[llvm] r312338 - llvm-isel-fuzzer: Make buildable and testable without libFuzzer

[Kostya Serebryany via llvm-commits]

Can we reuse lib/fuzzer/standalone/StandaloneFuzzTargetMain.c for this
purpose?
Also, it's possible to link against libFuzzer w/o using the coverage
instrumentation.

On Fri, Sep 1, 2017 at 10:02 AM, Justin Bogner via llvm-commits <
llvm-commits at lists.llvm.org> wrote:

> Author: bogner
> Date: Fri Sep  1 10:02:22 2017
> New Revision: 312338
>
> URL: http://llvm.org/viewvc/llvm-project?rev=312338&view=rev
> Log:
> llvm-isel-fuzzer: Make buildable and testable without libFuzzer
>
> This adds a dummy main so we can build and run the llvm-isel-fuzzer
> functionality when we aren't building LLVM with coverage. The approach
> here should serve as a template to stop in-tree fuzzers from
> bitrotting (See llvm.org/pr34314).
>
> Note that I'll probably move most of the logic in DummyISelFuzzer's
> `main` to a library so it's easy to reuse it in other fuzz targets,
> but I'm planning on doing that in a follow up that also consolidates
> argument handling in our LLVMFuzzerInitialize implementations.
>
> Added:
>     llvm/trunk/tools/llvm-isel-fuzzer/DummyISelFuzzer.cpp
> Modified:
>     llvm/trunk/cmake/modules/AddLLVM.cmake
>     llvm/trunk/tools/llvm-isel-fuzzer/CMakeLists.txt
>
> Modified: llvm/trunk/cmake/modules/AddLLVM.cmake
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/cmake/
> modules/AddLLVM.cmake?rev=312338&r1=312337&r2=312338&view=diff
> ============================================================
> ==================
> --- llvm/trunk/cmake/modules/AddLLVM.cmake (original)
> +++ llvm/trunk/cmake/modules/AddLLVM.cmake Fri Sep  1 10:02:22 2017
> @@ -893,11 +893,15 @@ macro(add_llvm_utility name)
>  endmacro(add_llvm_utility name)
>
>  macro(add_llvm_fuzzer name)
> +  cmake_parse_arguments(ARG "" "DUMMY_MAIN" "" ${ARGN})
>    if( LLVM_USE_SANITIZE_COVERAGE )
>      set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fsanitize=fuzzer")
> -    add_llvm_executable(${name} ${ARGN})
> +    add_llvm_executable(${name} ${ARG_UNPARSED_ARGUMENTS})
>      set_target_properties(${name} PROPERTIES FOLDER "Fuzzers")
> -  endif()
> +  elseif( ARG_DUMMY_MAIN )
> +    add_llvm_executable(${name} ${ARG_DUMMY_MAIN}
> ${ARG_UNPARSED_ARGUMENTS})
> +    set_target_properties(${name} PROPERTIES FOLDER "Fuzzers")
> +endif()
>  endmacro()
>
>  macro(add_llvm_target target_name)
>
> Modified: llvm/trunk/tools/llvm-isel-fuzzer/CMakeLists.txt
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/tools/llvm-
> isel-fuzzer/CMakeLists.txt?rev=312338&r1=312337&r2=312338&view=diff
> ============================================================
> ==================
> --- llvm/trunk/tools/llvm-isel-fuzzer/CMakeLists.txt (original)
> +++ llvm/trunk/tools/llvm-isel-fuzzer/CMakeLists.txt Fri Sep  1 10:02:22
> 2017
> @@ -12,4 +12,5 @@ set(LLVM_LINK_COMPONENTS
>      Support
>      Target
>  )
> -add_llvm_fuzzer(llvm-isel-fuzzer llvm-isel-fuzzer.cpp)
> +add_llvm_fuzzer(llvm-isel-fuzzer llvm-isel-fuzzer.cpp
> +  DUMMY_MAIN DummyISelFuzzer.cpp)
>
> Added: llvm/trunk/tools/llvm-isel-fuzzer/DummyISelFuzzer.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/tools/llvm-
> isel-fuzzer/DummyISelFuzzer.cpp?rev=312338&view=auto
> ============================================================
> ==================
> --- llvm/trunk/tools/llvm-isel-fuzzer/DummyISelFuzzer.cpp (added)
> +++ llvm/trunk/tools/llvm-isel-fuzzer/DummyISelFuzzer.cpp Fri Sep  1
> 10:02:22 2017
> @@ -0,0 +1,56 @@
> +//===--- DummyFuzzerMain.cpp - Entry point to sanity check the fuzzer
> -----===//
> +//
> +//                     The LLVM Compiler Infrastructure
> +//
> +// This file is distributed under the University of Illinois Open Source
> +// License. See LICENSE.TXT for details.
> +//
> +//===------------------------------------------------------
> ----------------===//
> +//
> +// Implementation of main so we can build and test without linking
> libFuzzer.
> +//
> +//===------------------------------------------------------
> ----------------===//
> +
> +#include "llvm/ADT/StringRef.h"
> +#include "llvm/Support/Compiler.h"
> +#include "llvm/Support/Error.h"
> +#include "llvm/Support/MemoryBuffer.h"
> +#include "llvm/Support/raw_ostream.h"
> +
> +using namespace llvm;
> +
> +extern "C" int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size);
> +extern "C" LLVM_ATTRIBUTE_WEAK int LLVMFuzzerInitialize(int *argc,
> +                                                        char ***argv) {
> +  return 0;
> +}
> +
> +int main(int argc, char *argv[]) {
> +  errs() << "*** This tool was not linked to libFuzzer.\n"
> +         << "*** No fuzzing will be performed.\n";
> +  if (int RC = LLVMFuzzerInitialize(&argc, &argv)) {
> +    errs() << "Initialization failed\n";
> +    return RC;
> +  }
> +
> +  for (int I = 1; I < argc; ++I) {
> +    StringRef Arg(argv[I]);
> +    if (Arg.startswith("-")) {
> +      if (Arg.equals("-ignore_remaining_args=1"))
> +        break;
> +      continue;
> +    }
> +
> +    auto BufOrErr = MemoryBuffer::getFile(Arg, /*FileSize-*/ -1,
> +                                          /*RequiresNullTerminator=*/
> false);
> +    if (std::error_code EC = BufOrErr.getError()) {
> +      errs() << "Error reading file: " << Arg << ": " << EC.message() <<
> "\n";
> +      return 1;
> +    }
> +    std::unique_ptr<MemoryBuffer> Buf = std::move(BufOrErr.get());
> +    errs() << "Running: " << Arg << " (" << Buf->getBufferSize() << "
> bytes)\n";
> +    LLVMFuzzerTestOneInput(
> +        reinterpret_cast<const uint8_t *>(Buf->getBufferStart()),
> +        Buf->getBufferSize());
> +  }
> +}
>
>
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