Tracking Issue for `#[align(...)]` on function items (fn_align)

[repnop]

This feature allows specifying an alignment for function items by adding the #[repr(align(...))] attribute to them.
The feature gate for the issue is #![feature(fn_align)]

Example

#[align(16)]
fn requires_alignment() {
    // ...
}

Steps

• Accept RFC
  • RFC: Add an attribute for raising the alignment of various items rfcs#3806
• Implementation (Allow specifying alignment for functions #81234)
• Adjust documentation
• Stabilization PR
  • Stabilize fn_align: #[align(N)] on functions #140261

Blocking issues

• Function alignment does not work on wasm #143368
• What does this mean on the language level? It can't be quite as easy as "function pointers, cast to an integer, are divisible by the alignment" -- that's incorrect on ARM.

[evanrichter]

Is it be possible to apply this to methods as well?

#![feature(fn_align)]

#[repr(align(1))]
fn main() {
    Bar::foo();
}

struct Bar;

impl Bar {
    #[repr(align(1))]
    fn foo() {
        println!("bar");
    }
}

error[E0517]: attribute should be applied to a struct, enum, function, or union
  --> src/main.rs:11:12
   |
11 |       #[repr(align(1))]
   |              ^^^^^^^^
12 | /     fn foo() {
13 | |         println!("bar");
14 | |     }
   | |_____- not a struct, enum, function, or union

For more information about this error, try `rustc --explain E0517`.
error: could not compile `asdf` due to previous error

[repnop]

I don't see why not? (I'm surprised it doesn't work already honestly lol) I'll see if I can find some time to investigate that and make another PR to allow that 👍

[bunnie]

Thanks for opening this, I just bumped my head into this exact problem as well!

[workingjubilee]

This should come with a command-line flag to address the request made in #128830 for global code alignment control.