new paths     */
           trim_execs,                /* Execs done to trim input files   */
           bytes_trim_in,             /* Bytes coming into the trimmer    */
           bytes_trim_out,            /* Bytes coming outa the trimmer    */
           blocks_eff_total,          /* Blocks subject to effector maps  */
           blocks_eff_select;         /* Blocks selected as fuzzable      */

static u32 subseq_tmouts;             /* Number of timeouts in a row      */

static u8 *stage_name = "init",       /* Name of the current fuzz stage   */
          *stage_short,               /* Short stage name                 */
          *syncing_party;             /* Currently syncing with...        */

static s32 stage_cur, stage_max;      /* Stage progression                */
static s32 splicing_with = -1;        /* Splicing with which test case?   */

static u32 master_id, master_max;     /* Master instance job splitting    */

static u32 syncing_case;              /* Syncing with case #...           */

static s32 stage_cur_byte,            /* Byte offset of current stage op  */
           stage_cur_val;             /* Value used for stage op          */

static u8  stage_val_type;            /* Value type (STAGE_VAL_*)         */

static u64 stage_finds[32],           /* Patterns found per fuzz stage    */
           stage_cycles[32];          /* Execs per fuzz stage             */

static u32 rand_cnt;                  /* Random number counter            */

static u64 total_cal_us,              /* Total calibration time (us)      */
           total_cal_cycles;          /* Total calibration cycles         */

static u64 total_bitmap_size,         /* Total bit count for all bitmaps  */
           total_bitmap_entries;      /* Number of bitmaps counted        */

static s32 cpu_core_count;            /* CPU core count                   */

#ifdef HAVE_AFFINITY

static s32 cpu_aff = -1;       	      /* Selected CPU core                */

#endif /* HAVE_AFFINITY */

static FILE* plot_file;               /* Gnuplot output file              */

struct queue_entry {

  u8* fname;                          /* File name for the test case      */
  u32 len;                            /* Input length                     */

  u8  cal_failed,                     /* Calibration failed?              */
      trim_done,                      /* Trimmed?                         */
      was_fuzzed,                     /* Had any fuzzing done yet?        */
      passed_det,                     /* Deterministic stages passed?     */
      has_new_cov,                    /* Triggers new coverage?           */
      var_behavior,                   /* Variable behavior?               */
      favored,                        /* Currently favored?               */
      fs_redundant;                   /* Marked as redundant in the fs?   */

  u32 bitmap_size,                    /* Number of bits set in bitmap     */
      exec_cksum;                     /* Checksum of the execution trace  */

  u64 exec_us,                        /* Execution time (us)              */
      handicap,                       /* Number of queue cycles behind    */
      depth;                          /* Path depth                       */

  u8* trace_mini;                     /* Trace bytes, if kept             */
  u32 tc_ref;                         /* Trace bytes ref count            */

  struct queue_entry *next,           /* Next element, if any             */
                     *next_100;       /* 100 elements ahead               */

};

static struct queue_entry *queue,     /* Fuzzing queue (linked list)      */
                          *queue_cur, /* Current offset within the queue  */
                          *queue_top, /* Top of the list                  */
                          *q_prev100; /* Previous 100 marker              */

static struct queue_entry*
  top_rated[MAP_SIZE];                /* Top entries for bitmap bytes     */

struct extra_data {
  u8* data;                           /* Dictionary token data            */
  u32 len;                            /* Dictionary token length          */
  u32 hit_cnt;                        /* Use count in the corpus          */
};

static struct extra_data* extras;     /* Extra tokens to fuzz with        */
static u32 extras_cnt;                /* Total number of tokens read      */

static struct extra_data* a_extras;   /* Automatically selected extras    */
static u32 a_extras_cnt;              /* Total number of tokens available */

static u8* (*post_handler)(u8* buf, u32* len);

/* Interesting values, as per config.h */

static s8  interesting_8[]  = { INTERESTING_8 };
static s16 interesting_16[] = { INTERESTING_8, INTERESTING_16 };
static s32 interesting_32[] = { INTERESTING_8, INTERESTING_16, INTERESTING_32 };

/* Fuzzing stages */

enum {
  /* 00 */ STAGE_FLIP1,
  /* 01 */ STAGE_FLIP2,
  /* 02 */ STAGE_FLIP4,
  /* 03 */ STAGE_FLIP8,
  /* 04 */ STAGE_FLIP16,
  /* 05 */ STAGE_FLIP32,
  /* 06 */ STAGE_ARITH8,
  /* 07 */ STAGE_ARITH16,
  /* 08 */ STAGE_ARITH32,
  /* 09 */ STAGE_INTEREST8,
  /* 10 */ STAGE_INTEREST16,
  /* 11 */ STAGE_INTEREST32,
  /* 12 */ STAGE_EXTRAS_UO,
  /* 13 */ STAGE_EXTRAS_UI,
  /* 14 */ STAGE_EXTRAS_AO,
  /* 15 */ STAGE_HAVOC,
  /* 16 */ STAGE_SPLICE
};

/* Stage value types */

enum {
  /* 00 */ STAGE_VAL_NONE,
  /* 01 */ STAGE_VAL_LE,
  /* 02 */ STAGE_VAL_BE
};

/* Execution status fault codes */

enum {
  /* 00 */ FAULT_NONE,
  /* 01 */ FAULT_TMOUT,
  /* 02 */ FAULT_CRASH,
  /* 03 */ FAULT_ERROR,
  /* 04 */ FAULT_NOINST,
  /* 05 */ FAULT_NOBITS
};


/* Get unix time in milliseconds */

static u64 get_cur_time(void) {

  struct timeval tv;
  struct timezone tz;

  gettimeofday(&tv, &tz);

  return (tv.tv_sec * 1000ULL) + (tv.tv_usec / 1000);

}


/* Get unix time in microseconds */

static u64 get_cur_time_us(void) {

  struct timeval tv;
  struct timezone tz;

  gettimeofday(&tv, &tz);

  return (tv.tv_sec * 1000000ULL) + tv.tv_usec;

}


/* Generate a random number (from 0 to limit - 1). This may
   have slight bias. */

static inline u32 UR(u32 limit) {

  if (unlikely(!rand_cnt--)) {

    u32 seed[2];

    ck_read(dev_urandom_fd, &seed, sizeof(seed), "/dev/urandom");

    srandom(seed[0]);
    rand_cnt = (RESEED_RNG / 2) + (seed[1] % RESEED_RNG);

  }

  return random() % limit;

}


/* Shuffle an array of pointers. Might be slightly biased. */

static void shuffle_ptrs(void** ptrs, u32 cnt) {

  u32 i;

  for (i = 0; i < cnt - 2; i++) {

    u32 j = i + UR(cnt - i);
    void *s = ptrs[i];
    ptrs[i] = ptrs[j];
    ptrs[j] = s;

  }

}


#ifdef HAVE_AFFINITY

/* Build a list of processes bound to specific cores. Returns -1 if nothing
   can be found. Assumes an upper bound of 4k CPUs. */

static void bind_to_free_cpu(void) {

  DIR* d;
  struct dirent* de;
  cpu_set_t c;

  u8 cpu_used[4096] = { 0 };
  u32 i;

  if (cpu_core_count < 2) return;

  if (getenv("AFL_NO_AFFINITY")) {

    WARNF("Not binding to a CPU core (AFL_NO_AFFINITY set).");
    return;

  }

  d = opendir("/proc");

  if (!d) {

    WARNF("Unable to access /proc - can't scan for free CPU cores.");
    return;

  }

  ACTF("Checking CPU core loadout...");

  /* Introduce some jitter, in case multiple AFL tasks are doing the same
     thing at the same time... */

  usleep(R(1000) * 250);

  /* Scan all /proc/<pid>/status entries, checking for Cpus_allowed_list.
     Flag all processes bound to a specific CPU using cpu_used[]. This will
     fail for some exotic binding setups, but is likely good enough in almost
     all real-world use cases. */

  while ((de = readdir(d))) {

    u8* fn;
    FILE* f;
    u8 tmp[MAX_LINE];
    u8 has_vmsize = 0;

    if (!isdigit(de->d_name[0])) continue;

    fn = alloc_printf("/proc/%s/status", de->d_name);

    if (!(f = fopen(fn, "r"))) {
      ck_free(fn);
      continue;
    }

    while (fgets(tmp, MAX_LINE, f)) {

      u32 hval;

      /* Processes without VmSize are probably kernel tasks. */

      if (!strncmp(tmp, "VmSize:\t", 8)) has_vmsize = 1;

      if (!strncmp(tmp, "Cpus_allowed_list:\t", 19) &&
          !strchr(tmp, '-') && !strchr(tmp, ',') &&
          sscanf(tmp + 19, "%u", &hval) == 1 && hval < sizeof(cpu_used) &&
          has_vmsize) {

        cpu_used[hval] = 1;
        break;

      }

    }

    ck_free(fn);
    fclose(f);

  }

  closedir(d);
  if (cpu_to_bind_given) {

    if (cpu_to_bind >= cpu_core_count)
      FATAL("The CPU core id to bind should be between 0 and %u", cpu_core_count - 1);
    
    if (cpu_used[cpu_to_bind])
      FATAL("The CPU core #%u to bind is not free!", cpu_to_bind);

    i = cpu_to_bind;
    
  } else {

    for (i = 0; i < cpu_core_count; i++) if (!cpu_used[i]) break;
    
  }

  if (i == cpu_core_count) {

    SAYF("\n" cLRD "[-] " cRST
         "Uh-oh, looks like all %u CPU cores on your system are allocated to\n"
         "    other instances of afl-fuzz (or similar CPU-locked tasks). Starting\n"
         "    another fuzzer on this machine is probably a bad plan, but if you are\n"
         "    absolutely sure, you can set AFL_NO_AFFINITY and try again.\n",
         cpu_core_count);

    FATAL("No more free CPU cores");

  }

  OKF("Found a free CPU core, binding to #%u.", i);

  cpu_aff = i;

  CPU_ZERO(&c);
  CPU_SET(i, &c);

  if (sched_setaffinity(0, sizeof(c), &c))
    PFATAL("sched_setaffinity failed");

}

#endif /* HAVE_AFFINITY */

#ifndef IGNORE_FINDS

/* Helper function to compare buffers; returns first and last differing offset. We
   use this to find reasonable locations for splicing two files. */
//定位ptr1和ptr2的第一处差异的偏移和最后一处差异的偏移。
static void locate_diffs(u8* ptr1, u8* ptr2, u32 len, s32* first, s32* last) {

  s32 f_loc = -1;
  s32 l_loc = -1;
  u32 pos;

  for (pos = 0; pos < len; pos++) {

    if (*(ptr1++) != *(ptr2++)) {

      if (f_loc == -1) f_loc = pos;//只在f_loc为初始值-1时更新一次
      l_loc = pos;//无条件更新

    }

  }

  *first = f_loc;
  *last = l_loc;

  return;

}

#endif /* !IGNORE_FINDS */


/* Describe integer. Uses 12 cyclic static buffers for return values. The value
   returned should be five characters or less for all the integers we reasonably
   expect to see. */

static u8* DI(u64 val) {

  static u8 tmp[12][16];
  static u8 cur;

  cur = (cur + 1) % 12;

#define CHK_FORMAT(_divisor, _limit_mult, _fmt, _cast) do { \
    if (val < (_divisor) * (_limit_mult)) { \
      sprintf(tmp[cur], _fmt, ((_cast)val) / (_divisor)); \
      return tmp[cur]; \
    } \
  } while (0)

  /* 0-9999 */
  CHK_FORMAT(1, 10000, "%llu", u64);

  /* 10.0k - 99.9k */
  CHK_FORMAT(1000, 99.95, "%0.01fk", double);

  /* 100k - 999k */
  CHK_FORMAT(1000, 1000, "%lluk", u64);

  /* 1.00M - 9.99M */
  CHK_FORMAT(1000 * 1000, 9.995, "%0.02fM", double);

  /* 10.0M - 99.9M */
  CHK_FORMAT(1000 * 1000, 99.95, "%0.01fM", double);

  /* 100M - 999M */
  CHK_FORMAT(1000 * 1000, 1000, "%lluM", u64);

  /* 1.00G - 9.99G */
  CHK_FORMAT(1000LL * 1000 * 1000, 9.995, "%0.02fG", double);

  /* 10.0G - 99.9G */
  CHK_FORMAT(1000LL * 1000 * 1000, 99.95, "%0.01fG", double);

  /* 100G - 999G */
  CHK_FORMAT(1000LL * 1000 * 1000, 1000, "%lluG", u64);

  /* 1.00T - 9.99G */
  CHK_FORMAT(1000LL * 1000 * 1000 * 1000, 9.995, "%0.02fT", double);

  /* 10.0T - 99.9T */
  CHK_FORMAT(1000LL * 1000 * 1000 * 1000, 99.95, "%0.01fT", double);

  /* 100T+ */
  strcpy(tmp[cur], "infty");
  return tmp[cur];

}


/* Describe float. Similar to the above, except with a single 
   static buffer. */

static u8* DF(double val) {

  static u8 tmp[16];

  if (val < 99.995) {
    sprintf(tmp, "%0.02f", val);
    return tmp;
  }

  if (val < 999.95) {
    sprintf(tmp, "%0.01f", val);
    return tmp;
  }

  return DI((u64)val);

}


/* Describe integer as memory size. */

static u8* DMS(u64 val) {

  static u8 tmp[12][16];
  static u8 cur;

  cur = (cur + 1) % 12;

  /* 0-9999 */
  CHK_FORMAT(1, 10000, "%llu B", u64);

  /* 10.0k - 99.9k */
  CHK_FORMAT(1024, 99.95, "%0.01f kB", double);

  /* 100k - 999k */
  CHK_FORMAT(1024, 1000, "%llu kB", u64);

  /* 1.00M - 9.99M */
  CHK_FORMAT(1024 * 1024, 9.995, "%0.02f MB", double);

  /* 10.0M - 99.9M */
  CHK_FORMAT(1024 * 1024, 99.95, "%0.01f MB", double);

  /* 100M - 999M */
  CHK_FORMAT(1024 * 1024, 1000, "%llu MB", u64);

  /* 1.00G - 9.99G */
  CHK_FORMAT(1024LL * 1024 * 1024, 9.995, "%0.02f GB", double);

  /* 10.0G - 99.9G */
  CHK_FORMAT(1024LL * 1024 * 1024, 99.95, "%0.01f GB", double);

  /* 100G - 999G */
  CHK_FORMAT(1024LL * 1024 * 1024, 1000, "%llu GB", u64);

  /* 1.00T - 9.99G */
  CHK_FORMAT(1024LL * 1024 * 1024 * 1024, 9.995, "%0.02f TB", double);

  /* 10.0T - 99.9T */
  CHK_FORMAT(1024LL * 1024 * 1024 * 1024, 99.95, "%0.01f TB", double);

#undef CHK_FORMAT

  /* 100T+ */
  strcpy(tmp[cur], "infty");
  return tmp[cur];

}


/* Describe time delta. Returns one static buffer, 34 chars of less. */

static u8* DTD(u64 cur_ms, u64 event_ms) {

  static u8 tmp[64];
  u64 delta;
  s32 t_d, t_h, t_m, t_s;

  if (!event_ms) return "none seen yet";

  delta = cur_ms - event_ms;

  t_d = delta / 1000 / 60 / 60 / 24;
  t_h = (delta / 1000 / 60 / 60) % 24;
  t_m = (delta / 1000 / 60) % 60;
  t_s = (delta / 1000) % 60;

  sprintf(tmp, "%s days, %u hrs, %u min, %u sec", DI(t_d), t_h, t_m, t_s);
  return tmp;

}


/* Mark deterministic checks as done for a particular queue entry. We use the
   .state file to avoid repeating deterministic fuzzing when resuming aborted
   scans. */

static void mark_as_det_done(struct queue_entry* q) {

  u8* fn = strrchr(q->fname, '/');
  s32 fd;

  fn = alloc_printf("%s/queue/.state/deterministic_done/%s", out_dir, fn + 1);

  fd = open(fn, O_WRONLY | O_CREAT | O_EXCL, 0600);
  if (fd < 0) PFATAL("Unable to create '%s'", fn);
  close(fd);

  ck_free(fn);

  q->passed_det = 1;

}


/* Mark as variable. Create symlinks if possible to make it easier to examine
   the files. */

static void mark_as_variable(struct queue_entry* q) {

  u8 *fn = strrchr(q->fname, '/') + 1, *ldest;

  ldest = alloc_printf("../../%s", fn);
  fn = alloc_printf("%s/queue/.state/variable_behavior/%s", out_dir, fn);

  if (symlink(ldest, fn)) {

    s32 fd = open(fn, O_WRONLY | O_CREAT | O_EXCL, 0600);
    if (fd < 0) PFATAL("Unable to create '%s'", fn);
    close(fd);

  }

  ck_free(ldest);
  ck_free(fn);

  q->var_behavior = 1;

}


/* Mark / unmark as redundant (edge-only). This is not used for restoring state,
   but may be useful for post-processing datasets. */

static void mark_as_redundant(struct queue_entry* q, u8 state) {

  u8* fn;
  s32 fd;

  if (state == q->fs_redundant) return;

  q->fs_redundant = state;

  fn = strrchr(q->fname, '/');
  fn = alloc_printf("%s/queue/.state/redundant_edges/%s", out_dir, fn + 1);

  if (state) {

    fd = open(fn, O_WRONLY | O_CREAT | O_EXCL, 0600);
    if (fd < 0) PFATAL("Unable to create '%s'", fn);
    close(fd);

  } else {

    if (unlink(fn)) PFATAL("Unable to remove '%s'", fn);

  }

  ck_free(fn);

}


/* Append new test case to the queue. */

static void add_to_queue(u8* fname, u32 len, u8 passed_det) {

  struct queue_entry* q = ck_alloc(sizeof(struct queue_entry));

  q->fname        = fname;
  q->len          = len;
  q->depth        = cur_depth + 1;
  q->passed_det   = passed_det;

  if (q->depth > max_depth) max_depth = q->depth;

  if (queue_top) {

    queue_top->next = q;
    queue_top = q;

  } else q_prev100 = queue = queue_top = q;

  queued_paths++;
  pending_not_fuzzed++;

  cycles_wo_finds = 0;

  /* Set next_100 pointer for every 100th element (index 0, 100, etc) to allow faster iteration. */
  if ((queued_paths - 1) % 100 == 0 && queued_paths > 1) {

    q_prev100->next_100 = q;
    q_prev100 = q;

  }

  last_path_time = get_cur_time();

}


/* Destroy the entire queue. */

EXP_ST void destroy_queue(void) {

  struct queue_entry *q = queue, *n;

  while (q) {

    n = q->next;
    ck_free(q->fname);
    ck_free(q->trace_mini);
    ck_free(q);
    q = n;

  }

}


/* Write bitmap to file. The bitmap is useful mostly for the secret
   -B option, to focus a separate fuzzing session on a particular
   interesting input without rediscovering all the others. */

EXP_ST void write_bitmap(void) {

  u8* fname;
  s32 fd;

  if (!bitmap_changed) return;
  bitmap_changed = 0;

  fname = alloc_printf("%s/fuzz_bitmap", out_dir);
  fd = open(fname, O_WRONLY | O_CREAT | O_TRUNC, 0600);

  if (fd < 0) PFATAL("Unable to open '%s'", fname);

  ck_write(fd, virgin_bits, MAP_SIZE, fname);

  close(fd);
  ck_free(fname);

}


/* Read bitmap from file. This is for the -B option again. */

EXP_ST void read_bitmap(u8* fname) {

  s32 fd = open(fname, O_RDONLY);

  if (fd < 0) PFATAL("Unable to open '%s'", fname);

  ck_read(fd, virgin_bits, MAP_SIZE, fname);

  close(fd);

}


/* Check if the current execution path brings anything new to the table.
   Update virgin bits to reflect the finds. Returns 1 if the only change is
   the hit-count for a particular tuple; 2 if there are new tuples seen. 
   Updates the map, so subsequent calls will always return 0.

   This function is called after every exec() on a fairly large buffer, so
   it needs to be fast. We do this in 32-bit and 64-bit flavors. */

static inline u8 has_new_bits(u8* virgin_map) {
//某个特定tuple的命中数发生变化--返回1;有新的tuples--返回2;
#ifdef WORD_SIZE_64

  u64* current = (u64*)trace_bits;
  u64* virgin  = (u64*)virgin_map;

  u32  i = (MAP_SIZE >> 3);

#else

  u32* current = (u32*)trace_bits;
  u32* virgin  = (u32*)virgin_map;

  u32  i = (MAP_SIZE >> 2);

#endif /* ^WORD_SIZE_64 */

  u8   ret = 0;

  while (i--) {

    /* Optimize for (*current & *virgin) == 0 - i.e., no bits in current bitmap
       that have not been already cleared from the virgin map - since this will
       almost always be the case. */

    if (unlikely(*current) && unlikely(*current & *virgin)) {

      if (likely(ret < 2)) {

        u8* cur = (u8*)current;
        u8* vir = (u8*)virgin;

        /* Looks like we have not found any new bytes yet; see if any non-zero
           bytes in current[] are pristine in virgin[]. */

#ifdef WORD_SIZE_64

        if ((cur[0] && vir[0] == 0xff) || (cur[1] && vir[1] == 0xff) ||
            (cur[2] && vir[2] == 0xff) || (cur[3] && vir[3] == 0xff) ||
            (cur[4] && vir[4] == 0xff) || (cur[5] && vir[5] == 0xff) ||
            (cur[6] && vir[6] == 0xff) || (cur[7] && vir[7] == 0xff)) ret = 2;
        else ret = 1;

#else

        if ((cur[0] && vir[0] == 0xff) || (cur[1] && vir[1] == 0xff) ||
            (cur[2] && vir[2] == 0xff) || (cur[3] && vir[3] == 0xff)) ret = 2;
        else ret = 1;

#endif /* ^WORD_SIZE_64 */

      }

      *virgin &= ~*current;

    }

    current++;
    virgin++;

  }

  if (ret && virgin_map == virgin_bits) bitmap_changed = 1;

  return ret;

}


/* Count the number of bits set in the provided bitmap. Used for the status
   screen several times every second, does not have to be fast. */

static u32 count_bits(u8* mem) {

  u32* ptr = (u32*)mem;
  u32  i   = (MAP_SIZE >> 2);
  u32  ret = 0;

  while (i--) {

    u32 v = *(ptr++);

    /* This gets called on the inverse, virgin bitmap; optimize for sparse
       data. */

    if (v == 0xffffffff) {
      ret += 32;
      continue;
    }

    v -= ((v >> 1) & 0x55555555);
    v = (v & 0x33333333) + ((v >> 2) & 0x33333333);
    ret += (((v + (v >> 4)) & 0xF0F0F0F) * 0x01010101) >> 24;

  }

  return ret;

}


#define FF(_b)  (0xff << ((_b) << 3))

/* Count the number of bytes set in the bitmap. Called fairly sporadically,
   mostly to update the status screen or calibrate and examine confirmed
   new paths. */

static u32 count_bytes(u8* mem) {

  u32* ptr = (u32*)mem;
  u32  i   = (MAP_SIZE >> 2);
  u32  ret = 0;

  while (i--) {

    u32 v = *(ptr++);

    if (!v) continue;
    if (v & FF(0)) ret++;
    if (v & FF(1)) ret++;
    if (v & FF(2)) ret++;
    if (v & FF(3)) ret++;

  }

  return ret;

}


/* Count the number of non-255 bytes set in the bitmap. Used strictly for the
   status screen, several calls per second or so. */

static u32 count_non_255_bytes(u8* mem) {

  u32* ptr = (u32*)mem;
  u32  i   = (MAP_SIZE >> 2);
  u32  ret = 0;

  while (i--) {

    u32 v = *(ptr++);

    /* This is called on the virgin bitmap, so optimize for the most likely
       case. */

    if (v == 0xffffffff) continue;
    if ((v & FF(0)) != FF(0)) ret++;
    if ((v & FF(1)) != FF(1)) ret++;
    if ((v & FF(2)) != FF(2)) ret++;
    if ((v & FF(3)) != FF(3)) ret++;

  }

  return ret;

}


/* Destructively simplify trace by eliminating hit count information
   and replacing it with 0x80 or 0x01 depending on whether the tuple
   is hit or not. Called on every new crash or timeout, should be
   reasonably fast. */
//通过消除命中计数信息破坏性简化trace,无命中则字节值为0x00替换成0x01,[0x01,0xFF]次命中的字节一律替换成0x80
static const u8 simplify_lookup[256] = { 

  [0]         = 1,
  [1 ... 255] = 128

};

#ifdef WORD_SIZE_64

static void simplify_trace(u64* mem) {

  u32 i = MAP_SIZE >> 3;

  while (i--) {

    /* Optimize for sparse bitmaps. */

    if (unlikely(*mem)) {

      u8* mem8 = (u8*)mem;

      mem8[0] = simplify_lookup[mem8[0]];
      mem8[1] = simplify_lookup[mem8[1]];
      mem8[2] = simplify_lookup[mem8[2]];
      mem8[3] = simplify_lookup[mem8[3]];
      mem8[4] = simplify_lookup[mem8[4]];
      mem8[5] = simplify_lookup[mem8[5]];
      mem8[6] = simplify_lookup[mem8[6]];
      mem8[7] = simplify_lookup[mem8[7]];

    } else *mem = 0x0101010101010101ULL;

    mem++;

  }

}

#else

static void simplify_trace(u32* mem) {

  u32 i = MAP_SIZE >> 2;

  while (i--) {

    /* Optimize for sparse bitmaps. */

    if (unlikely(*mem)) {//unlikely不影响条件判断,而是表示这个条件判断通常不成立,即通常为false or 0,即更有可能执行else的语句,会指导编译器将else的语句编译到前面来

      u8* mem8 = (u8*)mem;

      mem8[0] = simplify_lookup[mem8[0]];//simplify_lookup 通过消除命中计数信息破坏性简化trace,无命中则字节值为0x00替换成0x01,[0x01,0xFF]次命中的字节一律替换成0x80
      mem8[1] = simplify_lookup[mem8[1]];
      mem8[2] = simplify_lookup[mem8[2]];
      mem8[3] = simplify_lookup[mem8[3]];

    } else *mem = 0x01010101;

    mem++;
  }

}

#endif /* ^WORD_SIZE_64 */


/* Destructively classify execution counts in a trace. This is used as a
   preprocessing step for any newly acquired traces. Called on every exec,
   must be fast. */

static const u8 count_class_lookup8[256] = {

  [0]           = 0,
  [1]           = 1,
  [2]           = 2,
  [3]           = 4,
  [4 ... 7]     = 8,
  [8 ... 15]    = 16,
  [16 ... 31]   = 32,
  [32 ... 127]  = 64,
  [128 ... 255] = 128

};
//AFL在统计一条路径的执行次数时，
static u16 count_class_lookup16[65536];


EXP_ST void init_count_class16(void) {
//count_class_lookup8支持用一个字节表示路径的执行次数，并通过lookup8数组进行快速规整；lookup16将执行次数扩展成2个字节，因此用lookup8的规整逻辑，创建一个lookup16，即用lookup8的规整逻辑分别设置高8位和低8位
  u32 b1, b2;

  for (b1 = 0; b1 < 256; b1++) 
    for (b2 = 0; b2 < 256; b2++)
      count_class_lookup16[(b1 << 8) + b2] = 
        (count_class_lookup8[b1] << 8) |
        count_class_lookup8[b2];

}


#ifdef WORD_SIZE_64

static inline void classify_counts(u64* mem) {

  u32 i = MAP_SIZE >> 3;

  while (i--) {

    /* Optimize for sparse bitmaps. */

    if (unlikely(*mem)) {

      u16* mem16 = (u16*)mem;

      mem16[0] = count_class_lookup16[mem16[0]];
      mem16[1] = count_class_lookup16[mem16[1]];
      mem16[2] = count_class_lookup16[mem16[2]];
      mem16[3] = count_class_lookup16[mem16[3]];

    }

    mem++;

  }

}

#else

static inline void classify_counts(u32* mem) {

  u32 i = MAP_SIZE >> 2;

  while (i--) {

    /* Optimize for sparse bitmaps. */

    if (unlikely(*mem)) {

      u16* mem16 = (u16*)mem;

      mem16[0] = count_class_lookup16[mem16[0]];
      mem16[1] = count_class_lookup16[mem16[1]];

    }

    mem++;

  }

}

#endif /* ^WORD_SIZE_64 */


/* Get rid of shared memory (atexit handler). */

static void remove_shm(void) {

  shmctl(shm_id, IPC_RMID, NULL);

}


/* Compact trace bytes into a smaller bitmap. We effectively just drop the
   count information here. This is called only sporadically, for some
   new paths. */

static void minimize_bits(u8* dst, u8* src) {

  u32 i = 0;

  while (i < MAP_SIZE) {

    if (*(src++)) dst[i >> 3] |= 1 << (i & 7);
    i++;

  }

}


/* When we bump into a new path, we call this to see if the path appears
   more "favorable" than any of the existing ones. The purpose of the
   "favorables" is to have a minimal set of paths that trigger all the bits
   seen in the bitmap so far, and focus on fuzzing them at the expense of
   the rest.

   The first step of the process is to maintain a list of top_rated[] entries
   for every byte in the bitmap. We win that slot if there is no previous
   contender, or if the contender has a more favorable speed x size factor. */

static void update_bitmap_score(struct queue_entry* q) {

  u32 i;
  u64 fav_factor = q->exec_us * q->len;//因子fav_factor用时间×长度作为评判一个testcase的依据

  /* For every byte set in trace_bits[], see if there is a previous winner,
     and how it compares to us. */

  for (i = 0; i < MAP_SIZE; i++)

    if (trace_bits[i]) {

       if (top_rated[i]) {//如果top_rated中已经存在与trace_bits的第i位对应的case,就进入下面的比较逻辑,如果没有,就直接在top_rate[i]中插入q

         /* Faster-executing or smaller test cases are favored. */

         if (fav_factor > top_rated[i]->exec_us * top_rated[i]->len) continue;//更快执行或者更小的测试用例更受afl欢迎.如果此处fav_factor更大,afl会直接跳过这一case,直接计算下一个case.但这里这种简陋的策略,有改进的空间吗

         /* Looks like we're going to win. Decrease ref count for the
            previous winner, discard its trace_bits[] if necessary. */

         if (!--top_rated[i]->tc_ref) {//trace bytes ref count.  如果--tc_ref==0,说明这一bit上空出来了
           ck_free(top_rated[i]->trace_mini);//trace_mini:trace bytes, if kept
           top_rated[i]->trace_mini = 0;
         }

       }

       /* Insert ourselves as the new winner. */

       top_rated[i] = q;
       q->tc_ref++;

       if (!q->trace_mini) {
         q->trace_mini = ck_alloc(MAP_SIZE >> 3);//trace_mini中每个位对应bitmap中的一个byte  就是trace_bits变trace_bytes
         minimize_bits(q->trace_mini, trace_bits);//把trace_bits存进更紧凑的trace_bytes里,用计数的方式记录原trace_bits中的每个byte中多少个bits置1
       }

       score_changed = 1;

     }

}


/* The second part of the mechanism discussed above is a routine that
   goes over top_rated[] entries, and then sequentially grabs winners for
   previously-unseen bytes (temp_v) and marks them as favored, at least
   until the next run. The favored entries are given more air time during
   all fuzzing steps. */

static void cull_queue(void) {

  struct queue_entry* q;
  static u8 temp_v[MAP_SIZE >> 3];
  u32 i;

  if (dumb_mode || !score_changed) return;//执行下列逻辑的前提是运行在非dumb mode并且score有被更新过

  score_changed = 0;

  memset(temp_v, 255, MAP_SIZE >> 3);//把temp_v的(1<<13)字节塞满0xFF

  queued_favored  = 0;
  pending_favored = 0;

  q = queue;

  while (q) {
    q->favored = 0;
    q = q->next;
  }

  /* Let's see if anything in the bitmap isn't captured in temp_v.
     If yes, and if it has a top_rated[] contender, let's use it. */

  for (i = 0; i < MAP_SIZE; i++)
    if (top_rated[i] && (temp_v[i >> 3] & (1 << (i & 7)))) {//temp_v是以字节为单位存放,&&后的条件判断是判断temp_v中每一bit是否为1  即byte to bit.

      u32 j = MAP_SIZE >> 3;

      /* Remove all bits belonging to the current entry from temp_v. */

      while (j--) 
        if (top_rated[i]->trace_mini[j])
          temp_v[j] &= ~top_rated[i]->trace_mini[j];//trace_mini中所有"1"位,在temp_v中都置0

      top_rated[i]->favored = 1;
      queued_favored++;

      if (!top_rated[i]->was_fuzzed) pending_favored++;//如果还没fuzz过,就给pending_favored计数加一,等待fuzzing

    }

  q = queue;

  while (q) {
    mark_as_redundant(q, !q->favored);//遍历queue,如果这个条目不是favored,就标记为redundant(多余的)
    q = q->next;
  }

}


/* Configure shared memory and virgin_bits. This is called at startup. */

EXP_ST void setup_shm(void) {

  u8* shm_str;

  if (!in_bitmap) memset(virgin_bits, 255, MAP_SIZE);

  memset(virgin_tmout, 255, MAP_SIZE);
  memset(virgin_crash, 255, MAP_SIZE);

  shm_id = shmget(IPC_PRIVATE, MAP_SIZE, IPC_CREAT | IPC_EXCL | 0600);//shmget用来创建共享内存,int shmget(key_t key, size_t size, int shmflg)
//reference:https://www.cnblogs.com/52php/p/5861372.html  shm相关操作
  if (shm_id < 0) PFATAL("shmget() failed");

  atexit(remove_shm);

  shm_str = alloc_printf("%d", shm_id);

  /* If somebody is asking us to fuzz instrumented binaries in dumb mode,
     we don't want them to detect instrumentation, since we won't be sending
     fork server commands. This should be replaced with better auto-detection
     later on, perhaps? */
//有趣的问题，dumb模式下fuzz一个插桩后的程序
  if (!dumb_mode) setenv(SHM_ENV_VAR, shm_str, 1);//如果不是dumb mode 就设置SHM_ENV_VAR的环境变量 值为shm_id

  ck_free(shm_str);

  trace_bits = shmat(shm_id, NULL, 0);//启动对该shared memory的访问,并把共享内存连接到当前进程的地址空间,  at=>attach 第二个参数shm_addr指定共享内存在当前进程中的地址,通常为NULL,表示由系统决定共享内存的地址
  
  if (trace_bits == (void *)-1) PFATAL("shmat() failed");

}


/* Load postprocessor, if available. */

static void setup_post(void) {

  void* dh;
  u8* fn = getenv("AFL_POST_LIBRARY");
  u32 tlen = 6;

  if (!fn) return;

  ACTF("Loading postprocessor from '%s'...", fn);

  dh = dlopen(fn, RTLD_NOW);
  if (!dh) FATAL("%s", dlerror());

  post_handler = dlsym(dh, "afl_postprocess");
  if (!post_handler) FATAL("Symbol 'afl_postprocess' not found.");

  /* Do a quick test. It's better to segfault now than later =) */

  post_handler("hello", &tlen);

  OKF("Postprocessor installed successfully.");

}


/* Read all testcases from the input directory, then queue them for testing.
   Called at startup. */

static void read_testcases(void) {

  struct dirent **nl;
  s32 nl_cnt;
  u32 i;
  u8* fn;

  /* Auto-detect non-in-place resumption attempts. */

  fn = alloc_printf("%s/queue", in_dir);
  if (!access(fn, F_OK)) in_dir = fn; else ck_free(fn);

  ACTF("Scanning '%s'...", in_dir);

  /* We use scandir() + alphasort() rather than readdir() because otherwise,
     the ordering  of test cases would vary somewhat randomly and would be
     difficult to control. */
//readdir会导致测试用例的顺序出现很大的随机性？
  nl_cnt = scandir(in_dir, &nl, NULL, alphasort);

  if (nl_cnt < 0) {

    if (errno == ENOENT || errno == ENOTDIR)

      SAYF("\n" cLRD "[-] " cRST
           "The input directory does not seem to be valid - try again. The fuzzer needs\n"
           "    one or more test case to start with - ideally, a small file under 1 kB\n"
           "    or so. The cases must be stored as regular files directly in the input\n"
           "    directory.\n");

    PFATAL("Unable to open '%s'", in_dir);

  }

  if (shuffle_queue && nl_cnt > 1) {

    ACTF("Shuffling queue...");
    shuffle_ptrs((void**)nl, nl_cnt);//洗牌

  }

  for (i = 0; i < nl_cnt; i++) {

    struct stat st;

    u8* fn = alloc_printf("%s/%s", in_dir, nl[i]->d_name);
    u8* dfn = alloc_printf("%s/.state/deterministic_done/%s", in_dir, nl[i]->d_name);

    u8  passed_det = 0;

    free(nl[i]); /* not tracked */
 
    if (lstat(fn, &st) || access(fn, R_OK))//lstat，获取fn指向的testcase，获取状态存入st；同时要求fn可读
      PFATAL("Unable to access '%s'", fn);

    /* This also takes care of . and .. */

    if (!S_ISREG(st.st_mode) || !st.st_size || strstr(fn, "/README.txt")) {//S_ISREG():如果参数(struct stat中的st_mode成员)是常规文件，则计算结果为true。
//如果文件不是常规文件，或者获取不到文件size，或者发现输入时README.txt 就算了
      ck_free(fn);
      ck_free(dfn);
      continue;

    }

    if (st.st_size > MAX_FILE) //testcase太大也不行 MAX_FILE是2^20 但是注释是小于100MB，单位和st_size都是bytes，这100MB怎么算的
      FATAL("Test case '%s' is too big (%s, limit is %s)", fn,
            DMS(st.st_size), DMS(MAX_FILE));

    /* Check for metadata that indicates that deterministic fuzzing
       is complete for this entry. We don't want to repeat deterministic
       fuzzing when resuming aborted scans, because it would be pointless
       and probably very time-consuming. */

    if (!access(dfn, F_OK)) passed_det = 1;//F_OK判断dfn文件是否存在
    ck_free(dfn);

    add_to_queue(fn, st.st_size, passed_det);

  }

  free(nl); /* not tracked */

  if (!queued_paths) {

    SAYF("\n" cLRD "[-] " cRST
         "Looks like there are no valid test cases in the input directory! The fuzzer\n"
         "    needs one or more test case to start with - ideally, a small file under\n"
         "    1 kB or so. The cases must be stored as regular files directly in the\n"
         "    input directory.\n");

    FATAL("No usable test cases in '%s'", in_dir);

  }

  last_path_time = 0;
  queued_at_start = queued_paths;

}


/* Helper function for load_extras. */

static int compare_extras_len(const void* p1, const void* p2) {
  struct extra_data *e1 = (struct extra_data*)p1,
                    *e2 = (struct extra_data*)p2;

  return e1->len - e2->len;
}

static int compare_extras_use_d(const void* p1, const void* p2) {
  struct extra_data *e1 = (struct extra_data*)p1,
                    *e2 = (struct extra_data*)p2;

  return e2->hit_cnt - e1->hit_cnt;
}


/* Read extras from a file, sort by size. */

static void load_extras_file(u8* fname, u32* min_len, u32* max_len,
                             u32 dict_level) {

  FILE* f;
  u8  buf[MAX_LINE];
  u8  *lptr;
  u32 cur_line = 0;

  f = fopen(fname, "r");

  if (!f) PFATAL("Unable to open '%s'", fname);

  while ((lptr = fgets(buf, MAX_LINE, f))) {

    u8 *rptr, *wptr;
    u32 klen = 0;

    cur_line++;

    /* Trim on left and right. */

    while (isspace(*lptr)) lptr++;

    rptr = lptr + strlen(lptr) - 1;
    while (rptr >= lptr && isspace(*rptr)) rptr--;
    rptr++;
    *rptr = 0;

    /* Skip empty lines and comments. */

    if (!*lptr || *lptr == '#') continue;

    /* All other lines must end with '"', which we can consume. */

    rptr--;

    if (rptr < lptr || *rptr != '"')
      FATAL("Malformed name=\"value\" pair in line %u.", cur_line);

    *rptr = 0;

    /* Skip alphanumerics and dashes (label). */

    while (isalnum(*lptr) || *lptr == '_') lptr++;

    /* If @number follows, parse that. */

    if (*lptr == '@') {

      lptr++;
      if (atoi(lptr) > dict_level) continue;
      while (isdigit(*lptr)) lptr++;

    }

    /* Skip whitespace and = signs. */

    while (isspace(*lptr) || *lptr == '=') lptr++;

    /* Consume opening '"'. */

    if (*lptr != '"')
      FATAL("Malformed name=\"keyword\" pair in line %u.", cur_line);

    lptr++;

    if (!*lptr) FATAL("Empty keyword in line %u.", cur_line);

    /* Okay, let's allocate memory and copy data between "...", handling
       \xNN escaping, \\, and \". */

    extras = ck_realloc_block(extras, (extras_cnt + 1) *
               sizeof(struct extra_data));

    wptr = extras[extras_cnt].data = ck_alloc(rptr - lptr);

    while (*lptr) {

      char* hexdigits = "0123456789abcdef";

      switch (*lptr) {

        case 1 ... 31:
        case 128 ... 255:
          FATAL("Non-printable characters in line %u.", cur_line);

        case '\\':

          lptr++;

          if (*lptr == '\\' || *lptr == '"') {
            *(wptr++) = *(lptr++);
            klen++;
            break;
          }

          if (*lptr != 'x' || !isxdigit(lptr[1]) || !isxdigit(lptr[2]))
            FATAL("Invalid escaping (not \\xNN) in line %u.", cur_line);

          *(wptr++) =
            ((strchr(hexdigits, tolower(lptr[1])) - hexdigits) << 4) |
            (strchr(hexdigits, tolower(lptr[2])) - hexdigits);

          lptr += 3;
          klen++;

          break;

        default:

          *(wptr++) = *(lptr++);
          klen++;

      }

    }

    extras[extras_cnt].len = klen;

    if (extras[extras_cnt].len > MAX_DICT_FILE)
      FATAL("Keyword too big in line %u (%s, limit is %s)", cur_line,
            DMS(klen), DMS(MAX_DICT_FILE));

    if (*min_len > klen) *min_len = klen;
    if (*max_len < klen) *max_len = klen;

    extras_cnt++;

  }

  fclose(f);

}


/* Read extras from the extras directory and sort them by size. */

static void load_extras(u8* dir) {

  DIR* d;
  struct dirent* de;
  u32 min_len = MAX_DICT_FILE, max_len = 0, dict_level = 0;
  u8* x;

  /* If the name ends with @, extract level and continue. */

  if ((x = strchr(dir, '@'))) {

    *x = 0;
    dict_level = atoi(x + 1);

  }

  ACTF("Loading extra dictionary from '%s' (level %u)...", dir, dict_level);

  d = opendir(dir);

  if (!d) {

    if (errno == ENOTDIR) {
      load_extras_file(dir, &min_len, &max_len, dict_level);
      goto check_and_sort;
    }

    PFATAL("Unable to open '%s'", dir);

  }

  if (x) FATAL("Dictionary levels not supported for directories.");

  while ((de = readdir(d))) {

    struct stat st;
    u8* fn = alloc_printf("%s/%s", dir, de->d_name);
    s32 fd;

    if (lstat(fn, &st) || access(fn, R_OK))
      PFATAL("Unable to access '%s'", fn);

    /* This also takes care of . and .. */
    if (!S_ISREG(st.st_mode) || !st.st_size) {

      ck_free(fn);
      continue;

    }

    if (st.st_size > MAX_DICT_FILE)
      FATAL("Extra '%s' is too big (%s, limit is %s)", fn,
            DMS(st.st_size), DMS(MAX_DICT_FILE));

    if (min_len > st.st_size) min_len = st.st_size;
    if (max_len < st.st_size) max_len = st.st_size;

    extras = ck_realloc_block(extras, (extras_cnt + 1) *
               sizeof(struct extra_data));

    extras[extras_cnt].data = ck_alloc(st.st_size);
    extras[extras_cnt].len  = st.st_size;

    fd = open(fn, O_RDONLY);

    if (fd < 0) PFATAL("Unable to open '%s'", fn);

    ck_read(fd, extras[extras_cnt].data, st.st_size, fn);

    close(fd);
    ck_free(fn);

    extras_cnt++;

  }

  closedir(d);

check_and_sort:

  if (!extras_cnt) FATAL("No usable files in '%s'", dir);

  qsort(extras, extras_cnt, sizeof(struct extra_data), compare_extras_len);

  OKF("Loaded %u extra tokens, size range %s to %s.", extras_cnt,
      DMS(min_len), DMS(max_len));

  if (max_len > 32)
    WARNF("Some tokens are relatively large (%s) - consider trimming.",
          DMS(max_len));

  if (extras_cnt > MAX_DET_EXTRAS)
    WARNF("More than %u tokens - will use them probabilistically.",
          MAX_DET_EXTRAS);

}




/* Helper function for maybe_add_auto() */

static inline u8 memcmp_nocase(u8* m1, u8* m2, u32 len) {

  while (len--) if (tolower(*(m1++)) ^ tolower(*(m2++))) return 1;
  return 0;

}


/* Maybe add automatic extra. */

static void maybe_add_auto(u8* mem, u32 len) {

  u32 i;

  /* Allow users to specify that they don't want auto dictionaries. */

  if (!MAX_AUTO_EXTRAS || !USE_AUTO_EXTRAS) return;

  /* Skip runs of identical bytes. */

  for (i = 1; i < len; i++)
    if (mem[0] ^ mem[i]) break;

  if (i == len) return;//匹配字典

  /* Reject builtin interesting values. */

  if (len == 2) {

    i = sizeof(interesting_16) >> 1;//i=sizeof({8+16})>>2 => i=12 

    while (i--) 
      if (*((u16*)mem) == interesting_16[i] ||
          *((u16*)mem) == SWAP16(interesting_16[i])) return;//SWAP16 将16位unsigned int的前8位和后8位互换

  }

  if (len == 4) {

    i = sizeof(interesting_32) >> 2;//i = 14

    while (i--) 
      if (*((u32*)mem) == interesting_32[i] ||
          *((u32*)mem) == SWAP32(interesting_32[i])) return;//[31-24][23-16][15-8][7-0]=>[7-0][15-8][23-16][31-24]  SWAP16和SWAP32实现的其实就是大小端转换

  }

  /* Reject anything that matches existing extras. Do a case-insensitive
     match. We optimize by exploiting the fact that extras[] are sorted
     by size. */

  for (i = 0; i < extras_cnt; i++)
    if (extras[i].len >= len) break;//extras按照size排序，用这个loop快速定位len

  for (; i < extras_cnt && extras[i].len == len; i++)
    if (!memcmp_nocase(extras[i].data, mem, len)) return;//不分大小写的字符串匹配

  /* Last but not least, check a_extras[] for matches. There are no
     guarantees of a particular sort order. */

  auto_changed = 1;

  for (i = 0; i < a_extras_cnt; i++) {

    if (a_extras[i].len == len && !memcmp_nocase(a_extras[i].data, mem, len)) {

      a_extras[i].hit_cnt++;
      goto sort_a_extras;

    }

  }

  /* At this point, looks like we're dealing with a new entry. So, let's
     append it if we have room. Otherwise, let's randomly evict some other
     entry from the bottom half of the list. */

  if (a_extras_cnt < MAX_AUTO_EXTRAS) {

    a_extras = ck_realloc_block(a_extras, (a_extras_cnt + 1) *
                                sizeof(struct extra_data));

    a_extras[a_extras_cnt].data = ck_memdup(mem, len);
    a_extras[a_extras_cnt].len  = len;
    a_extras_cnt++;

  } else {

    i = MAX_AUTO_EXTRAS / 2 +
        UR((MAX_AUTO_EXTRAS + 1) / 2);

    ck_free(a_extras[i].data);

    a_extras[i].data    = ck_memdup(mem, len);
    a_extras[i].len     = len;
    a_extras[i].hit_cnt = 0;

  }

sort_a_extras:

  /* First, sort all auto extras by use count, descending order. */

  qsort(a_extras, a_extras_cnt, sizeof(struct extra_data),
        compare_extras_use_d);

  /* Then, sort the top USE_AUTO_EXTRAS entries by size. */

  qsort(a_extras, MIN(USE_AUTO_EXTRAS, a_extras_cnt),
        sizeof(struct extra_data), compare_extras_len);

}


/* Save automatically generated extras. */

static void save_auto(void) {

  u32 i;

  if (!auto_changed) return;//为0就直接返回,非零就继续往下执行
  auto_changed = 0;// 非零就把自己置零

  for (i = 0; i < MIN(USE_AUTO_EXTRAS, a_extras_cnt); i++) {

    u8* fn = alloc_printf("%s/queue/.state/auto_extras/auto_%06u", out_dir, i);
    s32 fd;

    fd = open(fn, O_WRONLY | O_CREAT | O_TRUNC, 0600);

    if (fd < 0) PFATAL("Unable to create '%s'", fn);

    ck_write(fd, a_extras[i].data, a_extras[i].len, fn);

    close(fd);
    ck_free(fn);

  }

}


/* Load automatically generated extras. */

static void load_auto(void) {

  u32 i;

  for (i = 0; i < USE_AUTO_EXTRAS; i++) {

    u8  tmp[MAX_AUTO_EXTRA + 1];
    u8* fn = alloc_printf("%s/.state/auto_extras/auto_%06u", in_dir, i);
    s32 fd, len;

    fd = open(fn, O_RDONLY, 0600);

    if (fd < 0) {

      if (errno != ENOENT) PFATAL("Unable to open '%s'", fn);
      ck_free(fn);
      break;

    }

    /* We read one byte more to cheaply detect tokens that are too
       long (and skip them). */

    len = read(fd, tmp, MAX_AUTO_EXTRA + 1);
//比最大长度多读1位，就能简单的实现"太短不要，太长不要"
    if (len < 0) PFATAL("Unable to read from '%s'", fn);

    if (len >= MIN_AUTO_EXTRA && len <= MAX_AUTO_EXTRA)
      maybe_add_auto(tmp, len);

    close(fd);
    ck_free(fn);

  }

  if (i) OKF("Loaded %u auto-discovered dictionary tokens.", i);
  else OKF("No auto-generated dictionary tokens to reuse.");

}


/* Destroy extras. */

static void destroy_extras(void) {

  u32 i;

  for (i = 0; i < extras_cnt; i++) 
    ck_free(extras[i].data);

  ck_free(extras);

  for (i = 0; i < a_extras_cnt; i++) 
    ck_free(a_extras[i].data);

  ck_free(a_extras);

}


/* Spin up fork server (instrumented mode only). The idea is explained here:

   http://lcamtuf.blogspot.com/2014/10/fuzzing-binaries-without-execve.html

   In essence, the instrumentation allows us to skip execve(), and just keep
   cloning a stopped child. So, we just execute once, and then send commands
   through a pipe. The other part of this logic is in afl-as.h. */

EXP_ST void init_forkserver(char** argv) {

  static struct itimerval it;
  int st_pipe[2], ctl_pipe[2];
  int status;
  s32 rlen;

  ACTF("Spinning up the fork server...");

  if (pipe(st_pipe) || pipe(ctl_pipe)) PFATAL("pipe() failed");

  forksrv_pid = fork();

  if (forksrv_pid < 0) PFATAL("fork() failed");

  if (!forksrv_pid) {

    struct rlimit r;

    /* Umpf. On OpenBSD, the default fd limit for root users is set to
       soft 128. Let's try to fix that... */

    if (!getrlimit(RLIMIT_NOFILE, &r) && r.rlim_cur < FORKSRV_FD + 2) {

      r.rlim_cur = FORKSRV_FD + 2;
      setrlimit(RLIMIT_NOFILE, &r); /* Ignore errors */

    }

    if (mem_limit) {

      r.rlim_max = r.rlim_cur = ((rlim_t)mem_limit) << 20;

#ifdef RLIMIT_AS

      setrlimit(RLIMIT_AS, &r); /* Ignore errors */

#else

      /* This takes care of OpenBSD, which doesn't have RLIMIT_AS, but
         according to reliable sources, RLIMIT_DATA covers anonymous
         maps - so we should be getting good protection against OOM bugs. */

      setrlimit(RLIMIT_DATA, &r); /* Ignore errors */

#endif /* ^RLIMIT_AS */


    }

    /* Dumping cores is slow and can lead to anomalies if SIGKILL is delivered
       before the dump is complete. */

    r.rlim_max = r.rlim_cur = 0;

    setrlimit(RLIMIT_CORE, &r); /* Ignore errors */

    /* Isolate the process and configure standard descriptors. If out_file is
       specified, stdin is /dev/null; otherwise, out_fd is cloned instead. */

    setsid();

    dup2(dev_null_fd, 1);
    dup2(dev_null_fd, 2);

    if (out_file) {

      dup2(dev_null_fd, 0);

    } else {

      dup2(out_fd, 0);
      close(out_fd);

    }

    /* Set up control and status pipes, close the unneeded original fds. */

    if (dup2(ctl_pipe[0], FORKSRV_FD) < 0) PFATAL("dup2() failed");
    if (dup2(st_pipe[1], FORKSRV_FD + 1) < 0) PFATAL("dup2() failed");

    close(ctl_pipe[0]);
    close(ctl_pipe[1]);
    close(st_pipe[0]);
    close(st_pipe[1]);

    close(out_dir_fd);
    close(dev_null_fd);
    close(dev_urandom_fd);
    close(fileno(plot_file));

    /* This should improve performance a bit, since it stops the linker from
       doing extra work post-fork(). */

    if (!getenv("LD_BIND_LAZY")) setenv("LD_BIND_NOW", "1", 0);
//LD_BIND_LAZY 运行时链接程序执行延迟绑定的缺省模式   LD_BIND_NOW覆盖运行时链接程序执行延迟绑定的缺省模式
    /* Set sane defaults for ASAN if nothing else specified. */

    setenv("ASAN_OPTIONS", "abort_on_error=1:"
                           "detect_leaks=0:"
                           "symbolize=0:"
                           "allocator_may_return_null=1", 0);

    /* MSAN is tricky, because it doesn't support abort_on_error=1 at this
       point. So, we do this in a very hacky way. */

    setenv("MSAN_OPTIONS", "exit_code=" STRINGIFY(MSAN_ERROR) ":"
                           "symbolize=0:"
                           "abort_on_error=1:"
                           "allocator_may_return_null=1:"
                           "msan_track_origins=0", 0);

    execv(target_path, argv);

    /* Use a distinctive bitmap signature to tell the parent about execv()
       falling through. */

    *(u32*)trace_bits = EXEC_FAIL_SIG;
    exit(0);

  }

  /* Close the unneeded endpoints. */

  close(ctl_pipe[0]);
  close(st_pipe[1]);

  fsrv_ctl_fd = ctl_pipe[1];
  fsrv_st_fd  = st_pipe[0];

  /* Wait for the fork server to come up, but don't wait too long. */

  it.it_value.tv_sec = ((exec_tmout * FORK_WAIT_MULT) / 1000);
  it.it_value.tv_usec = ((exec_tmout * FORK_WAIT_MULT) % 1000) * 1000;

  setitimer(ITIMER_REAL, &it, NULL);

  rlen = read(fsrv_st_fd, &status, 4);

  it.it_value.tv_sec = 0;
  it.it_value.tv_usec = 0;

  setitimer(ITIMER_REAL, &it, NULL);

  /* If we have a four-byte "hello" message from the server, we're all set.
     Otherwise, try to figure out what went wrong. */

  if (rlen == 4) {
    OKF("All right - fork server is up.");
    return;
  }

  if (child_timed_out)
    FATAL("Timeout while initializing fork server (adjusting -t may help)");

  if (waitpid(forksrv_pid, &status, 0) <= 0)
    PFATAL("waitpid() failed");

  if (WIFSIGNALED(status)) {

    if (mem_limit && mem_limit < 500 && uses_asan) {

      SAYF("\n" cLRD "[-] " cRST
           "Whoops, the target binary crashed suddenly, before receiving any input\n"
           "    from the fuzzer! Since it seems to be built with ASAN and you have a\n"
           "    restrictive memory limit configured, this is expected; please read\n"
           "    %s/notes_for_asan.txt for help.\n", doc_path);

    } else if (!mem_limit) {

      SAYF("\n" cLRD "[-] " cRST
           "Whoops, the target binary crashed suddenly, before receiving any input\n"
           "    from the fuzzer! There are several probable explanations:\n\n"

           "    - The binary is just buggy and explodes entirely on its own. If so, you\n"
           "      need to fix the underlying problem or find a better replacement.\n\n"

#ifdef __APPLE__

           "    - On MacOS X, the semantics of fork() syscalls are non-standard and may\n"
           "      break afl-fuzz performance optimizations when running platform-specific\n"
           "      targets. To fix this, set AFL_NO_FORKSRV=1 in the environment.\n\n"

#endif /* __APPLE__ */

           "    - Less likely, there is a horrible bug in the fuzzer. If other options\n"
           "      fail, poke <lcamtuf@coredump.cx> for troubleshooting tips.\n");

    } else {

      SAYF("\n" cLRD "[-] " cRST
           "Whoops, the target binary crashed suddenly, before receiving any input\n"
           "    from the fuzzer! There are several probable explanations:\n\n"

           "    - The current memory limit (%s) is too restrictive, causing the\n"
           "      target to hit an OOM condition in the dynamic linker. Try bumping up\n"
           "      the limit with the -m setting in the command line. A simple way confirm\n"
           "      this diagnosis would be:\n\n"

#ifdef RLIMIT_AS
           "      ( ulimit -Sv $[%llu << 10]; /path/to/fuzzed_app )\n\n"
#else
           "      ( ulimit -Sd $[%llu << 10]; /path/to/fuzzed_app )\n\n"
#endif /* ^RLIMIT_AS */

           "      Tip: you can use http://jwilk.net/software/recidivm to quickly\n"
           "      estimate the required amount of virtual memory for the binary.\n\n"

           "    - The binary is just buggy and explodes entirely on its own. If so, you\n"
           "      need to fix the underlying problem or find a better replacement.\n\n"

#ifdef __APPLE__

           "    - On MacOS X, the semantics of fork() syscalls are non-standard and may\n"
           "      break afl-fuzz performance optimizations when running platform-specific\n"
           "      targets. To fix this, set AFL_NO_FORKSRV=1 in the environment.\n\n"

#endif /* __APPLE__ */

           "    - Less likely, there is a horrible bug in the fuzzer. If other options\n"
           "      fail, poke <lcamtuf@coredump.cx> for troubleshooting tips.\n",
           DMS(mem_limit << 20), mem_limit - 1);

    }

    FATAL("Fork server crashed with signal %d", WTERMSIG(status));

  }

  if (*(u32*)trace_bits == EXEC_FAIL_SIG)
    FATAL("Unable to execute target application ('%s')", argv[0]);

  if (mem_limit && mem_limit < 500 && uses_asan) {

    SAYF("\n" cLRD "[-] " cRST
           "Hmm, looks like the target binary terminated before we could complete a\n"
           "    handshake with the injected code. Since it seems to be built with ASAN and\n"
           "    you have a restrictive memory limit configured, this is expected; please\n"
           "    read %s/notes_for_asan.txt for help.\n", doc_path);

  } else if (!mem_limit) {

    SAYF("\n" cLRD "[-] " cRST
         "Hmm, looks like the target binary terminated before we could complete a\n"
         "    handshake with the injected code. Perhaps there is a horrible bug in the\n"
         "    fuzzer. Poke <lcamtuf@coredump.cx> for troubleshooting tips.\n");

  } else {

    SAYF("\n" cLRD "[-] " cRST
         "Hmm, looks like the target binary terminated before we could complete a\n"
         "    handshake with the injected code. There are %s probable explanations:\n\n"

         "%s"
         "    - The current memory limit (%s) is too restrictive, causing an OOM\n"
         "      fault in the dynamic linker. This can be fixed with the -m option. A\n"
         "      simple way to confirm the diagnosis may be:\n\n"

#ifdef RLIMIT_AS
         "      ( ulimit -Sv $[%llu << 10]; /path/to/fuzzed_app )\n\n"
#else
         "      ( ulimit -Sd $[%llu << 10]; /path/to/fuzzed_app )\n\n"
#endif /* ^RLIMIT_AS */

         "      Tip: you can use http://jwilk.net/software/recidivm to quickly\n"
         "      estimate the required amount of virtual memory for the binary.\n\n"

         "    - Less likely, there is a horrible bug in the fuzzer. If other options\n"
         "      fail, poke <lcamtuf@coredump.cx> for troubleshooting tips.\n",
         getenv(DEFER_ENV_VAR) ? "three" : "two",
         getenv(DEFER_ENV_VAR) ?
         "    - You are using deferred forkserver, but __AFL_INIT() is never\n"
         "      reached before the program terminates.\n\n" : "",
         DMS(mem_limit << 20), mem_limit - 1);

  }

  FATAL("Fork server handshake failed");

}


/* Execute target application, monitoring for timeouts. Return status
   information. The called program will update trace_bits[]. */

static u8 run_target(char** argv, u32 timeout) {

  static struct itimerval it;
  static u32 prev_timed_out = 0;
  static u64 exec_ms = 0;

  int status = 0;
  u32 tb4;

  child_timed_out = 0;

  /* After this memset, trace_bits[] are effectively volatile, so we
     must prevent any earlier operations from venturing into that
     territory. */

  memset(trace_bits, 0, MAP_SIZE);
  MEM_BARRIER();

  /* If we're running in "dumb" mode, we can't rely on the fork server
     logic compiled into the target program, so we will just keep calling
     execve(). There is a bit of code duplication between here and 
     init_forkserver(), but c'est la vie. */

  if (dumb_mode == 1 || no_forkserver) {//如果afl-fuzz运行在dumb_mode中或者没有forkserver

    child_pid = fork();//尝试fork一个字进程,返回一个child_pid

    if (child_pid < 0) PFATAL("fork() failed");

    if (!child_pid) {//如果返回的pid为0,说明当前进程即为子进程

      struct rlimit r;//rlimit 表示进程资源限制的结构体,两个元素: rlim_t rlim_cur; rlim_t rlim_max

      if (mem_limit) {//如果设置了内存限制

        r.rlim_max = r.rlim_cur = ((rlim_t)mem_limit) << 20;//mem_limit左移20位,就是以MB为单位,存入rlimit结构体中

#ifdef RLIMIT_AS

        setrlimit(RLIMIT_AS, &r); /* Ignore errors */
//RLIMIT_AS 进程虚拟内存的最大size
#else

        setrlimit(RLIMIT_DATA, &r); /* Ignore errors */
//进程数据段(initialized data, uninitialized和heap)的最大size
#endif /* ^RLIMIT_AS */

      }

      r.rlim_max = r.rlim_cur = 0;

      setrlimit(RLIMIT_CORE, &r); /* Ignore errors */
//进程可能dump进core文件的最大值 单位byte
      /* Isolate the process and configure standard descriptors. If out_file is
         specified, stdin is /dev/null; otherwise, out_fd is cloned instead. */

      setsid();//脱离从父进程继承而来的已打开终端,隶属进程组和隶属的会话

      dup2(dev_null_fd, 1);
      dup2(dev_null_fd, 2);

      if (out_file) {

        dup2(dev_null_fd, 0);

      } else {

        dup2(out_fd, 0);
        close(out_fd);

      }

      /* On Linux, would be faster to use O_CLOEXEC. Maybe TODO. */

      close(dev_null_fd);
      close(out_dir_fd);
      close(dev_urandom_fd);
      close(fileno(plot_file));

      /* Set sane defaults for ASAN if nothing else specified. */

      setenv("ASAN_OPTIONS", "abort_on_error=1:"
                             "detect_leaks=0:"
                             "symbolize=0:"
                             "allocator_may_return_null=1", 0);

      setenv("MSAN_OPTIONS", "exit_code=" STRINGIFY(MSAN_ERROR) ":"
                             "symbolize=0:"
                             "msan_track_origins=0", 0);

      execv(target_path, argv);

      /* Use a distinctive bitmap value to tell the parent about execv()
         falling through. */

      *(u32*)trace_bits = EXEC_FAIL_SIG; //EXEC_FAIL_SIG 0xfee1dead 用来指示执行失败的位图签名
      exit(0);

    }

  } else {//afl-fuzz运行在非dumb模式,fork server会上线

    s32 res;

    /* In non-dumb mode, we have the fork server up and running, so simply
       tell it to have at it, and then read back PID. */

    if ((res = write(fsrv_ctl_fd, &prev_timed_out, 4)) != 4) {//fsrv_ctl_fd fork server控制管道(写)

      if (stop_soon) return 0;
      RPFATAL(res, "Unable to request new process from fork server (OOM?)");

    }

    if ((res = read(fsrv_st_fd, &child_pid, 4)) != 4) {//fsrv_st_fd sork server状态管道(读)

      if (stop_soon) return 0;
      RPFATAL(res, "Unable to request new process from fork server (OOM?)");

    }

    if (child_pid <= 0) FATAL("Fork server is misbehaving (OOM?)");

  }

  /* Configure timeout, as requested by user, then wait for child to terminate. */
//配置itimer  timeout的单位应该是毫秒,将毫秒拆分成秒和微秒两部分
  it.it_value.tv_sec = (timeout / 1000);//配置秒
  it.it_value.tv_usec = (timeout % 1000) * 1000;//配置微秒

  setitimer(ITIMER_REAL, &it, NULL);

  /* The SIGALRM handler simply kills the child_pid and sets child_timed_out. */

  if (dumb_mode == 1 || no_forkserver) {

    if (waitpid(child_pid, &status, 0) <= 0) PFATAL("waitpid() failed");

  } else {

    s32 res;

    if ((res = read(fsrv_st_fd, &status, 4)) != 4) {

      if (stop_soon) return 0;
      RPFATAL(res, "Unable to communicate with fork server (OOM?)");

    }

  }

  if (!WIFSTOPPED(status)) child_pid = 0;

  getitimer(ITIMER_REAL, &it);
  exec_ms = (u64) timeout - (it.it_value.tv_sec * 1000 +
                             it.it_value.tv_usec / 1000);

  it.it_value.tv_sec = 0;
  it.it_value.tv_usec = 0;

  setitimer(ITIMER_REAL, &it, NULL);

  total_execs++;

  /* Any subsequent operations on trace_bits must not be moved by the
     compiler below this point. Past this location, trace_bits[] behave
     very normally and do not have to be treated as volatile. */
//避免编译器过度优化
  MEM_BARRIER();

  tb4 = *(u32*)trace_bits;

#ifdef WORD_SIZE_64
  classify_counts((u64*)trace_bits);
#else
  classify_counts((u32*)trace_bits);
#endif /* ^WORD_SIZE_64 */

  prev_timed_out = child_timed_out;

  /* Report outcome to caller. */

  if (WIFSIGNALED(status) && !stop_soon) {

    kill_signal = WTERMSIG(status);

    if (child_timed_out && kill_signal == SIGKILL) return FAULT_TMOUT;

    return FAULT_CRASH;

  }

  /* A somewhat nasty hack for MSAN, which doesn't support abort_on_error and
     must use a special exit code. */

  if (uses_asan && WEXITSTATUS(status) == MSAN_ERROR) {
    kill_signal = 0;
    return FAULT_CRASH;
  }

  if ((dumb_mode == 1 || no_forkserver) && tb4 == EXEC_FAIL_SIG)
    return FAULT_ERROR;

  /* It makes sense to account for the slowest units only if the testcase was run
  under the user defined timeout. */
  if (!(timeout > exec_tmout) && (slowest_exec_ms < exec_ms)) {
    slowest_exec_ms = exec_ms;
  }

  return FAULT_NONE;

}


/* Write modified data to file for testing. If out_file is set, the old file
   is unlinked and a new one is created. Otherwise, out_fd is rewound and
   truncated. */

static void write_to_testcase(void* mem, u32 len) {

  s32 fd = out_fd;

  if (out_file) {

    unlink(out_file); /* Ignore errors. */

    fd = open(out_file, O_WRONLY | O_CREAT | O_EXCL, 0600);

    if (fd < 0) PFATAL("Unable to create '%s'", out_file);

  } else lseek(fd, 0, SEEK_SET);

  ck_write(fd, mem, len, out_file);

  if (!out_file) {

    if (ftruncate(fd, len)) PFATAL("ftruncate() failed");
    lseek(fd, 0, SEEK_SET);

  } else close(fd);

}


/* The same, but with an adjustable gap. Used for trimming. */

static void write_with_gap(void* mem, u32 len, u32 skip_at, u32 skip_len) {

  s32 fd = out_fd;
  u32 tail_len = len - skip_at - skip_len;

  if (out_file) {

    unlink(out_file); /* Ignore errors. */

    fd = open(out_file, O_WRONLY | O_CREAT | O_EXCL, 0600);

    if (fd < 0) PFATAL("Unable to create '%s'", out_file);

  } else lseek(fd, 0, SEEK_SET);

  if (skip_at) ck_write(fd, mem, skip_at, out_file);

  if (tail_len) ck_write(fd, mem + skip_at + skip_len, tail_len, out_file);

  if (!out_file) {

    if (ftruncate(fd, len - skip_len)) PFATAL("ftruncate() failed");
    lseek(fd, 0, SEEK_SET);

  } else close(fd);

}


static void show_stats(void);

/* Calibrate a new test case. This is done when processing the input directory
   to warn about flaky or otherwise problematic test cases early on; and when
   new paths are discovered to detect variable behavior and so on. */

static u8 calibrate_case(char** argv, struct queue_entry* q, u8* use_mem,
                         u32 handicap, u8 from_queue) {
//handicap表示为经历的cycles数,以此体现该case的阻碍
  static u8 first_trace[MAP_SIZE];

  u8  fault = 0, new_bits = 0, var_detected = 0, hnb = 0,
      first_run = (q->exec_cksum == 0);//每次执行后都会紧跟一个checksum的计算,如果q->exec_chsum为0,说明当前执行为第一次执行

  u64 start_us, stop_us;

  s32 old_sc = stage_cur, old_sm = stage_max;
  u32 use_tmout = exec_tmout;
  u8* old_sn = stage_name;

  /* Be a bit more generous about timeouts when resuming sessions, or when
     trying to calibrate already-added finds. This helps avoid trouble due
     to intermittent latency. */

  if (!from_queue || resuming_fuzz)
    use_tmout = MAX(exec_tmout + CAL_TMOUT_ADD,
                    exec_tmout * CAL_TMOUT_PERC / 100);

  q->cal_failed++;

  stage_name = "calibration";
  stage_max  = fast_cal ? 3 : CAL_CYCLES;//校准的轮数.减少轮数了来实现快速校准.但是有些程序的行为在多次运行中可能有差异

  /* Make sure the forkserver is up before we do anything, and let's not
     count its spin-up time toward binary calibration. */

  if (dumb_mode != 1 && !no_forkserver && !forksrv_pid)
    init_forkserver(argv);//初始化一个forkserver

  if (q->exec_cksum) {//如果获取得到cksum,说明当前queue_entry不是第一次执行

    memcpy(first_trace, trace_bits, MAP_SIZE);//trace_bits的内容,copy进first_trace
    hnb = has_new_bits(virgin_bits);//检查bitmap virgin_bits中是否有新的bits
    if (hnb > new_bits) new_bits = hnb;//初始new_bits为0所以会直接hnb赋值

  }

  start_us = get_cur_time_us();

  for (stage_cur = 0; stage_cur < stage_max; stage_cur++) {

    u32 cksum;

    if (!first_run && !(stage_cur % stats_update_freq)) show_stats();

    write_to_testcase(use_mem, q->len);//将修改后的数据写入文件
//这里的use_mem 根据对calibrate_case()的调用者的不同,use_mem也不同
//第一次调用是perform_dry_run,这一参数为 use_mem = ck_alloc_nozero(q->len)
    fault = run_target(argv, use_tmout);//执行target 返回状态信息 同时更新tarce_bits

    /* stop_soon is set by the handler for Ctrl+C. When it's pressed,
       we want to bail out quickly. */

    if (stop_soon || fault != crash_mode) goto abort_calibration;//如果输入了CTRL+C或者执行target后返回的状态信息不是crash_mode 就中止校准状态 跳转到abort_calibration

    if (!dumb_mode && !stage_cur && !count_bytes(trace_bits)) {//count_bytes 计数bitmap中设置的字节数,目的主要是更新状态屏幕以及校准/检查新路径
      fault = FAULT_NOINST;
      goto abort_calibration;
    }

    cksum = hash32(trace_bits, MAP_SIZE, HASH_CONST);//将trace_bits作一个hash

    if (q->exec_cksum != cksum) {//如果队列中记录的checksum与当前执行计算出的checksum不同

      hnb = has_new_bits(virgin_bits);//更新一次hnb
      if (hnb > new_bits) new_bits = hnb;

      if (q->exec_cksum) {//如果当前queue_entry执行过,

        u32 i;

        for (i = 0; i < MAP_SIZE; i++) {

          if (!var_bytes[i] && first_trace[i] != trace_bits[i]) {//var_bytes:看起来是变量的字节;

            var_bytes[i] = 1;
            stage_max    = CAL_CYCLES_LONG;

          }//这个循环是在找新增的变量字节

        }

        var_detected = 1;

      } else {//如果是第一次执行,把trace_bits copy进first_trace

        q->exec_cksum = cksum;
        memcpy(first_trace, trace_bits, MAP_SIZE);

      }

    }

  }

  stop_us = get_cur_time_us();

  total_cal_us     += stop_us - start_us;
  total_cal_cycles += stage_max;

  /* OK, let's collect some stats about the performance of this test case.
     This is used for fuzzing air time calculations in calculate_score(). */

  q->exec_us     = (stop_us - start_us) / stage_max;
  q->bitmap_size = count_bytes(trace_bits);
  q->handicap    = handicap;//handicap:Number of queue cyclees behind
  q->cal_failed  = 0;

  total_bitmap_size += q->bitmap_size;
  total_bitmap_entries++;

  update_bitmap_score(q);//更新top_rated和q->trace_mini

  /* If this case didn't result in new output from the instrumentation, tell
     parent. This is a non-critical problem, but something to warn the user
     about. */

  if (!dumb_mode && first_run && !fault && !new_bits) fault = FAULT_NOBITS;//如果这个case没有从插桩中产生新的输出,就告诉parent.具体表现就是没有fault又没有new_bits

abort_calibration:

  if (new_bits == 2 && !q->has_new_cov) {
    q->has_new_cov = 1;//如果这次执行涉及发现了新的tuple,就认为发现了新的coverage
    queued_with_cov++;
  }

  /* Mark variable paths. */

  if (var_detected) {

    var_byte_count = count_bytes(var_bytes);//统计发现了多少字节是变量

    if (!q->var_behavior) {
      mark_as_variable(q);//q->var_behavior置1,并且在out_dir中同步记录
      queued_variable++;
    }

  }

  stage_name = old_sn;
  stage_cur  = old_sc;
  stage_max  = old_sm;

  if (!first_run) show_stats();

  return fault;

}


/* Examine map coverage. Called once, for first test case. */

static void check_map_coverage(void) {
//check方式就是计数trace_bits
  u32 i;

  if (count_bytes(trace_bits) < 100) return;

  for (i = (1 << (MAP_SIZE_POW2 - 1)); i < MAP_SIZE; i++)
    if (trace_bits[i]) return;

  WARNF("Recompile binary with newer version of afl to improve coverage!");

}


/* Perform dry run of all test cases to confirm that the app is working as
   expected. This is done only for the initial inputs, and only once. */

static void perform_dry_run(char** argv) {

  struct queue_entry* q = queue;
  u32 cal_failures = 0;
  u8* skip_crashes = getenv("AFL_SKIP_CRASHES");

  while (q) {

    u8* use_mem;
    u8  res;
    s32 fd;

    u8* fn = strrchr(q->fname, '/') + 1;

    ACTF("Attempting dry run with '%s'...", fn);

    fd = open(q->fname, O_RDONLY);
    if (fd < 0) PFATAL("Unable to open '%s'", q->fname);

    use_mem = ck_alloc_nozero(q->len);

    if (read(fd, use_mem, q->len) != q->len)
      FATAL("Short read from '%s'", q->fname);

    close(fd);

    res = calibrate_case(argv, q, use_mem, 0, 1);//校准测试用例;初始化forkserver;
    ck_free(use_mem);

    if (stop_soon) return;

    if (res == crash_mode || res == FAULT_NOBITS)
      SAYF(cGRA "    len = %u, map size = %u, exec speed = %llu us\n" cRST, 
           q->len, q->bitmap_size, q->exec_us);

    switch (res) {//根据不同的FAULT,选择不同的处理方式

      case FAULT_NONE:

        if (q == queue) check_map_coverage();//如果没有发生FAULT,并且q是queue的头部(即测试的第一个testcase),就检查coverage

        if (crash_mode) FATAL("Test case '%s' does *NOT* crash", fn);

        break;

      case FAULT_TMOUT:

        if (timeout_given) {

          /* The -t nn+ syntax in the command line sets timeout_given to '2' and
             instructs afl-fuzz to tolerate but skip queue entries that time
             out. */

          if (timeout_given > 1) {
            WARNF("Test case results in a timeout (skipping)");
            q->cal_failed = CAL_CHANCES;
            cal_failures++;
            break;
          }

          SAYF("\n" cLRD "[-] " cRST
               "The program took more than %u ms to process one of the initial test cases.\n"
               "    Usually, the right thing to do is to relax the -t option - or to delete it\n"
               "    altogether and allow the fuzzer to auto-calibrate. That said, if you know\n"
               "    what you are doing and want to simply skip the unruly test cases, append\n"
               "    '+' at the end of the value passed to -t ('-t %u+').\n", exec_tmout,
               exec_tmout);

          FATAL("Test case '%s' results in a timeout", fn);

        } else {

          SAYF("\n" cLRD "[-] " cRST
               "The program took more than %u ms to process one of the initial test cases.\n"
               "    This is bad news; raising the limit with the -t option is possible, but\n"
               "    will probably make the fuzzing process extremely slow.\n\n"

               "    If this test case is just a fluke, the other option is to just avoid it\n"
               "    altogether, and find one that is less of a CPU hog.\n", exec_tmout);

          FATAL("Test case '%s' results in a timeout", fn);

        }

      case FAULT_CRASH:  

        if (crash_mode) break;

        if (skip_crashes) {
          WARNF("Test case results in a crash (skipping)");
          q->cal_failed = CAL_CHANCES;
          cal_failures++;
          break;
        }

        if (mem_limit) {//如果进了Crash mode,又设置了内存限制,会直接给你报下面的内存不足的"小作文"?

          SAYF("\n" cLRD "[-] " cRST
               "Oops, the program crashed with one of the test cases provided. There are\n"
               "    several possible explanations:\n\n"

               "    - The test case causes known crashes under normal working conditions. If\n"
               "      so, please remove it. The fuzzer should be seeded with interesting\n"
               "      inputs - but not ones that cause an outright crash.\n\n"

               "    - The current memory limit (%s) is too low for this program, causing\n"
               "      it to die due to OOM when parsing valid files. To fix this, try\n"
               "      bumping it up with the -m setting in the command line. If in doubt,\n"
               "      try something along the lines of:\n\n"

#ifdef RLIMIT_AS
               "      ( ulimit -Sv $[%llu << 10]; /path/to/binary [...] <testcase )\n\n"
#else
               "      ( ulimit -Sd $[%llu << 10]; /path/to/binary [...] <testcase )\n\n"
#endif /* ^RLIMIT_AS */

               "      Tip: you can use http://jwilk.net/software/recidivm to quickly\n"
               "      estimate the required amount of virtual memory for the binary. Also,\n"
               "      if you are using ASAN, see %s/notes_for_asan.txt.\n\n"

#ifdef __APPLE__
  
               "    - On MacOS X, the semantics of fork() syscalls are non-standard and may\n"
               "      break afl-fuzz performance optimizations when running platform-specific\n"
               "      binaries. To fix this, set AFL_NO_FORKSRV=1 in the environment.\n\n"

#endif /* __APPLE__ */

               "    - Least likely, there is a horrible bug in the fuzzer. If other options\n"
               "      fail, poke <lcamtuf@coredump.cx> for troubleshooting tips.\n",
               DMS(mem_limit << 20), mem_limit - 1, doc_path);

        } else {

          SAYF("\n" cLRD "[-] " cRST
               "Oops, the program crashed with one of the test cases provided. There are\n"
               "    several possible explanations:\n\n"

               "    - The test case causes known crashes under normal working conditions. If\n"
               "      so, please remove it. The fuzzer should be seeded with interesting\n"
               "      inputs - but not ones that cause an outright crash.\n\n"

#ifdef __APPLE__
  
               "    - On MacOS X, the semantics of fork() syscalls are non-standard and may\n"
               "      break afl-fuzz performance optimizations when running platform-specific\n"
               "      binaries. To fix this, set AFL_NO_FORKSRV=1 in the environment.\n\n"

#endif /* __APPLE__ */

               "    - Least likely, there is a horrible bug in the fuzzer. If other options\n"
               "      fail, poke <lcamtuf@coredump.cx> for troubleshooting tips.\n");

        }

        FATAL("Test case '%s' results in a crash", fn);

      case FAULT_ERROR:

        FATAL("Unable to execute target application ('%s')", argv[0]);

      case FAULT_NOINST:

        FATAL("No instrumentation detected");

      case FAULT_NOBITS: 

        useless_at_start++;//无用的起始路径

        if (!in_bitmap && !shuffle_queue)
          WARNF("No new instrumentation output, test case may be useless.");

        break;

    }

    if (q->var_behavior) WARNF("Instrumentation output varies across runs.");

    q = q->next;

  }

  if (cal_failures) {

    if (cal_failures == queued_paths)//如果所有case都timeout或者crash了,那基本没什么办法
      FATAL("All test cases time out%s, giving up!",
            skip_crashes ? " or crash" : "");

    WARNF("Skipped %u test cases (%0.02f%%) due to timeouts%s.", cal_failures,
          ((double)cal_failures) * 100 / queued_paths,
          skip_crashes ? " or crashes" : "");

    if (cal_failures * 5 > queued_paths)//如果有20%以上timeout或者crash,可能设置里出了问题
      WARNF(cLRD "High percentage of rejected test cases, check settings!");

  }

  OKF("All test cases processed.");

}


/* Helper function: link() if possible, copy otherwise. */

static void link_or_copy(u8* old_path, u8* new_path) {

  s32 i = link(old_path, new_path);
  s32 sfd, dfd;
  u8* tmp;

  if (!i) return;

  sfd = open(old_path, O_RDONLY);
  if (sfd < 0) PFATAL("Unable to open '%s'", old_path);

  dfd = open(new_path, O_WRONLY | O_CREAT | O_EXCL, 0600);
  if (dfd < 0) PFATAL("Unable to create '%s'", new_path);

  tmp = ck_alloc(64 * 1024);

  while ((i = read(sfd, tmp, 64 * 1024)) > 0) 
    ck_write(dfd, tmp, i, new_path);

  if (i < 0) PFATAL("read() failed");

  ck_free(tmp);
  close(sfd);
  close(dfd);

}


static void nuke_resume_dir(void);

/* Create hard links for input test cases in the output directory, choosing
   good names and pivoting accordingly. */

static void pivot_inputs(void) {

  struct queue_entry* q = queue;
  u32 id = 0;

  ACTF("Creating hard links for all input files...");

  while (q) {

    u8  *nfn, *rsl = strrchr(q->fname, '/');
    u32 orig_id;

    if (!rsl) rsl = q->fname; else rsl++;

    /* If the original file name conforms to the syntax and the recorded
       ID matches the one we'd assign, just use the original file name.
       This is valuable for resuming fuzzing runs. */

#ifndef SIMPLE_FILES
#  define CASE_PREFIX "id:"
#else
#  define CASE_PREFIX "id_"
#endif /* ^!SIMPLE_FILES */

    if (!strncmp(rsl, CASE_PREFIX, 3) &&
        sscanf(rsl + 3, "%06u", &orig_id) == 1 && orig_id == id) {

      u8* src_str;
      u32 src_id;

      resuming_fuzz = 1;
      nfn = alloc_printf("%s/queue/%s", out_dir, rsl);

      /* Since we're at it, let's also try to find parent and figure out the
         appropriate depth for this entry. */

      src_str = strchr(rsl + 3, ':');

      if (src_str && sscanf(src_str + 1, "%06u", &src_id) == 1) {

        struct queue_entry* s = queue;
        while (src_id-- && s) s = s->next;
        if (s) q->depth = s->depth + 1;

        if (max_depth < q->depth) max_depth = q->depth;

      }

    } else {

      /* No dice - invent a new name, capturing the original one as a
         substring. */

#ifndef SIMPLE_FILES

      u8* use_name = strstr(rsl, ",orig:");

      if (use_name) use_name += 6; else use_name = rsl;
      nfn = alloc_printf("%s/queue/id:%06u,orig:%s", out_dir, id, use_name);

#else

      nfn = alloc_printf("%s/queue/id_%06u", out_dir, id);

#endif /* ^!SIMPLE_FILES */

    }

    /* Pivot to the new queue entry. */

    link_or_copy(q->fname, nfn);
    ck_free(q->fname);
    q->fname = nfn;

    /* Make sure that the passed_det value carries over, too. */

    if (q->passed_det) mark_as_det_done(q);

    q = q->next;
    id++;

  }

  if (in_place_resume) nuke_resume_dir();

}


#ifndef SIMPLE_FILES

/* Construct a file name for a new test case, capturing the operation
   that led to its discovery. Uses a static buffer. */
//为新的testcase生成文件名,文件名中简要表示了该case的信息
static u8* describe_op(u8 hnb) {

  static u8 ret[256];

  if (syncing_party) {

    sprintf(ret, "sync:%s,src:%06u", syncing_party, syncing_case);//开启并行fuzzing的话,会标上所在的party,同步的case

  } else {

    sprintf(ret, "src:%06u", current_entry);//非并行,就单列当前的case

    if (splicing_with >= 0)
      sprintf(ret + strlen(ret), "+%06u", splicing_with);//与之进行拼接的名称

    sprintf(ret + strlen(ret), ",op:%s", stage_short);//缩写 阶段名

    if (stage_cur_byte >= 0) {

      sprintf(ret + strlen(ret), ",pos:%u", stage_cur_byte);

      if (stage_val_type != STAGE_VAL_NONE)
        sprintf(ret + strlen(ret), ",val:%s%+d", 
                (stage_val_type == STAGE_VAL_BE) ? "be:" : "",
                stage_cur_val);

    } else sprintf(ret + strlen(ret), ",rep:%u", stage_cur_val);

  }

  if (hnb == 2) strcat(ret, ",+cov");

  return ret;

}

#endif /* !SIMPLE_FILES */


/* Write a message accompanying the crash directory :-) */

static void write_crash_readme(void) {

  u8* fn = alloc_printf("%s/crashes/README.txt", out_dir);
  s32 fd;
  FILE* f;

  fd = open(fn, O_WRONLY | O_CREAT | O_EXCL, 0600);
  ck_free(fn);

  /* Do not die on errors here - that would be impolite. */

  if (fd < 0) return;

  f = fdopen(fd, "w");

  if (!f) {
    close(fd);
    return;
  }

  fprintf(f, "Command line used to find this crash:\n\n"

             "%s\n\n"

             "If you can't reproduce a bug outside of afl-fuzz, be sure to set the same\n"
             "memory limit. The limit used for this fuzzing session was %s.\n\n"

             "Need a tool to minimize test cases before investigating the crashes or sending\n"
             "them to a vendor? Check out the afl-tmin that comes with the fuzzer!\n\n"

             "Found any cool bugs in open-source tools using afl-fuzz? If yes, please drop\n"
             "me a mail at <lcamtuf@coredump.cx> once the issues are fixed - I'd love to\n"
             "add your finds to the gallery at:\n\n"

             "  http://lcamtuf.coredump.cx/afl/\n\n"

             "Thanks :-)\n",

             orig_cmdline, DMS(mem_limit << 20)); /* ignore errors */

  fclose(f);

}


/* Check if the result of an execve() during routine fuzzing is interesting,
   save or queue the input test case for further analysis if so. Returns 1 if
   entry is saved, 0 otherwise. */

static u8 save_if_interesting(char** argv, void* mem, u32 len, u8 fault) {

  u8  *fn = "";
  u8  hnb;
  s32 fd;
  u8  keeping = 0, res;

  if (fault == crash_mode) {//条件成立的两种可能:两者为0,即没有timeout也没有crash,afl也没开crash mode;两者为2,即target发生了crash,同时开启了crash mode

    /* Keep only if there are new bits in the map, add to queue for
       future fuzzing, etc. */

    if (!(hnb = has_new_bits(virgin_bits))) {//如果没有new bits,就看看有没有crash,有的话crash总数+1,但是依旧返回0,认为这个case不是很有趣
      if (crash_mode) total_crashes++;
      return 0;
    }    

#ifndef SIMPLE_FILES

    fn = alloc_printf("%s/queue/id:%06u,%s", out_dir, queued_paths,
                      describe_op(hnb));

#else

    fn = alloc_printf("%s/queue/id_%06u", out_dir, queued_paths);

#endif /* ^!SIMPLE_FILES */

    add_to_queue(fn, len, 0);

    if (hnb == 2) {
      queue_top->has_new_cov = 1;
      queued_with_cov++;
    }

    queue_top->exec_cksum = hash32(trace_bits, MAP_SIZE, HASH_CONST);

    /* Try to calibrate inline; this also calls update_bitmap_score() when
       successful. */

    res = calibrate_case(argv, queue_top, mem, queue_cycle - 1, 0);//又一次校准

    if (res == FAULT_ERROR)
      FATAL("Unable to execute target application");

    fd = open(fn, O_WRONLY | O_CREAT | O_EXCL, 0600);
    if (fd < 0) PFATAL("Unable to create '%s'", fn);
    ck_write(fd, mem, len, fn);
    close(fd);

    keeping = 1;//如果出现crash,这里把keeping置1,后续代码执行时,会根据是否出现crash决定是否保留case

  }

  switch (fault) {

    case FAULT_TMOUT:

      /* Timeouts are not very interesting, but we're still obliged to keep
         a handful of samples. We use the presence of new bits in the
         hang-specific bitmap as a signal of uniqueness. In "dumb" mode, we
         just keep everything. */

      total_tmouts++;

      if (unique_hangs >= KEEP_UNIQUE_HANG) return keeping;

      if (!dumb_mode) {

#ifdef WORD_SIZE_64
        simplify_trace((u64*)trace_bits);
#else
        simplify_trace((u32*)trace_bits);//简化trace  舍弃具体的hit数,仅保留是否hit标记
#endif /* ^WORD_SIZE_64 */

        if (!has_new_bits(virgin_tmout)) return keeping;

      }

      unique_tmouts++;

      /* Before saving, we make sure that it's a genuine hang by re-running
         the target with a more generous timeout (unless the default timeout
         is already generous). */

      if (exec_tmout < hang_tmout) {//可能exec_tmout太小,导致没有运行到crash就被认为timeout了,所以这里用更大的hang_tmout(如果更大)来运行target

        u8 new_fault;
        write_to_testcase(mem, len);
        new_fault = run_target(argv, hang_tmout);//再次运行target,这次使用hang_tmout作为阈值,检查是否会有新的fault状态

        /* A corner case that one user reported bumping into: increasing the
           timeout actually uncovers a crash. Make sure we don't discard it if
           so. */

        if (!stop_soon && new_fault == FAULT_CRASH) goto keep_as_crash;//如果发现crash,直接跳转到crash的流程

        if (stop_soon || new_fault != FAULT_TMOUT) return keeping;

      }

#ifndef SIMPLE_FILES

      fn = alloc_printf("%s/hangs/id:%06llu,%s", out_dir,
                        unique_hangs, describe_op(0));

#else

      fn = alloc_printf("%s/hangs/id_%06llu", out_dir,
                        unique_hangs);

#endif /* ^!SIMPLE_FILES */

      unique_hangs++;

      last_hang_time = get_cur_time();

      break;

    case FAULT_CRASH:

keep_as_crash:

      /* This is handled in a manner roughly similar to timeouts,
         except for slightly different limits and no need to re-run test
         cases. */

      total_crashes++;

      if (unique_crashes >= KEEP_UNIQUE_CRASH) return keeping;

      if (!dumb_mode) {

#ifdef WORD_SIZE_64
        simplify_trace((u64*)trace_bits);
#else
        simplify_trace((u32*)trace_bits);
#endif /* ^WORD_SIZE_64 */

        if (!has_new_bits(virgin_crash)) return keeping;

      }

      if (!unique_crashes) write_crash_readme();

#ifndef SIMPLE_FILES

      fn = alloc_printf("%s/crashes/id:%06llu,sig:%02u,%s", out_dir,
                        unique_crashes, kill_signal, describe_op(0));

#else

      fn = alloc_printf("%s/crashes/id_%06llu_%02u", out_dir, unique_crashes,
                        kill_signal);

#endif /* ^!SIMPLE_FILES */

      unique_crashes++;

      last_crash_time = get_cur_time();
      last_crash_execs = total_execs;

      break;

    case FAULT_ERROR: FATAL("Unable to execute target application");

    default: return keeping;

  }

  /* If we're here, we apparently want to save the crash or hang
     test case, too. */

  fd = open(fn, O_WRONLY | O_CREAT | O_EXCL, 0600);
  if (fd < 0) PFATAL("Unable to create '%s'", fn);
  ck_write(fd, mem, len, fn);
  close(fd);

  ck_free(fn);

  return keeping;

}


/* When resuming, try to find the queue position to start from. This makes sense
   only when resuming, and when we can find the original fuzzer_stats. */

static u32 find_start_position(void) {

  static u8 tmp[4096]; /* Ought to be enough for anybody. */

  u8  *fn, *off;
  s32 fd, i;
  u32 ret;

  if (!resuming_fuzz) return 0;

  if (in_place_resume) fn = alloc_printf("%s/fuzzer_stats", out_dir);
  else fn = alloc_printf("%s/../fuzzer_stats", in_dir);

  fd = open(fn, O_RDONLY);
  ck_free(fn);

  if (fd < 0) return 0;

  i = read(fd, tmp, sizeof(tmp) - 1); (void)i; /* Ignore errors */
  close(fd);

  off = strstr(tmp, "cur_path          : ");
  if (!off) return 0;

  ret = atoi(off + 20);
  if (ret >= queued_paths) ret = 0;
  return ret;

}


/* The same, but for timeouts. The idea is that when resuming sessions without
   -t given, we don't want to keep auto-scaling the timeout over and over
   again to prevent it from growing due to random flukes. */

static void find_timeout(void) {

  static u8 tmp[4096]; /* Ought to be enough for anybody. */

  u8  *fn, *off;
  s32 fd, i;
  u32 ret;

  if (!resuming_fuzz) return;

  if (in_place_resume) fn = alloc_printf("%s/fuzzer_stats", out_dir);
  else fn = alloc_printf("%s/../fuzzer_stats", in_dir);

  fd = open(fn, O_RDONLY);
  ck_free(fn);

  if (fd < 0) return;

  i = read(fd, tmp, sizeof(tmp) - 1); (void)i; /* Ignore errors */
  close(fd);

  off = strstr(tmp, "exec_timeout      : ");
  if (!off) return;

  ret = atoi(off + 20);
  if (ret <= 4) return;

  exec_tmout = ret;
  timeout_given = 3;

}


/* Update stats file for unattended monitoring. */

static void write_stats_file(double bitmap_cvg, double stability, double eps) {

  static double last_bcvg, last_stab, last_eps;
  static struct rusage usage;

  u8* fn = alloc_printf("%s/fuzzer_stats", out_dir);
  s32 fd;
  FILE* f;

  fd = open(fn, O_WRONLY | O_CREAT | O_TRUNC, 0600);

  if (fd < 0) PFATAL("Unable to create '%s'", fn);

  ck_free(fn);

  f = fdopen(fd, "w");

  if (!f) PFATAL("fdopen() failed");

  /* Keep last values in case we're called from another context
     where exec/sec stats and such are not readily available. */

  if (!bitmap_cvg && !stability && !eps) {
    bitmap_cvg = last_bcvg;
    stability  = last_stab;
    eps        = last_eps;
  } else {
    last_bcvg = bitmap_cvg;
    last_stab = stability;
    last_eps  = eps;
  }

  fprintf(f, "start_time        : %llu\n"
             "last_update       : %llu\n"
             "fuzzer_pid        : %u\n"
             "cycles_done       : %llu\n"
             "execs_done        : %llu\n"
             "execs_per_sec     : %0.02f\n"
             "paths_total       : %u\n"
             "paths_favored     : %u\n"
             "paths_found       : %u\n"
             "paths_imported    : %u\n"
             "max_depth         : %u\n"
             "cur_path          : %u\n" /* Must match find_start_position() */
             "pending_favs      : %u\n"
             "pending_total     : %u\n"
             "variable_paths    : %u\n"
             "stability         : %0.02f%%\n"
             "bitmap_cvg        : %0.02f%%\n"
             "unique_crashes    : %llu\n"
             "unique_hangs      : %llu\n"
             "last_path         : %llu\n"
             "last_crash        : %llu\n"
             "last_hang         : %llu\n"
             "execs_since_crash : %llu\n"
             "exec_timeout      : %u\n" /* Must match find_timeout() */
             "afl_banner        : %s\n"
             "afl_version       : " VERSION "\n"
             "target_mode       : %s%s%s%s%s%s%s\n"
             "command_line      : %s\n"
             "slowest_exec_ms   : %llu\n",
             start_time / 1000, get_cur_time() / 1000, getpid(),
             queue_cycle ? (queue_cycle - 1) : 0, total_execs, eps,
             queued_paths, queued_favored, queued_discovered, queued_imported,
             max_depth, current_entry, pending_favored, pending_not_fuzzed,
             queued_variable, stability, bitmap_cvg, unique_crashes,
             unique_hangs, last_path_time / 1000, last_crash_time / 1000,
             last_hang_time / 1000, total_execs - last_crash_execs,
             exec_tmout, use_banner,
             qemu_mode ? "qemu " : "", dumb_mode ? " dumb " : "",
             no_forkserver ? "no_forksrv " : "", crash_mode ? "crash " : "",
             persistent_mode ? "persistent " : "", deferred_mode ? "deferred " : "",
             (qemu_mode || dumb_mode || no_forkserver || crash_mode ||
              persistent_mode || deferred_mode) ? "" : "default",
             orig_cmdline, slowest_exec_ms);
             /* ignore errors */

  /* Get rss value from the children
     We must have killed the forkserver process and called waitpid
     before calling getrusage */
  if (getrusage(RUSAGE_CHILDREN, &usage)) {
      WARNF("getrusage failed");
  } else if (usage.ru_maxrss == 0) {
    fprintf(f, "peak_rss_mb       : not available while afl is running\n");
  } else {
#ifdef __APPLE__
    fprintf(f, "peak_rss_mb       : %zu\n", usage.ru_maxrss >> 20);
#else
    fprintf(f, "peak_rss_mb       : %zu\n", usage.ru_maxrss >> 10);
#endif /* ^__APPLE__ */
  }

  fclose(f);

}


/* Update the plot file if there is a reason to. */

static void maybe_update_plot_file(double bitmap_cvg, double eps) {

  static u32 prev_qp, prev_pf, prev_pnf, prev_ce, prev_md;
  static u64 prev_qc, prev_uc, prev_uh;

  if (prev_qp == queued_paths && prev_pf == pending_favored && 
      prev_pnf == pending_not_fuzzed && prev_ce == current_entry &&
      prev_qc == queue_cycle && prev_uc == unique_crashes &&
      prev_uh == unique_hangs && prev_md == max_depth) return;

  prev_qp  = queued_paths;
  prev_pf  = pending_favored;
  prev_pnf = pending_not_fuzzed;
  prev_ce  = current_entry;
  prev_qc  = queue_cycle;
  prev_uc  = unique_crashes;
  prev_uh  = unique_hangs;
  prev_md  = max_depth;

  /* Fields in the file:

     unix_time, cycles_done, cur_path, paths_total, paths_not_fuzzed,
     favored_not_fuzzed, unique_crashes, unique_hangs, max_depth,
     execs_per_sec */

  fprintf(plot_file, 
          "%llu, %llu, %u, %u, %u, %u, %0.02f%%, %llu, %llu, %u, %0.02f\n",
          get_cur_time() / 1000, queue_cycle - 1, current_entry, queued_paths,
          pending_not_fuzzed, pending_favored, bitmap_cvg, unique_crashes,
          unique_hangs, max_depth, eps); /* ignore errors */

  fflush(plot_file);

}



/* A helper function for maybe_delete_out_dir(), deleting all prefixed
   files in a directory. */

static u8 delete_files(u8* path, u8* prefix) {

  DIR* d;
  struct dirent* d_ent;

  d = opendir(path);

  if (!d) return 0;

  while ((d_ent = readdir(d))) {

    if (d_ent->d_name[0] != '.' && (!prefix ||
        !strncmp(d_ent->d_name, prefix, strlen(prefix)))) {

      u8* fname = alloc_printf("%s/%s", path, d_ent->d_name);
      if (unlink(fname)) PFATAL("Unable to delete '%s'", fname);
      ck_free(fname);

    }

  }

  closedir(d);

  return !!rmdir(path);

}


/* Get the number of runnable processes, with some simple smoothing. */

static double get_runnable_processes(void) {

  static double res;

#if defined(__APPLE__) || defined(__FreeBSD__) || defined (__OpenBSD__)

  /* I don't see any portable sysctl or so that would quickly give us the
     number of runnable processes; the 1-minute load average can be a
     semi-decent approximation, though. */

  if (getloadavg(&res, 1) != 1) return 0;

#else

  /* On Linux, /proc/stat is probably the best way; load averages are
     computed in funny ways and sometimes don't reflect extremely short-lived
     processes well. */

  FILE* f = fopen("/proc/stat", "r");
  u8 tmp[1024];
  u32 val = 0;

  if (!f) return 0;

  while (fgets(tmp, sizeof(tmp), f)) {

    if (!strncmp(tmp, "procs_running ", 14) ||
        !strncmp(tmp, "procs_blocked ", 14)) val += atoi(tmp + 14);

  }
 
  fclose(f);

  if (!res) {

    res = val;

  } else {

    res = res * (1.0 - 1.0 / AVG_SMOOTHING) +
          ((double)val) * (1.0 / AVG_SMOOTHING);

  }

#endif /* ^(__APPLE__ || __FreeBSD__ || __OpenBSD__) */

  return res;

}


/* Delete the temporary directory used for in-place session resume. */

static void nuke_resume_dir(void) {

  u8* fn;

  fn = alloc_printf("%s/_resume/.state/deterministic_done", out_dir);
  if (delete_files(fn, CASE_PREFIX)) goto dir_cleanup_failed;
  ck_free(fn);

  fn = alloc_printf("%s/_resume/.state/auto_extras", out_dir);
  if (delete_files(fn, "auto_")) goto dir_cleanup_failed;
  ck_free(fn);

  fn = alloc_printf("%s/_resume/.state/redundant_edges", out_dir);
  if (delete_files(fn, CASE_PREFIX)) goto dir_cleanup_failed;
  ck_free(fn);

  fn = alloc_printf("%s/_resume/.state/variable_behavior", out_dir);
  if (delete_files(fn, CASE_PREFIX)) goto dir_cleanup_failed;
  ck_free(fn);

  fn = alloc_printf("%s/_resume/.state", out_dir);
  if (rmdir(fn) && errno != ENOENT) goto dir_cleanup_failed;
  ck_free(fn);

  fn = alloc_printf("%s/_resume", out_dir);
  if (delete_files(fn, CASE_PREFIX)) goto dir_cleanup_failed;
  ck_free(fn);

  return;

dir_cleanup_failed:

  FATAL("_resume directory cleanup failed");

}


/* Delete fuzzer output directory if we recognize it as ours, if the fuzzer
   is not currently running, and if the last run time isn't too great. */

static void maybe_delete_out_dir(void) {

  FILE* f;
  u8 *fn = alloc_printf("%s/fuzzer_stats", out_dir);

  /* See if the output directory is locked. If yes, bail out. If not,
     create a lock that will persist for the lifetime of the process
     (this requires leaving the descriptor open).*/

  out_dir_fd = open(out_dir, O_RDONLY);
  if (out_dir_fd < 0) PFATAL("Unable to open '%s'", out_dir);

#ifndef __sun

  if (flock(out_dir_fd, LOCK_EX | LOCK_NB) && errno == EWOULDBLOCK) {

    SAYF("\n" cLRD "[-] " cRST
         "Looks like the job output directory is being actively used by another\n"
         "    instance of afl-fuzz. You will need to choose a different %s\n"
         "    or stop the other process first.\n",
         sync_id ? "fuzzer ID" : "output location");

    FATAL("Directory '%s' is in use", out_dir);

  }

#endif /* !__sun */

  f = fopen(fn, "r");

  if (f) {

    u64 start_time, last_update;

    if (fscanf(f, "start_time     : %llu\n"
                  "last_update    : %llu\n", &start_time, &last_update) != 2)
      FATAL("Malformed data in '%s'", fn);

    fclose(f);

    /* Let's see how much work is at stake. */

    if (!in_place_resume && last_update - start_time > OUTPUT_GRACE * 60) {

      SAYF("\n" cLRD "[-] " cRST
           "The job output directory already exists and contains the results of more\n"
           "    than %u minutes worth of fuzzing. To avoid data loss, afl-fuzz will *NOT*\n"
           "    automatically delete this data for you.\n\n"

           "    If you wish to start a new session, remove or rename the directory manually,\n"
           "    or specify a different output location for this job. To resume the old\n"
           "    session, put '-' as the input directory in the command line ('-i -') and\n"
           "    try again.\n", OUTPUT_GRACE);

       FATAL("At-risk data found in '%s'", out_dir);

    }

  }

  ck_free(fn);

  /* The idea for in-place resume is pretty simple: we temporarily move the old
     queue/ to a new location that gets deleted once import to the new queue/
     is finished. If _resume/ already exists, the current queue/ may be
     incomplete due to an earlier abort, so we want to use the old _resume/
     dir instead, and we let rename() fail silently. */

  if (in_place_resume) {

    u8* orig_q = alloc_printf("%s/queue", out_dir);

    in_dir = alloc_printf("%s/_resume", out_dir);

    rename(orig_q, in_dir); /* Ignore errors */

    OKF("Output directory exists, will attempt session resume.");

    ck_free(orig_q);

  } else {

    OKF("Output directory exists but deemed OK to reuse.");

  }

  ACTF("Deleting old session data...");

  /* Okay, let's get the ball rolling! First, we need to get rid of the entries
     in <out_dir>/.synced/.../id:*, if any are present. */

  if (!in_place_resume) {

    fn = alloc_printf("%s/.synced", out_dir);
    if (delete_files(fn, NULL)) goto dir_cleanup_failed;
    ck_free(fn);

  }

  /* Next, we need to clean up <out_dir>/queue/.state/ subdirectories: */

  fn = alloc_printf("%s/queue/.state/deterministic_done", out_dir);
  if (delete_files(fn, CASE_PREFIX)) goto dir_cleanup_failed;
  ck_free(fn);

  fn = alloc_printf("%s/queue/.state/auto_extras", out_dir);
  if (delete_files(fn, "auto_")) goto dir_cleanup_failed;
  ck_free(fn);

  fn = alloc_printf("%s/queue/.state/redundant_edges", out_dir);
  if (delete_files(fn, CASE_PREFIX)) goto dir_cleanup_failed;
  ck_free(fn);

  fn = alloc_printf("%s/queue/.state/variable_behavior", out_dir);
  if (delete_files(fn, CASE_PREFIX)) goto dir_cleanup_failed;
  ck_free(fn);

  /* Then, get rid of the .state subdirectory itself (should be empty by now)
     and everything matching <out_dir>/queue/id:*. */

  fn = alloc_printf("%s/queue/.state", out_dir);
  if (rmdir(fn) && errno != ENOENT) goto dir_cleanup_failed;
  ck_free(fn);

  fn = alloc_printf("%s/queue", out_dir);
  if (delete_files(fn, CASE_PREFIX)) goto dir_cleanup_failed;
  ck_free(fn);

  /* All right, let's do <out_dir>/crashes/id:* and <out_dir>/hangs/id:*. */

  if (!in_place_resume) {

    fn = alloc_printf("%s/crashes/README.txt", out_dir);
    unlink(fn); /* Ignore errors */
    ck_free(fn);

  }

  fn = alloc_printf("%s/crashes", out_dir);

  /* Make backup of the crashes directory if it's not empty and if we're
     doing in-place resume. */

  if (in_place_resume && rmdir(fn)) {

    time_t cur_t = time(0);
    struct tm* t = localtime(&cur_t);

#ifndef SIMPLE_FILES

    u8* nfn = alloc_printf("%s.%04u-%02u-%02u-%02u:%02u:%02u", fn,
                           t->tm_year + 1900, t->tm_mon + 1, t->tm_mday,
                           t->tm_hour, t->tm_min, t->tm_sec);

#else

    u8* nfn = alloc_printf("%s_%04u%02u%02u%02u%02u%02u", fn,
                           t->tm_year + 1900, t->tm_mon + 1, t->tm_mday,
                           t->tm_hour, t->tm_min, t->tm_sec);

#endif /* ^!SIMPLE_FILES */

    rename(fn, nfn); /* Ignore errors. */
    ck_free(nfn);

  }

  if (delete_files(fn, CASE_PREFIX)) goto dir_cleanup_failed;
  ck_free(fn);

  fn = alloc_printf("%s/hangs", out_dir);

  /* Backup hangs, too. */

  if (in_place_resume && rmdir(fn)) {

    time_t cur_t = time(0);
    struct tm* t = localtime(&cur_t);

#ifndef SIMPLE_FILES

    u8* nfn = alloc_printf("%s.%04u-%02u-%02u-%02u:%02u:%02u", fn,
                           t->tm_year + 1900, t->tm_mon + 1, t->tm_mday,
                           t->tm_hour, t->tm_min, t->tm_sec);

#else

    u8* nfn = alloc_printf("%s_%04u%02u%02u%02u%02u%02u", fn,
                           t->tm_year + 1900, t->tm_mon + 1, t->tm_mday,
                           t->tm_hour, t->tm_min, t->tm_sec);

#endif /* ^!SIMPLE_FILES */

    rename(fn, nfn); /* Ignore errors. */
    ck_free(nfn);

  }

  if (delete_files(fn, CASE_PREFIX)) goto dir_cleanup_failed;
  ck_free(fn);

  /* And now, for some finishing touches. */

  fn = alloc_printf("%s/.cur_input", out_dir);
  if (unlink(fn) && errno != ENOENT) goto dir_cleanup_failed;
  ck_free(fn);

  fn = alloc_printf("%s/fuzz_bitmap", out_dir);
  if (unlink(fn) && errno != ENOENT) goto dir_cleanup_failed;
  ck_free(fn);

  if (!in_place_resume) {
    fn  = alloc_printf("%s/fuzzer_stats", out_dir);
    if (unlink(fn) && errno != ENOENT) goto dir_cleanup_failed;
    ck_free(fn);
  }

  fn = alloc_printf("%s/plot_data", out_dir);
  if (unlink(fn) && errno != ENOENT) goto dir_cleanup_failed;
  ck_free(fn);

  OKF("Output dir cleanup successful.");

  /* Wow... is that all? If yes, celebrate! */

  return;

dir_cleanup_failed:

  SAYF("\n" cLRD "[-] " cRST
       "Whoops, the fuzzer tried to reuse your output directory, but bumped into\n"
       "    some files that shouldn't be there or that couldn't be removed - so it\n"
       "    decided to abort! This happened while processing this path:\n\n"

       "    %s\n\n"
       "    Please examine and manually delete the files, or specify a different\n"
       "    output location for the tool.\n", fn);

  FATAL("Output directory cleanup failed");

}


static void check_term_size(void);


/* A spiffy retro stats screen! This is called every stats_update_freq
   execve() calls, plus in several other circumstances. */

static void show_stats(void) {

  static u64 last_stats_ms, last_plot_ms, last_ms, last_execs;
  static double avg_exec;
  double t_byte_ratio, stab_ratio; 

  u64 cur_ms;
  u32 t_bytes, t_bits;

  u32 banner_len, banner_pad;
  u8  tmp[256];

  cur_ms = get_cur_time();

  /* If not enough time has passed since last UI update, bail out. */

  if (cur_ms - last_ms < 1000 / UI_TARGET_HZ) return;

  /* Check if we're past the 10 minute mark. */

  if (cur_ms - start_time > 10 * 60 * 1000) run_over10m = 1;

  /* Calculate smoothed exec speed stats. */

  if (!last_execs) {
  
    avg_exec = ((double)total_execs) * 1000 / (cur_ms - start_time);

  } else {

    double cur_avg = ((double)(total_execs - last_execs)) * 1000 /
                     (cur_ms - last_ms);

    /* If there is a dramatic (5x+) jump in speed, reset the indicator
       more quickly. */

    if (cur_avg * 5 < avg_exec || cur_avg / 5 > avg_exec)
      avg_exec = cur_avg;

    avg_exec = avg_exec * (1.0 - 1.0 / AVG_SMOOTHING) +
               cur_avg * (1.0 / AVG_SMOOTHING);

  }

  last_ms = cur_ms;
  last_execs = total_execs;

  /* Tell the callers when to contact us (as measured in execs). */

  stats_update_freq = avg_exec / (UI_TARGET_HZ * 10);
  if (!stats_update_freq) stats_update_freq = 1;

  /* Do some bitmap stats. */

  t_bytes = count_non_255_bytes(virgin_bits);//计数virgin_bits中非0xFF的字节
  t_byte_ratio = ((double)t_bytes * 100) / MAP_SIZE;

  if (t_bytes) 
    stab_ratio = 100 - ((double)var_byte_count) * 100 / t_bytes;
  else
    stab_ratio = 100;

  /* Roughly every minute, update fuzzer stats and save auto tokens. */

  if (cur_ms - last_stats_ms > STATS_UPDATE_SEC * 1000) {//当前时间-上次更新状态时间  每60秒更新一次状态   但是 last_stats_ms不初始化就直接用?

    last_stats_ms = cur_ms;
    write_stats_file(t_byte_ratio, stab_ratio, avg_exec);
    save_auto();
    write_bitmap();

  }

  /* Every now and then, write plot data. */

  if (cur_ms - last_plot_ms > PLOT_UPDATE_SEC * 1000) {//每5秒 写一次plot数据

    last_plot_ms = cur_ms;
    maybe_update_plot_file(t_byte_ratio, avg_exec);
 
  }

  /* Honor AFL_EXIT_WHEN_DONE and AFL_BENCH_UNTIL_CRASH. */

  if (!dumb_mode && cycles_wo_finds > 100 && !pending_not_fuzzed &&
      getenv("AFL_EXIT_WHEN_DONE")) stop_soon = 2;//AFL_EXIT_WHEN_DONE 完成fuzzing之后退出afl 这里认为空转100轮(即100轮中没有发现新路径)即为DONE,就退出

  if (total_crashes && getenv("AFL_BENCH_UNTIL_CRASH")) stop_soon = 2;//AFL_BENCH_UNTIL_CRASH 在发现第一个crash之后退出afl

  /* If we're not on TTY, bail out. */

  if (not_on_tty) return;

  /* Compute some mildly useful bitmap stats. */

  t_bits = (MAP_SIZE << 3) - count_bits(virgin_bits);//计算bitmap中已经被afl触及的bits,及总bits数目 - virgin_bits

  /* Now, for the visuals... */

  if (clear_screen) {

    SAYF(TERM_CLEAR CURSOR_HIDE);
    clear_screen = 0;

    check_term_size();

  }

  SAYF(TERM_HOME);

  if (term_too_small) {

    SAYF(cBRI "Your terminal is too small to display the UI.\n"
         "Please resize terminal window to at least 80x25.\n" cRST);

    return;

  }

  /* Let's start by drawing a centered banner. */

  banner_len = (crash_mode ? 24 : 22) + strlen(VERSION) + strlen(use_banner);
  banner_pad = (80 - banner_len) / 2;
  memset(tmp, ' ', banner_pad);

  sprintf(tmp + banner_pad, "%s " cLCY VERSION cLGN
          " (%s)",  crash_mode ? cPIN "peruvian were-rabbit" : 
          cYEL "american fuzzy lop", use_banner);

  SAYF("\n%s\n\n", tmp);

  /* "Handy" shortcuts for drawing boxes... */

#define bSTG    bSTART cGRA
#define bH2     bH bH
#define bH5     bH2 bH2 bH
#define bH10    bH5 bH5
#define bH20    bH10 bH10
#define bH30    bH20 bH10
#define SP5     "     "
#define SP10    SP5 SP5
#define SP20    SP10 SP10

  /* Lord, forgive me this. */

  SAYF(SET_G1 bSTG bLT bH bSTOP cCYA " process timing " bSTG bH30 bH5 bH2 bHB
       bH bSTOP cCYA " overall results " bSTG bH5 bRT "\n");

  if (dumb_mode) {//这一块跟afl监控窗口中cycle done数字的颜色相关.afl用字体颜色指示这一次fuzzing的进度

    strcpy(tmp, cRST);//dumb mode中不设置颜色 cRST指代重置颜色

  } else {

    u64 min_wo_finds = (cur_ms - last_path_time) / 1000 / 60;

    /* First queue cycle: don't stop now! */
    if (queue_cycle == 1 || min_wo_finds < 15) strcpy(tmp, cMGN); else//一轮cycle或者没有新发现的时间小于15分钟,cycle的颜色为紫色

    /* Subsequent cycles, but we're still making finds. */
    if (cycles_wo_finds < 25 || min_wo_finds < 30) strcpy(tmp, cYEL); else//25轮以内没有新发现,或者30分钟内没有新发现,黄色

    /* No finds for a long time and no test cases to try. */
    if (cycles_wo_finds > 100 && !pending_not_fuzzed && min_wo_finds > 120)//100轮以上没有新发现,且队列中没有等待的case,且120分钟以上没有新发现,使用亮绿色
      strcpy(tmp, cLGN);

    /* Default: cautiously OK to stop? */
    else strcpy(tmp, cLBL);//其他情况下 使用亮蓝色

  }

  SAYF(bV bSTOP "        run time : " cRST "%-34s " bSTG bV bSTOP
       "  cycles done : %s%-5s  " bSTG bV "\n",
       DTD(cur_ms, start_time), tmp, DI(queue_cycle - 1));

  /* We want to warn people about not seeing new paths after a full cycle,
     except when resuming fuzzing or running in non-instrumented mode. */

  if (!dumb_mode && (last_path_time || resuming_fuzz || queue_cycle == 1 ||
      in_bitmap || crash_mode)) {

    SAYF(bV bSTOP "   last new path : " cRST "%-34s ",
         DTD(cur_ms, last_path_time));

  } else {

    if (dumb_mode)

      SAYF(bV bSTOP "   last new path : " cPIN "n/a" cRST 
           " (non-instrumented mode)        ");

     else

      SAYF(bV bSTOP "   last new path : " cRST "none yet " cLRD
           "(odd, check syntax!)      ");

  }

  SAYF(bSTG bV bSTOP "  total paths : " cRST "%-5s  " bSTG bV "\n",
       DI(queued_paths));

  /* Highlight crashes in red if found, denote going over the KEEP_UNIQUE_CRASH
     limit with a '+' appended to the count. */

  sprintf(tmp, "%s%s", DI(unique_crashes),
          (unique_crashes >= KEEP_UNIQUE_CRASH) ? "+" : "");

  SAYF(bV bSTOP " last uniq crash : " cRST "%-34s " bSTG bV bSTOP
       " uniq crashes : %s%-6s " bSTG bV "\n",
       DTD(cur_ms, last_crash_time), unique_crashes ? cLRD : cRST,
       tmp);

  sprintf(tmp, "%s%s", DI(unique_hangs),
         (unique_hangs >= KEEP_UNIQUE_HANG) ? "+" : "");

  SAYF(bV bSTOP "  last uniq hang : " cRST "%-34s " bSTG bV bSTOP 
       "   uniq hangs : " cRST "%-6s " bSTG bV "\n",
       DTD(cur_ms, last_hang_time), tmp);

  SAYF(bVR bH bSTOP cCYA " cycle progress " bSTG bH20 bHB bH bSTOP cCYA
       " map coverage " bSTG bH bHT bH20 bH2 bH bVL "\n");

  /* This gets funny because we want to print several variable-length variables
     together, but then cram them into a fixed-width field - so we need to
     put them in a temporary buffer first. */

  sprintf(tmp, "%s%s (%0.02f%%)", DI(current_entry),
          queue_cur->favored ? "" : "*",
          ((double)current_entry * 100) / queued_paths);

  SAYF(bV bSTOP "  now processing : " cRST "%-17s " bSTG bV bSTOP, tmp);

  sprintf(tmp, "%0.02f%% / %0.02f%%", ((double)queue_cur->bitmap_size) * 
          100 / MAP_SIZE, t_byte_ratio);

  SAYF("    map density : %s%-21s " bSTG bV "\n", t_byte_ratio > 70 ? cLRD : 
       ((t_bytes < 200 && !dumb_mode) ? cPIN : cRST), tmp);

  sprintf(tmp, "%s (%0.02f%%)", DI(cur_skipped_paths),
          ((double)cur_skipped_paths * 100) / queued_paths);

  SAYF(bV bSTOP " paths timed out : " cRST "%-17s " bSTG bV, tmp);

  sprintf(tmp, "%0.02f bits/tuple",
          t_bytes ? (((double)t_bits) / t_bytes) : 0);

  SAYF(bSTOP " count coverage : " cRST "%-21s " bSTG bV "\n", tmp);

  SAYF(bVR bH bSTOP cCYA " stage progress " bSTG bH20 bX bH bSTOP cCYA
       " findings in depth " bSTG bH20 bVL "\n");

  sprintf(tmp, "%s (%0.02f%%)", DI(queued_favored),
          ((double)queued_favored) * 100 / queued_paths);

  /* Yeah... it's still going on... halp? */

  SAYF(bV bSTOP "  now trying : " cRST "%-21s " bSTG bV bSTOP 
       " favored paths : " cRST "%-22s " bSTG bV "\n", stage_name, tmp);

  if (!stage_max) {

    sprintf(tmp, "%s/-", DI(stage_cur));

  } else {

    sprintf(tmp, "%s/%s (%0.02f%%)", DI(stage_cur), DI(stage_max),
            ((double)stage_cur) * 100 / stage_max);

  }

  SAYF(bV bSTOP " stage execs : " cRST "%-21s " bSTG bV bSTOP, tmp);

  sprintf(tmp, "%s (%0.02f%%)", DI(queued_with_cov),
          ((double)queued_with_cov) * 100 / queued_paths);

  SAYF("  new edges on : " cRST "%-22s " bSTG bV "\n", tmp);

  sprintf(tmp, "%s (%s%s unique)", DI(total_crashes), DI(unique_crashes),
          (unique_crashes >= KEEP_UNIQUE_CRASH) ? "+" : "");

  if (crash_mode) {

    SAYF(bV bSTOP " total execs : " cRST "%-21s " bSTG bV bSTOP
         "   new crashes : %s%-22s " bSTG bV "\n", DI(total_execs),
         unique_crashes ? cLRD : cRST, tmp);

  } else {

    SAYF(bV bSTOP " total execs : " cRST "%-21s " bSTG bV bSTOP
         " total crashes : %s%-22s " bSTG bV "\n", DI(total_execs),
         unique_crashes ? cLRD : cRST, tmp);

  }

  /* Show a warning about slow execution. */

  if (avg_exec < 100) {

    sprintf(tmp, "%s/sec (%s)", DF(avg_exec), avg_exec < 20 ?
            "zzzz..." : "slow!");

    SAYF(bV bSTOP "  exec speed : " cLRD "%-21s ", tmp);

  } else {

    sprintf(tmp, "%s/sec", DF(avg_exec));
    SAYF(bV bSTOP "  exec speed : " cRST "%-21s ", tmp);

  }

  sprintf(tmp, "%s (%s%s unique)", DI(total_tmouts), DI(unique_tmouts),
          (unique_hangs >= KEEP_UNIQUE_HANG) ? "+" : "");

  SAYF (bSTG bV bSTOP "  total tmouts : " cRST "%-22s " bSTG bV "\n", tmp);

  /* Aaaalmost there... hold on! */

  SAYF(bVR bH cCYA bSTOP " fuzzing strategy yields " bSTG bH10 bH bHT bH10
       bH5 bHB bH bSTOP cCYA " path geometry " bSTG bH5 bH2 bH bVL "\n");

  if (skip_deterministic) {

    strcpy(tmp, "n/a, n/a, n/a");

  } else {

    sprintf(tmp, "%s/%s, %s/%s, %s/%s",
            DI(stage_finds[STAGE_FLIP1]), DI(stage_cycles[STAGE_FLIP1]),
            DI(stage_finds[STAGE_FLIP2]), DI(stage_cycles[STAGE_FLIP2]),
            DI(stage_finds[STAGE_FLIP4]), DI(stage_cycles[STAGE_FLIP4]));

  }

  SAYF(bV bSTOP "   bit flips : " cRST "%-37s " bSTG bV bSTOP "    levels : "
       cRST "%-10s " bSTG bV "\n", tmp, DI(max_depth));

  if (!skip_deterministic)
    sprintf(tmp, "%s/%s, %s/%s, %s/%s",
            DI(stage_finds[STAGE_FLIP8]), DI(stage_cycles[STAGE_FLIP8]),
            DI(stage_finds[STAGE_FLIP16]), DI(stage_cycles[STAGE_FLIP16]),
            DI(stage_finds[STAGE_FLIP32]), DI(stage_cycles[STAGE_FLIP32]));

  SAYF(bV bSTOP "  byte flips : " cRST "%-37s " bSTG bV bSTOP "   pending : "
       cRST "%-10s " bSTG bV "\n", tmp, DI(pending_not_fuzzed));

  if (!skip_deterministic)
    sprintf(tmp, "%s/%s, %s/%s, %s/%s",
            DI(stage_finds[STAGE_ARITH8]), DI(stage_cycles[STAGE_ARITH8]),
            DI(stage_finds[STAGE_ARITH16]), DI(stage_cycles[STAGE_ARITH16]),
            DI(stage_finds[STAGE_ARITH32]), DI(stage_cycles[STAGE_ARITH32]));

  SAYF(bV bSTOP " arithmetics : " cRST "%-37s " bSTG bV bSTOP "  pend fav : "
       cRST "%-10s " bSTG bV "\n", tmp, DI(pending_favored));

  if (!skip_deterministic)
    sprintf(tmp, "%s/%s, %s/%s, %s/%s",
            DI(stage_finds[STAGE_INTEREST8]), DI(stage_cycles[STAGE_INTEREST8]),
            DI(stage_finds[STAGE_INTEREST16]), DI(stage_cycles[STAGE_INTEREST16]),
            DI(stage_finds[STAGE_INTEREST32]), DI(stage_cycles[STAGE_INTEREST32]));

  SAYF(bV bSTOP "  known ints : " cRST "%-37s " bSTG bV bSTOP " own finds : "
       cRST "%-10s " bSTG bV "\n", tmp, DI(queued_discovered));

  if (!skip_deterministic)
    sprintf(tmp, "%s/%s, %s/%s, %s/%s",
            DI(stage_finds[STAGE_EXTRAS_UO]), DI(stage_cycles[STAGE_EXTRAS_UO]),
            DI(stage_finds[STAGE_EXTRAS_UI]), DI(stage_cycles[STAGE_EXTRAS_UI]),
            DI(stage_finds[STAGE_EXTRAS_AO]), DI(stage_cycles[STAGE_EXTRAS_AO]));

  SAYF(bV bSTOP "  dictionary : " cRST "%-37s " bSTG bV bSTOP
       "  imported : " cRST "%-10s " bSTG bV "\n", tmp,
       sync_id ? DI(queued_imported) : (u8*)"n/a");

  sprintf(tmp, "%s/%s, %s/%s",
          DI(stage_finds[STAGE_HAVOC]), DI(stage_cycles[STAGE_HAVOC]),
          DI(stage_finds[STAGE_SPLICE]), DI(stage_cycles[STAGE_SPLICE]));

  SAYF(bV bSTOP "       havoc : " cRST "%-37s " bSTG bV bSTOP, tmp);

  if (t_bytes) sprintf(tmp, "%0.02f%%", stab_ratio);
    else strcpy(tmp, "n/a");

  SAYF(" stability : %s%-10s " bSTG bV "\n", (stab_ratio < 85 && var_byte_count > 40) 
       ? cLRD : ((queued_variable && (!persistent_mode || var_byte_count > 20))
       ? cMGN : cRST), tmp);

  if (!bytes_trim_out) {

    sprintf(tmp, "n/a, ");

  } else {

    sprintf(tmp, "%0.02f%%/%s, ",
            ((double)(bytes_trim_in - bytes_trim_out)) * 100 / bytes_trim_in,
            DI(trim_execs));

  }

  if (!blocks_eff_total) {

    u8 tmp2[128];

    sprintf(tmp2, "n/a");
    strcat(tmp, tmp2);

  } else {

    u8 tmp2[128];

    sprintf(tmp2, "%0.02f%%",
            ((double)(blocks_eff_total - blocks_eff_select)) * 100 /
            blocks_eff_total);

    strcat(tmp, tmp2);

  }

  SAYF(bV bSTOP "        trim : " cRST "%-37s " bSTG bVR bH20 bH2 bH2 bRB "\n"
       bLB bH30 bH20 bH2 bH bRB bSTOP cRST RESET_G1, tmp);

  /* Provide some CPU utilization stats. */

  if (cpu_core_count) {

    double cur_runnable = get_runnable_processes();//获取当前可运行的进程数
    u32 cur_utilization = cur_runnable * 100 / cpu_core_count;

    u8* cpu_color = cCYA;

    /* If we could still run one or more processes, use green. */

    if (cpu_core_count > 1 && cur_runnable + 1 <= cpu_core_count)
      cpu_color = cLGN;

    /* If we're clearly oversubscribed, use red. */

    if (!no_cpu_meter_red && cur_utilization >= 150) cpu_color = cLRD;//如果cpu使用率高于150，将这一条目在终端内显示为红色

#ifdef HAVE_AFFINITY

    if (cpu_aff >= 0) {

      SAYF(SP10 cGRA "[cpu%03u:%s%3u%%" cGRA "]\r" cRST, 
           MIN(cpu_aff, 999), cpu_color,
           MIN(cur_utilization, 999));

    } else {

      SAYF(SP10 cGRA "   [cpu:%s%3u%%" cGRA "]\r" cRST,
           cpu_color, MIN(cur_utilization, 999));
 
   }

#else

    SAYF(SP10 cGRA "   [cpu:%s%3u%%" cGRA "]\r" cRST,
         cpu_color, MIN(cur_utilization, 999));

#endif /* ^HAVE_AFFINITY */

  } else SAYF("\r");

  /* Hallelujah! */

  fflush(0);

}


/* Display quick statistics at the end of processing the input directory,
   plus a bunch of warnings. Some calibration stuff also ended up here,
   along with several hardcoded constants. Maybe clean up eventually. */

static void show_init_stats(void) {

  struct queue_entry* q = queue;
  u32 min_bits = 0, max_bits = 0;
  u64 min_us = 0, max_us = 0;
  u64 avg_us = 0;
  u32 max_len = 0;

  if (total_cal_cycles) avg_us = total_cal_us / total_cal_cycles;//计算平均时间

  while (q) {//遍历队列,统计一轮队列执行之后的最短执行时间,最长执行时间,最小bitmap_size,最大bitmap_size,最大testcase长度

    if (!min_us || q->exec_us < min_us) min_us = q->exec_us;
    if (q->exec_us > max_us) max_us = q->exec_us;

    if (!min_bits || q->bitmap_size < min_bits) min_bits = q->bitmap_size;
    if (q->bitmap_size > max_bits) max_bits = q->bitmap_size;

    if (q->len > max_len) max_len = q->len;

    q = q->next;

  }

  SAYF("\n");

  if (avg_us > (qemu_mode ? 50000 : 10000)) //常规模式下平均校准时间超过10000μs就提示"slow",qemu mode下放宽到50000μs
    WARNF(cLRD "The target binary is pretty slow! See %s/perf_tips.txt.",
          doc_path);

  /* Let's keep things moving with slow binaries. */
//对于执行速度慢的binary,AFL会选择增大havoc_div,从而影响havoc阶段中stage_max的值,减少havoc阶段的长度
  if (avg_us > 50000) havoc_div = 10;     /* 0-19 execs/sec   */ //例Line.6143  stage_max   = SPLICE_HAVOC * perf_score / havoc_div / 100;
  else if (avg_us > 20000) havoc_div = 5; /* 20-49 execs/sec  */
  else if (avg_us > 10000) havoc_div = 2; /* 50-100 execs/sec */

  if (!resuming_fuzz) {//如果不是恢复先前的fuzzing,这里会把一些基础提示信息都过一遍

    if (max_len > 50 * 1024)//如果testcase超过50KB,提示"huge"
      WARNF(cLRD "Some test cases are huge (%s) - see %s/perf_tips.txt!",
            DMS(max_len), doc_path);
    else if (max_len > 10 * 1024)//如果testcase超过10KB,提示"big"
      WARNF("Some test cases are big (%s) - see %s/perf_tips.txt.",
            DMS(max_len), doc_path);

    if (useless_at_start && !in_bitmap)//perform_dry_run()中,如果这次执行没有发生fault,没有发现new_bits,就会标记为FAULT_NOBITS,然后useless_at_start计数+1.如果useless_at_start!=0,并且没有在一开始提供input_bitmap,AFL会提示选择一个更小的集合,因为其中有些testcase没有用
      WARNF(cLRD "Some test cases look useless. Consider using a smaller set.");

    if (queued_paths > 100)//100个测试用例太多了
      WARNF(cLRD "You probably have far too many input files! Consider trimming down.");
    else if (queued_paths > 20)//20个测试用例也有点多
      WARNF("You have lots of input files; try starting small.");

  }

  OKF("Here are some useful stats:\n\n"

      cGRA "    Test case count : " cRST "%u favored, %u variable, %u total\n"
      cGRA "       Bitmap range : " cRST "%u to %u bits (average: %0.02f bits)\n"
      cGRA "        Exec timing : " cRST "%s to %s us (average: %s us)\n",
      queued_favored, queued_variable, queued_paths, min_bits, max_bits, 
      ((double)total_bitmap_size) / (total_bitmap_entries ? total_bitmap_entries : 1),
      DI(min_us), DI(max_us), DI(avg_us));

  if (!timeout_given) {//如果没有人工提供timeout,那这里根据binary的执行时间赋予一个倍数作为timeout

    /* Figure out the appropriate timeout. The basic idea is: 5x average or
       1x max, rounded up to EXEC_TM_ROUND ms and capped at 1 second.

       If the program is slow, the multiplier is lowered to 2x or 3x, because
       random scheduler jitter is less likely to have any impact, and because
       our patience is wearing thin =) */

    if (avg_us > 50000) exec_tmout = avg_us * 2 / 1000;//如果平均执行时间超过50000μs,timeout设置为平均值的2倍,"/1000"的目的是μs和ms的转换
    else if (avg_us > 10000) exec_tmout = avg_us * 3 / 1000;//如果avg_us在[10000,50000]之中,倍数为3
    else exec_tmout = avg_us * 5 / 1000;//执行比较快的Binary,倍数就选择为5

    exec_tmout = MAX(exec_tmout, max_us / 1000);//初步的timeout计算出来后,还要求不能超过实际执行中的最大执行时间
    exec_tmout = (exec_tmout + EXEC_TM_ROUND) / EXEC_TM_ROUND * EXEC_TM_ROUND;//EXEC_TM_ROUND 20 自动缩放时的超时舍入因子
//exec_tmout = (exec_tmout+20)/20*20
    if (exec_tmout > EXEC_TIMEOUT) exec_tmout = EXEC_TIMEOUT;//最后AFL内部有一个固定的EXEC_TIMEOUT 1000,任何执行无论如何不能超过EXEC_TIMEOUT

    ACTF("No -t option specified, so I'll use exec timeout of %u ms.", 
         exec_tmout);

    timeout_given = 1;

  } else if (timeout_given == 3) {//find_timeout()中,针对resuming_fuzz,afl会去out_dir中找stats,然后读取exec_timeout,这种情况下就直接用已经确定的timeout

    ACTF("Applying timeout settings from resumed session (%u ms).", exec_tmout);

  }

  /* In dumb mode, re-running every timing out test case with a generous time
     limit is very expensive, so let's select a more conservative default. */
//dumb mode下要重新运行每个超时的testcase开销太大,所以直接选择一个更保守的默认timeout,即将上述计算出的timeout再放宽要求
  if (dumb_mode && !getenv("AFL_HANG_TMOUT"))
    hang_tmout = MIN(EXEC_TIMEOUT, exec_tmout * 2 + 100);//在1000和exec_tmout*2+100中选择最小值

  OKF("All set and ready to roll!");

}


/* Find first power of two greater or equal to val (assuming val under
   2^31). */

static u32 next_p2(u32 val) {

  u32 ret = 1;
  while (val > ret) ret <<= 1;
  return ret;

} 


/* Trim all new test cases to save cycles when doing deterministic checks. The
   trimmer uses power-of-two increments somewhere between 1/16 and 1/1024 of
   file size, to keep the stage short and sweet. */

static u8 trim_case(char** argv, struct queue_entry* q, u8* in_buf) {

  static u8 tmp[64];
  static u8 clean_trace[MAP_SIZE];

  u8  needs_write = 0, fault = 0;
  u32 trim_exec = 0;
  u32 remove_len;
  u32 len_p2;

  /* Although the trimmer will be less useful when variable behavior is
     detected, it will still work to some extent, so we don't check for
     this. */

  if (q->len < 5) return 0;//如果case的length小于5就没有修建必要,直接返回

  stage_name = tmp;
  bytes_trim_in += q->len;//

  /* Select initial chunk len, starting with large steps. */

  len_p2 = next_p2(q->len);//计算len_p2,取大于q->len的2的幂的最小值

  remove_len = MAX(len_p2 / TRIM_START_STEPS, TRIM_MIN_BYTES);//起始的trim步长取len_p2/16和4中的最大值,最小步长为4字节

  /* Continue until the number of steps gets too high or the stepover
     gets too small. */

  while (remove_len >= MAX(len_p2 / TRIM_END_STEPS, TRIM_MIN_BYTES)) {//每轮循环过后步长减半,最终步长会小于TRIM_MIN_BYTES,此时循环结束

    u32 remove_pos = remove_len;

    sprintf(tmp, "trim %s/%s", DI(remove_len), DI(remove_len));

    stage_cur = 0;
    stage_max = q->len / remove_len;

    while (remove_pos < q->len) {//每次循环,删除位向后移一个步长

      u32 trim_avail = MIN(remove_len, q->len - remove_pos);//可以删减的长度
      u32 cksum;

      write_with_gap(in_buf, q->len, remove_pos, trim_avail);//将in_buf中q->len长度的case,从remove_pos开始,跳过trim_avail长度的字符串

      fault = run_target(argv, exec_tmout);//用新的trimmed in_buf运行target,记录fault状态
      trim_execs++;

      if (stop_soon || fault == FAULT_ERROR) goto abort_trimming;

      /* Note that we don't keep track of crashes or hangs here; maybe TODO? */

      cksum = hash32(trace_bits, MAP_SIZE, HASH_CONST);

      /* If the deletion had no impact on the trace, make it permanent. This
         isn't perfect for variable-path inputs, but we're just making a
         best-effort pass, so it's not a big deal if we end up with false
         negatives every now and then. */

      if (cksum == q->exec_cksum) {//比较修剪前后两次的bitmap的checksum,如果相等,即trim对程序运行没有影响,就保留这次修剪

        u32 move_tail = q->len - remove_pos - trim_avail;

        q->len -= trim_avail;
        len_p2  = next_p2(q->len);

        memmove(in_buf + remove_pos, in_buf + remove_pos + trim_avail, 
                move_tail);//从in_buf + remove_pos + trim_avail位置复制move_tail长度的字符串到in_buf + remove_pos,效果就是删除了中间这段字符串

        /* Let's save a clean trace, which will be needed by
           update_bitmap_score once we're done with the trimming stuff. */

        if (!needs_write) {

          needs_write = 1;
          memcpy(clean_trace, trace_bits, MAP_SIZE);//从trace_bits复制一份clean_trace作备份

        }

      } else remove_pos += remove_len;

      /* Since this can be slow, update the screen every now and then. */

      if (!(trim_exec++ % stats_update_freq)) show_stats();
      stage_cur++;

    }

    remove_len >>= 1;//每次循环,步长减半

  }

  /* If we have made changes to in_buf, we also need to update the on-disk
     version of the test case. */

  if (needs_write) {

    s32 fd;

    unlink(q->fname); /* ignore errors */

    fd = open(q->fname, O_WRONLY | O_CREAT | O_EXCL, 0600);

    if (fd < 0) PFATAL("Unable to create '%s'", q->fname);

    ck_write(fd, in_buf, q->len, q->fname);
    close(fd);

    memcpy(trace_bits, clean_trace, MAP_SIZE);
    update_bitmap_score(q);//更新bitmap评分

  }

abort_trimming:

  bytes_trim_out += q->len;
  return fault;

}


/* Write a modified test case, run program, process results. Handle
   error conditions, returning 1 if it's time to bail out. This is
   a helper function for fuzz_one(). */

EXP_ST u8 common_fuzz_stuff(char** argv, u8* out_buf, u32 len) {

  u8 fault;

  if (post_handler) {

    out_buf = post_handler(out_buf, &len);
    if (!out_buf || !len) return 0;

  }

  write_to_testcase(out_buf, len);

  fault = run_target(argv, exec_tmout);//用处理后的新case运行target

  if (stop_soon) return 1;

  if (fault == FAULT_TMOUT) {

    if (subseq_tmouts++ > TMOUT_LIMIT) {
      cur_skipped_paths++;
      return 1;//出现TMOUT就舍弃这个case
    }

  } else subseq_tmouts = 0;

  /* Users can hit us with SIGUSR1 to request the current input
     to be abandoned. */

  if (skip_requested) {

     skip_requested = 0;
     cur_skipped_paths++;
     return 1;

  }

  /* This handles FAULT_ERROR for us: */

  queued_discovered += save_if_interesting(argv, out_buf, len, fault);

  if (!(stage_cur % stats_update_freq) || stage_cur + 1 == stage_max)
    show_stats();

  return 0;

}


/* Helper to choose random block len for block operations in fuzz_one().
   Doesn't return zero, provided that max_len is > 0. */

static u32 choose_block_len(u32 limit) {

  u32 min_value, max_value;
  u32 rlim = MIN(queue_cycle, 3);

  if (!run_over10m) rlim = 1;//运行时间超过10分钟，rilm=1

  switch (UR(rlim)) {

    case 0:  min_value = 1;
             max_value = HAVOC_BLK_SMALL;
             break;

    case 1:  min_value = HAVOC_BLK_SMALL;
             max_value = HAVOC_BLK_MEDIUM;
             break;

    default: 

             if (UR(10)) {

               min_value = HAVOC_BLK_MEDIUM;
               max_value = HAVOC_BLK_LARGE;

             } else {

               min_value = HAVOC_BLK_LARGE;
               max_value = HAVOC_BLK_XL;

             }
//随机设置block长度取值的上下限
  }

  if (min_value >= limit) min_value = 1;//如果min_value比limit都大了，那干脆Min设置成1，保证limit>=min

  return min_value + UR(MIN(max_value, limit) - min_value + 1);//在min和MIN(max,limit)之间取一个随机数

}


/* Calculate case desirability score to adjust the length of havoc fuzzing.
   A helper function for fuzz_one(). Maybe some of these constants should
   go into config.h. */

static u32 calculate_score(struct queue_entry* q) {

  u32 avg_exec_us = total_cal_us / total_cal_cycles;
  u32 avg_bitmap_size = total_bitmap_size / total_bitmap_entries;
  u32 perf_score = 100;

  /* Adjust score based on execution speed of this path, compared to the
     global average. Multiplier ranges from 0.1x to 3x. Fast inputs are
     less expensive to fuzz, so we're giving them more air time. */

  if (q->exec_us * 0.1 > avg_exec_us) perf_score = 10;
  else if (q->exec_us * 0.25 > avg_exec_us) perf_score = 25;
  else if (q->exec_us * 0.5 > avg_exec_us) perf_score = 50;
  else if (q->exec_us * 0.75 > avg_exec_us) perf_score = 75;
  else if (q->exec_us * 4 < avg_exec_us) perf_score = 300;
  else if (q->exec_us * 3 < avg_exec_us) perf_score = 200;
  else if (q->exec_us * 2 < avg_exec_us) perf_score = 150;

  /* Adjust score based on bitmap size. The working theory is that better
     coverage translates to better targets. Multiplier from 0.25x to 3x. */

  if (q->bitmap_size * 0.3 > avg_bitmap_size) perf_score *= 3;
  else if (q->bitmap_size * 0.5 > avg_bitmap_size) perf_score *= 2;
  else if (q->bitmap_size * 0.75 > avg_bitmap_size) perf_score *= 1.5;
  else if (q->bitmap_size * 3 < avg_bitmap_size) perf_score *= 0.25;
  else if (q->bitmap_size * 2 < avg_bitmap_size) perf_score *= 0.5;
  else if (q->bitmap_size * 1.5 < avg_bitmap_size) perf_score *= 0.75;

  /* Adjust score based on handicap. Handicap is proportional to how late
     in the game we learned about this path. Latecomers are allowed to run
     for a bit longer until they catch up with the rest. */

  if (q->handicap >= 4) {

    perf_score *= 4;
    q->handicap -= 4;

  } else if (q->handicap) {

    perf_score *= 2;
    q->handicap--;

  }

  /* Final adjustment based on input depth, under the assumption that fuzzing
     deeper test cases is more likely to reveal stuff that can't be
     discovered with traditional fuzzers. */

  switch (q->depth) {

    case 0 ... 3:   break;
    case 4 ... 7:   perf_score *= 2; break;
    case 8 ... 13:  perf_score *= 3; break;
    case 14 ... 25: perf_score *= 4; break;
    default:        perf_score *= 5;

  }

  /* Make sure that we don't go over limit. */

  if (perf_score > HAVOC_MAX_MULT * 100) perf_score = HAVOC_MAX_MULT * 100;
//给一个分数上限
  return perf_score;

}


/* Helper function to see if a particular change (xor_val = old ^ new) could
   be a product of deterministic bit flips with the lengths and stepovers
   attempted by afl-fuzz. This is used to avoid dupes in some of the
   deterministic fuzzing operations that follow bit flips. We also
   return 1 if xor_val is zero, which implies that the old and attempted new
   values are identical and the exec would be a waste of time. */

static u8 could_be_bitflip(u32 xor_val) {

  u32 sh = 0;

  if (!xor_val) return 1;//但是这个应该不可能

  /* Shift left until first bit set. */

  while (!(xor_val & 1)) { sh++; xor_val >>= 1; }//不停右移,直到遇到第一个为1的位

  /* 1-, 2-, and 4-bit patterns are OK anywhere. */
//0b1 0b11 0b1111 对应bitflip四个粒度 arith阶段的ARITH_MAX为35(0b100011)
  if (xor_val == 1 || xor_val == 3 || xor_val == 15) return 1;

  /* 8-, 16-, and 32-bit patterns are OK only if shift factor is
     divisible by 8, since that's the stepover for these ops. */

  if (sh & 7) return 0;//仅当sh可被8整除时,才考虑8,16,32位模式
//对应8位,16位,32位的粒度
  if (xor_val == 0xff || xor_val == 0xffff || xor_val == 0xffffffff)
    return 1;

  return 0;

}


/* Helper function to see if a particular value is reachable through
   arithmetic operations. Used for similar purposes. */

static u8 could_be_arith(u32 old_val, u32 new_val, u8 blen) {

  u32 i, ov = 0, nv = 0, diffs = 0;

  if (old_val == new_val) return 1;

  /* See if one-byte adjustments to any byte could produce this result. */

  for (i = 0; i < blen; i++) {

    u8 a = old_val >> (8 * i),
       b = new_val >> (8 * i);

    if (a != b) { diffs++; ov = a; nv = b; }

  }

  /* If only one byte differs and the values are within range, return 1. */

  if (diffs == 1) {

    if ((u8)(ov - nv) <= ARITH_MAX ||
        (u8)(nv - ov) <= ARITH_MAX) return 1;

  }

  if (blen == 1) return 0;

  /* See if two-byte adjustments to any byte would produce this result. */

  diffs = 0;

  for (i = 0; i < blen / 2; i++) {

    u16 a = old_val >> (16 * i),
        b = new_val >> (16 * i);

    if (a != b) { diffs++; ov = a; nv = b; }

  }

  /* If only one word differs and the values are within range, return 1. */

  if (diffs == 1) {

    if ((u16)(ov - nv) <= ARITH_MAX ||
        (u16)(nv - ov) <= ARITH_MAX) return 1;

    ov = SWAP16(ov); nv = SWAP16(nv);

    if ((u16)(ov - nv) <= ARITH_MAX ||
        (u16)(nv - ov) <= ARITH_MAX) return 1;

  }

  /* Finally, let's do the same thing for dwords. */

  if (blen == 4) {

    if ((u32)(old_val - new_val) <= ARITH_MAX ||
        (u32)(new_val - old_val) <= ARITH_MAX) return 1;

    new_val = SWAP32(new_val);
    old_val = SWAP32(old_val);

    if ((u32)(old_val - new_val) <= ARITH_MAX ||
        (u32)(new_val - old_val) <= ARITH_MAX) return 1;

  }

  return 0;

}


/* Last but not least, a similar helper to see if insertion of an 
   interesting integer is redundant given the insertions done for
   shorter blen. The last param (check_le) is set if the caller
   already executed LE insertion for current blen and wants to see
   if BE variant passed in new_val is unique. */

static u8 could_be_interest(u32 old_val, u32 new_val, u8 blen, u8 check_le) {

  u32 i, j;

  if (old_val == new_val) return 1;

  /* See if one-byte insertions from interesting_8 over old_val could
     produce new_val. */

  for (i = 0; i < blen; i++) {

    for (j = 0; j < sizeof(interesting_8); j++) {

      u32 tval = (old_val & ~(0xff << (i * 8))) |
                 (((u8)interesting_8[j]) << (i * 8));

      if (new_val == tval) return 1;

    }

  }

  /* Bail out unless we're also asked to examine two-byte LE insertions
     as a preparation for BE attempts. */

  if (blen == 2 && !check_le) return 0;

  /* See if two-byte insertions over old_val could give us new_val. */

  for (i = 0; i < blen - 1; i++) {

    for (j = 0; j < sizeof(interesting_16) / 2; j++) {

      u32 tval = (old_val & ~(0xffff << (i * 8))) |
                 (((u16)interesting_16[j]) << (i * 8));

      if (new_val == tval) return 1;

      /* Continue here only if blen > 2. */

      if (blen > 2) {

        tval = (old_val & ~(0xffff << (i * 8))) |
               (SWAP16(interesting_16[j]) << (i * 8));

        if (new_val == tval) return 1;

      }

    }

  }

  if (blen == 4 && check_le) {

    /* See if four-byte insertions could produce the same result
       (LE only). */

    for (j = 0; j < sizeof(interesting_32) / 4; j++)
      if (new_val == (u32)interesting_32[j]) return 1;

  }

  return 0;

}


/* Take the current entry from the queue, fuzz it for a while. This
   function is a tad too long... returns 0 if fuzzed successfully, 1 if
   skipped or bailed out. */

static u8 fuzz_one(char** argv) {

  s32 len, fd, temp_len, i, j;
  u8  *in_buf, *out_buf, *orig_in, *ex_tmp, *eff_map = 0;
  u64 havoc_queued,  orig_hit_cnt, new_hit_cnt;
  u32 splice_cycle = 0, perf_score = 100, orig_perf, prev_cksum, eff_cnt = 1;

  u8  ret_val = 1, doing_det = 0;

  u8  a_collect[MAX_AUTO_EXTRA];
  u32 a_len = 0;

#ifdef IGNORE_FINDS

  /* In IGNORE_FINDS mode, skip any entries that weren't in the
     initial data set. */

  if (queue_cur->depth > 1) return 1;

#else

  if (pending_favored) {//如果有favored的case在等待,afl会考虑跳过当前的普通case

    /* If we have any favored, non-fuzzed new arrivals in the queue,
       possibly skip to them at the expense of already-fuzzed or non-favored
       cases. */

    if ((queue_cur->was_fuzzed || !queue_cur->favored) &&
        UR(100) < SKIP_TO_NEW_PROB) return 1;//如果队列中当前case是fuzz过的,且不是favored,默认以99%的概率跳过

  } else if (!dumb_mode && !queue_cur->favored && queued_paths > 10) {//如果队列中没有favored case,在非dumb mode中,如果当前case非favored,且队列中排了10个以上的case,afl会考虑以一定概率放弃没产出的case

    /* Otherwise, still possibly skip non-favored cases, albeit less often.
       The odds of skipping stuff are higher for already-fuzzed inputs and
       lower for never-fuzzed entries. */

    if (queue_cycle > 1 && !queue_cur->was_fuzzed) {//cycle大于1之后,afl才会进行skip

      if (UR(100) < SKIP_NFAV_NEW_PROB) return 1;//没有新的favors,当前case没有fuzz过,75%概率跳过

    } else {

      if (UR(100) < SKIP_NFAV_OLD_PROB) return 1;//没有新的favors,当前case已经fuzz过,95%概率跳过

    }

  }

#endif /* ^IGNORE_FINDS */

  if (not_on_tty) {
    ACTF("Fuzzing test case #%u (%u total, %llu uniq crashes found)...",
         current_entry, queued_paths, unique_crashes);
    fflush(stdout);
  }

  /* Map the test case into memory. */
//不跳过,那就在把testcase导入内存里
  fd = open(queue_cur->fname, O_RDONLY);

  if (fd < 0) PFATAL("Unable to open '%s'", queue_cur->fname);

  len = queue_cur->len;

  orig_in = in_buf = mmap(0, len, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0);

  if (orig_in == MAP_FAILED) PFATAL("Unable to mmap '%s'", queue_cur->fname);

  close(fd);

  /* We could mmap() out_buf as MAP_PRIVATE, but we end up clobbering every
     single byte anyway, so it wouldn't give us any performance or memory usage
     benefits. */

  out_buf = ck_alloc_nozero(len);

  subseq_tmouts = 0;

  cur_depth = queue_cur->depth;//路径深度

  /*******************************************
   * CALIBRATION (only if failed earlier on) *
   *******************************************/

  if (queue_cur->cal_failed) {//如果在之前的校准中失败了,再次执行校准

    u8 res = FAULT_TMOUT;

    if (queue_cur->cal_failed < CAL_CHANCES) {

      /* Reset exec_cksum to tell calibrate_case to re-execute the testcase
         avoiding the usage of an invalid trace_bits.
         For more info: https://github.com/AFLplusplus/AFLplusplus/pull/425 */

      queue_cur->exec_cksum = 0;

      res = calibrate_case(argv, queue_cur, in_buf, queue_cycle - 1, 0);

      if (res == FAULT_ERROR)//如果不能执行target,抛出异常
        FATAL("Unable to execute target application");

    }

    if (stop_soon || res != crash_mode) {
      cur_skipped_paths++;
      goto abandon_entry;//如果crash mode下没有发生crash 或者 crash mode下发生了fault,抛弃这个case
    }

  }

  /************
   * TRIMMING *
   ************/

  if (!dumb_mode && !queue_cur->trim_done) {

    u8 res = trim_case(argv, queue_cur, in_buf);//修剪case,

    if (res == FAULT_ERROR)
      FATAL("Unable to execute target application");

    if (stop_soon) {
      cur_skipped_paths++;
      goto abandon_entry;
    }

    /* Don't retry trimming, even if it failed. */

    queue_cur->trim_done = 1;//trim只对每个case进行一次,无论成功与否

    if (len != queue_cur->len) len = queue_cur->len;//更新修建后的case长度

  }

  memcpy(out_buf, in_buf, len);

  /*********************
   * PERFORMANCE SCORE *
   *********************/

  orig_perf = perf_score = calculate_score(queue_cur);//计算case的分数,根据queue_cur中记录的执行时长(越小越好),bitmap_size(越大越好),handicap(在fuzzing过程后期进入队列的case,可以有更多的时间测试),路径深度(越深越好)

  /* Skip right away if -d is given, if we have done deterministic fuzzing on
     this entry ourselves (was_fuzzed), or if it has gone through deterministic
     testing in earlier, resumed runs (passed_det). */

  if (skip_deterministic || queue_cur->was_fuzzed || queue_cur->passed_det)
    goto havoc_stage;//如果设置了-d,或者当前case已经fuzz过,或者该case已经通过了deterministic,直接跳转到havoc_stage

  /* Skip deterministic fuzzing if exec path checksum puts this out of scope
     for this master instance. */

  if (master_max && (queue_cur->exec_cksum % master_max) != master_id - 1)
    goto havoc_stage;//TODO 这个逻辑我是真没看懂

  doing_det = 1;

  /*********************************************
   * SIMPLE BITFLIP (+dictionary construction) *
   *********************************************/

#define FLIP_BIT(_ar, _b) do { \
    u8* _arf = (u8*)(_ar); \
    u32 _bf = (_b); \
    _arf[(_bf) >> 3] ^= (128 >> ((_bf) & 7)); \
  } while (0)

  /* Single walking bit. */

  stage_short = "flip1";
  stage_max   = len << 3;//获取case长度,单位Bit
  stage_name  = "bitflip 1/1";

  stage_val_type = STAGE_VAL_NONE;

  orig_hit_cnt = queued_paths + unique_crashes;//原始命中次数=队列中的case数+已经发现的互不相同的crash数

  prev_cksum = queue_cur->exec_cksum;

  for (stage_cur = 0; stage_cur < stage_max; stage_cur++) {

    stage_cur_byte = stage_cur >> 3;

    FLIP_BIT(out_buf, stage_cur);//依次对每个位作位翻转

    if (common_fuzz_stuff(argv, out_buf, len)) goto abandon_entry;//common_fuzz_stuff会运行变异后的case,决定这个翻转是否interesting

    FLIP_BIT(out_buf, stage_cur);//经过上面的测试,将这个bit翻转回来,确保每一轮循环产生的新case与原始case只有一位之差

    /* While flipping the least significant bit in every byte, pull of an extra
       trick to detect possible syntax tokens. In essence, the idea is that if
       you have a binary blob like this:

       xxxxxxxxIHDRxxxxxxxx

       ...and changing the leading and trailing bytes causes variable or no
       changes in program flow, but touching any character in the "IHDR" string
       always produces the same, distinctive path, it's highly likely that
       "IHDR" is an atomically-checked magic value of special significance to
       the fuzzed format.

       We do this here, rather than as a separate stage, because it's a nice
       way to keep the operation approximately "free" (i.e., no extra execs).
       
       Empirically, performing the check when flipping the least significant bit
       is advantageous, compared to doing it at the time of more disruptive
       changes, where the program flow may be affected in more violent ways.

       The caveat is that we won't generate dictionaries in the -d mode or -S
       mode - but that's probably a fair trade-off.

       This won't work particularly well with paths that exhibit variable
       behavior, but fails gracefully, so we'll carry out the checks anyway.

      */
//下面的if用于寻找token,找到就存入extra,
    if (!dumb_mode && (stage_cur & 7) == 7) {//如果翻转的是最低有效位

      u32 cksum = hash32(trace_bits, MAP_SIZE, HASH_CONST);

      if (stage_cur == stage_max - 1 && cksum == prev_cksum) {//如果stage_cur移动到了末尾,而checksum没有变化的话,就连带最后一个字符过长度check然后执行maybe_add_auto 后续在auto extras(over)阶段拿出来使用

        /* If at end of file and we are still collecting a string, grab the
           final character and force output. */

        if (a_len < MAX_AUTO_EXTRA) a_collect[a_len] = out_buf[stage_cur >> 3];
        a_len++;

        if (a_len >= MIN_AUTO_EXTRA && a_len <= MAX_AUTO_EXTRA)
          maybe_add_auto(a_collect, a_len);

      } else if (cksum != prev_cksum) {//如果依次翻转一段连续字节的最低有效位后,bitmap都发生了变化,afl就认为这是一段固定的token,然后进maybe_add_auto

        /* Otherwise, if the checksum has changed, see if we have something
           worthwhile queued up, and collect that if the answer is yes. */

        if (a_len >= MIN_AUTO_EXTRA && a_len <= MAX_AUTO_EXTRA)//token的长度要求在[3,32]中
          maybe_add_auto(a_collect, a_len);

        a_len = 0;
        prev_cksum = cksum;

      }

      /* Continue collecting string, but only if the bit flip actually made
         any difference - we don't want no-op tokens. */

      if (cksum != queue_cur->exec_cksum) {

        if (a_len < MAX_AUTO_EXTRA) a_collect[a_len] = out_buf[stage_cur >> 3];        
        a_len++;

      }

    }

  }
//刷新以下指标
  new_hit_cnt = queued_paths + unique_crashes;

  stage_finds[STAGE_FLIP1]  += new_hit_cnt - orig_hit_cnt;
  stage_cycles[STAGE_FLIP1] += stage_max;

  /* Two walking bits. */
//类似与bitflip 1/1 这里是每次翻转相邻2位.这里不再考虑找token
  stage_name  = "bitflip 2/1";
  stage_short = "flip2";
  stage_max   = (len << 3) - 1;

  orig_hit_cnt = new_hit_cnt;

  for (stage_cur = 0; stage_cur < stage_max; stage_cur++) {

    stage_cur_byte = stage_cur >> 3;

    FLIP_BIT(out_buf, stage_cur);
    FLIP_BIT(out_buf, stage_cur + 1);

    if (common_fuzz_stuff(argv, out_buf, len)) goto abandon_entry;

    FLIP_BIT(out_buf, stage_cur);
    FLIP_BIT(out_buf, stage_cur + 1);

  }

  new_hit_cnt = queued_paths + unique_crashes;

  stage_finds[STAGE_FLIP2]  += new_hit_cnt - orig_hit_cnt;
  stage_cycles[STAGE_FLIP2] += stage_max;

  /* Four walking bits. */

  stage_name  = "bitflip 4/1";
  stage_short = "flip4";
  stage_max   = (len << 3) - 3;

  orig_hit_cnt = new_hit_cnt;

  for (stage_cur = 0; stage_cur < stage_max; stage_cur++) {

    stage_cur_byte = stage_cur >> 3;

    FLIP_BIT(out_buf, stage_cur);
    FLIP_BIT(out_buf, stage_cur + 1);
    FLIP_BIT(out_buf, stage_cur + 2);
    FLIP_BIT(out_buf, stage_cur + 3);

    if (common_fuzz_stuff(argv, out_buf, len)) goto abandon_entry;

    FLIP_BIT(out_buf, stage_cur);
    FLIP_BIT(out_buf, stage_cur + 1);
    FLIP_BIT(out_buf, stage_cur + 2);
    FLIP_BIT(out_buf, stage_cur + 3);

  }

  new_hit_cnt = queued_paths + unique_crashes;

  stage_finds[STAGE_FLIP4]  += new_hit_cnt - orig_hit_cnt;
  stage_cycles[STAGE_FLIP4] += stage_max;

  /* Effector map setup. These macros calculate:

     EFF_APOS      - position of a particular file offset in the map.
     EFF_ALEN      - length of a map with a particular number of bytes.
     EFF_SPAN_ALEN - map span for a sequence of bytes.

   */
//在进行bytefilp前,afl生成一个effector map
//EFFAPOS:以byte为单位,在map中定位一个文件偏移
//EFF_REM:可能是remain?,(_x)&0x111,目的大概是查看文件能否恰好转换为整数个字节
//EFF_ALEN:map的长度,单位字节,EFF_APOS获取最后一位,考虑EFF_REM,如果最后有小于1字节的残留位,额外增加一字节.举例的话,假设_l=9,此时APOS(_l)=1,!!EFF_REM(_l)=1.双叹号表示,所有非零值都转换成1,否则为0
//EFF_SPAN_ALEN:
#define EFF_APOS(_p)          ((_p) >> EFF_MAP_SCALE2)
#define EFF_REM(_x)           ((_x) & ((1 << EFF_MAP_SCALE2) - 1))
#define EFF_ALEN(_l)          (EFF_APOS(_l) + !!EFF_REM(_l))
#define EFF_SPAN_ALEN(_p, _l) (EFF_APOS((_p) + (_l) - 1) - EFF_APOS(_p) + 1)

  /* Initialize effector map for the next step (see comments below). Always
     flag first and last byte as doing something. */

  eff_map    = ck_alloc(EFF_ALEN(len));//开辟足够容纳effector map的空间
  eff_map[0] = 1;//首位置1

  if (EFF_APOS(len - 1) != 0) {
    eff_map[EFF_APOS(len - 1)] = 1;//末位置1,不一定是末位,如果len&0x111的话,那就是倒数第二位置1
    eff_cnt++;
  }

  /* Walking byte. */

  stage_name  = "bitflip 8/8";
  stage_short = "flip8";
  stage_max   = len;

  orig_hit_cnt = new_hit_cnt;

  for (stage_cur = 0; stage_cur < stage_max; stage_cur++) {

    stage_cur_byte = stage_cur;

    out_buf[stage_cur] ^= 0xFF;//字节翻转

    if (common_fuzz_stuff(argv, out_buf, len)) goto abandon_entry;//执行common_fuzz_stuff 记录执行状态

    /* We also use this stage to pull off a simple trick: we identify
       bytes that seem to have no effect on the current execution path
       even when fully flipped - and we skip them during more expensive
       deterministic stages, such as arithmetics or known ints. */
//通过effector map,识别对当前执行路径没有影响的字节,从而跳过arithmetics和known ints
    if (!eff_map[EFF_APOS(stage_cur)]) {//仅当effector map中当前字节标记为0时才进行以下代码

      u32 cksum;

      /* If in dumb mode or if the file is very short, just flag everything
         without wasting time on checksums. */

      if (!dumb_mode && len >= EFF_MIN_LEN)//如果不是dumb mode或者文件太小,就认真执行hash32,否则就将当前记录的cksum取反,作为新的cksum,直接视作checksum变了,略过高开销的hash32
        cksum = hash32(trace_bits, MAP_SIZE, HASH_CONST);
      else
        cksum = ~queue_cur->exec_cksum;

      if (cksum != queue_cur->exec_cksum) {//如果前后两次的checksum发生了变化,那么执行路径发生了变化
        eff_map[EFF_APOS(stage_cur)] = 1;//将该字节在effector_map中置1,表示该字节"有效",即会影响执行路径
        eff_cnt++;//eff_cnt会计数有效字节数
      }

    }

    out_buf[stage_cur] ^= 0xFF;

  }

  /* If the effector map is more than EFF_MAX_PERC dense, just flag the
     whole thing as worth fuzzing, since we wouldn't be saving much time
     anyway. */

  if (eff_cnt != EFF_ALEN(len) &&
      eff_cnt * 100 / EFF_ALEN(len) > EFF_MAX_PERC) {//如果不是整个case的所有字节都有效,但是有效字节的比例超过90%,那干脆整个effector map置1,认为整个case都值得fuzzing

    memset(eff_map, 1, EFF_ALEN(len));

    blocks_eff_select += EFF_ALEN(len);//blocks_eff_select只用在screen上

  } else {

    blocks_eff_select += eff_cnt;

  }

  blocks_eff_total += EFF_ALEN(len);//blocks_eff_total也是应用在screen上

  new_hit_cnt = queued_paths + unique_crashes;

  stage_finds[STAGE_FLIP8]  += new_hit_cnt - orig_hit_cnt;
  stage_cycles[STAGE_FLIP8] += stage_max;

  /* Two walking bytes. */

  if (len < 2) goto skip_bitflip;

  stage_name  = "bitflip 16/8";
  stage_short = "flip16";
  stage_cur   = 0;
  stage_max   = len - 1;

  orig_hit_cnt = new_hit_cnt;

  for (i = 0; i < len - 1; i++) {

    /* Let's consult the effector map... */
//查看effector map中相邻两位,
    if (!eff_map[EFF_APOS(i)] && !eff_map[EFF_APOS(i + 1)]) {
      stage_max--;//stage_max表示实际执行的双字节翻转次数,所以如果这里条件成立跳过了这一轮循环,表示节省一次翻转次数,max--
      continue;
    }

    stage_cur_byte = i;

    *(u16*)(out_buf + i) ^= 0xFFFF;

    if (common_fuzz_stuff(argv, out_buf, len)) goto abandon_entry;
    stage_cur++;

    *(u16*)(out_buf + i) ^= 0xFFFF;


  }

  new_hit_cnt = queued_paths + unique_crashes;

  stage_finds[STAGE_FLIP16]  += new_hit_cnt - orig_hit_cnt;
  stage_cycles[STAGE_FLIP16] += stage_max;

  if (len < 4) goto skip_bitflip;

  /* Four walking bytes. */

  stage_name  = "bitflip 32/8";
  stage_short = "flip32";
  stage_cur   = 0;
  stage_max   = len - 3;

  orig_hit_cnt = new_hit_cnt;

  for (i = 0; i < len - 3; i++) {

    /* Let's consult the effector map... */
    if (!eff_map[EFF_APOS(i)] && !eff_map[EFF_APOS(i + 1)] &&
        !eff_map[EFF_APOS(i + 2)] && !eff_map[EFF_APOS(i + 3)]) {
      stage_max--;
      continue;
    }

    stage_cur_byte = i;

    *(u32*)(out_buf + i) ^= 0xFFFFFFFF;

    if (common_fuzz_stuff(argv, out_buf, len)) goto abandon_entry;
    stage_cur++;

    *(u32*)(out_buf + i) ^= 0xFFFFFFFF;

  }

  new_hit_cnt = queued_paths + unique_crashes;

  stage_finds[STAGE_FLIP32]  += new_hit_cnt - orig_hit_cnt;
  stage_cycles[STAGE_FLIP32] += stage_max;

skip_bitflip:
//如果跳过位翻转,就直接跳到下面的arithmetic stage
  if (no_arith) goto skip_arith;

  /**********************
   * ARITHMETIC INC/DEC *
   **********************/

  /* 8-bit arithmetics. */

  stage_name  = "arith 8/8";
  stage_short = "arith8";
  stage_cur   = 0;
  stage_max   = 2 * len * ARITH_MAX;//len:每个字节都变异,2:加或减,ARITH_MAX:每个字节加减1到35

  stage_val_type = STAGE_VAL_LE;

  orig_hit_cnt = new_hit_cnt;

  for (i = 0; i < len; i++) {

    u8 orig = out_buf[i];

    /* Let's consult the effector map... */

    if (!eff_map[EFF_APOS(i)]) {
      stage_max -= 2 * ARITH_MAX;
      continue;
    }//借助effector_map,仅探索有效位

    stage_cur_byte = i;

    for (j = 1; j <= ARITH_MAX; j++) {

      u8 r = orig ^ (orig + j);//原始值与原始值+j作异或

      /* Do arithmetic operations only if the result couldn't be a product
         of a bitflip. */

      if (!could_be_bitflip(r)) {//判断orig+j能否由orig通过bitsflip得来,可以的话表示bitflip阶段已经尝试过,所以可以略过这一轮循环

        stage_cur_val = j;
        out_buf[i] = orig + j;

        if (common_fuzz_stuff(argv, out_buf, len)) goto abandon_entry;
        stage_cur++;

      } else stage_max--;

      r =  orig ^ (orig - j);//尝试将原始值减去一个数是否是bitflip可以实现的

      if (!could_be_bitflip(r)) {

        stage_cur_val = -j;
        out_buf[i] = orig - j;

        if (common_fuzz_stuff(argv, out_buf, len)) goto abandon_entry;
        stage_cur++;

      } else stage_max--;

      out_buf[i] = orig;

    }

  }

  new_hit_cnt = queued_paths + unique_crashes;

  stage_finds[STAGE_ARITH8]  += new_hit_cnt - orig_hit_cnt;
  stage_cycles[STAGE_ARITH8] += stage_max;

  /* 16-bit arithmetics, both endians. */
//类似8位算术,但是16位开始会考虑大小端
  if (len < 2) goto skip_arith;

  stage_name  = "arith 16/8";
  stage_short = "arith16";
  stage_cur   = 0;
  stage_max   = 4 * (len - 1) * ARITH_MAX;//正负,大小端  所以是4种组合

  orig_hit_cnt = new_hit_cnt;

  for (i = 0; i < len - 1; i++) {

    u16 orig = *(u16*)(out_buf + i);

    /* Let's consult the effector map... */

    if (!eff_map[EFF_APOS(i)] && !eff_map[EFF_APOS(i + 1)]) {
      stage_max -= 4 * ARITH_MAX;
      continue;
    }

    stage_cur_byte = i;

    for (j = 1; j <= ARITH_MAX; j++) {

      u16 r1 = orig ^ (orig + j),//小端
          r2 = orig ^ (orig - j),
          r3 = orig ^ SWAP16(SWAP16(orig) + j),//用SWAP16实现大小端转换,原始双字节,大小端转换后+j,再大小端转换回来,就能实现大端加减
          r4 = orig ^ SWAP16(SWAP16(orig) - j);

      /* Try little endian addition and subtraction first. Do it only
         if the operation would affect more than one byte (hence the 
         & 0xff overflow checks) and if it couldn't be a product of
         a bitflip. */

      stage_val_type = STAGE_VAL_LE; 

      if ((orig & 0xff) + j > 0xff && !could_be_bitflip(r1)) {//尝试低8位+j,如果大于0xff,说明没有溢出

        stage_cur_val = j;
        *(u16*)(out_buf + i) = orig + j;

        if (common_fuzz_stuff(argv, out_buf, len)) goto abandon_entry;
        stage_cur++;
 
      } else stage_max--;

      if ((orig & 0xff) < j && !could_be_bitflip(r2)) {//考虑减法的时候,保证j比低8位大???????????保证下溢?

        stage_cur_val = -j;
        *(u16*)(out_buf + i) = orig - j;

        if (common_fuzz_stuff(argv, out_buf, len)) goto abandon_entry;
        stage_cur++;

      } else stage_max--;

      /* Big endian comes next. Same deal. */

      stage_val_type = STAGE_VAL_BE;


      if ((orig >> 8) + j > 0xff && !could_be_bitflip(r3)) {

        stage_cur_val = j;
        *(u16*)(out_buf + i) = SWAP16(SWAP16(orig) + j);

        if (common_fuzz_stuff(argv, out_buf, len)) goto abandon_entry;
        stage_cur++;

      } else stage_max--;

      if ((orig >> 8) < j && !could_be_bitflip(r4)) {

        stage_cur_val = -j;
        *(u16*)(out_buf + i) = SWAP16(SWAP16(orig) - j);

        if (common_fuzz_stuff(argv, out_buf, len)) goto abandon_entry;
        stage_cur++;

      } else stage_max--;

      *(u16*)(out_buf + i) = orig;

    }

  }

  new_hit_cnt = queued_paths + unique_crashes;

  stage_finds[STAGE_ARITH16]  += new_hit_cnt - orig_hit_cnt;
  stage_cycles[STAGE_ARITH16] += stage_max;

  /* 32-bit arithmetics, both endians. */

  if (len < 4) goto skip_arith;

  stage_name  = "arith 32/8";
  stage_short = "arith32";
  stage_cur   = 0;
  stage_max   = 4 * (len - 3) * ARITH_MAX;

  orig_hit_cnt = new_hit_cnt;

  for (i = 0; i < len - 3; i++) {

    u32 orig = *(u32*)(out_buf + i);

    /* Let's consult the effector map... */

    if (!eff_map[EFF_APOS(i)] && !eff_map[EFF_APOS(i + 1)] &&
        !eff_map[EFF_APOS(i + 2)] && !eff_map[EFF_APOS(i + 3)]) {
      stage_max -= 4 * ARITH_MAX;
      continue;
    }

    stage_cur_byte = i;

    for (j = 1; j <= ARITH_MAX; j++) {

      u32 r1 = orig ^ (orig + j),
          r2 = orig ^ (orig - j),
          r3 = orig ^ SWAP32(SWAP32(orig) + j),
          r4 = orig ^ SWAP32(SWAP32(orig) - j);

      /* Little endian first. Same deal as with 16-bit: we only want to
         try if the operation would have effect on more than two bytes. */

      stage_val_type = STAGE_VAL_LE;

      if ((orig & 0xffff) + j > 0xffff && !could_be_bitflip(r1)) {

        stage_cur_val = j;
        *(u32*)(out_buf + i) = orig + j;

        if (common_fuzz_stuff(argv, out_buf, len)) goto abandon_entry;
        stage_cur++;

      } else stage_max--;

      if ((orig & 0xffff) < j && !could_be_bitflip(r2)) {

        stage_cur_val = -j;
        *(u32*)(out_buf + i) = orig - j;

        if (common_fuzz_stuff(argv, out_buf, len)) goto abandon_entry;
        stage_cur++;

      } else stage_max--;

      /* Big endian next. */

      stage_val_type = STAGE_VAL_BE;

      if ((SWAP32(orig) & 0xffff) + j > 0xffff && !could_be_bitflip(r3)) {

        stage_cur_val = j;
        *(u32*)(out_buf + i) = SWAP32(SWAP32(orig) + j);

        if (common_fuzz_stuff(argv, out_buf, len)) goto abandon_entry;
        stage_cur++;

      } else stage_max--;

      if ((SWAP32(orig) & 0xffff) < j && !could_be_bitflip(r4)) {

        stage_cur_val = -j;
        *(u32*)(out_buf + i) = SWAP32(SWAP32(orig) - j);

        if (common_fuzz_stuff(argv, out_buf, len)) goto abandon_entry;
        stage_cur++;

      } else stage_max--;

      *(u32*)(out_buf + i) = orig;

    }

  }

  new_hit_cnt = queued_paths + unique_crashes;

  stage_finds[STAGE_ARITH32]  += new_hit_cnt - orig_hit_cnt;
  stage_cycles[STAGE_ARITH32] += stage_max;

skip_arith:
//arithmetic阶段之后 就是直接去赋予一些interesting的值 比如interesting_8和interesting_16中
  /**********************
   * INTERESTING VALUES *
   **********************/

  stage_name  = "interest 8/8";
  stage_short = "int8";
  stage_cur   = 0;
  stage_max   = len * sizeof(interesting_8);

  stage_val_type = STAGE_VAL_LE;

  orig_hit_cnt = new_hit_cnt;

  /* Setting 8-bit integers. */

  for (i = 0; i < len; i++) {

    u8 orig = out_buf[i];

    /* Let's consult the effector map... */

    if (!eff_map[EFF_APOS(i)]) {
      stage_max -= sizeof(interesting_8);
      continue;
    }//依旧借助eff_map  只操作有效位

    stage_cur_byte = i;

    for (j = 0; j < sizeof(interesting_8); j++) {

      /* Skip if the value could be a product of bitflips or arithmetics. */

      if (could_be_bitflip(orig ^ (u8)interesting_8[j]) ||
          could_be_arith(orig, (u8)interesting_8[j], 1)) {//类似arith stage.如果修改后的值,可以通过bitflip或arith得到,那就没有必要去尝试这个值. 但是这里有个问题,设置no_arith是可以跳过arith_stage的,那这里其实会出现:arith被跳过,而这里遇到了一个值,满足could_be_arith,于是也被跳过,那实际上这个值就没被运行
        stage_max--;
        continue;
      }

      stage_cur_val = interesting_8[j];
      out_buf[i] = interesting_8[j];

      if (common_fuzz_stuff(argv, out_buf, len)) goto abandon_entry;

      out_buf[i] = orig;
      stage_cur++;

    }

  }

  new_hit_cnt = queued_paths + unique_crashes;

  stage_finds[STAGE_INTEREST8]  += new_hit_cnt - orig_hit_cnt;
  stage_cycles[STAGE_INTEREST8] += stage_max;

  /* Setting 16-bit integers, both endians. */

  if (no_arith || len < 2) goto skip_interest;//如果选择跳过arith stage,那以下的多字节interest也跳过

  stage_name  = "interest 16/8";
  stage_short = "int16";
  stage_cur   = 0;
  stage_max   = 2 * (len - 1) * (sizeof(interesting_16) >> 1);

  orig_hit_cnt = new_hit_cnt;

  for (i = 0; i < len - 1; i++) {

    u16 orig = *(u16*)(out_buf + i);

    /* Let's consult the effector map... */

    if (!eff_map[EFF_APOS(i)] && !eff_map[EFF_APOS(i + 1)]) {
      stage_max -= sizeof(interesting_16);
      continue;
    }

    stage_cur_byte = i;

    for (j = 0; j < sizeof(interesting_16) / 2; j++) {

      stage_cur_val = interesting_16[j];

      /* Skip if this could be a product of a bitflip, arithmetics,
         or single-byte interesting value insertion. */

      if (!could_be_bitflip(orig ^ (u16)interesting_16[j]) &&
          !could_be_arith(orig, (u16)interesting_16[j], 2) &&
          !could_be_interest(orig, (u16)interesting_16[j], 2, 0)) {//对于多字节interesting value,还考虑这是不是能通过单字节interesting value获得.

        stage_val_type = STAGE_VAL_LE;

        *(u16*)(out_buf + i) = interesting_16[j];

        if (common_fuzz_stuff(argv, out_buf, len)) goto abandon_entry;
        stage_cur++;

      } else stage_max--;

      if ((u16)interesting_16[j] != SWAP16(interesting_16[j]) &&
          !could_be_bitflip(orig ^ SWAP16(interesting_16[j])) &&
          !could_be_arith(orig, SWAP16(interesting_16[j]), 2) &&
          !could_be_interest(orig, SWAP16(interesting_16[j]), 2, 1)) {

        stage_val_type = STAGE_VAL_BE;

        *(u16*)(out_buf + i) = SWAP16(interesting_16[j]);
        if (common_fuzz_stuff(argv, out_buf, len)) goto abandon_entry;
        stage_cur++;

      } else stage_max--;

    }

    *(u16*)(out_buf + i) = orig;

  }

  new_hit_cnt = queued_paths + unique_crashes;

  stage_finds[STAGE_INTEREST16]  += new_hit_cnt - orig_hit_cnt;
  stage_cycles[STAGE_INTEREST16] += stage_max;

  if (len < 4) goto skip_interest;

  /* Setting 32-bit integers, both endians. */

  stage_name  = "interest 32/8";
  stage_short = "int32";
  stage_cur   = 0;
  stage_max   = 2 * (len - 3) * (sizeof(interesting_32) >> 2);

  orig_hit_cnt = new_hit_cnt;

  for (i = 0; i < len - 3; i++) {

    u32 orig = *(u32*)(out_buf + i);

    /* Let's consult the effector map... */

    if (!eff_map[EFF_APOS(i)] && !eff_map[EFF_APOS(i + 1)] &&
        !eff_map[EFF_APOS(i + 2)] && !eff_map[EFF_APOS(i + 3)]) {
      stage_max -= sizeof(interesting_32) >> 1;
      continue;
    }

    stage_cur_byte = i;

    for (j = 0; j < sizeof(interesting_32) / 4; j++) {

      stage_cur_val = interesting_32[j];

      /* Skip if this could be a product of a bitflip, arithmetics,
         or word interesting value insertion. */

      if (!could_be_bitflip(orig ^ (u32)interesting_32[j]) &&
          !could_be_arith(orig, interesting_32[j], 4) &&
          !could_be_interest(orig, interesting_32[j], 4, 0)) {

        stage_val_type = STAGE_VAL_LE;

        *(u32*)(out_buf + i) = interesting_32[j];

        if (common_fuzz_stuff(argv, out_buf, len)) goto abandon_entry;
        stage_cur++;

      } else stage_max--;

      if ((u32)interesting_32[j] != SWAP32(interesting_32[j]) &&
          !could_be_bitflip(orig ^ SWAP32(interesting_32[j])) &&
          !could_be_arith(orig, SWAP32(interesting_32[j]), 4) &&
          !could_be_interest(orig, SWAP32(interesting_32[j]), 4, 1)) {

        stage_val_type = STAGE_VAL_BE;

        *(u32*)(out_buf + i) = SWAP32(interesting_32[j]);
        if (common_fuzz_stuff(argv, out_buf, len)) goto abandon_entry;
        stage_cur++;

      } else stage_max--;

    }

    *(u32*)(out_buf + i) = orig;

  }

  new_hit_cnt = queued_paths + unique_crashes;

  stage_finds[STAGE_INTEREST32]  += new_hit_cnt - orig_hit_cnt;
  stage_cycles[STAGE_INTEREST32] += stage_max;

skip_interest:

  /********************
   * DICTIONARY STUFF *
   ********************/
//interesting阶段是afl预设了一些认为会有特殊含义的数值,dictionary环节则是由用户提供一些值
  if (!extras_cnt) goto skip_user_extras;//字典如果是空的就没必要进行这个stage

  /* Overwrite with user-supplied extras. */
//该环节是字典中的值覆写内存
  stage_name  = "user extras (over)";
  stage_short = "ext_UO";
  stage_cur   = 0;
  stage_max   = extras_cnt * len;//把字典里的值再每个位置都用一遍

  stage_val_type = STAGE_VAL_NONE;

  orig_hit_cnt = new_hit_cnt;

  for (i = 0; i < len; i++) {

    u32 last_len = 0;

    stage_cur_byte = i;

    /* Extras are sorted by size, from smallest to largest. This means
       that we don't have to worry about restoring the buffer in
       between writes at a particular offset determined by the outer
       loop. */

    for (j = 0; j < extras_cnt; j++) {

      /* Skip extras probabilistically if extras_cnt > MAX_DET_EXTRAS. Also
         skip them if there's no room to insert the payload, if the token
         is redundant, or if its entire span has no bytes set in the effector
         map. */

      if ((extras_cnt > MAX_DET_EXTRAS && UR(extras_cnt) >= MAX_DET_EXTRAS) ||
          extras[j].len > len - i ||
          !memcmp(extras[j].data, out_buf + i, extras[j].len) ||
          !memchr(eff_map + EFF_APOS(i), 1, EFF_SPAN_ALEN(i, extras[j].len))) {

        stage_max--;
        continue;

      }

      last_len = extras[j].len;
      memcpy(out_buf + i, extras[j].data, last_len);

      if (common_fuzz_stuff(argv, out_buf, len)) goto abandon_entry;

      stage_cur++;

    }

    /* Restore all the clobbered memory. */
    memcpy(out_buf + i, in_buf + i, last_len);

  }

  new_hit_cnt = queued_paths + unique_crashes;

  stage_finds[STAGE_EXTRAS_UO]  += new_hit_cnt - orig_hit_cnt;
  stage_cycles[STAGE_EXTRAS_UO] += stage_max;

  /* Insertion of user-supplied extras. */
//该环节是将字典值插入内存,会引起输入长度的变化
  stage_name  = "user extras (insert)";
  stage_short = "ext_UI";
  stage_cur   = 0;
  stage_max   = extras_cnt * (len + 1);

  orig_hit_cnt = new_hit_cnt;

  ex_tmp = ck_alloc(len + MAX_DICT_FILE);

  for (i = 0; i <= len; i++) {

    stage_cur_byte = i;

    for (j = 0; j < extras_cnt; j++) {

      if (len + extras[j].len > MAX_FILE) {
        stage_max--; 
        continue;
      }

      /* Insert token */
      memcpy(ex_tmp + i, extras[j].data, extras[j].len);

      /* Copy tail */
      memcpy(ex_tmp + i + extras[j].len, out_buf + i, len - i);

      if (common_fuzz_stuff(argv, ex_tmp, len + extras[j].len)) {
        ck_free(ex_tmp);
        goto abandon_entry;
      }

      stage_cur++;

    }

    /* Copy head */
    ex_tmp[i] = out_buf[i];

  }

  ck_free(ex_tmp);

  new_hit_cnt = queued_paths + unique_crashes;

  stage_finds[STAGE_EXTRAS_UI]  += new_hit_cnt - orig_hit_cnt;
  stage_cycles[STAGE_EXTRAS_UI] += stage_max;

skip_user_extras:

  if (!a_extras_cnt) goto skip_extras;
//这一阶段类似 user extras(over)  但这一阶段的token都是bitflip阶段自动生成的
  stage_name  = "auto extras (over)";
  stage_short = "ext_AO";
  stage_cur   = 0;
  stage_max   = MIN(a_extras_cnt, USE_AUTO_EXTRAS) * len;

  stage_val_type = STAGE_VAL_NONE;

  orig_hit_cnt = new_hit_cnt;

  for (i = 0; i < len; i++) {

    u32 last_len = 0;

    stage_cur_byte = i;

    for (j = 0; j < MIN(a_extras_cnt, USE_AUTO_EXTRAS); j++) {

      /* See the comment in the earlier code; extras are sorted by size. */

      if (a_extras[j].len > len - i ||
          !memcmp(a_extras[j].data, out_buf + i, a_extras[j].len) ||
          !memchr(eff_map + EFF_APOS(i), 1, EFF_SPAN_ALEN(i, a_extras[j].len))) {

        stage_max--;
        continue;

      }

      last_len = a_extras[j].len;
      memcpy(out_buf + i, a_extras[j].data, last_len);

      if (common_fuzz_stuff(argv, out_buf, len)) goto abandon_entry;

      stage_cur++;

    }

    /* Restore all the clobbered memory. */
    memcpy(out_buf + i, in_buf + i, last_len);

  }

  new_hit_cnt = queued_paths + unique_crashes;

  stage_finds[STAGE_EXTRAS_AO]  += new_hit_cnt - orig_hit_cnt;
  stage_cycles[STAGE_EXTRAS_AO] += stage_max;

skip_extras:

  /* If we made this to here without jumping to havoc_stage or abandon_entry,
     we're properly done with deterministic steps and can mark it as such
     in the .state/ directory. */

  if (!queue_cur->passed_det) mark_as_det_done(queue_cur);//无论是跳过了det阶段还是认真经过了det阶段,这里都会在queue中标记这个case完成了deterministic

  /****************
   * RANDOM HAVOC *
   ****************/
//接下来的就是随机的破坏性变异阶段
havoc_stage:

  stage_cur_byte = -1;

  /* The havoc stage mutation code is also invoked when splicing files; if the
     splice_cycle variable is set, generate different descriptions and such. */

  if (!splice_cycle) {//拼接文件的时候也会调用havoc,为了区分这是splice_cycle还是常规的cycle,设置这个变量作为判断条件

    stage_name  = "havoc";
    stage_short = "havoc";
    stage_max   = (doing_det ? HAVOC_CYCLES_INIT : HAVOC_CYCLES) *
                  perf_score / havoc_div / 100;//Line.5159,如果满足一些条件(比如当前case已经fuzz过,或者命令行参数带了-d等)程序就会在doing_det置位前直接跳转到havoc,所以doing_det表示会执行deterministic stage,也表示经过det stage的case,基本可以说是第一次执行random havoc stage.

  } else {

    static u8 tmp[32];

    perf_score = orig_perf;

    sprintf(tmp, "splice %u", splice_cycle);
    stage_name  = tmp;
    stage_short = "splice";
    stage_max   = SPLICE_HAVOC * perf_score / havoc_div / 100;//perf_score由calculate_score()计算;havoc_div在Line.4439被赋值,与平均执行时长关联

  }

  if (stage_max < HAVOC_MIN) stage_max = HAVOC_MIN;//random havoc阶段最少也要进行16次

  temp_len = len;

  orig_hit_cnt = queued_paths + unique_crashes;

  havoc_queued = queued_paths;

  /* We essentially just do several thousand runs (depending on perf_score)
     where we take the input file and make random stacked tweaks. */

  for (stage_cur = 0; stage_cur < stage_max; stage_cur++) {

    u32 use_stacking = 1 << (1 + UR(HAVOC_STACK_POW2));//use_stacking=2^8=256

    stage_cur_val = use_stacking;
 
    for (i = 0; i < use_stacking; i++) {

      switch (UR(15 + ((extras_cnt + a_extras_cnt) ? 2 : 0))) {//switch来控制这一轮循环中采用16种havoc策略中的具体哪一种。case15/16仅当dictionary中有值时才会有可能被使用

        case 0:

          /* Flip a single bit somewhere. Spooky! */
//随机翻转某个bit
          FLIP_BIT(out_buf, UR(temp_len << 3));
          break;

        case 1: 

          /* Set byte to interesting value. */
//设置随机某个字节为8位Interesting value
          out_buf[UR(temp_len)] = interesting_8[UR(sizeof(interesting_8))];
          break;

        case 2:

          /* Set word to interesting value, randomly choosing endian. */
//设置随机某个字为16位interesting value,随机字节序
          if (temp_len < 2) break;

          if (UR(2)) {

            *(u16*)(out_buf + UR(temp_len - 1)) =
              interesting_16[UR(sizeof(interesting_16) >> 1)];

          } else {

            *(u16*)(out_buf + UR(temp_len - 1)) = SWAP16(
              interesting_16[UR(sizeof(interesting_16) >> 1)]);

          }

          break;

        case 3:

          /* Set dword to interesting value, randomly choosing endian. */
//设置某个随机双字为32位interesting value,随机字节序
          if (temp_len < 4) break;

          if (UR(2)) {
  
            *(u32*)(out_buf + UR(temp_len - 3)) =
              interesting_32[UR(sizeof(interesting_32) >> 2)];

          } else {

            *(u32*)(out_buf + UR(temp_len - 3)) = SWAP32(
              interesting_32[UR(sizeof(interesting_32) >> 2)]);

          }

          break;

        case 4:

          /* Randomly subtract from byte. */
//某个随机字节，减去某个随机数值
          out_buf[UR(temp_len)] -= 1 + UR(ARITH_MAX);
          break;

        case 5:

          /* Randomly add to byte. */
//随机字节，加随机数
          out_buf[UR(temp_len)] += 1 + UR(ARITH_MAX);
          break;

        case 6:

          /* Randomly subtract from word, random endian. */
//随机字，减随机数，随机字节序
          if (temp_len < 2) break;

          if (UR(2)) {

            u32 pos = UR(temp_len - 1);

            *(u16*)(out_buf + pos) -= 1 + UR(ARITH_MAX);

          } else {

            u32 pos = UR(temp_len - 1);
            u16 num = 1 + UR(ARITH_MAX);

            *(u16*)(out_buf + pos) =
              SWAP16(SWAP16(*(u16*)(out_buf + pos)) - num);

          }

          break;

        case 7:

          /* Randomly add to word, random endian. */
//随机字，加随机数，随机字节序
          if (temp_len < 2) break;

          if (UR(2)) {

            u32 pos = UR(temp_len - 1);

            *(u16*)(out_buf + pos) += 1 + UR(ARITH_MAX);

          } else {

            u32 pos = UR(temp_len - 1);
            u16 num = 1 + UR(ARITH_MAX);

            *(u16*)(out_buf + pos) =
              SWAP16(SWAP16(*(u16*)(out_buf + pos)) + num);

          }

          break;

        case 8:

          /* Randomly subtract from dword, random endian. */
//随机双字，减随机数，随机字节序
          if (temp_len < 4) break;

          if (UR(2)) {

            u32 pos = UR(temp_len - 3);

            *(u32*)(out_buf + pos) -= 1 + UR(ARITH_MAX);

          } else {

            u32 pos = UR(temp_len - 3);
            u32 num = 1 + UR(ARITH_MAX);

            *(u32*)(out_buf + pos) =
              SWAP32(SWAP32(*(u32*)(out_buf + pos)) - num);

          }

          break;

        case 9:

          /* Randomly add to dword, random endian. */
// 随机双字，加随机数，随机字节序
          if (temp_len < 4) break;

          if (UR(2)) {

            u32 pos = UR(temp_len - 3);

            *(u32*)(out_buf + pos) += 1 + UR(ARITH_MAX);

          } else {

            u32 pos = UR(temp_len - 3);
            u32 num = 1 + UR(ARITH_MAX);

            *(u32*)(out_buf + pos) =
              SWAP32(SWAP32(*(u32*)(out_buf + pos)) + num);

          }

          break;

        case 10:

          /* Just set a random byte to a random value. Because,
             why not. We use XOR with 1-255 to eliminate the
             possibility of a no-op. */
//随机字节设置为随机数。原理是原数值异或1~255的一个随机数，这样能避免无效操作的可能性，即随机数就是原数值
          out_buf[UR(temp_len)] ^= 1 + UR(255);
          break;

        case 11 ... 12: {

            /* Delete bytes. We're making this a bit more likely
               than insertion (the next option) in hopes of keeping
               files reasonably small. */
//随机位置删除连续的若干字节，设置case11...12都是这个逻辑，目的是提高删减case的概率，保持case较小
            u32 del_from, del_len;

            if (temp_len < 2) break;

            /* Don't delete too much. */

            del_len = choose_block_len(temp_len - 1);//生成一个随机数，作为删除字节的长度

            del_from = UR(temp_len - del_len + 1);

            memmove(out_buf + del_from, out_buf + del_from + del_len,
                    temp_len - del_from - del_len);

            temp_len -= del_len;

            break;

          }

        case 13:
//随机位置插入一段字节。75%概率克隆原case中一段内容；25%概率插入一段固定的随机值(e.g. 0x44444444)，随机值的选取，50%概率选取0x00~0xFF中随机值，50%概率取out_buf中随机某位
          if (temp_len + HAVOC_BLK_XL < MAX_FILE) {//

            /* Clone bytes (75%) or insert a block of constant bytes (25%). */

            u8  actually_clone = UR(4);
            u32 clone_from, clone_to, clone_len;
            u8* new_buf;

            if (actually_clone) {

              clone_len  = choose_block_len(temp_len);
              clone_from = UR(temp_len - clone_len + 1);

            } else {

              clone_len = choose_block_len(HAVOC_BLK_XL);
              clone_from = 0;

            }

            clone_to   = UR(temp_len);

            new_buf = ck_alloc_nozero(temp_len + clone_len);

            /* Head */

            memcpy(new_buf, out_buf, clone_to);

            /* Inserted part */

            if (actually_clone)
              memcpy(new_buf + clone_to, out_buf + clone_from, clone_len);
            else
              memset(new_buf + clone_to,
                     UR(2) ? UR(256) : out_buf[UR(temp_len)], clone_len);

            /* Tail */
            memcpy(new_buf + clone_to + clone_len, out_buf + clone_to,
                   temp_len - clone_to);

            ck_free(out_buf);
            out_buf = new_buf;
            temp_len += clone_len;

          }

          break;

        case 14: {

            /* Overwrite bytes with a randomly selected chunk (75%) or fixed
               bytes (25%). */
//随机位置覆盖一段字节。75%克隆一段内容，25%用随机的相同数值填充
            u32 copy_from, copy_to, copy_len;

            if (temp_len < 2) break;

            copy_len  = choose_block_len(temp_len - 1);

            copy_from = UR(temp_len - copy_len + 1);
            copy_to   = UR(temp_len - copy_len + 1);

            if (UR(4)) {

              if (copy_from != copy_to)
                memmove(out_buf + copy_to, out_buf + copy_from, copy_len);

            } else memset(out_buf + copy_to,
                          UR(2) ? UR(256) : out_buf[UR(temp_len)], copy_len);

            break;

          }

        /* Values 15 and 16 can be selected only if there are any extras
           present in the dictionaries. */

        case 15: {

            /* Overwrite bytes with an extra. */
//随机位置用extra覆盖若干字节
            if (!extras_cnt || (a_extras_cnt && UR(2))) {
//如果没有用户指定的extras（提供100%概率通过条件判断），或者可用的token为基数个（50%概率通过条件判断，因为UR(2)），使用auto extras
              /* No user-specified extras or odds in our favor. Let's use an
                 auto-detected one. */

              u32 use_extra = UR(a_extras_cnt);
              u32 extra_len = a_extras[use_extra].len;
              u32 insert_at;

              if (extra_len > temp_len) break;

              insert_at = UR(temp_len - extra_len + 1);
              memcpy(out_buf + insert_at, a_extras[use_extra].data, extra_len);

            } else {

              /* No auto extras or odds in our favor. Use the dictionary. */

              u32 use_extra = UR(extras_cnt);
              u32 extra_len = extras[use_extra].len;
              u32 insert_at;

              if (extra_len > temp_len) break;

              insert_at = UR(temp_len - extra_len + 1);
              memcpy(out_buf + insert_at, extras[use_extra].data, extra_len);

            }

            break;

          }

        case 16: {
//随机位置用extra插入若干字节
            u32 use_extra, extra_len, insert_at = UR(temp_len + 1);
            u8* new_buf;

            /* Insert an extra. Do the same dice-rolling stuff as for the
               previous case. */

            if (!extras_cnt || (a_extras_cnt && UR(2))) {

              use_extra = UR(a_extras_cnt);
              extra_len = a_extras[use_extra].len;

              if (temp_len + extra_len >= MAX_FILE) break;

              new_buf = ck_alloc_nozero(temp_len + extra_len);

              /* Head */
              memcpy(new_buf, out_buf, insert_at);

              /* Inserted part */
              memcpy(new_buf + insert_at, a_extras[use_extra].data, extra_len);

            } else {

              use_extra = UR(extras_cnt);
              extra_len = extras[use_extra].len;

              if (temp_len + extra_len >= MAX_FILE) break;

              new_buf = ck_alloc_nozero(temp_len + extra_len);

              /* Head */
              memcpy(new_buf, out_buf, insert_at);

              /* Inserted part */
              memcpy(new_buf + insert_at, extras[use_extra].data, extra_len);

            }

            /* Tail */
            memcpy(new_buf + insert_at + extra_len, out_buf + insert_at,
                   temp_len - insert_at);

            ck_free(out_buf);
            out_buf   = new_buf;
            temp_len += extra_len;

            break;

          }

      }

    }

    if (common_fuzz_stuff(argv, out_buf, temp_len))
      goto abandon_entry;

    /* out_buf might have been mangled a bit, so let's restore it to its
       original size and shape. */

    if (temp_len < len) out_buf = ck_realloc(out_buf, len);
    temp_len = len;
    memcpy(out_buf, in_buf, len);

    /* If we're finding new stuff, let's run for a bit longer, limits
       permitting. */

    if (queued_paths != havoc_queued) {

      if (perf_score <= HAVOC_MAX_MULT * 100) {
        stage_max  *= 2;
        perf_score *= 2;
      }

      havoc_queued = queued_paths;

    }

  }

  new_hit_cnt = queued_paths + unique_crashes;

  if (!splice_cycle) {
    stage_finds[STAGE_HAVOC]  += new_hit_cnt - orig_hit_cnt;
    stage_cycles[STAGE_HAVOC] += stage_max;
  } else {
    stage_finds[STAGE_SPLICE]  += new_hit_cnt - orig_hit_cnt;
    stage_cycles[STAGE_SPLICE] += stage_max;
  }

#ifndef IGNORE_FINDS

  /************
   * SPLICING *
   ************/

  /* This is a last-resort strategy triggered by a full round with no findings.
     It takes the current input file, randomly selects another input, and
     splices them together at some offset, then relies on the havoc
     code to mutate that blob. */
//如果一整轮都没有收获，就会触发这最后一个策略。随机选择另一个输入文件，以一定的偏移与当前的输入文件进行拼接，然后依靠havoc进行变异
retry_splicing:

  if (use_splicing && splice_cycle++ < SPLICE_CYCLES &&
      queued_paths > 1 && queue_cur->len > 1) {

    struct queue_entry* target;
    u32 tid, split_at;
    u8* new_buf;
    s32 f_diff, l_diff;

    /* First of all, if we've modified in_buf for havoc, let's clean that
       up... */

    if (in_buf != orig_in) {//这个阶段拼接的两个case要求是未做过修改的，所以检查in_buf是否作过改动，然后还原成origin_input
      ck_free(in_buf);
      in_buf = orig_in;
      len = queue_cur->len;
    }

    /* Pick a random queue entry and seek to it. Don't splice with yourself. */

    do { tid = UR(queued_paths); } while (tid == current_entry);//根据testcase队列长度随机生成一个数作为tid。while()中的条件保证tid不是当前的currrent_entry

    splicing_with = tid;
    target = queue;

    while (tid >= 100) { target = target->next_100; tid -= 100; }
    while (tid--) target = target->next;//快速找到target target即为作为拼接材料的"另一个输入文件"

    /* Make sure that the target has a reasonable length. */

    while (target && (target->len < 2 || target == queue_cur)) {
      target = target->next;
      splicing_with++;
    }

    if (!target) goto retry_splicing;

    /* Read the testcase into a new buffer. */

    fd = open(target->fname, O_RDONLY);

    if (fd < 0) PFATAL("Unable to open '%s'", target->fname);

    new_buf = ck_alloc_nozero(target->len);

    ck_read(fd, new_buf, target->len, target->fname);//testcase读进new_buf

    close(fd);

    /* Find a suitable splicing location, somewhere between the first and
       the last differing byte. Bail out if the difference is just a single
       byte or so. */

    locate_diffs(in_buf, new_buf, MIN(len, target->len), &f_diff, &l_diff);//这个函数定位in_buf和new_buf的第一个差异偏移和最后一个差异偏移。但是这个函数有改进空间吗。比如头尾都带token的testcase，一个是ABCDEEEABCD，另一个是ABCDFFFFABCD，f_diff在4，l_diff在10，按照下面的步骤，如果我选择从pos=9开始拼接，那我就会把BCD拼接过去形成ABCDEEEABBCD，这样token就被破坏了。这样可能算是一些小概率事件，但是是不是可以用一些其他策略去保护token，或者设计一些更优雅的拼接方式（虽然动用splicing已经不应该考虑优雅了）

    if (f_diff < 0 || l_diff < 2 || f_diff == l_diff) {
      ck_free(new_buf);//f_diff:在locate_diffs()中，first和last初始值为-1，表示未找到差异位，如果f_diff<0表示该值仍为-1，即没有差异，retry;l_diff<2:TODO 无法理解，只在头部出现差异就放弃拼接？;f_diff == l_diff:表示两者只有1位差异，retry
      goto retry_splicing;
    }

    /* Split somewhere between the first and last differing byte. */

    split_at = f_diff + UR(l_diff - f_diff);

    /* Do the thing. */

    len = target->len;
    memcpy(new_buf, in_buf, split_at);
    in_buf = new_buf;

    ck_free(out_buf);
    out_buf = ck_alloc_nozero(len);
    memcpy(out_buf, in_buf, len);

    goto havoc_stage;

  }

#endif /* !IGNORE_FINDS */

  ret_val = 0;

abandon_entry:

  splicing_with = -1;

  /* Update pending_not_fuzzed count if we made it through the calibration
     cycle and have not seen this entry before. */

  if (!stop_soon && !queue_cur->cal_failed && !queue_cur->was_fuzzed) {
    queue_cur->was_fuzzed = 1;
    pending_not_fuzzed--;
    if (queue_cur->favored) pending_favored--;
  }

  munmap(orig_in, queue_cur->len);

  if (in_buf != orig_in) ck_free(in_buf);
  ck_free(out_buf);
  ck_free(eff_map);

  return ret_val;

#undef FLIP_BIT

}


/* Grab interesting test cases from other fuzzers. */

static void sync_fuzzers(char** argv) {

  DIR* sd;
  struct dirent* sd_ent;
  u32 sync_cnt = 0;

  sd = opendir(sync_dir);
  if (!sd) PFATAL("Unable to open '%s'", sync_dir);

  stage_max = stage_cur = 0;
  cur_depth = 0;

  /* Look at the entries created for every other fuzzer in the sync directory. */

  while ((sd_ent = readdir(sd))) {

    static u8 stage_tmp[128];

    DIR* qd;
    struct dirent* qd_ent;
    u8 *qd_path, *qd_synced_path;
    u32 min_accept = 0, next_min_accept;

    s32 id_fd;

    /* Skip dot files and our own output directory. */

    if (sd_ent->d_name[0] == '.' || !strcmp(sync_id, sd_ent->d_name)) continue;

    /* Skip anything that doesn't have a queue/ subdirectory. */

    qd_path = alloc_printf("%s/%s/queue", sync_dir, sd_ent->d_name);

    if (!(qd = opendir(qd_path))) {
      ck_free(qd_path);
      continue;
    }

    /* Retrieve the ID of the last seen test case. */

    qd_synced_path = alloc_printf("%s/.synced/%s", out_dir, sd_ent->d_name);

    id_fd = open(qd_synced_path, O_RDWR | O_CREAT, 0600);

    if (id_fd < 0) PFATAL("Unable to create '%s'", qd_synced_path);

    if (read(id_fd, &min_accept, sizeof(u32)) > 0) 
      lseek(id_fd, 0, SEEK_SET);

    next_min_accept = min_accept;

    /* Show stats */    

    sprintf(stage_tmp, "sync %u", ++sync_cnt);
    stage_name = stage_tmp;
    stage_cur  = 0;
    stage_max  = 0;

    /* For every file queued by this fuzzer, parse ID and see if we have looked at
       it before; exec a test case if not. */

    while ((qd_ent = readdir(qd))) {

      u8* path;
      s32 fd;
      struct stat st;

      if (qd_ent->d_name[0] == '.' ||
          sscanf(qd_ent->d_name, CASE_PREFIX "%06u", &syncing_case) != 1 || 
          syncing_case < min_accept) continue;

      /* OK, sounds like a new one. Let's give it a try. */

      if (syncing_case >= next_min_accept)
        next_min_accept = syncing_case + 1;

      path = alloc_printf("%s/%s", qd_path, qd_ent->d_name);

      /* Allow this to fail in case the other fuzzer is resuming or so... */

      fd = open(path, O_RDONLY);

      if (fd < 0) {
         ck_free(path);
         continue;
      }

      if (fstat(fd, &st)) PFATAL("fstat() failed");

      /* Ignore zero-sized or oversized files. */

      if (st.st_size && st.st_size <= MAX_FILE) {

        u8  fault;
        u8* mem = mmap(0, st.st_size, PROT_READ, MAP_PRIVATE, fd, 0);

        if (mem == MAP_FAILED) PFATAL("Unable to mmap '%s'", path);

        /* See what happens. We rely on save_if_interesting() to catch major
           errors and save the test case. */

        write_to_testcase(mem, st.st_size);

        fault = run_target(argv, exec_tmout);//执行这个target,获取fault状态

        if (stop_soon) return;

        syncing_party = sd_ent->d_name;
        queued_imported += save_if_interesting(argv, mem, st.st_size, fault);//根据收集到的相关执行状态等信息判断这个case是否interesting,如果有趣则保存,返回1
        syncing_party = 0;

        munmap(mem, st.st_size);

        if (!(stage_cur++ % stats_update_freq)) show_stats();//每执行stats_update_freq次,更新一次stats

      }

      ck_free(path);
      close(fd);

    }

    ck_write(id_fd, &next_min_accept, sizeof(u32), qd_synced_path);

    close(id_fd);
    closedir(qd);
    ck_free(qd_path);
    ck_free(qd_synced_path);
    
  }  

  closedir(sd);

}


/* Handle stop signal (Ctrl-C, etc). */

static void handle_stop_sig(int sig) {

  stop_soon = 1; 

  if (child_pid > 0) kill(child_pid, SIGKILL);
  if (forksrv_pid > 0) kill(forksrv_pid, SIGKILL);

}


/* Handle skip request (SIGUSR1). */

static void handle_skipreq(int sig) {

  skip_requested = 1;

}

/* Handle timeout (SIGALRM). */

static void handle_timeout(int sig) {

  if (child_pid > 0) {

    child_timed_out = 1; 
    kill(child_pid, SIGKILL);

  } else if (child_pid == -1 && forksrv_pid > 0) {

    child_timed_out = 1; 
    kill(forksrv_pid, SIGKILL);

  }

}


/* Do a PATH search and find target binary to see that it exists and
   isn't a shell script - a common and painful mistake. We also check for
   a valid ELF header and for evidence of AFL instrumentation. */

EXP_ST void check_binary(u8* fname) {

  u8* env_path = 0;
  struct stat st;

  s32 fd;
  u8* f_data;
  u32 f_len = 0;

  ACTF("Validating target binary...");

  if (strchr(fname, '/') || !(env_path = getenv("PATH"))) {

    target_path = ck_strdup(fname);
    if (stat(target_path, &st) || !S_ISREG(st.st_mode) ||
        !(st.st_mode & 0111) || (f_len = st.st_size) < 4)
      FATAL("Program '%s' not found or not executable", fname);
//存在文件，文件正常，可执行，target binary的size必须大于等于4bytes
  } else {

    while (env_path) {

      u8 *cur_elem, *delim = strchr(env_path, ':');

      if (delim) {

        cur_elem = ck_alloc(delim - env_path + 1);
        memcpy(cur_elem, env_path, delim - env_path);
        delim++;

      } else cur_elem = ck_strdup(env_path);

      env_path = delim;

      if (cur_elem[0])
        target_path = alloc_printf("%s/%s", cur_elem, fname);
      else
        target_path = ck_strdup(fname);

      ck_free(cur_elem);

      if (!stat(target_path, &st) && S_ISREG(st.st_mode) &&
          (st.st_mode & 0111) && (f_len = st.st_size) >= 4) break;

      ck_free(target_path);
      target_path = 0;

    }

    if (!target_path) FATAL("Program '%s' not found or not executable", fname);

  }

  if (getenv("AFL_SKIP_BIN_CHECK")) return;

  /* Check for blatant user errors. */

  if ((!strncmp(target_path, "/tmp/", 5) && !strchr(target_path + 5, '/')) ||
      (!strncmp(target_path, "/var/tmp/", 9) && !strchr(target_path + 9, '/')))
     FATAL("Please don't keep binaries in /tmp or /var/tmp");

  fd = open(target_path, O_RDONLY);

  if (fd < 0) PFATAL("Unable to open '%s'", target_path);

  f_data = mmap(0, f_len, PROT_READ, MAP_PRIVATE, fd, 0);

  if (f_data == MAP_FAILED) PFATAL("Unable to mmap file '%s'", target_path);

  close(fd);

  if (f_data[0] == '#' && f_data[1] == '!') {
//识别target是否是脚本。
    SAYF("\n" cLRD "[-] " cRST
         "Oops, the target binary looks like a shell script. Some build systems will\n"
         "    sometimes generate shell stubs for dynamically linked programs; try static\n"
         "    library mode (./configure --disable-shared) if that's the case.\n\n"

         "    Another possible cause is that you are actually trying to use a shell\n" 
         "    wrapper around the fuzzed component. Invoking shell can slow down the\n" 
         "    fuzzing process by a factor of 20x or more; it's best to write the wrapper\n"
         "    in a compiled language instead.\n");

    FATAL("Program '%s' is a shell script", target_path);

  }

#ifndef __APPLE__

  if (f_data[0] != 0x7f || memcmp(f_data + 1, "ELF", 3))
    FATAL("Program '%s' is not an ELF binary", target_path);

#else

  if (f_data[0] != 0xCF || f_data[1] != 0xFA || f_data[2] != 0xED)
    FATAL("Program '%s' is not a 64-bit Mach-O binary", target_path);

#endif /* ^!__APPLE__ */

  if (!qemu_mode && !dumb_mode &&
      !memmem(f_data, f_len, SHM_ENV_VAR, strlen(SHM_ENV_VAR) + 1)) {

    SAYF("\n" cLRD "[-] " cRST
         "Looks like the target binary is not instrumented! The fuzzer depends on\n"
         "    compile-time instrumentation to isolate interesting test cases while\n"
         "    mutating the input data. For more information, and for tips on how to\n"
         "    instrument binaries, please see %s/README.\n\n"

         "    When source code is not available, you may be able to leverage QEMU\n"
         "    mode support. Consult the README for tips on how to enable this.\n"

         "    (It is also possible to use afl-fuzz as a traditional, \"dumb\" fuzzer.\n"
         "    For that, you can use the -n option - but expect much worse results.)\n",
         doc_path);

    FATAL("No instrumentation detected");

  }

  if (qemu_mode &&
      memmem(f_data, f_len, SHM_ENV_VAR, strlen(SHM_ENV_VAR) + 1)) {

    SAYF("\n" cLRD "[-] " cRST
         "This program appears to be instrumented with afl-gcc, but is being run in\n"
         "    QEMU mode (-Q). This is probably not what you want - this setup will be\n"
         "    slow and offer no practical benefits.\n");

    FATAL("Instrumentation found in -Q mode");

  }

  if (memmem(f_data, f_len, "libasan.so", 10) ||
      memmem(f_data, f_len, "__msan_init", 11)) uses_asan = 1;

  /* Detect persistent & deferred init signatures in the binary. */

  if (memmem(f_data, f_len, PERSIST_SIG, strlen(PERSIST_SIG) + 1)) {

    OKF(cPIN "Persistent mode binary detected.");
    setenv(PERSIST_ENV_VAR, "1", 1);
    persistent_mode = 1;

  } else if (getenv("AFL_PERSISTENT")) {

    WARNF("AFL_PERSISTENT is no longer supported and may misbehave!");

  }

  if (memmem(f_data, f_len, DEFER_SIG, strlen(DEFER_SIG) + 1)) {

    OKF(cPIN "Deferred forkserver binary detected.");
    setenv(DEFER_ENV_VAR, "1", 1);
    deferred_mode = 1;

  } else if (getenv("AFL_DEFER_FORKSRV")) {

    WARNF("AFL_DEFER_FORKSRV is no longer supported and may misbehave!");

  }

  if (munmap(f_data, f_len)) PFATAL("unmap() failed");

}


/* Trim and possibly create a banner for the run. */

static void fix_up_banner(u8* name) {

  if (!use_banner) {

    if (sync_id) {

      use_banner = sync_id;

    } else {

      u8* trim = strrchr(name, '/');
      if (!trim) use_banner = name; else use_banner = trim + 1;

    }

  }

  if (strlen(use_banner) > 40) {

    u8* tmp = ck_alloc(44);
    sprintf(tmp, "%.40s...", use_banner);
    use_banner = tmp;

  }

}


/* Check if we're on TTY. */

static void check_if_tty(void) {

  struct winsize ws;

  if (getenv("AFL_NO_UI")) {
    OKF("Disabling the UI because AFL_NO_UI is set.");
    not_on_tty = 1;
    return;
  }

  if (ioctl(1, TIOCGWINSZ, &ws)) {

    if (errno == ENOTTY) {
      OKF("Looks like we're not running on a tty, so I'll be a bit less verbose.");
      not_on_tty = 1;
    }

    return;
  }

}


/* Check terminal dimensions after resize. */

static void check_term_size(void) {

  struct winsize ws;

  term_too_small = 0;

  if (ioctl(1, TIOCGWINSZ, &ws)) return;

  if (ws.ws_row == 0 && ws.ws_col == 0) return;
  if (ws.ws_row < 25 || ws.ws_col < 80) term_too_small = 1;

}



/* Display usage hints. */

static void usage(u8* argv0) {

  SAYF("\n%s [ options ] -- /path/to/fuzzed_app [ ... ]\n\n"

       "Required parameters:\n\n"

       "  -i dir        - input directory with test cases\n"
       "  -o dir        - output directory for fuzzer findings\n\n"

       "Execution control settings:\n\n"

       "  -f file       - location read by the fuzzed program (stdin)\n"
       "  -t msec       - timeout for each run (auto-scaled, 50-%u ms)\n"
       "  -m megs       - memory limit for child process (%u MB)\n"
       "  -Q            - use binary-only instrumentation (QEMU mode)\n\n"     
 
       "Fuzzing behavior settings:\n\n"

       "  -d            - quick & dirty mode (skips deterministic steps)\n"
       "  -n            - fuzz without instrumentation (dumb mode)\n"
       "  -x dir        - optional fuzzer dictionary (see README)\n\n"

       "Other stuff:\n\n"

       "  -T text       - text banner to show on the screen\n"
       "  -M / -S id    - distributed mode (see parallel_fuzzing.txt)\n"
       "  -C            - crash exploration mode (the peruvian rabbit thing)\n"
       "  -V            - show version number and exit\n\n"
       "  -b cpu_id     - bind the fuzzing process to the specified CPU core\n\n"

       "For additional tips, please consult %s/README.\n\n",

       argv0, EXEC_TIMEOUT, MEM_LIMIT, doc_path);

  exit(1);

}


/* Prepare output directories and fds. */

EXP_ST void setup_dirs_fds(void) {

  u8* tmp;
  s32 fd;

  ACTF("Setting up output directories...");

  if (sync_id && mkdir(sync_dir, 0700) && errno != EEXIST)
      PFATAL("Unable to create '%s'", sync_dir);

  if (mkdir(out_dir, 0700)) {

    if (errno != EEXIST) PFATAL("Unable to create '%s'", out_dir);

    maybe_delete_out_dir();

  } else {

    if (in_place_resume)
      FATAL("Resume attempted but old output directory not found");

    out_dir_fd = open(out_dir, O_RDONLY);

#ifndef __sun

    if (out_dir_fd < 0 || flock(out_dir_fd, LOCK_EX | LOCK_NB))
      PFATAL("Unable to flock() output directory.");

#endif /* !__sun */

  }

  /* Queue directory for any starting & discovered paths. */
//queue目录存放起始和发现的路径。路径？
  tmp = alloc_printf("%s/queue", out_dir);
  if (mkdir(tmp, 0700)) PFATAL("Unable to create '%s'", tmp);
  ck_free(tmp);

  /* Top-level directory for queue metadata used for session
     resume and related tasks. */

  tmp = alloc_printf("%s/queue/.state/", out_dir);
  if (mkdir(tmp, 0700)) PFATAL("Unable to create '%s'", tmp);
  ck_free(tmp);

  /* Directory for flagging queue entries that went through
     deterministic fuzzing in the past. */

  tmp = alloc_printf("%s/queue/.state/deterministic_done/", out_dir);
  if (mkdir(tmp, 0700)) PFATAL("Unable to create '%s'", tmp);
  ck_free(tmp);

  /* Directory with the auto-selected dictionary entries. */

  tmp = alloc_printf("%s/queue/.state/auto_extras/", out_dir);
  if (mkdir(tmp, 0700)) PFATAL("Unable to create '%s'", tmp);
  ck_free(tmp);

  /* The set of paths currently deemed redundant. */

  tmp = alloc_printf("%s/queue/.state/redundant_edges/", out_dir);
  if (mkdir(tmp, 0700)) PFATAL("Unable to create '%s'", tmp);
  ck_free(tmp);

  /* The set of paths showing variable behavior. */

  tmp = alloc_printf("%s/queue/.state/variable_behavior/", out_dir);
  if (mkdir(tmp, 0700)) PFATAL("Unable to create '%s'", tmp);
  ck_free(tmp);

  /* Sync directory for keeping track of cooperating fuzzers. */

  if (sync_id) {

    tmp = alloc_printf("%s/.synced/", out_dir);

    if (mkdir(tmp, 0700) && (!in_place_resume || errno != EEXIST))
      PFATAL("Unable to create '%s'", tmp);

    ck_free(tmp);

  }

  /* All recorded crashes. */

  tmp = alloc_printf("%s/crashes", out_dir);
  if (mkdir(tmp, 0700)) PFATAL("Unable to create '%s'", tmp);
  ck_free(tmp);

  /* All recorded hangs. */

  tmp = alloc_printf("%s/hangs", out_dir);
  if (mkdir(tmp, 0700)) PFATAL("Unable to create '%s'", tmp);
  ck_free(tmp);

  /* Generally useful file descriptors. */

  dev_null_fd = open("/dev/null", O_RDWR);
  if (dev_null_fd < 0) PFATAL("Unable to open /dev/null");

  dev_urandom_fd = open("/dev/urandom", O_RDONLY);
  if (dev_urandom_fd < 0) PFATAL("Unable to open /dev/urandom");

  /* Gnuplot output file. */

  tmp = alloc_printf("%s/plot_data", out_dir);
  fd = open(tmp, O_WRONLY | O_CREAT | O_EXCL, 0600);
  if (fd < 0) PFATAL("Unable to create '%s'", tmp);
  ck_free(tmp);

  plot_file = fdopen(fd, "w");
  if (!plot_file) PFATAL("fdopen() failed");

  fprintf(plot_file, "# unix_time, cycles_done, cur_path, paths_total, "
                     "pending_total, pending_favs, map_size, unique_crashes, "
                     "unique_hangs, max_depth, execs_per_sec\n");
                     /* ignore errors */

}


/* Setup the output file for fuzzed data, if not using -f. */

EXP_ST void setup_stdio_file(void) {

  u8* fn = alloc_printf("%s/.cur_input", out_dir);

  unlink(fn); /* Ignore errors */

  out_fd = open(fn, O_RDWR | O_CREAT | O_EXCL, 0600);

  if (out_fd < 0) PFATAL("Unable to create '%s'", fn);

  ck_free(fn);

}


/* Make sure that core dumps don't go to a program. */

static void check_crash_handling(void) {

#ifdef __APPLE__

  /* Yuck! There appears to be no simple C API to query for the state of 
     loaded daemons on MacOS X, and I'm a bit hesitant to do something
     more sophisticated, such as disabling crash reporting via Mach ports,
     until I get a box to test the code. So, for now, we check for crash
     reporting the awful way. */
  
  if (system("launchctl list 2>/dev/null | grep -q '\\.ReportCrash$'")) return;

  SAYF("\n" cLRD "[-] " cRST
       "Whoops, your system is configured to forward crash notifications to an\n"
       "    external crash reporting utility. This will cause issues due to the\n"
       "    extended delay between the fuzzed binary malfunctioning and this fact\n"
       "    being relayed to the fuzzer via the standard waitpid() API.\n\n"
       "    To avoid having crashes misinterpreted as timeouts, please run the\n" 
       "    following commands:\n\n"

       "    SL=/System/Library; PL=com.apple.ReportCrash\n"
       "    launchctl unload -w ${SL}/LaunchAgents/${PL}.plist\n"
       "    sudo launchctl unload -w ${SL}/LaunchDaemons/${PL}.Root.plist\n");

  if (!getenv("AFL_I_DONT_CARE_ABOUT_MISSING_CRASHES"))
    FATAL("Crash reporter detected");

#else

  /* This is Linux specific, but I don't think there's anything equivalent on
     *BSD, so we can just let it slide for now. */

  s32 fd = open("/proc/sys/kernel/core_pattern", O_RDONLY);
  u8  fchar;

  if (fd < 0) return;

  ACTF("Checking core_pattern...");

  if (read(fd, &fchar, 1) == 1 && fchar == '|') {

    SAYF("\n" cLRD "[-] " cRST
         "Hmm, your system is configured to send core dump notifications to an\n"
         "    external utility. This will cause issues: there will be an extended delay\n"
         "    between stumbling upon a crash and having this information relayed to the\n"
         "    fuzzer via the standard waitpid() API.\n\n"

         "    To avoid having crashes misinterpreted as timeouts, please log in as root\n" 
         "    and temporarily modify /proc/sys/kernel/core_pattern, like so:\n\n"

         "    echo core >/proc/sys/kernel/core_pattern\n");

    if (!getenv("AFL_I_DONT_CARE_ABOUT_MISSING_CRASHES"))
      FATAL("Pipe at the beginning of 'core_pattern'");

  }
 
  close(fd);

#endif /* ^__APPLE__ */

}


/* Check CPU governor. */

static void check_cpu_governor(void) {
//reference:https://zhuanlan.zhihu.com/p/33753019
  FILE* f;
  u8 tmp[128];
  u64 min = 0, max = 0;

  if (getenv("AFL_SKIP_CPUFREQ")) return;

  f = fopen("/sys/devices/system/cpu/cpu0/cpufreq/scaling_governor", "r");
  if (!f) return;

  ACTF("Checking CPU scaling governor...");

  if (!fgets(tmp, 128, f)) PFATAL("fgets() failed");

  fclose(f);

  if (!strncmp(tmp, "perf", 4)) return;

  f = fopen("/sys/devices/system/cpu/cpu0/cpufreq/scaling_min_freq", "r");

  if (f) {
    if (fscanf(f, "%llu", &min) != 1) min = 0;
    fclose(f);
  }

  f = fopen("/sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq", "r");

  if (f) {
    if (fscanf(f, "%llu", &max) != 1) max = 0;
    fclose(f);
  }

  if (min == max) return;

  SAYF("\n" cLRD "[-] " cRST
       "Whoops, your system uses on-demand CPU frequency scaling, adjusted\n"
       "    between %llu and %llu MHz. Unfortunately, the scaling algorithm in the\n"
       "    kernel is imperfect and can miss the short-lived processes spawned by\n"
       "    afl-fuzz. To keep things moving, run these commands as root:\n\n"

       "    cd /sys/devices/system/cpu\n"
       "    echo performance | tee cpu*/cpufreq/scaling_governor\n\n"

       "    You can later go back to the original state by replacing 'performance' with\n"
       "    'ondemand'. If you don't want to change the settings, set AFL_SKIP_CPUFREQ\n"
       "    to make afl-fuzz skip this check - but expect some performance drop.\n",
       min / 1024, max / 1024);

  FATAL("Suboptimal CPU scaling governor");

}


/* Count the number of logical CPU cores. */

static void get_core_count(void) {

  u32 cur_runnable = 0;

#if defined(__APPLE__) || defined(__FreeBSD__) || defined (__OpenBSD__)

  size_t s = sizeof(cpu_core_count);

  /* On *BSD systems, we can just use a sysctl to get the number of CPUs. */

#ifdef __APPLE__

  if (sysctlbyname("hw.logicalcpu", &cpu_core_count, &s, NULL, 0) < 0)
    return;

#else

  int s_name[2] = { CTL_HW, HW_NCPU };

  if (sysctl(s_name, 2, &cpu_core_count, &s, NULL, 0) < 0) return;

#endif /* ^__APPLE__ */

#else

#ifdef HAVE_AFFINITY

  cpu_core_count = sysconf(_SC_NPROCESSORS_ONLN);

#else

  FILE* f = fopen("/proc/stat", "r");
  u8 tmp[1024];

  if (!f) return;

  while (fgets(tmp, sizeof(tmp), f))
    if (!strncmp(tmp, "cpu", 3) && isdigit(tmp[3])) cpu_core_count++;

  fclose(f);

#endif /* ^HAVE_AFFINITY */

#endif /* ^(__APPLE__ || __FreeBSD__ || __OpenBSD__) */

  if (cpu_core_count > 0) {

    cur_runnable = (u32)get_runnable_processes();

#if defined(__APPLE__) || defined(__FreeBSD__) || defined (__OpenBSD__)

    /* Add ourselves, since the 1-minute average doesn't include that yet. */

    cur_runnable++;

#endif /* __APPLE__ || __FreeBSD__ || __OpenBSD__ */

    OKF("You have %u CPU core%s and %u runnable tasks (utilization: %0.0f%%).",
        cpu_core_count, cpu_core_count > 1 ? "s" : "",
        cur_runnable, cur_runnable * 100.0 / cpu_core_count);

    if (cpu_core_count > 1) {

      if (cur_runnable > cpu_core_count * 1.5) {

        WARNF("System under apparent load, performance may be spotty.");

      } else if (cur_runnable + 1 <= cpu_core_count) {

        OKF("Try parallel jobs - see %s/parallel_fuzzing.txt.", doc_path);
  
      }

    }

  } else {

    cpu_core_count = 0;
    WARNF("Unable to figure out the number of CPU cores.");

  }

}


/* Validate and fix up out_dir and sync_dir when using -S. */

static void fix_up_sync(void) {

  u8* x = sync_id;

  if (dumb_mode)
    FATAL("-S / -M and -n are mutually exclusive");//并行fuzzing 不允许非插桩模式

  if (skip_deterministic) {

    if (force_deterministic)
      FATAL("use -S instead of -M -d");//Master强制开启deterministic 因此不能对Master附加skip_deterministic
    else
      FATAL("-S already implies -d");//从fuzzer暗含了skip_deterministic

  }

  while (*x) {

    if (!isalnum(*x) && *x != '_' && *x != '-')//限制fuzzer_id仅能使用字母数字和'_','-'
      FATAL("Non-alphanumeric fuzzer ID specified via -S or -M");

    x++;

  }

  if (strlen(sync_id) > 32) FATAL("Fuzzer ID too long");//id长度不超过32位

  x = alloc_printf("%s/%s", out_dir, sync_id);

  sync_dir = out_dir;
  out_dir  = x;//原来预设的out_dir作为同步目录sync_dir  将out_dir/sync_id作为当前主/从fuzzer各自的输出目录

  if (!force_deterministic) {
    skip_deterministic = 1;
    use_splicing = 1;
  }

}


/* Handle screen resize (SIGWINCH). */

static void handle_resize(int sig) {
  clear_screen = 1;
}


/* Check ASAN options. */

static void check_asan_opts(void) {
  u8* x = getenv("ASAN_OPTIONS");

  if (x) {

    if (!strstr(x, "abort_on_error=1"))
      FATAL("Custom ASAN_OPTIONS set without abort_on_error=1 - please fix!");

    if (!strstr(x, "symbolize=0"))
      FATAL("Custom ASAN_OPTIONS set without symbolize=0 - please fix!");

  }

  x = getenv("MSAN_OPTIONS");

  if (x) {

    if (!strstr(x, "exit_code=" STRINGIFY(MSAN_ERROR)))
      FATAL("Custom MSAN_OPTIONS set without exit_code="
            STRINGIFY(MSAN_ERROR) " - please fix!");

    if (!strstr(x, "symbolize=0"))
      FATAL("Custom MSAN_OPTIONS set without symbolize=0 - please fix!");

  }

} 


/* Detect @@ in args. */

EXP_ST void detect_file_args(char** argv) {

  u32 i = 0;
  u8* cwd = getcwd(NULL, 0);//current working direction

  if (!cwd) PFATAL("getcwd() failed");

  while (argv[i]) {

    u8* aa_loc = strstr(argv[i], "@@");

    if (aa_loc) {

      u8 *aa_subst, *n_arg;

      /* If we don't have a file name chosen yet, use a safe default. */

      if (!out_file)//和-f参数相关联，如果没有给输出文件的名称，就使用".cur_input"作为默认名称
        out_file = alloc_printf("%s/.cur_input", out_dir);

      /* Be sure that we're always using fully-qualified paths. */

      if (out_file[0] == '/') aa_subst = out_file;//检测out_file[0]是否是绝对路径
      else aa_subst = alloc_printf("%s/%s", cwd, out_file);//如果不是的话就用cwd作为路径

      /* Construct a replacement argv value. */

      *aa_loc = 0;
      n_arg = alloc_printf("%s%s%s", argv[i], aa_subst, aa_loc + 2);
      argv[i] = n_arg;//把@@替换成aa_subst
      *aa_loc = '@';

      if (out_file[0] != '/') ck_free(aa_subst);

    }

    i++;

  }

  free(cwd); /* not tracked */

}


/* Set up signal handlers. More complicated that needs to be, because libc on
   Solaris doesn't resume interrupted reads(), sets SA_RESETHAND when you call
   siginterrupt(), and does other unnecessary things. */

EXP_ST void setup_signal_handlers(void) {

  struct sigaction sa;
//  struct sigaction
//  {
//   void     (*sa_handler)(int);
//   void     (*sa_sigaction)(int, siginfo_t *, void *);
//   sigset_t  sa_mask;
//   int       sa_flags;
//   void     (*sa_restorer)(void);
//  };
//reference:https://www.cnblogs.com/wblyuyang/archive/2012/11/13/2768923.html
  sa.sa_handler   = NULL;
  sa.sa_flags     = SA_RESTART;
  sa.sa_sigaction = NULL;

  sigemptyset(&sa.sa_mask);//将信号集初始化为空

  /* Various ways of saying "stop". */
//  #include <signal.h>
//  int sigaction(int signum, const struct sigaction *act, struct sigaction *oldact);
//  signum:要操作的信号   act:要设置的对该信号的处理方法    oldact:该信号的原处理方法

//reference:https://zh.wikipedia.org/wiki/Unix%E4%BF%A1%E5%8F%B7
  sa.sa_handler = handle_stop_sig;
  sigaction(SIGHUP, &sa, NULL);//挂起
  sigaction(SIGINT, &sa, NULL);//终端中断信号
  sigaction(SIGTERM, &sa, NULL);//终止信号
//为SIGHUP,SIGINT,SIGTERM注册handle_stop_sig处理函数
  /* Exec timeout notifications. */

  sa.sa_handler = handle_timeout;
  sigaction(SIGALRM, &sa, NULL);//计时器告警

  /* Window resize */

  sa.sa_handler = handle_resize;
  sigaction(SIGWINCH, &sa, NULL);//终端窗口大小已变化

  /* SIGUSR1: skip entry */

  sa.sa_handler = handle_skipreq;
  sigaction(SIGUSR1, &sa, NULL);//用户自定义信号1 此处为忽略入口

  /* Things we don't care about. */

  sa.sa_handler = SIG_IGN;
  sigaction(SIGTSTP, &sa, NULL);//终端中止信号
  sigaction(SIGPIPE, &sa, NULL);//写入一个没有连接另一端的管道

}


/* Rewrite argv for QEMU. */

static char** get_qemu_argv(u8* own_loc, char** argv, int argc) {

  char** new_argv = ck_alloc(sizeof(char*) * (argc + 4));
  u8 *tmp, *cp, *rsl, *own_copy;

  /* Workaround for a QEMU stability glitch. */

  setenv("QEMU_LOG", "nochain", 1);

  memcpy(new_argv + 3, argv + 1, sizeof(char*) * argc);

  new_argv[2] = target_path;
  new_argv[1] = "--";

  /* Now we need to actually find the QEMU binary to put in argv[0]. */

  tmp = getenv("AFL_PATH");

  if (tmp) {

    cp = alloc_printf("%s/afl-qemu-trace", tmp);//尝试从AFL_PATH里找qemu

    if (access(cp, X_OK))
      FATAL("Unable to find '%s'", tmp);

    target_path = new_argv[0] = cp;
    return new_argv;

  }

  own_copy = ck_strdup(own_loc);
  rsl = strrchr(own_copy, '/');

  if (rsl) {

    *rsl = 0;

    cp = alloc_printf("%s/afl-qemu-trace", own_copy);
    ck_free(own_copy);

    if (!access(cp, X_OK)) {

      target_path = new_argv[0] = cp;
      return new_argv;

    }

  } else ck_free(own_copy);

  if (!access(BIN_PATH "/afl-qemu-trace", X_OK)) {

    target_path = new_argv[0] = ck_strdup(BIN_PATH "/afl-qemu-trace");
    return new_argv;

  }

  SAYF("\n" cLRD "[-] " cRST
       "Oops, unable to find the 'afl-qemu-trace' binary. The binary must be built\n"
       "    separately by following the instructions in qemu_mode/README.qemu. If you\n"
       "    already have the binary installed, you may need to specify AFL_PATH in the\n"
       "    environment.\n\n"

       "    Of course, even without QEMU, afl-fuzz can still work with binaries that are\n"
       "    instrumented at compile time with afl-gcc. It is also possible to use it as a\n"
       "    traditional \"dumb\" fuzzer by specifying '-n' in the command line.\n");

  FATAL("Failed to locate 'afl-qemu-trace'.");

}


/* Make a copy of the current command line. */

static void save_cmdline(u32 argc, char** argv) {

  u32 len = 1, i;
  u8* buf;

  for (i = 0; i < argc; i++)
    len += strlen(argv[i]) + 1;
  
  buf = orig_cmdline = ck_alloc(len);

  for (i = 0; i < argc; i++) {

    u32 l = strlen(argv[i]);

    memcpy(buf, argv[i], l);
    buf += l;

    if (i != argc - 1) *(buf++) = ' ';

  }

  *buf = 0;

}


#ifndef AFL_LIB

/* Main entry point */

int main(int argc, char** argv) {

  s32 opt;
  u64 prev_queued = 0;
  u32 sync_interval_cnt = 0, seek_to;
  u8  *extras_dir = 0;
  u8  mem_limit_given = 0;
  u8  exit_1 = !!getenv("AFL_BENCH_JUST_ONE");
  char** use_argv;

  struct timeval tv;
  struct timezone tz;

  SAYF(cCYA "afl-fuzz " cBRI VERSION cRST " by <lcamtuf@google.com>\n");

  doc_path = access(DOC_PATH, F_OK) ? "docs" : DOC_PATH;

  gettimeofday(&tv, &tz);
  srandom(tv.tv_sec ^ tv.tv_usec ^ getpid());

  while ((opt = getopt(argc, argv, "+i:o:f:m:b:t:T:dnCB:S:M:x:QV")) > 0)//分析命令行参数  第三个参数为选项字符串optstring，"o:"表示"o"后必须带参数，中间有无空格都接受；两个冒号表示参数可选，但有参数时，参数和选项之间不能带空格;optstring如果以'+'起始，表示不能包含optstring以外的参数，否则getopt停止，并返回-1
  //reference:http://www.cnitblog.com/zouzheng/archive/2007/04/02/25034.aspx
  //reference:https://www.cnblogs.com/yusenwu/p/4756219.html

    switch (opt) {

      case 'i': /* input dir */

        if (in_dir) FATAL("Multiple -i options not supported");
        in_dir = optarg;

        if (!strcmp(in_dir, "-")) in_place_resume = 1;//resume?恢复？继续执行上一次fuzzing？

        break;

      case 'o': /* output dir */

        if (out_dir) FATAL("Multiple -o options not supported");
        out_dir = optarg;
        break;

      case 'M': { /* master sync ID */
//并行fuzzing，通过-M设置主fuzzer
          u8* c;

          if (sync_id) FATAL("Multiple -S or -M options not supported");
          sync_id = ck_strdup(optarg);//ck_strdup：分配一个chunk，并将optarg copy进chunk

          if ((c = strchr(sync_id, ':'))) {//sync_id中第一次搜索到':'的位置

            *c = 0;

            if (sscanf(c + 1, "%u/%u", &master_id, &master_max) != 2 ||
                !master_id || !master_max || master_id > master_max ||
                master_max > 1000000) FATAL("Bogus master ID passed to -M");//从c+1(即sync_id的':'后一位)读取两个数值，master_id(当前主fuzzer的id)和master_max(允许的主fuzzer最大数量，难道还能复数个master的吗)，同时id和max都为非零，id必须不大于max，max不能超过100,0000
//这里有一点，很多博客上写的-M -S的用法比如"-M fuzzer1"，也不会导致afl-fuzz报错，只是会跳过这一段check
          }

          force_deterministic = 1;//强制开启deterministic阶段

        }

        break;

      case 'S': 
//并行fuzzing 设置从fuzzer   slave
        if (sync_id) FATAL("Multiple -S or -M options not supported");
        sync_id = ck_strdup(optarg);
        break;

      case 'f': /* target file */

        if (out_file) FATAL("Multiple -f options not supported");
        out_file = optarg;
        break;

      case 'x': /* dictionary */

        if (extras_dir) FATAL("Multiple -x options not supported");
        extras_dir = optarg;
        break;

      case 't': { /* timeout */
//设置afl-fuzz对测试程序每次执行判定超时的阈值
          u8 suffix = 0;

          if (timeout_given) FATAL("Multiple -t options not supported");

          if (sscanf(optarg, "%u%c", &exec_tmout, &suffix) < 1 ||
              optarg[0] == '-') FATAL("Bad syntax used for -t");//从optarg中读取一个数值作为timeout的数值，再读取一个字符作为后缀

          if (exec_tmout < 5) FATAL("Dangerously low value of -t");

          if (suffix == '+') timeout_given = 2; else timeout_given = 1;//具体可以看line 2792 后缀'+'表示依旧设置timeout，但是忽略这一事件，不把这一输入放入输入队列

          break;

      }

      case 'm': { /* mem limit */
//设置afl-fuzz允许使用的内存上限
          u8 suffix = 'M';

          if (mem_limit_given) FATAL("Multiple -m options not supported");
          mem_limit_given = 1;

          if (!strcmp(optarg, "none")) {
//参数none表示不限制内存限制
            mem_limit = 0;
            break;

          }

          if (sscanf(optarg, "%llu%c", &mem_limit, &suffix) < 1 ||
              optarg[0] == '-') FATAL("Bad syntax used for -m");//允许内存大小带后缀，afl-fuzz识别K,M,G,T四个后缀，默认为M

          switch (suffix) {

            case 'T': mem_limit *= 1024 * 1024; break;
            case 'G': mem_limit *= 1024; break;
            case 'k': mem_limit /= 1024; break;
            case 'M': break;

            default:  FATAL("Unsupported suffix or bad syntax for -m");

          }

          if (mem_limit < 5) FATAL("Dangerously low value of -m");

          if (sizeof(rlim_t) == 4 && mem_limit > 2000)//sizeof(rlim_t)用来判断当前系统是32位还是64位，32位系统下限制内存资源不超过2000M
            FATAL("Value of -m out of range on 32-bit systems");

        }

        break;
      
      case 'b': { /* bind CPU core */
//绑定空闲的CPU核心
          if (cpu_to_bind_given) FATAL("Multiple -b options not supported");
          cpu_to_bind_given = 1;

          if (sscanf(optarg, "%u", &cpu_to_bind) < 1 ||
              optarg[0] == '-') FATAL("Bad syntax used for -b");

          break;

      }

      case 'd': /* skip deterministic */
//选择跳过deterministic阶段，直接进行havoc stage
//deterministic阶段包括 bit/byte flips, arithmetics, interesting values, dictionary, extra这几个阶段
        if (skip_deterministic) FATAL("Multiple -d options not supported");
        skip_deterministic = 1;
        use_splicing = 1;//mutation中激活splicing拼接方式
        break;

      case 'B': /* load bitmap */

        /* This is a secret undocumented option! It is useful if you find
           an interesting test case during a normal fuzzing process, and want
           to mutate it without rediscovering any of the test cases already
           found during an earlier run.

           To use this mode, you need to point -B to the fuzz_bitmap produced
           by an earlier run for the exact same binary... and that's it.

           I only used this once or twice to get variants of a particular
           file, so I'm not making this an official setting. */
//没写进文档里的一个选项，有趣。
//直接导入一个早先测试中得到的bitmap，这样就能在本次测试中避免从头开始fuzzing
        if (in_bitmap) FATAL("Multiple -B options not supported");

        in_bitmap = optarg;
        read_bitmap(in_bitmap);//把bitmap写进virgin_bits
        break;

      case 'C': /* crash mode */
//crash mode具体可以看https://lcamtuf.blogspot.com/2014/11/afl-fuzz-crash-exploration-mode.html
//允许使用crash作为testcase进行测试，这样可以在短时间内生成少量相关但略有不同的crash
        if (crash_mode) FATAL("Multiple -C options not supported");
        crash_mode = FAULT_CRASH;//这里会给crash_mode赋值2,后续逻辑中时常会出现fault==crash_mode 就是考虑是否出现了crash,同时afl开启了crash mode
        break;

      case 'n': /* dumb mode */
//不插桩模式
        if (dumb_mode) FATAL("Multiple -n options not supported");
        if (getenv("AFL_DUMB_FORKSRV")) dumb_mode = 2; else dumb_mode = 1;//1为不插桩不开启forkserver；2为不插桩，启动forkserver

        break;

      case 'T': /* banner */

        if (use_banner) FATAL("Multiple -T options not supported");
        use_banner = optarg;
        break;

      case 'Q': /* QEMU mode */

        if (qemu_mode) FATAL("Multiple -Q options not supported");
        qemu_mode = 1;

        if (!mem_limit_given) mem_limit = MEM_LIMIT_QEMU;//如果没有设置-m 此处默认内存限制 #define MEM_LIMIT_QEMU      200

        break;

      case 'V': /* Show version number */

        /* Version number has been printed already, just quit. */
        exit(0);

      default:

        usage(argv[0]);

    }

  if (optind == argc || !in_dir || !out_dir) usage(argv[0]);//optind argv的当前索引值

  setup_signal_handlers();//设置信号处理函数
  check_asan_opts();//检查ASAN选项是否正确设置

  if (sync_id) fix_up_sync();//如果参数带了-M或-S 就去设置输出和同步目录

  if (!strcmp(in_dir, out_dir))
    FATAL("Input and output directories can't be the same");

  if (dumb_mode) {

    if (crash_mode) FATAL("-C and -n are mutually exclusive");
    if (qemu_mode)  FATAL("-Q and -n are mutually exclusive");//不插桩用不了crash mode和qemu mode

  }

  if (getenv("AFL_NO_FORKSRV"))    no_forkserver    = 1;
  if (getenv("AFL_NO_CPU_RED"))    no_cpu_meter_red = 1;
  if (getenv("AFL_NO_ARITH"))      no_arith         = 1;//跳过deterministic stage里的arithmetic stage
  if (getenv("AFL_SHUFFLE_QUEUE")) shuffle_queue    = 1;//对输入队列进行洗牌
  if (getenv("AFL_FAST_CAL"))      fast_cal         = 1;//快速校准

  if (getenv("AFL_HANG_TMOUT")) {
    hang_tmout = atoi(getenv("AFL_HANG_TMOUT"));
    if (!hang_tmout) FATAL("Invalid value of AFL_HANG_TMOUT");
  }

  if (dumb_mode == 2 && no_forkserver)
    FATAL("AFL_DUMB_FORKSRV and AFL_NO_FORKSRV are mutually exclusive");

  if (getenv("AFL_PRELOAD")) {
    setenv("LD_PRELOAD", getenv("AFL_PRELOAD"), 1);//可以使用AFL_PRELOAD来设置LD_PRELOAD
    //动态库加载顺序 LD_PRELOAD > LD_LIBRARY_PATH > /etc/ld.so.cache > /lib>/usr/lib
    setenv("DYLD_INSERT_LIBRARIES", getenv("AFL_PRELOAD"), 1);
  }

  if (getenv("AFL_LD_PRELOAD"))
    FATAL("Use AFL_PRELOAD instead of AFL_LD_PRELOAD");

  save_cmdline(argc, argv);//copy一份当前的命令行

  fix_up_banner(argv[optind]);

  check_if_tty();//查看当前是否在tty中。如果不在tty中的话，AFL会将输出信息作精简

  get_core_count();//获取cpu核心数量

#ifdef HAVE_AFFINITY
  bind_to_free_cpu();
#endif /* HAVE_AFFINITY */

  check_crash_handling();//设置core dump，检查/proc/sys/kernel/core_pattern
  check_cpu_governor();//检查CPU调频策略。ondemand策略算法不完善，可能会错过afl-fuzz产生的短暂进程

  setup_post();//加载postprocessor 
  setup_shm();//分配shared memory和virgin_bits空间
  init_count_class16();//根据ount_class_lookup8创建一个ount_class_lookup16

  setup_dirs_fds();//设置输出目录out_dir，包括该目录下的若干子目录
  read_testcases();//从input_dir读取所有测试用例，放入队列
  load_auto();//加载自动生成的extras

  pivot_inputs();//设置输出目录里的测试用例的硬链接

  if (extras_dir) load_extras(extras_dir);//加载extra目录里的extras

  if (!timeout_given) find_timeout();//如果没有设置timeout，如果先前已经有对目标进行过fuzzing，就去in_dir和out_dir里的fuzzer_stats里找exec_timeout

  detect_file_args(argv + optind + 1);//检测命令行中的@@

  if (!out_file) setup_stdio_file();//没有设置-f的话，就用.cur_input作默认stdio文件名

  check_binary(argv[optind]);//检查target binary:确保其存在且不是shell script;文件存在且可执行;文件路径不是/tmp或/var/tmp;非qemu mode或dumb mode下，target binary已经完成插桩

  start_time = get_cur_time();

  if (qemu_mode)
    use_argv = get_qemu_argv(argv[0], argv + optind, argc - optind);//qemu模式下 为QEMU重写命令行参数
  else
    use_argv = argv + optind;

  perform_dry_run(use_argv);//测试执行in_dir中所有testcase

  cull_queue();//精简队列,遍历top_rate中的条目,依次获取先前未见过的字节(temp_v)中的winner并标记位favored,favored条目在fuzzing过程中会得到更多的air time

  show_init_stats();//在处理input_dir的最后显示一些快速的统计信息和一些warning.一些校准的东西和一些硬编码的常数也都在这里结束.

  seek_to = find_start_position();//如果是first run,直接返回0,如果是resuming fuzz,就从out_dir的stats中找开始点

  write_stats_file(0, 0, 0);//更新stats_file
  save_auto();//保存自动生成的extras

  if (stop_soon) goto stop_fuzzing;

  /* Woop woop woop */

  if (!not_on_tty) {//确认一下在不在tty上
    sleep(4);
    start_time += 4000;
    if (stop_soon) goto stop_fuzzing;
  }

  while (1) {//主循环

    u8 skipped_fuzz;

    cull_queue();//精简队列

    if (!queue_cur) {//如果queue_cur当前队列中的偏移为0,认为队列已空,那就开启新的一轮

      queue_cycle++;//queue_cycle表示已完成的轮数
      current_entry     = 0;//复位当前的队列条目ID
      cur_skipped_paths = 0;//复位当前cycle中舍弃的输入
      queue_cur         = queue;//复位,回到queue的头部

      while (seek_to) {//seek_to = find_start_position()  这个循环就是把current_entry和queue_cur定位到start_position
        current_entry++;
        seek_to--;
        queue_cur = queue_cur->next;
      }

      show_stats();//显示经典的数据统计窗口.此外该函数中每分钟会更新fuzzer stats,auto tokens,保存bitmap

      if (not_on_tty) {
        ACTF("Entering queue cycle %llu.", queue_cycle);
        fflush(stdout);
      }

      /* If we had a full queue cycle with no new finds, try
         recombination strategies next. */

      if (queued_paths == prev_queued) {//如果当前队列中的测试用例数与上一轮中队列中测试用例数相等

        if (use_splicing) cycles_wo_finds++; else use_splicing = 1;//如果用了splicing,但还是没新发现,那就cycles_wo_finds++,否则就启用splicing,尝试找新发现

      } else cycles_wo_finds = 0;//两轮测试用例数不等,说明有新发现,那cycles_wo_finds复位

      prev_queued = queued_paths;

      if (sync_id && queue_cycle == 1 && getenv("AFL_IMPORT_FIRST"))//如果设置了-M或-S,afl会在执行操作之前先从其他instance中获取测试用例
        sync_fuzzers(use_argv);//从同步目录sync_dir中获取有趣的测试用例

    }

    skipped_fuzz = fuzz_one(use_argv);//最核心的fuzz_one 包括testcase的变异策略都在这其中进行.如果成功fuzz,返回0;如果被跳过或者bailed out,返回1

    if (!stop_soon && sync_id && !skipped_fuzz) {
      
      if (!(sync_interval_cnt++ % SYNC_INTERVAL))
        sync_fuzzers(use_argv);

    }

    if (!stop_soon && exit_1) stop_soon = 2;

    if (stop_soon) break;

    queue_cur = queue_cur->next;
    current_entry++;

  }

  if (queue_cur) show_stats();

  /* If we stopped programmatically, we kill the forkserver and the current runner. 
     If we stopped manually, this is done by the signal handler. */
  if (stop_soon == 2) {
      if (child_pid > 0) kill(child_pid, SIGKILL);
      if (forksrv_pid > 0) kill(forksrv_pid, SIGKILL);
  }
  /* Now that we've killed the forkserver, we wait for it to be able to get rusage stats. */
  if (waitpid(forksrv_pid, NULL, 0) <= 0) {
    WARNF("error waitpid\n");
  }

  write_bitmap();
  write_stats_file(0, 0, 0);
  save_auto();

stop_fuzzing:

  SAYF(CURSOR_SHOW cLRD "\n\n+++ Testing aborted %s +++\n" cRST,
       stop_soon == 2 ? "programmatically" : "by user");

  /* Running for more than 30 minutes but still doing first cycle? */

  if (queue_cycle == 1 && get_cur_time() - start_time > 30 * 60 * 1000) {

    SAYF("\n" cYEL "[!] " cRST
           "Stopped during the first cycle, results may be incomplete.\n"
           "    (For info on resuming, see %s/README.)\n", doc_path);

  }

  fclose(plot_file);
  destroy_queue();
  destroy_extras();
  ck_free(target_path);
  ck_free(sync_id);

  alloc_report();

  OKF("We're done here. Have a nice day!\n");

  exit(0);

}

#endif /* !AFL_LIB */