Official binaries for `wasm32-unknown-unknown` (and potentially other WASM platforms?) contain code for the wrong architecture

[emilazy]

The compiler-builtins crate compiles C code for WASM platforms since rust-lang/compiler-builtins#566. This works if the C compiler is Clang, as it passes the appropriate -target. However, in a GCC build environment this means that the cc crate will end up silently compiling code for the wrong architecture entirely. This means that, for example, the compiler-builtins shipping for wasm32-unknown-unknown via Rustup contains object files like the following:

45c91108d938afe8-cmpti2.o: ELF 64-bit LSB relocatable, x86-64, version 1 (SYSV), with debug_info, not stripped

I suppose that the build for these needs to arrange for Clang to be present, or perhaps even specified explicitly in the target.*.{cc,cxx,linker} settings.

(Was redirected here from rust-lang/compiler-builtins#732.)

[jyn514]

@emilazy are you interested in fixing this? i think there are three main steps:

1. give a hard error in bootstrap when using gcc to compile for wasm
2. change our CI to use clang instead of gcc
3. add a test that compiling a sample program for wasm32-unknown doesn't give any linker warnings

optionally, you could also change bootstrap to default to clang instead of cc for wasm32-unknown.

i'm happy to mentor this.

@rustbot label E-mentor

[JayAndJef]

Hi @jyn514! If @emilazy doesn't want to take on this issue, I would be glad to. I'm not sure if this is beyond the scope of mine or yours, however, as i'm looking for a good first issue in rustc to resolve - would you be willing to mentor?

[jyn514]

I'm still willing to mentor. I think this would be a challenging first issue but you could do it if you're motivated. There are lots of small things to change, but you will (mostly) have short feedback loops, and finding which parts of the code are relevant will not be too hard I think. Take a look at src/bootstrap, at the dev guide for bootstrap, and at the wasm32-unknown platform docs. This check should probably (?) live in sanity.rs, which has flaws, but it's what we have right now.

[JayAndJef]

I think I'll take this issue on. Are there any steps I need to take besides forking the repository, such as claiming this issue or moving to a different platform to communicate with you?

[jyn514]

both those, yeah - i think @rustbot claim is the current syntax?

i'm on zulip as "jyn".