* Add differential fuzzing against V8
This commit adds a differential fuzzing target to Wasmtime along the
lines of the wasmi and spec interpreters we already have, but with V8
instead. The intention here is that wasmi is unlikely to receive updates
over time (e.g. for SIMD), and the spec interpreter is not suitable for
fuzzing against in general due to its performance characteristics. The
hope is that V8 is indeed appropriate to fuzz against because it's
naturally receiving updates and it also is expected to have good
performance.
Here the `rusty_v8` crate is used which provides bindings to V8 as well
as precompiled binaries by default. This matches exactly the use case we
need and at least for now I think the `rusty_v8` crate will be
maintained by the Deno folks as they continue to develop it. If it
becomes an issue though maintaining we can evaluate other options to
have differential fuzzing against.
For now this commit enables the SIMD and bulk-memory feature of
fuzz-target-generation which should enable them to get
differentially-fuzzed with V8 in addition to the compilation fuzzing
we're already getting.
* Use weak linkage for GDB jit helpers
This should help us deduplicate our symbol with other JIT runtimes, if
any. For now this leans on some C helpers to define the weak linkage
since Rust doesn't support that on stable yet.
* Don't use rusty_v8 on MinGW
They don't have precompiled libraries there.
* Fix msvc build
* Comment about execution
* Update wasm-smith to 0.7.0
* Canonicalize NaN with wasm-smith for differential fuzzing
This then also enables floating point executing in wasmi in addition to
the spec interpreter. With NaN canonicalization at the wasm level this
means that we should be producing deterministic results between Wasmtime
and these alternative implementations.
This PR adds a new fuzz target, `differential_wasmi`, that runs a
Cranelift-based Wasm backend alongside a simple third-party Wasm
interpeter crate (`wasmi`). The fuzzing runs the first function in a
given module to completion on each side, and then diffs the return value
and linear memory contents.
This strategy should provide end-to-end coverage including both the Wasm
translation to CLIF (which has seen some subtle and scary bugs at
times), the lowering from CLIF to VCode, the register allocation, and
the final code emission.
This PR also adds a feature `experimental_x64` to the fuzzing crate (and
the chain of dependencies down to `cranelift-codegen`) so that we can
fuzz the new x86-64 backend as well as the current one.
