global_asm! does not register location information to LLVM, resulting in suboptimal error reporting.

[eddyb]

Quick example (run on playground):

#![feature(asm, global_asm)]

global_asm!("GlobalThisIsNotAnInstruction");

fn main() {
    unsafe {
        asm!("MainThisIsNotAnInstruction");
    }
}

Current error output is:

error: invalid instruction mnemonic 'globalthisisnotaninstruction'
  |
note: instantiated into assembly here
 --> <inline asm>:1:1
  |
1 | GlobalThisIsNotAnInstruction
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: invalid instruction mnemonic 'mainthisisnotaninstruction'
 --> src/main.rs:7:15
  |
7 |         asm!("MainThisIsNotAnInstruction");
  |               ^
  |
note: instantiated into assembly here
 --> <inline asm>:2:2
  |
2 |     MainThisIsNotAnInstruction
  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^

The reason asm! has location information is because it attaches !srcloc metadata on the call asm instruction, whereas global_asm! does nothing of the sort.

It's not clear from the LLVM documentation whether !srcloc (or something equivalent) is supported for module asm, so this might be blocked on LLVM implementing it in the first place.

This came up as @Jasper-Bekkers tried iimplementing AsmMethods::codegen_global_asm for rustc_codegen_spirv and noticed there was no Span being passed, and (presumably the more worrying aspect) that hir::GlobalAsm contains no Span either - it probably should (given that hir::InlineAsm has line_spans: &[Span]).

cc @Amanieu @mrhota

[Amanieu]

It's not clear from the LLVM documentation whether !srcloc (or something equivalent) is supported for module asm

It isn't.