Implement DWARF parser for better backtraces about wazero

[justinclift]

As a general thought, there were DWARF 5 pieces added to the main Go tool chain a while back:

• https://go-review.googlesource.com/c/go/+/175137/
• https://go-review.googlesource.com/c/go/+/175138/2

So, things might not be completely from scratch. 😄

[r8d8]

Hi @mathetake
Does this issue still relevant?
Looking to contribute and landed with it

[codefromthecrypt]

@r8d8 I think this definitely is still relevant, and we'd want to start with backtrace enhancement. If I understand you correctly, you are interested in contributing this? If so, I'd recommend starting small as this may touch a few different spots and iterating small can give you less burden especially in an area that is not 100pct defined in spec.

@mathetake https://github.com/yurydelendik/webassembly-dwarf is abandoned and the author isn't replying to issues anymore. We should ask the actual spec about this and cite something with a future to avoid compatibility drift, possibly asking other implementers which "specs" they plan to use. We can tentatively use the dead one of course, but some time before 1.0 we need to firm this up. wdyt?

[mathetake]

DWARF in Wasm is added in tool-conventions which says:

These conventions are not part of the WebAssembly standard, and are not required of WebAssembly-consuming implementations to execute WebAssembly code. Tools producing and working with WebAssembly in other ways also need not follow any of these conventions. They exist only to support tools that wish to interoperate with other tools at a higher abstraction level than just WebAssembly itself.

Meaning there won't be any formal specification, but instead we have to follow the (personally hosted) specification (https://yurydelendik.github.io/webassembly-dwarf/). So we’ll have to choose a way and possibly compare against another implementation. Fortunately the implementation is stable in the sense that major wasm runtimes and compilers implement it (clang/LLVM, wasmtime, V8).

As for contribution, I think this could be multiple weeks or even months of full-time work. This includes; implementing a binary parser for DWARF 5 (note that there's nothing we can reference or use in the exiting Go ecosystem meaning that we have to implement literally from scratch), refactor the JIT compiler and interpreter so they can track original Wasm instruction address to the our runtime representation), etc.

That said, I would recommend as @codefromthecrypt suggested to start small rather than an overwhelming one like this.

[r8d8]

@codefromthecrypt @mathetake
Thanks for your reply.
Will take a look into WASI support direction.

[mathetake]

Oh that's cool! Thank you for the info! @justinclift