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Various improvements to differential fuzzing #4845

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merged 5 commits into from
Sep 2, 2022
Merged

Various improvements to differential fuzzing #4845

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d7a2bf9
Improve wasmi differential fuzzer
alexcrichton Sep 2, 2022
faa0628
Support differential fuzzing where no engines match
alexcrichton Sep 2, 2022
d8faf0f
Improve proposal support in differential fuzzer
alexcrichton Sep 2, 2022
c2bb4e1
Improve handling of traps in differential fuzzing
alexcrichton Sep 2, 2022
6898c18
Fix fuzzer tests
alexcrichton Sep 2, 2022
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9 changes: 6 additions & 3 deletions crates/fuzzing/src/oracles/engine.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -13,7 +13,7 @@ pub fn choose(
u: &mut Unstructured<'_>,
existing_config: &Config,
allowed: &[&str],
) -> arbitrary::Result<Box<dyn DiffEngine>> {
) -> arbitrary::Result<Option<Box<dyn DiffEngine>>> {
// Filter out any engines that cannot match the `existing_config` or are not
// `allowed`.
let mut engines: Vec<Box<dyn DiffEngine>> = vec![];
Expand Down Expand Up @@ -54,13 +54,16 @@ pub fn choose(
}
}

if engines.is_empty() {
return Ok(None);
}
Comment on lines +57 to +59
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Slightly surprised we would ever have a case where we can't run the test case in Wasmtime. What is even the point at that time?

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I think the issue this is addressing is if testing Wasmtime against Wasmtime has been disabled using the ALLOWED_ENGINES environment variable.

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Ah yeah this is only applicable when you're doing something like ALLOWED_ENGINES=wasmi locally where I was trying to only differentially-execute against wasmi


// Use the input of the fuzzer to pick an engine that we'll be fuzzing
// Wasmtime against.
assert!(!engines.is_empty());
let index: usize = u.int_in_range(0..=engines.len() - 1)?;
let engine = engines.swap_remove(index);
log::debug!("selected engine: {}", engine.name());
Ok(engine)
Ok(Some(engine))
}

/// Provide a way to instantiate Wasm modules.
Expand Down
9 changes: 7 additions & 2 deletions fuzz/fuzz_targets/differential.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -86,8 +86,13 @@ fn run(data: &[u8]) -> Result<()> {
};
log_wasm(&wasm);

// Choose a left-hand side Wasm engine.
let mut lhs = engine::choose(&mut u, &config, unsafe { &ALLOWED_ENGINES })?;
// Choose a left-hand side Wasm engine. If no engine could be chosen then
// that means the configuration selected above doesn't match any allowed
// engine (configured via an env var) so the test case is thrown out.
let mut lhs = match engine::choose(&mut u, &config, unsafe { &ALLOWED_ENGINES })? {
Some(engine) => engine,
None => return Ok(()),
};
let lhs_instance = lhs.instantiate(&wasm);
STATS.bump_engine(lhs.name());

Expand Down