* fuzz: improve the API of the `wasm-spec-interpreter` crate
This change addresses key parts of #4852 by improving the bindings to
the OCaml spec interpreter. The new API allows users to `instantiate` a
module, `interpret` named functions on that instance, and `export`
globals and memories from that instance. This currently leaves the
existing implementation ("instantiate and interpret the first function in
a module") present under a new name: `interpret_legacy`.
* fuzz: adapt the differential spec engine to the new API
This removes the legacy uses in the differential spec engine, replacing
them with the new `instantiate`-`interpret`-`export` API from the
`wasm-spec-interpreter` crate.
* fix: make instance access thread-safe
This changes the OCaml-side definition of the instance so that each
instance carries round a reference to a "global store" that's specific
to that instantiation. Because everything is updated by reference there
should be no visible behavioural change on the Rust side, apart from
everything suddenly being thread-safe (modulo the fact that access to
the OCaml runtime still needs to be locked). This fix will need to be
generalised slightly in future if we want to allow multiple modules to
be instantiated in the same store.
Co-authored-by: conrad-watt <cnrdwtt@gmail.com>
Co-authored-by: Alex Crichton <alex@alexcrichton.com>
This commit updates the build script which clones the spec interpreter
for fuzzing to specifically pin at a hardcoded revision. This is
intended at improving reproducibility if we hit any issues while fuzzing
to ensure that the same wasmtime revision is always using the same spec
interpreter revision.
In #3186, we found an issue that requires patching the spec interpreter
for now. Our plan is to have a `fuzzing` branch in our spec-repo mirror
that lets us make these fixes locally before they are upstreamed.
This PR updates the build script for the spec-interpreter wrapper
crate to clone this particular `fuzzing` branch instead of the main
branch.
The WebAssembly spec interpreter is written in OCaml and the new crate
uses `ocaml-interop` along with a small OCaml wrapper to interpret Wasm
modules in-process. The build process for this crate is currently
Linux-specific: it requires several OCaml packages (e.g. `apt install -y
ocaml-nox ocamlbuild`) as well as `make`, `cp`, and `ar`.
