When the `stacks` fuzzer hits a stack overflow the trace generated by Wasmtime will have one more frame than the trace generated by the wasm itself. This comes about due to the wasm not actually pushing the final frame when it stack overflows. The host, however, will still see the final frame that triggered the stack overflow. In this situation the fuzzer asserts that the host has one extra frame and then discards the frame.
Fuzzing Infrastructure for Wasmtime
This crate provides test case generators and oracles for use with fuzzing.
These generators and oracles are generally independent of the fuzzing engine
that might be using them and driving the whole fuzzing process (e.g. libFuzzer
or AFL). As such, this crate does not contain any actual fuzz targets
itself. Those are generally just a couple lines of glue code that plug raw input
from (for example) libFuzzer into a generator, and then run one or more
oracles on the generated test case.
If you're looking for the actual fuzz target definitions we currently have, they
live in wasmtime/fuzz/fuzz_targets/* and are driven by cargo fuzz and
libFuzzer.