[PATCH] D45744: Add experimental feature to not use AFL's deferred forkserver.

[Jonathan Metzman via Phabricator via llvm-commits]

metzman created this revision.
Herald added subscribers: Sanitizers, llvm-commits, delcypher.

A small but substantial minority of libFuzzer-based fuzzers run code
that does not play well with fork in global constructors or
LLVMFuzzerInitialize. This patch allows these fuzzers to use
afl_driver by allowing them to opt-out of using AFL's deferred forkserver
which deferres calling fork until after this code.


Repository:
  rCRT Compiler Runtime

https://reviews.llvm.org/D45744

Files:
  lib/fuzzer/afl/afl_driver.cpp


Index: lib/fuzzer/afl/afl_driver.cpp
===================================================================
--- lib/fuzzer/afl/afl_driver.cpp
+++ lib/fuzzer/afl/afl_driver.cpp
@@ -138,6 +138,17 @@
 static const char *kExtraStatsFormatString = "peak_rss_mb            : %u\n"
                                              "slowest_unit_time_sec  : %u\n";
 
+// Experimental feature to use afl_driver without AFL's deferred mode.
+// Needs to run before __afl_auto_init.
+__attribute__((constructor(0))) void __decide_deferred_forkserver(void) {
+  if (getenv("AFL_DRIVER_DONT_DEFER")) {
+    if (unsetenv("__AFL_DEFER_FORKSRV")) {
+      perror("Failed to unset __AFL_DEFER_FORKSRV");
+      abort();
+    }
+  }
+}
+
 // Copied from FuzzerUtil.cpp.
 size_t GetPeakRSSMb() {
   struct rusage usage;


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