Stream: git-wasmtime

Topic: wasmtime / issue #4677 fuzz: different results for `f64sqrt`

view this post on Zulip Wasmtime GitHub notifications bot (Aug 10 2022 at 18:30):

abrown labeled issue #4677:

Test Case

(module
  (type (;0;) (func (param f64) (result f64)))
  (func (;0;) (type 0) (param f64) (result f64)
    local.get 0
    f64.sqrt
  )
  (export "test" (func 0))
)

See crash log, crash input, and the WAT/Wasm file: fuzz-bug.zip.

Steps to Reproduce

$ RUST_LOG=wasmtime_fuzzing=debug cargo +nightly fuzz run differential_meta fuzz/artifacts/differential_meta/crash-4a7edd5b645711ba09c0356fceb14040e130e948

Expected Results

Wasmtime and the spec interpreter should have the same results for f64.sqrt.

Actual Results

Wasmtime and the spec interpreter have different results:

[2022-08-10T18:27:26Z DEBUG wasmtime_fuzzing::oracles] Evaluating: test([F64(18442240474082181119)])
[2022-08-10T18:27:26Z DEBUG wasmtime_fuzzing::oracles]  -> results on spec: Ok([F64(9221120237041090560)])
[2022-08-10T18:27:26Z DEBUG wasmtime_fuzzing::oracles]  -> results on wasmtime: Ok([F64(18444492273895866368)])

Versions and Environment

Wasmtime version or commit: meta-diff branch

Operating system: Fedora 35

Architecture: x86-64

Extra Info

@conrad-watt, any thoughts on this one?

view this post on Zulip Wasmtime GitHub notifications bot (Aug 10 2022 at 18:30):

abrown opened issue #4677:

Test Case

(module
  (type (;0;) (func (param f64) (result f64)))
  (func (;0;) (type 0) (param f64) (result f64)
    local.get 0
    f64.sqrt
  )
  (export "test" (func 0))
)

See crash log, crash input, and the WAT/Wasm file: fuzz-bug.zip.

Steps to Reproduce

$ RUST_LOG=wasmtime_fuzzing=debug cargo +nightly fuzz run differential_meta fuzz/artifacts/differential_meta/crash-4a7edd5b645711ba09c0356fceb14040e130e948

Expected Results

Wasmtime and the spec interpreter should have the same results for f64.sqrt.

Actual Results

Wasmtime and the spec interpreter have different results:

[2022-08-10T18:27:26Z DEBUG wasmtime_fuzzing::oracles] Evaluating: test([F64(18442240474082181119)])
[2022-08-10T18:27:26Z DEBUG wasmtime_fuzzing::oracles]  -> results on spec: Ok([F64(9221120237041090560)])
[2022-08-10T18:27:26Z DEBUG wasmtime_fuzzing::oracles]  -> results on wasmtime: Ok([F64(18444492273895866368)])

Versions and Environment

Wasmtime version or commit: meta-diff branch

Operating system: Fedora 35

Architecture: x86-64

Extra Info

@conrad-watt, any thoughts on this one?

view this post on Zulip Wasmtime GitHub notifications bot (Aug 10 2022 at 18:38):

alexcrichton commented on issue #4677:

This looks like a case where the debug printing could probably be improved along the lines of what wasmtime-wast does. The F64(N) is actually a float where the bit pattern of the float is represented by N which means the values in question are:

    -1.7976931348623157e308
    NaN
    NaN

so both the spec interpreter and Wasmtime are producing NaN, they're just producing different signs for the nan. I think spec-wise this is allowed and indicates that we'll need to perform nan normalization of results perhaps.

This is only an issue for the single-instruction-module generator since the wasm-smith generator already has nan canonicalization enabled at the wasm bytecode level to paper over differences between engines.

view this post on Zulip Wasmtime GitHub notifications bot (Aug 10 2022 at 21:36):

abrown commented on issue #4677:

Thanks; I've updated my branch to take this into account (somewhat).

view this post on Zulip Wasmtime GitHub notifications bot (Aug 10 2022 at 21:36):

abrown closed issue #4677:

Test Case

(module
  (type (;0;) (func (param f64) (result f64)))
  (func (;0;) (type 0) (param f64) (result f64)
    local.get 0
    f64.sqrt
  )
  (export "test" (func 0))
)

See crash log, crash input, and the WAT/Wasm file: fuzz-bug.zip.

Steps to Reproduce

$ RUST_LOG=wasmtime_fuzzing=debug cargo +nightly fuzz run differential_meta fuzz/artifacts/differential_meta/crash-4a7edd5b645711ba09c0356fceb14040e130e948

Expected Results

Wasmtime and the spec interpreter should have the same results for f64.sqrt.

Actual Results

Wasmtime and the spec interpreter have different results:

[2022-08-10T18:27:26Z DEBUG wasmtime_fuzzing::oracles] Evaluating: test([F64(18442240474082181119)])
[2022-08-10T18:27:26Z DEBUG wasmtime_fuzzing::oracles]  -> results on spec: Ok([F64(9221120237041090560)])
[2022-08-10T18:27:26Z DEBUG wasmtime_fuzzing::oracles]  -> results on wasmtime: Ok([F64(18444492273895866368)])

Versions and Environment

Wasmtime version or commit: meta-diff branch

Operating system: Fedora 35

Architecture: x86-64

Extra Info

@conrad-watt, any thoughts on this one?

Last updated: Dec 23 2024 at 12:05 UTC