README.md

Roc-fuzz-internal

Warning: This repro is being deprecated, but is mostly meant for fuzzing compiler implementations for memory leaks.

The goal of this repo is to enable fuzzing of roc applications. The main target is fuzzing parts of the standard library. It should hopefully be able to catch some bugs especially memory safety ones in the zig builtins.

Note: On the sanitizers really only fully catch bugs on linux. If you are on mac, fuzzing is likely to be less productive.

Dependencies

This requires cargo-fuzz which can be installed with: cargo install cargo-fuzz

If using any sanitizer other than the fuzzer, it also requires nightly rust to enable.

How to use

This requires a special build of the compiler with the sanitizers feature flag. Start by building roc from source:

cargo build --features sanitizers --bin roc

Note: From this point forward, roc means the binary generate from the above command in target/debug/roc

Note: If you have roc in your path, you should be able to just use the run.sh or run-many.sh scripts to do everything below automatically. That said, the script does require installing gum.

Next, we can use roc to build a fuzz target. They all live in the roc_targets directory. For building fuzz targets, we need to enable sanitizers. At a minimum, the cargo-fuzz sanitizer is required. On top of that address, memory, and thread sanitizers are available. I advise using address sanitizer in general. We can build strFromUtf8.roc with:

ROC_SANITIZERS="address,cargo-fuzz" roc build --no-link roc_targets/strFromUtf8.roc

This will generate an instrumented object file. For this platform we need a static library. That can be create with:

ar rcs roc_targets/libroc-fuzz.a roc_targets/libroc-fuzz.o

Now that we have the generated static library, we can compile and run the fuzz target (note that this requires the nightly toolchain):

cargo +nightly fuzz run roc-fuzz

Other Notes

If you switch from fuzzing one applications to another, remember to clear the fuzz/corpus and fuzz/artifacts directories.

For more options run cargo fuzz run --help.

Fuzzing can be done with optimized builds. Just add --optimize to the roc build invocation and -O to the cargo fuzz run invocation.

In the future, I hope to add a way to pretty print the crashes. That should help a human understand them better.