[LibFuzzer] Fix NumberOfCpuCores() for Mac OSX

[delcypher]

Summary

[LibFuzzer] Fix `NumberOfCpuCores()` on Mac OSX.

The nprocs command does not exist under Mac OSX so use
sysctl instead on that platform.

Whilst I'm here

• Use pclose() instead of fclose() which the popen() documentation says should be used.
• Check for errors that were previously unhandled.

[kcc]

Grrr, those pesky #ifdefs. This code could be as easily written in C++ instead of the C preprocessor. (well, almost)

#define in one place in FuzzerInternal.h things like LIBFUZZER_LINUX and LIBFUZZER_MAC (0 or 1).
Then do
if(LIBFUZZER_LINUX) .. else if (LIBFUZZER_MAC) ... else { assert(0 && "text")}

[delcypher]

• Remove use of ifdefs
• Add some more error checking.

[delcypher]

@kcc I've added a bunch of error checking in this patch too and also replace fclose() with pclose(). If you don't like these changes I can remove this so this patch only adds Mac OSX support and nothing else.

[kcc]

lib/Fuzzer/FuzzerUtil.cpp

115–116

move this to where you initialize it.

117

In most of similar cases we do
Printf("WARNING:

127

fold this into the next warning and assume #CPUs == 1 instead of failing

147

This code uses different coding style (ReturnCode or PcloseRet)

[delcypher]

Address @kcc 's comments.

[delcypher]

@kcc Thanks for the fast review! I've tried to address your comments in the new version of the patch.

[kcc]

A few nits to make the code shorter.
Ok to commit with those fixes.

lib/Fuzzer/FuzzerUtil.cpp

115–116

Naming: CmdLIne

115–116

int N = 1;

124

if (pclose(F))

Printf("...")

146

with the default N = 1 you can just remove this.

[delcypher]

lib/Fuzzer/FuzzerUtil.cpp

146

If the command returns the string "0" then N will still get set to 0 regardless of the default which means the assert is still needed.

[delcypher]

Address @kcc 's comments apart from assert before return.

[kcc]

LGTM

lib/Fuzzer/FuzzerUtil.cpp

146

But then you probably don't want the assert, just return 1.

[delcypher]

• Replace assert with `if ()`
• Remove stray comma in Printf() which lead to a crash

[delcypher]

@kcc is this change what you meant?

[kcc]

LGTM, although this many warnings for this code might be an overkill

[delcypher]

@kcc

LGTM, although this many warnings for this code might be an overkill

Probably. We can always remove these warnings at a later date.

lib/Fuzzer/FuzzerUtil.cpp

 void SetSigSegvHandler() { SetSigaction(SIGSEGV, CrashHandler); }
 void SetSigBusHandler() { SetSigaction(SIGBUS, CrashHandler); }
 void SetSigAbrtHandler() { SetSigaction(SIGABRT, CrashHandler); }
 void SetSigIllHandler() { SetSigaction(SIGILL, CrashHandler); }
 void SetSigFpeHandler() { SetSigaction(SIGFPE, CrashHandler); }
 void SetSigIntHandler() { SetSigaction(SIGINT, InterruptHandler); }
 void SetSigTermHandler() { SetSigaction(SIGTERM, InterruptHandler); }
 
 int NumberOfCpuCores() {
-  FILE *F = popen("nproc", "r");
-  int N = 0;
-  if (fscanf(F, "%d", &N) != 1)
+  const char *CmdLine = nullptr;
+  if (LIBFUZZER_LINUX) {
+    CmdLine = "nproc";
+  } else if (LIBFUZZER_APPLE) {
+    CmdLine = "sysctl -n hw.ncpu";
+  } else {
+    assert(0 && "NumberOfCpuCores() is not implemented for your platform");
+  }
+
+  FILE *F = popen(CmdLine, "r");
+  int N = 1;
+  if (!F || fscanf(F, "%d", &N) != 1) {
+    Printf("WARNING: Failed to parse output of command \"%s\" in %s(). "
+           "Assuming CPU count of 1.\n",
+           CmdLine, __func__);
     N = 1;
-  fclose(F);
+  }
+
+  if (pclose(F)) {
+    Printf("WARNING: Executing command \"%s\" failed in %s(). "
+           "Assuming CPU count of 1.\n",
+           CmdLine, __func__);
+    N = 1;
+  }
+  if (N < 1) {
+    Printf("WARNING: Reported CPU count (%d) from command \"%s\" was invalid "
+           "in %s(). Assuming CPU count of 1.\n",
+           N, CmdLine, __func__);
+    N = 1;
+  }
   return N;
 }
 
 int ExecuteCommand(const std::string &Command) {
   return system(Command.c_str());
 }
 
 bool ToASCII(uint8_t *Data, size_t Size) {
   bool Changed = false;
   for (size_t i = 0; i < Size; i++) {