Function execute

crates/fuzzing/src/single_module_fuzzer.rs:96–127

Executes a "single module fuzzer" given the raw `input` from libfuzzer. This will use the `input` to generate `T`, some configuration, which is then used by `gen_module` to generate a WebAssembly module. The module is then passed to `run` along with the configuration and remaining data that can be used as fuzz input. The main purpose of this function is to handle when `input` is actually a WebAs

(
    input: &'a [u8],
    run: fn(&[u8], KnownValid, T, &mut Unstructured<'a>) -> Result<U>,
    gen_module: fn(&mut T, &mut Unstructured<'a>) -> Result<(Vec<u8>, KnownValid)>,
)

/// we're still interested in the historical coverage of the original wasm
/// module.
pub fn execute<'a, T, U>(
    input: &'a [u8],
    run: fn(&[u8], KnownValid, T, &mut Unstructured<'a>) -> Result<U>,
    gen_module: fn(&mut T, &mut Unstructured<'a>) -> Result<(Vec<u8>, KnownValid)>,
) -> Result<U>
where
    T: Arbitrary<'a>,
{
    let (fuzz_data, module_in_input) = match extract_fuzz_input(input) {
        Ok(input) => {
            log::debug!("fuzz input was a valid module with trailing custom section");
            (input.fuzz_data, Some(input.module))
        }
        Err(e) => {
            log::debug!("fuzz input not a valid module: {e:?}");
            (input, None)
        }
    };
    let mut u = Unstructured::new(fuzz_data);
    let mut config = u.arbitrary()?;
    let (generated, known_valid) = gen_module(&mut config, &mut u)?;
    let module = module_in_input.unwrap_or(&generated);
    if let Ok(file) = std::env::var("WRITE_FUZZ_INPUT_TO") {
        std::fs::write(file, encode_module(&module, &fuzz_data)).unwrap();
    }
    let known_valid = if module_in_input.is_some() {
        KnownValid::No
    } else {
        known_valid
    };
    run(module, known_valid, config, &mut u)
}

/// Used as part of `execute` above to determine whether a module is known to
/// be valid ahead of time.