[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, 3 insertions, 6 deletions

diff --git a/llvm/lib/Fuzzer/FuzzerLoop.cpp b/llvm/lib/Fuzzer/FuzzerLoop.cpp
index 357f150..15a007b 100644
--- a/llvm/lib/Fuzzer/FuzzerLoop.cpp
+++ b/llvm/lib/Fuzzer/FuzzerLoop.cpp
@@ -47,9 +47,6 @@ __sanitizer_update_counter_bitset_and_clear_counters(uint8_t *bitset);
 __attribute__((weak)) uintptr_t
 __sanitizer_get_coverage_pc_buffer(uintptr_t **data);
 
-__attribute__((weak)) size_t LLVMFuzzerCustomMutator(uint8_t *Data, size_t Size,
-                                                     size_t MaxSize,
-                                                     unsigned int Seed);
 __attribute__((weak)) void __sanitizer_malloc_hook(void *ptr, size_t size);
 __attribute__((weak)) void __sanitizer_free_hook(void *ptr);
 __attribute__((weak)) void __lsan_enable();
@@ -695,9 +692,9 @@ void Fuzzer::MutateAndTestOne() {
 
   for (int i = 0; i < Options.MutateDepth; i++) {
     size_t NewSize = 0;
-    if (LLVMFuzzerCustomMutator)
-      NewSize = LLVMFuzzerCustomMutator(CurrentUnitData, Size,
-                                        Options.MaxLen, MD.GetRand().Rand());
+    if (EF.LLVMFuzzerCustomMutator)
+      NewSize = EF.LLVMFuzzerCustomMutator(CurrentUnitData, Size,
+                                           Options.MaxLen, MD.GetRand().Rand());
     else
       NewSize = MD.Mutate(CurrentUnitData, Size, Options.MaxLen);
     assert(NewSize > 0 && "Mutator returned empty unit");