[libFuzzer] Diff 5 - Split FuzzerExtFunction implementation for Linux, Apple and Windows.

[mpividori]

Summary

Implement external functions for Windows using weak symbols with alias.

[zturner]

This one looks fine, but since I'm not sure which CLs depend on which other CLs, to avoid weird merge conflicts I will wait until the first ones go in before submitting this.

[kcc]

lib/Fuzzer/CMakeLists.txt

15–16

do you have to change the file names?
We've spent quite some time with the Apple folks bike-shedding about these names...

[mpividori]

lib/Fuzzer/CMakeLists.txt

15–16

@kcc We have 3 different implementations, one for Windows, one for Apple and one for Linux. So I thought it would be sensible to name the files this way. What would you suggest?

[kcc]

Look at it from another side.
What if we decide to switch Linux implementation to use dlsym?
Or what if we port to FreeBSD, where "weak" works equally well.

My suggestion is to not rename the existing files and to call the new file
FuzzerExtFunctionsWindows.cpp or FuzzerExtFunctionsWeakAlias.cpp

[mpividori]

@kcc Yes, I agree. I will change that. Thanks

[mpividori]

Done.

[kcc]

lib/Fuzzer/FuzzerCorpus.h

17 ↗

(On Diff #80005)

is this a related change?

lib/Fuzzer/FuzzerExtFunctionsDlsym.cpp

17 ↗

(On Diff #80005)

do you need this change here?

lib/Fuzzer/FuzzerExtFunctionsWeak.cpp

16 ↗

(On Diff #80005)

do you need this change here?

lib/Fuzzer/FuzzerExtFunctionsWeakAlias.cpp

10

Implementation using weak aliases. Works for Windows.

[mpividori]

lib/Fuzzer/FuzzerCorpus.h

17 ↗

(On Diff #80005)

That header is required to include std::iota() declaration, in Windows. It is a detail, if you prefer, I can add that line in a different diff.
I apologize for these unrelated "details". This is the result of splitting a previous diff into many diffs.
Now that I understand how the review system works, I will be more careful with future diffs.

lib/Fuzzer/FuzzerExtFunctionsDlsym.cpp

17 ↗

(On Diff #80005)

@kcc Yes, it is needed to use the Printf() function.

lib/Fuzzer/FuzzerExtFunctionsWeak.cpp

16 ↗

(On Diff #80005)

@kcc I remove an empty line, so the 3 files FuzzerExtFunctions*.cpp have the same format. If you prefer, I can remove that change.

lib/Fuzzer/FuzzerExtFunctionsWeakAlias.cpp

10

@kcc Ok, I will add that comment.

[mpividori]

+ Remove unrelated changes.

[kcc]

LGTM

lib/Fuzzer/CMakeLists.txt

 set(LIBFUZZER_FLAGS_BASE "${CMAKE_CXX_FLAGS}")
 # Disable the coverage and sanitizer instrumentation for the fuzzer itself.
 set(CMAKE_CXX_FLAGS "${LIBFUZZER_FLAGS_BASE} -fno-sanitize=all -fno-sanitize-coverage=edge,trace-cmp,indirect-calls,8bit-counters -Werror")
 if( LLVM_USE_SANITIZE_COVERAGE )
   if(NOT "${LLVM_USE_SANITIZER}" STREQUAL "Address")
     message(FATAL_ERROR
       "LibFuzzer and its tests require LLVM_USE_SANITIZER=Address and "
       "LLVM_USE_SANITIZE_COVERAGE=YES to be set."
       )
   endif()
   add_library(LLVMFuzzerNoMainObjects OBJECT
     FuzzerCrossOver.cpp
     FuzzerDriver.cpp
     FuzzerExtFunctionsDlsym.cpp
     FuzzerExtFunctionsWeak.cpp
+    FuzzerExtFunctionsWeakAlias.cpp
     FuzzerIO.cpp
     FuzzerIOPosix.cpp
     FuzzerIOWindows.cpp
     FuzzerLoop.cpp
     FuzzerMutate.cpp
     FuzzerSHA1.cpp
     FuzzerTracePC.cpp
     FuzzerTraceState.cpp

lib/Fuzzer/FuzzerExtFunctionsWeakAlias.cpp

+//===- FuzzerExtFunctionsWeakAlias.cpp - Interface to external functions --===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+// Implementation using weak aliases. Works for Windows.
+//===----------------------------------------------------------------------===//
+#include "FuzzerDefs.h"
+#if LIBFUZZER_WINDOWS
+
+#include "FuzzerExtFunctions.h"
+#include "FuzzerIO.h"
+
+using namespace fuzzer;
+
+extern "C" {
+// Declare these symbols as weak to allow them to be optionally defined.
+#define EXT_FUNC(NAME, RETURN_TYPE, FUNC_SIG, WARN)                            \
+  RETURN_TYPE NAME ## Def FUNC_SIG {                                           \
+    Printf("ERROR: Function \"%s\" not defined.\n", #NAME);                    \
+    exit(1);                                                                   \
+  }                                                                            \
+  RETURN_TYPE NAME FUNC_SIG __attribute__ ((weak, alias (#NAME "Def")));
+
+#include "FuzzerExtFunctions.def"
+
+#undef EXT_FUNC
+}
+
+template <typename T>
+static T* GetFnPtr(T *Fun, T *FunDef, const char *FnName, bool WarnIfMissing) {
+  if (Fun == FunDef) {
+    if (WarnIfMissing)
+      Printf("WARNING: Failed to find function \"%s\".\n", FnName);
+    return nullptr;
+  }
+  return Fun;
+}
+
+namespace fuzzer {
+
+ExternalFunctions::ExternalFunctions() {
+#define EXT_FUNC(NAME, RETURN_TYPE, FUNC_SIG, WARN)                            \
+  this->NAME = GetFnPtr<decltype(::NAME)>(::NAME, ::NAME ## Def, #NAME, WARN);
+
+#include "FuzzerExtFunctions.def"
+
+#undef EXT_FUNC
+}
+} // namespace fuzzer
+#endif // LIBFUZZER_WINDOWS