wasmtime explore doesn't support cross-compiling

[jameysharp]

Steps to Reproduce

cargo run --features all-arch -- explore --target riscv64 crates/c-api/wasm-c-api/example/hello.wasm

If your native host is actually a riscv64 system, replace the target with something else such as x86_64.

Expected Results

Exploration written to crates/c-api/wasm-c-api/example/hello.explore.html

Actual Results

Error: compilation settings are not compatible with the native host

Caused by:
    target 'riscv64-unknown-unknown' specified in the configuration does not match the host

Versions and Environment

Wasmtime version or commit: c34567c

Operating system: Linux

Architecture: x86-64

Extra Info

Based on the error messages, apparently wasmtime explore winds up in Engine::check_compatible_with_native_host by way of Module::from_binary. I don't understand why this mode would use that path though.

Found this together with @michelledaviest while trying to understand some profiling results.

[alexcrichton]

The reason for this is due to this line where a Module is created and a Module is "proof of ready to run" which in a cross-compiled case is impossible since the native platform is never ready to run a different platform. Awhile back this is why Engine::precompile_module was added which skips "is this ready to run" checks and is suitable for cross-compilation (or enabling more features than the host has, stuff like that).

The problem here though is that Module has a good deal of useful metadata about the module that precompile_module doesn't return (it just returns a Vec<u8>). One option though would be to return -> Result<PrecompiledModule> which packages up all the necessary information.