Compiler null dereference when there are conflicting asm labels

[addrianyy]

Code

#![feature(asm)]

#[inline(always)]
fn f() {
    unsafe {
        asm!("test: nop");
    }
}

fn main() {
    f();
    f();
}

Meta

rustc 1.46.0-nightly (346aec9b0 2020-07-11)
binary: rustc
commit-hash: 346aec9b02f3c74f3fce97fd6bda24709d220e49
commit-date: 2020-07-11
host: x86_64-pc-windows-msvc
release: 1.46.0-nightly
LLVM version: 10.0

Error output

error: invalid symbol redefinition
 --> .\crash.rs:6:15
  |
6 |         asm!("test: nop");
  |               ^
  |
note: instantiated into assembly here
 --> <inline asm>:2:2
  |
2 |     test: nop
  |     ^
[crash due to null dereference]

Details

This bug only happens when compiling for Windows target with debug information. Command to reproduce crash:

rustc crash.rs --target x86_64-pc-windows-msvc -g

It was identified by eddyb that crash happens in LLVM function WinCOFFObjectWriter::assignFileOffsets.

[jonas-schievink]

On the playground this seems to hang instead

[Amanieu]

The asm! RFC and documentation specifically say that you should not define labels in inline assembly and instead only use local labels (0:, 1:, etc).

So your code is invalid, but having the compiler crash on invalid code is still a bug.

[asquared31415]

@rustbot claim

[Amanieu]

This no longer seems to crash. Probably fixed by LLVM at some point.

[Amanieu]

Actually it seems to still be crashing on x86_64-pc-windows-gnu and x86_64-pc-windows-msvc.

[asquared31415]

#87324 lints against using labels in this way, which is prohibited by the asm RFC and documented. #81088 is the primary issue for an ideal solution that lets this work.

Since this now errors by default, should this be closed?

[Amanieu]

Yes, I think we can close this.