LLVM name mangling workaround \x01 seems broken

[MauriceKayser]

I think #96444 might have broken the #[export_name = "\x01..."] LLVM workaround for avoiding the "@xyz" name mangling on x86. Compiling the following with i686-pc-windows-msvc results in error LNK2001: unresolved external symbol _☺test1@0:

#[export_name = "\x02test2"]
extern "stdcall" fn test2() {}

#[export_name = "\x01test1"]
extern "stdcall" fn test1() {}

I stumbled upon this when trying to use the \x01 workaround to specify the _aulldiv symbol, which the MSVC linker expects to be named __aulldiv (instead of __aulldiv@16) in #![no_std] x86 Windows crates.

[nbdd0121]

Yeah, my PR indeed doesn't special case \x01. I believe the \x01 thing is a special LLVM-specific hack and was never the proper solution. We probably want a proper solution to turn off symbol decoration in Windows.

[nbdd0121]

Are you trying to define or reference that symbol? You can use asm to workaround the issue.

[MauriceKayser]

We probably want a proper solution to turn off symbol decoration in Windows.

Agreed, there are other issues with the export_name / no_mangle architecture on Windows as well, like #67399.

Are you trying to define or reference that symbol? You can use asm to workaround the issue.

I am trying to get rid of the naked_functions feature in my crates (1, 2), by porting the naked assembly functions to Rust code. The naked function does not care about the calling convention, but the Rust implementation does.

[nbdd0121]

If you are getting rid of naked functions to remove nightly dependency, then you can switch to global_asm. If you are trying to reimplement the function in Rust, then what you could do is to add a global_asm! stub that jumps to the Rust implementation.

[apiraino]

WG-prioritization assigning priority (Zulip discussion).

@rustbot label -I-prioritize +P-low