Improved error messaging when unable to communicate with the fork server
MODIFY
src/afl-fuzz-run.c
src/afl-fuzz-run.c
@@ -178,7 +178,16 @@ u8 run_target(char** argv, u32 timeout) {
if ((res = read(fsrv_st_fd, &status, 4)) != 4) {
if (stop_soon) return 0;
- RPFATAL(res, "Unable to communicate with fork server (OOM?)");
+ SAYF("\n" cLRD "[-] " cRST
+ "Unable to communicate with fork server. Some possible reasons:\n\n"
+ " - You've run out of memory. Use -m to increase the the memory limit\n"
+ " to something higher than %lld.\n"
+ " - The binary or one of the libraries it uses manages to create\n"
+ " threads before the forkserver initializes.\n"
+ " - The binary, at least in some circumstances, exits in a way that\n"
+ " also kills the parent process - raise() could be the culprit.\n\n"
+ "If all else fails you can disable the fork server via AFL_NO_FORKSRV=1.\n", mem_limit);
+ RPFATAL(res, "Unable to communicate with fork server");
}

Improved error messaging when unable to communicate with the fork server