wasm: add DWARF sections

[walkingeyerobot]

What version of Go are you using (go version)?

$ go version
go version go1.12.5 linux/amd64

Output source maps for use with browser developer tools to enable simple step debugging inside browsers. Details of the spec can be found here: https://sourcemaps.info/spec.html

[agnivade]

If I am reading the link correctly, it is the spec for JS source maps. Wasm source maps are not part of a specification yet and it is still in progress. Discussion is ongoing here - WebAssembly/design#1051.

[walkingeyerobot]

It's the spec for sourcemaps within browser dev tools, not specific to javascript. Emscripten is already capable of outputting these for c++ compiled to wasm. See their docs at https://emscripten.org/docs/porting/Debugging.html for more detail.

[agnivade]

I see. Thanks.

[torbenschinke]

Meanwhile Chrome got native dwarf-support for wasm-files, see [1]. It could be a better / simpler alternative to embed debug symbols into the wasm file directly.

Also, one can derive source maps from embedded symbols using tools like [2]. So a dwarf support may be sufficient.

It looks like gc does not embed those symbols currently? Do you have any insights?

[1] https://developers.google.com/web/updates/2019/12/webassembly#enter_dwarf
[2] https://chromium.googlesource.com/external/github.com/kripken/emscripten/+/1.38.11/tools/wasm-sourcemap.py

[jeremyfaller]

The linker explicitly strips DWARF from generated wasm binaries. I would need to about the wasm binary format to add support for DWARF, but it's probably entirely doable to just tweak the linker to spit out DWARF.

[torbenschinke]

Yury Delendik has summarized his findings in [1] and it looks like each DWARF section has a custom section within the wasm binary, just like it shall be in ELF binaries.

[1]https://yurydelendik.github.io/webassembly-dwarf/

[torbenschinke]

@jeremyfaller Are you planning to work on adding support for DWARF?

[jeremyfaller]

Yeah, I'll take a look. It won't make 1.15 (that's frozen), but I'll put something together (on master) that can make 1.16.

[jeremyfaller]

This is looking less likely for me to get to for 1.16. I'm being lent over to the COVID exposure notification work. I would be happy to do code reviews for anyone that takes over. For now, I'm un-committing myself to delivering for 1.16.

[haselkern]

Hi @jeremyfaller! I would be willing to put some time and effort into this. Could you give me a quick rundown of what would need to be done to make this work?