[LibFuzzer] Reimplement how the optional user functions are called.

The motivation for this change is to fix linking issues on OSX.
However this only partially fixes linking issues (the uninstrumented
tests and a few others  won't succesfully link yet).

This change introduces a struct of function pointers
(``fuzzer::ExternalFuntions``) which when initialised will point to the
optional functions if they are available.  Currently these
``LLVMFuzzerInitialize`` and ``LLVMFuzzerCustomMutator`` functions.

Two implementations of ``fuzzer::ExternalFunctions`` constructor are
provided one for Linux and one for OSX.

The OSX implementation uses ``dlsym()`` because the prior implementation
using weak symbols does not work unless the additional flags are passed
to the linker.

The Linux implementation continues to use weak symbols because the
``dlsym()`` approach does not work unless additional flags are passed
to the linker.

Differential Revision: http://reviews.llvm.org/D20741

llvm-svn: 271491

1 files changed, 6 insertions, 8 deletions

diff --git a/llvm/lib/Fuzzer/FuzzerDriver.cpp b/llvm/lib/Fuzzer/FuzzerDriver.cpp
index 3dc062b9311..de5e461eda5 100644
--- a/llvm/lib/Fuzzer/FuzzerDriver.cpp
+++ b/llvm/lib/Fuzzer/FuzzerDriver.cpp
@@ -266,9 +266,13 @@ static bool AllInputsAreFiles() {
   return true;
 }
 
-static int FuzzerDriver(const std::vector<std::string> &Args,
-                        UserCallback Callback) {
+int FuzzerDriver(int *argc, char ***argv, UserCallback Callback) {
   using namespace fuzzer;
+  assert(argc && argv && "Argument pointers cannot be nullptr");
+  fuzzer::ExternalFunctions EF;
+  if (EF.LLVMFuzzerInitialize)
+    EF.LLVMFuzzerInitialize(argc, argv);
+  const std::vector<std::string> Args(*argv, *argv + *argc);
   assert(!Args.empty());
   ProgName = new std::string(Args[0]);
   ParseFlags(Args);
@@ -417,10 +421,4 @@ static int FuzzerDriver(const std::vector<std::string> &Args,
 
   exit(0);  // Don't let F destroy itself.
 }
-
-int FuzzerDriver(int argc, char **argv, UserCallback Callback) {
-  std::vector<std::string> Args(argv, argv + argc);
-  return FuzzerDriver(Args, Callback);
-}
-
 }  // namespace fuzzer