[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

116

move this to where you initialize it.

128

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

133

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

139

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

116

Naming: CmdLIne

126

int N = 1;

135

if (pclose(F))

Printf("...")

140

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

[delcypher]

lib/Fuzzer/FuzzerUtil.cpp

140

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

140

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 SetSigTermHandler() { SetSigaction(SIGTERM, InterruptHandler); }
 
 int NumberOfCpuCores() {
+#ifdef __linux__
   FILE *F = popen("nproc", "r");
+#elif __APPLE__
+  FILE *F = popen("sysctl -n hw.ncpu", "r");
+#else
+#error "NumberOfCpuCores() is not implemented for your platform"
+#endif
   int N = 0;
   if (fscanf(F, "%d", &N) != 1)
     N = 1;