Always print DSO map on Fuchsia libFuzzer launch

[aarongreen]

Summary

Fuchsia doesn't have /proc/id/maps, so it relies on the kernel logging system to provide the DSO map to be able to symbolize in the context of ASLR. The DSO map is logged automatically on Fuchsia when encountering a crash or writing to the sanitizer log for the first time in a process. There are several cases where libFuzzer doesn't encounter a crash, e.g. on timeouts, OOMs, and when configured to print new PCs as they become covered, to name a few. Therefore, this change always writes to the sanitizer log on startup to ensure the DSO map is available in the log.

[mcgrathr]

lgtm

compiler-rt/trunk/lib/fuzzer/FuzzerExtFunctions.def

 EXT_FUNC(__lsan_enable, void, (), false);
 EXT_FUNC(__lsan_disable, void, (), false);
 EXT_FUNC(__lsan_do_recoverable_leak_check, int, (), false);
 EXT_FUNC(__sanitizer_acquire_crash_state, int, (), true);
 EXT_FUNC(__sanitizer_install_malloc_and_free_hooks, int,
          (void (*malloc_hook)(const volatile void *, size_t),
           void (*free_hook)(const volatile void *)),
          false);
+EXT_FUNC(__sanitizer_log_write, void, (const char *buf, size_t len), false);
 EXT_FUNC(__sanitizer_purge_allocator, void, (), false);
 EXT_FUNC(__sanitizer_print_memory_profile, void, (size_t, size_t), false);
 EXT_FUNC(__sanitizer_print_stack_trace, void, (), true);
 EXT_FUNC(__sanitizer_symbolize_pc, void,
          (void *, const char *fmt, char *out_buf, size_t out_buf_size), false);
 EXT_FUNC(__sanitizer_get_module_and_offset_for_pc, int,
          (void *pc, char *module_path,
          size_t module_path_len,void **pc_offset), false);
 EXT_FUNC(__sanitizer_set_death_callback, void, (void (*)(void)), true);
 EXT_FUNC(__sanitizer_set_report_fd, void, (void*), false);
 EXT_FUNC(__msan_scoped_disable_interceptor_checks, void, (), false);
 EXT_FUNC(__msan_scoped_enable_interceptor_checks, void, (), false);
 EXT_FUNC(__msan_unpoison, void, (const volatile void *, size_t size), false);
 EXT_FUNC(__msan_unpoison_param, void, (size_t n), false);

compiler-rt/trunk/lib/fuzzer/FuzzerUtilFuchsia.cpp

 } // namespace
 
 bool Mprotect(void *Ptr, size_t Size, bool AllowReadWrite) {
   return false;  // UNIMPLEMENTED
 }
 
 // Platform specific functions.
 void SetSignalHandler(const FuzzingOptions &Options) {
+  // Make sure information from libFuzzer and the sanitizers are easy to
+  // reassemble. `__sanitizer_log_write` has the added benefit of ensuring the
+  // DSO map is always available for the symbolizer.
+  // A uint64_t fits in 20 chars, so 64 is plenty.
+  char Buf[64];
+  memset(Buf, 0, sizeof(Buf));
+  snprintf(Buf, sizeof(Buf), "==%lu== INFO: libFuzzer starting.\n", GetPid());
+  if (EF->__sanitizer_log_write)
+    __sanitizer_log_write(Buf, sizeof(Buf));
+  Printf("%s", Buf);
+
   // Set up alarm handler if needed.
   if (Options.UnitTimeoutSec > 0) {
     std::thread T(AlarmHandler, Options.UnitTimeoutSec / 2 + 1);
     T.detach();
   }
 
   // Set up interrupt handler if needed.
   if (Options.HandleInt || Options.HandleTerm) {