Tracking Issue for asm_goto

[nbdd0121]

The feature gate for the issue is #![feature(asm_goto)].

Summary

This feature adds a label<block> operand type to asm!.

Example:

unsafe {
    asm!(
        "jmp {}",
        label {
            println!("Jumped from asm!");
        }
    );
}

The block must have unit type.

Steps

• [ ] Implementation
• [ ] Adjust documentation (see instructions on rustc-dev-guide)
• [ ] Formatting for new syntax has been added to the Style Guide (nightly-style-procedure)
• [ ] Stabilization PR (see instructions on rustc-dev-guide)

Unresolved Questions

• LLVM miscompilation for asm goto with outputs https://github.com/llvm/llvm-project/issues/74483

@rustbot labels: +A-inline-assembly +F-asm

[Nilstrieb]

Where is this coming from? Is there a lang MCP or anything like that?

[nbdd0121]

This is outlined as a future possibility in RFC2873 which I am implementing in #119365.

[tgross35]

Could we support a named label rather than being only positional? Maybe

unsafe { asm!(
    "jmp {foo}",
    label foo {
        println!("Jumped from asm!");
    }
);}

(I mean that foo would be the alias for use in the format string, not that the label in assembly would wind up as foo:)

[bjorn3]

unsafe { asm!(
    "jmp {foo}",
    foo = label {
        println!("Jumped from asm!");
    }
);}

is closer to the syntax used by other operands.

[tgross35]

oh, that does actually work already. Awesome