[libFuzzer] Diff 29 - [AflDriver] Separate implementations of GetPeakRSSMb() for diff platforms.

[mpividori]

Summary

As far as I understand, the goal is to have only one file for afl_driver and make it self contained, even if we are repeating code from libFuzzer.
Taking that into account, I include the following modifications using macros inside afl_driver, to support different platforms.

As this code is the same than for libFuzzer, I would strongly prefer to develop a common static library: "FuzzerSupport", including all the IO and Utils functionalities. Then we could link against that library for libFuzzer and for the afl_driver.
I would like to know your opinion on this.
It would be very simple to add a cmake dependency: "target_link(AFLDriver FuzzerSupport)"
Also, I would like to update the code to remove the flags: LIBFUZZER_POSIX, LIBFUZZER_WINDOWS, etc. and move that logic to the cmake files.

Thanks

[zturner]

This one lgtm.

lib/Fuzzer/afl/afl_driver.cpp

 static FILE *extra_stats_file = NULL;
 static uint32_t previous_peak_rss = 0;
 auto slowest_unit_time_secs = std::chrono::seconds::zero();
 static const int kNumExtraStats = 2;
 static const char *kExtraStatsFormatString = "peak_rss_mb            : %u\n"
                                              "slowest_unit_time_sec  : %u\n";
 
 // Copied from FuzzerUtil.cpp.
+#if LIBFUZZER_POSIX
 size_t GetPeakRSSMb() {
   struct rusage usage;
   if (getrusage(RUSAGE_SELF, &usage))
     return 0;
   if (LIBFUZZER_LINUX) {
     // ru_maxrss is in KiB
     return usage.ru_maxrss >> 10;
   } else if (LIBFUZZER_APPLE) {
     // ru_maxrss is in bytes
     return usage.ru_maxrss >> 20;
   }
   assert(0 && "GetPeakRSSMb() is not implemented for your platform");
   return 0;
 }
+#elif LIBFUZZER_WINDOWS
+size_t GetPeakRSSMb() {
+  PROCESS_MEMORY_COUNTERS info;
+  if (!GetProcessMemoryInfo(GetCurrentProcess(), &info, sizeof(info)))
+    return 0;
+  return info.PeakWorkingSetSize >> 20;
+}
+#endif
 
 // Based on SetSigaction in FuzzerUtil.cpp
 static void SetSigaction(int signum,
                          void (*callback)(int, siginfo_t *, void *)) {
   struct sigaction sigact;
   memset(&sigact, 0, sizeof(sigact));
   sigact.sa_sigaction = callback;
   if (sigaction(signum, &sigact, 0)) {