[PATCH] D40923: [libFuzzer] Add preprocessor flag to explicitly enable weak symbols on Mac.

[Max Moroz via Phabricator via llvm-commits]

Dor1s created this revision.
Herald added subscribers: Sanitizers, llvm-commits.

Default implementation for Mac (i.e. FuzzerExtFunctionsDlsym.cpp) does
not work when LLVMFuzzer* interface functions are defined in different
translation units and compiled with "-fvisibility=hidden" flag, as the linker
removes those as a dead code.

That is an alternative solution if we cannot adjust Chromium build config:
https://chromium-review.googlesource.com/c/chromium/src/+/812108


Repository:
  rCRT Compiler Runtime

https://reviews.llvm.org/D40923

Files:
  lib/fuzzer/FuzzerExtFunctionsDlsym.cpp
  lib/fuzzer/FuzzerExtFunctionsWeak.cpp


Index: lib/fuzzer/FuzzerExtFunctionsWeak.cpp
===================================================================
--- lib/fuzzer/FuzzerExtFunctionsWeak.cpp
+++ lib/fuzzer/FuzzerExtFunctionsWeak.cpp
@@ -10,10 +10,11 @@
 // symbols. We don't use this approach on Apple platforms because it requires
 // clients of LibFuzzer to pass ``-U _<symbol_name>`` to the linker to allow
 // weak symbols to be undefined. That is a complication we don't want to expose
-// to clients right now.
+// to clients right now. However, if someone prefers that way, they need to
+// explicitly define LIBFUZZER_WITH_UNDEFINED_WEAK_SYMBOLS.
 //===----------------------------------------------------------------------===//
 #include "FuzzerDefs.h"
-#if LIBFUZZER_LINUX || LIBFUZZER_NETBSD
+#if LIBFUZZER_LINUX || LIBFUZZER_NETBSD || LIBFUZZER_WITH_UNDEFINED_WEAK_SYMBOLS
 
 #include "FuzzerExtFunctions.h"
 #include "FuzzerIO.h"
Index: lib/fuzzer/FuzzerExtFunctionsDlsym.cpp
===================================================================
--- lib/fuzzer/FuzzerExtFunctionsDlsym.cpp
+++ lib/fuzzer/FuzzerExtFunctionsDlsym.cpp
@@ -12,7 +12,7 @@
 // That is a complication we don't wish to expose to clients right now.
 //===----------------------------------------------------------------------===//
 #include "FuzzerDefs.h"
-#if LIBFUZZER_APPLE
+#if LIBFUZZER_APPLE && !LIBFUZZER_WITH_UNDEFINED_WEAK_SYMBOLS
 
 #include "FuzzerExtFunctions.h"
 #include "FuzzerIO.h"


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