[PATCH] D60008: Use binary write mode in WriteToFile function to avoid appended \r characters on Windows

[tuktuk via Phabricator via llvm-commits]

tuktuk added a comment.

There is a problem with that generic solution which is that nothing in it forces libfuzzer to generate multiple byte values and in my experiments the data I get is always very poorly distributed, so in practice it is not that generic.
I tried a fuzz target that would force libfuzzer to have at least one instance of every possible byte value, but libfuzzer wouldn't manage to generate appropriate data.
However I can confirm that the following fuzz target can be used to differentiate between pre-patch and patched versions following the (non-)reproducibility test we talked about:

  // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
  // See https://llvm.org/LICENSE.txt for license information.
  // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
  
  // Tests preservation of crashing inputs when writing to disk.
  #include <cstdint>
  
  extern "C" int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
      static bool Found[256];
  
      // Make sure Data is quite long
  
      if (Size < 1000) {
          return 0;
      }
  
      // Make sure Data has at least one '\n' byte value
  
      // Checking that Data has all possible byte values would be more satisfying
      // but libfuzzer doesn't seem powerful enough for this right now
  
      for (size_t i = 0; i < 256; ++i) {
          Found[i] = false;
      }
      for (size_t i = 0; i < Size; ++i) {
          Found[Data[i]] = true;
      }
      if (!Found['\n']) {
          return 0;
      }
  
      // Crash upon some hash value from Size and Data
  
      // Reproducibility will only happen if hash value is the same
  
      size_t Sum = Size;
      for (size_t i = 0; i < Size; ++i) {
          Sum += Data[i];
      }
      if (Sum % 100 == 19) {
          __builtin_trap();
      }
  
      return 0;
  }

I spent some time trying to understand llvm lit syntax but I couldn't produce a satisfying test file that I would be able to run from my Windows machine. Could you do this part? Thanks a lot.


Repository:
  rCRT Compiler Runtime

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  https://reviews.llvm.org/D60008/new/

https://reviews.llvm.org/D60008