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

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.

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

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 👍

feat: Add MessageMf

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

Rollup merge of rust-lang#110313 - fee1-dead-contrib:repr_align_metho…

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

Rollup merge of rust-lang#129421 - jdonszelmann:naked-repr-align-func…

Unrolled build for rust-lang#129421

Unrolled build for #142854

Rollup merge of rust-lang#142923 - folkertdev:min-function-alignment-…

Unrolled build for #142923

Rollup merge of #142854 - folkertdev:centralize-min-function-alignmen…

The PR description here is outdated, right? Could someone familiar with the feature update it?

Rollup merge of rust-lang#143206 - Jules-Bertholet:align-attr-fixes, …

Unrolled build for #143206

For the record, there is a new LLVM RFC related to function alignment that may interact with this feature: https://discourse.llvm.org/t/rfc-enhancing-function-alignment-attributes/88019

For the record, there is a new LLVM RFC related to function alignment that may interact with this feature: https://discourse.llvm.org/t/rfc-enhancing-function-alignment-attributes/88019

With that RFC, the Rust align attribute would correspond with LLVM minalign, I believe.

Rollup merge of #134213 - folkertdev:stabilize-naked-functions, r=tgr…

LLVM apparently backed out the align -> minalign change and the author is proposing adding a new prefalign attribute for that.

For those who try to use it, the current syntax is #[rustc_align(N)], not #[align(N)].

#[align(N)] simply errors, while #[repr(align(N))] suggests #[rustc_align(N)].

Please update the first comment.

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Tracking Issue for `#[align(...)]` on function items (fn_align) #82232

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Tracking Issue for #[align(...)] on function items (fn_align) #82232

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evanrichter commented on Aug 25, 2021

repnop commented on Aug 26, 2021

bunnie commented on Dec 25, 2022

workingjubilee commented on Aug 8, 2024

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RalfJung commented on Jul 3, 2025

nikic commented on Aug 22, 2025

Jules-Bertholet commented on Aug 22, 2025

workingjubilee commented on Jan 31, 2026

nazar-pc commented on May 1, 2026

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Tracking Issue for `#[align(...)]` on function items (fn_align) #82232