[LibFuzzer] Fix `-jobs=<N>` where <N> > 1 and the number of workers is > 1 on macOS.

The original `ExecuteCommand()` called `system()` from the C library.
The C library implementation of this on macOS contains a mutex which
serializes calls to `system()`. This prevented the `-jobs=` flag
from running copies of the fuzzing binary in parallel which is
the opposite of what is intended.

To fix this on macOS an alternative implementation of `ExecuteCommand()`
is provided that can be used concurrently. This is provided in
`FuzzerUtilDarwin.cpp` which is guarded to only compile code on Apple
platforms. The existing implementation has been moved to a new file
`FuzzerUtilLinux.cpp` which is guarded to only compile code on Linux.

This commit includes a simple test to check that LibFuzzer is being
executed in parallel when requested.

Differential Revision: https://reviews.llvm.org/D22742

llvm-svn: 278544

1 files changed, 0 insertions, 4 deletions

diff --git a/llvm/lib/Fuzzer/FuzzerUtil.cpp b/llvm/lib/Fuzzer/FuzzerUtil.cpp
index c2ae94c4d3d..a5218d422da 100644
--- a/llvm/lib/Fuzzer/FuzzerUtil.cpp
+++ b/llvm/lib/Fuzzer/FuzzerUtil.cpp
@@ -146,10 +146,6 @@ int NumberOfCpuCores() {
   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++) {