/src/wasm-tools/fuzz/src/lib.rs

Source
use arbitrary::{Result, Unstructured};
use std::fmt::Debug;
use std::sync::atomic::{AtomicUsize, Ordering::SeqCst};
use wasm_smith::{Component, Config, Module};

pub mod incremental_parse;
pub mod mutate;
pub mod no_traps;
pub mod print;
pub mod reencode;
pub mod roundtrip;
pub mod roundtrip_wit;
pub mod text_parser;
pub mod validate;
pub mod validate_valid_module;
pub mod wit64;

pub fn generate_valid_module(
    u: &mut Unstructured,
    configure: impl FnOnce(&mut Config, &mut Unstructured<'_>) -> Result<()>,
) -> Result<(Vec<u8>, Config)> {
    let mut config: Config = u.arbitrary()?;

    // These are disabled in the swarm config by default, but we want to test
    // them. Use the input data to determine whether these features are enabled.
    config.canonicalize_nans = u.arbitrary()?;
    config.custom_page_sizes_enabled = u.arbitrary()?;
    config.wide_arithmetic_enabled = u.arbitrary()?;
    config.shared_everything_threads_enabled = u.arbitrary()?;

    configure(&mut config, u)?;

    // Use wasm-smith to generate an arbitrary module and convert it to wasm
    // bytes.
    let mut module = Module::new(config.clone(), u)?;
    let bytes = module.to_bytes();

    // 10% of the time, ish, test that the `ensure_termination` method will
    // still produce a valid module.
    if u.ratio(1, 10)? {
        log::debug!("ensuring termination with 100 fuel");
        let _ = module.ensure_termination(100);
    }

    log_wasm(&bytes, &config);

    Ok((bytes, config))
}

pub fn generate_valid_component(
    u: &mut Unstructured,
    configure: impl FnOnce(&mut Config, &mut Unstructured<'_>) -> Result<()>,
) -> Result<(Vec<u8>, Config)> {
    let mut config: Config = u.arbitrary()?;

    // These are disabled in the swarm config by default, but we want to test
    // them. Use the input data to determine whether these features are enabled.
    config.simd_enabled = u.arbitrary()?;
    config.relaxed_simd_enabled = config.simd_enabled && u.arbitrary()?;
    config.exceptions_enabled = u.arbitrary()?;
    config.canonicalize_nans = u.arbitrary()?;

    configure(&mut config, u)?;

    // Use wasm-smith to generate an arbitrary component and convert it to wasm
    // bytes.
    let component = Component::new(config.clone(), u)?;
    let bytes = component.to_bytes();

    log_wasm(&bytes, &config);

    Ok((bytes, config))
}

pub fn validator_for_config(config: &Config) -> wasmparser::Validator {
    wasmparser::Validator::new_with_features(config.features())
}

// Optionally log the module and its configuration if we've gotten this
// far. Note that we don't do this unconditionally to avoid slowing down
// fuzzing, but this is expected to be enabled when debugging a failing
// fuzzer.
pub fn log_wasm(wasm: &[u8], config: impl Debug) {
    drop(env_logger::try_init());

    if !log::log_enabled!(log::Level::Debug) {
        return;
    }

    static CNT: AtomicUsize = AtomicUsize::new(0);

    let i = CNT.fetch_add(1, SeqCst);

    let wasm_file = format!("test{i}.wasm");
    let config_file = format!("test{i}.config");
    let wat_file = format!("test{i}.wat");

    log::debug!("writing test case to `{wasm_file}` ...");
    std::fs::write(&wasm_file, wasm).unwrap();
    std::fs::write(&config_file, format!("{config:#?}")).unwrap();
    if let Ok(wat) = wasmprinter::print_bytes(wasm) {
        log::debug!("writing text format to `{wat_file}` ...");
        std::fs::write(&wat_file, wat).unwrap();
    } else {
        drop(std::fs::remove_file(&wat_file));
    }
}
#[cfg(test)]
mod test {
    use arbitrary::{Result, Unstructured};
    use rand::{Rng, SeedableRng, rngs::SmallRng};

    fn gen_until_pass(mut f: impl FnMut(&mut Unstructured<'_>) -> Result<bool>) -> bool {
        let mut rng = SmallRng::seed_from_u64(0);
        let mut buf = vec![0; 2048];
        let n = 3000;
        for _ in 0..n {
            rng.fill_bytes(&mut buf);
            let mut u = Unstructured::new(&buf);

            if f(&mut u).unwrap() {
                return true;
            }
        }
        false
    }

    /// Runs `f` with random data until it returns `Ok(())` `iters` times.
    pub fn test_n_times(
        iters: u32,
        mut f: impl FnMut(&mut Unstructured<'_>) -> arbitrary::Result<()>,
    ) {
        let mut to_test = 0..iters;
        let ok = gen_until_pass(|b| {
            if f(b).is_ok() {
                Ok(to_test.next().is_none())
            } else {
                Ok(false)
            }
        });
        assert!(ok);
    }
}

Coverage Report

Created: 2026-09-28 08:25