fix lto cmplog stability issue

docs/Changelog.md

@@ -16,6 +16,7 @@ sending a mail to <afl-users+subscribe@googlegroups.com>.
     - fix a regression introduced in 3.10 that resulted in less
       coverage being detected. thanks to Collin May for reporting!
     - fix -n dumb mode (nobody should use this)
+    - fix stability issue with LTO and cmplog
   - afl-showmap, afl-tmin and afl-analyze now honor persistent mode
     for more speed. thanks to dloffre-snl for reporting!
   - Prevent accidently killing non-afl/fuzz services when aborting

src/afl-fuzz-run.c

@@ -291,8 +291,6 @@ static void write_with_gap(afl_state_t *afl, u8 *mem, u32 len, u32 skip_at,
 u8 calibrate_case(afl_state_t *afl, struct queue_entry *q, u8 *use_mem,
                   u32 handicap, u8 from_queue) {
 
-  if (unlikely(afl->shm.cmplog_mode)) { q->exec_cksum = 0; }
-
   u8 fault = 0, new_bits = 0, var_detected = 0, hnb = 0,
      first_run = (q->exec_cksum == 0);
   u64 start_us, stop_us, diff_us;
@@ -300,6 +298,8 @@ u8 calibrate_case(afl_state_t *afl, struct queue_entry *q, u8 *use_mem,
   u32 use_tmout = afl->fsrv.exec_tmout;
   u8 *old_sn = afl->stage_name;
 
+  if (unlikely(afl->shm.cmplog_mode)) { q->exec_cksum = 0; }
+
   /* 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. */
@@ -343,6 +343,32 @@ u8 calibrate_case(afl_state_t *afl, struct queue_entry *q, u8 *use_mem,
 
   }
 
+  /* we need a dummy run if this is LTO + cmplog */
+  if (unlikely(afl->shm.cmplog_mode)) {
+
+    write_to_testcase(afl, use_mem, q->len);
+
+    fault = fuzz_run_target(afl, &afl->fsrv, use_tmout);
+
+    /* afl->stop_soon is set by the handler for Ctrl+C. When it's pressed,
+       we want to bail out quickly. */
+
+    if (afl->stop_soon || fault != afl->crash_mode) { goto abort_calibration; }
+
+    if (!afl->non_instrumented_mode && !afl->stage_cur &&
+        !count_bytes(afl, afl->fsrv.trace_bits)) {
+
+      fault = FSRV_RUN_NOINST;
+      goto abort_calibration;
+
+    }
+
+#ifdef INTROSPECTION
+    if (unlikely(!q->bitsmap_size)) q->bitsmap_size = afl->bitsmap_size;
+#endif
+
+  }
+
   if (q->exec_cksum) {
 
     memcpy(afl->first_trace, afl->fsrv.trace_bits, afl->fsrv.map_size);