[PATCH] D70738: [libFuzzer] Add custom output function

[Manish Goregaokar via Phabricator via llvm-commits]

Manishearth added a comment.

In D70738#1773461 <https://reviews.llvm.org/D70738#1773461>, @kcc wrote:

> BTW, may I ask you to provide some details of your Rust fuzz target examples? 
>  (like the code of the fuzz target and the output with your patch)


There's a short example here <https://github.com/rust-fuzz/libfuzzer-sys/blob/master/example_arbitrary/src/main.rs#L5-L9>, but a real example where this would matter a LOT is something like

  fuzz_target!(|(s, b): (String, bool) | {
      if s == "hello" && b {
          panic!("success!");
      }
  });

We're actually still working on improving the behavior around this, right now it's a bit slow for silly reasons, but we'd like the above to work smoothly.

A running example I have locally is

  fuzz_target!(|data: (u8, u8)| {
      if 0 == data.0 && 70 == data.1 {
          panic!("no")
      }
  });

which produces the output

  SUMMARY: libFuzzer: deadly signal
  MS: 1 InsertByte-; base unit: 5ba93c9db0cff93f52b521d7420e43f6eda2784f
  0x0,0x46,
  \x00F
  artifact_prefix='/home/manishearth/mozilla/sand/fuzz/fuzz-test/fuzz/artifacts/fuzz_target_1/'; Test unit written to /home/manishearth/mozilla/sand/fuzz/fuzz-test/fuzz/artifacts/fuzz_target_1/crash-beb59e97091dd2f1ada25fea1abf7a70ac3ada78
  Base64: AEY=
  Formatted: (0, 70)

If you want to look at our output function, it's here <https://github.com/rust-fuzz/libfuzzer-sys/pull/48/files#diff-b4aea3e418ccdb71239b96952d9cddb6R149>, the `println!("Formatted: {:?}", data)` is doing the actual formatting.


Repository:
  rCRT Compiler Runtime

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https://reviews.llvm.org/D70738