implement `feature(c_variadic_naked_functions)` - #148770

folkertdev · 2025-11-09T21:14:04Z

tracking issue: #148767

This feature allows naked c-variadic function definitions with any ABI that is supported for foreign c-variadic functions.

#![feature(c_variadic, c_variadic_naked_functions)]

#[unsafe(naked)]
unsafe extern "win64" fn variadic_win64(_: u32, _: ...) -> u32 {
    core::arch::naked_asm!(
        r#"
        push    rax
        mov     qword ptr [rsp + 40], r9
        mov     qword ptr [rsp + 24], rdx
        mov     qword ptr [rsp + 32], r8
        lea     rax, [rsp + 40]
        mov     qword ptr [rsp], rax
        lea     eax, [rdx + rcx]
        add     eax, r8d
        pop     rcx
        ret
    "#,
    )
}

r? @workingjubilee

rustbot · 2025-11-09T21:14:08Z

workingjubilee is currently at their maximum review capacity.
They may take a while to respond.

workingjubilee · 2025-11-09T22:43:31Z

workingjubilee · 2025-11-11T21:39:14Z

seems fine.

@bors r+ rollup

bors · 2025-11-11T21:39:17Z

📌 Commit 9129b90 has been approved by workingjubilee

It is now in the queue for this repository.

…kingjubilee implement `feature(c_variadic_naked_functions)` tracking issue: rust-lang#148767 [#t-lang > C-variadic naked functions](https://rust-lang.zulipchat.com/#narrow/channel/213817-t-lang/topic/C-variadic.20naked.20functions/with/554593886) This feature allows naked c-variadic function definitions with any ABI that is supported for foreign c-variadic functions. ```rust #![feature(c_variadic, c_variadic_naked_functions)] #[unsafe(naked)] unsafe extern "win64" fn variadic_win64(_: u32, _: ...) -> u32 { core::arch::naked_asm!( r#" push rax mov qword ptr [rsp + 40], r9 mov qword ptr [rsp + 24], rdx mov qword ptr [rsp + 32], r8 lea rax, [rsp + 40] mov qword ptr [rsp], rax lea eax, [rdx + rcx] add eax, r8d pop rcx ret "#, ) } ``` r? `@workingjubilee`

…kingjubilee implement `feature(c_variadic_naked_functions)` tracking issue: rust-lang#148767 [#t-lang > C-variadic naked functions](https://rust-lang.zulipchat.com/#narrow/channel/213817-t-lang/topic/C-variadic.20naked.20functions/with/554593886) This feature allows naked c-variadic function definitions with any ABI that is supported for foreign c-variadic functions. ```rust #![feature(c_variadic, c_variadic_naked_functions)] #[unsafe(naked)] unsafe extern "win64" fn variadic_win64(_: u32, _: ...) -> u32 { core::arch::naked_asm!( r#" push rax mov qword ptr [rsp + 40], r9 mov qword ptr [rsp + 24], rdx mov qword ptr [rsp + 32], r8 lea rax, [rsp + 40] mov qword ptr [rsp], rax lea eax, [rdx + rcx] add eax, r8d pop rcx ret "#, ) } ``` r? ``@workingjubilee``

Rollup of 12 pull requests Successful merges: - #146627 (Simplify `jemalloc` setup) - #147753 (Suggest add bounding value for RangeTo) - #147974 (Improve diagnostics for buffer reuse with borrowed references) - #148080 ([rustdoc] Fix invalid jump to def macro link generation) - #148424 (bootstrap: Add snapshot tests for path-to-step handling) - #148500 (Update git index before running diff-index) - #148536 (cmse: add test for `async` and `const` functions) - #148770 (implement `feature(c_variadic_naked_functions)`) - #148819 (Remove specialized warning for removed target) - #148830 (miri subtree update) - #148833 (Update rustbook dependencies) - #148841 (Remove more `#[must_use]` from portable-simd) r? `@ghost` `@rustbot` modify labels: rollup

…kingjubilee implement `feature(c_variadic_naked_functions)` tracking issue: rust-lang#148767 [#t-lang > C-variadic naked functions](https://rust-lang.zulipchat.com/#narrow/channel/213817-t-lang/topic/C-variadic.20naked.20functions/with/554593886) This feature allows naked c-variadic function definitions with any ABI that is supported for foreign c-variadic functions. ```rust #![feature(c_variadic, c_variadic_naked_functions)] #[unsafe(naked)] unsafe extern "win64" fn variadic_win64(_: u32, _: ...) -> u32 { core::arch::naked_asm!( r#" push rax mov qword ptr [rsp + 40], r9 mov qword ptr [rsp + 24], rdx mov qword ptr [rsp + 32], r8 lea rax, [rsp + 40] mov qword ptr [rsp], rax lea eax, [rdx + rcx] add eax, r8d pop rcx ret "#, ) } ``` r? ```@workingjubilee```

Rollup of 16 pull requests Successful merges: - #146627 (Simplify `jemalloc` setup) - #147753 (Suggest add bounding value for RangeTo) - #147832 (rustdoc: Don't pass `RenderOptions` to `DocContext`) - #147974 (Improve diagnostics for buffer reuse with borrowed references) - #148080 ([rustdoc] Fix invalid jump to def macro link generation) - #148465 (Adjust spans into the `for` loops context before creating the new desugaring spans.) - #148500 (Update git index before running diff-index) - #148531 (rustc_target: introduce Abi, Env, Os) - #148536 (cmse: add test for `async` and `const` functions) - #148770 (implement `feature(c_variadic_naked_functions)`) - #148780 (fix filecheck typos in tests) - #148819 (Remove specialized warning for removed target) - #148830 (miri subtree update) - #148833 (Update rustbook dependencies) - #148834 (fix(rustdoc): Color doctest errors) - #148841 (Remove more `#[must_use]` from portable-simd) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of #148770 - folkertdev:naked-c-variadic, r=workingjubilee implement `feature(c_variadic_naked_functions)` tracking issue: #148767 [#t-lang > C-variadic naked functions](https://rust-lang.zulipchat.com/#narrow/channel/213817-t-lang/topic/C-variadic.20naked.20functions/with/554593886) This feature allows naked c-variadic function definitions with any ABI that is supported for foreign c-variadic functions. ```rust #![feature(c_variadic, c_variadic_naked_functions)] #[unsafe(naked)] unsafe extern "win64" fn variadic_win64(_: u32, _: ...) -> u32 { core::arch::naked_asm!( r#" push rax mov qword ptr [rsp + 40], r9 mov qword ptr [rsp + 24], rdx mov qword ptr [rsp + 32], r8 lea rax, [rsp + 40] mov qword ptr [rsp], rax lea eax, [rdx + rcx] add eax, r8d pop rcx ret "#, ) } ``` r? ````@workingjubilee````

Rollup of 16 pull requests Successful merges: - rust-lang/rust#146627 (Simplify `jemalloc` setup) - rust-lang/rust#147753 (Suggest add bounding value for RangeTo) - rust-lang/rust#147832 (rustdoc: Don't pass `RenderOptions` to `DocContext`) - rust-lang/rust#147974 (Improve diagnostics for buffer reuse with borrowed references) - rust-lang/rust#148080 ([rustdoc] Fix invalid jump to def macro link generation) - rust-lang/rust#148465 (Adjust spans into the `for` loops context before creating the new desugaring spans.) - rust-lang/rust#148500 (Update git index before running diff-index) - rust-lang/rust#148531 (rustc_target: introduce Abi, Env, Os) - rust-lang/rust#148536 (cmse: add test for `async` and `const` functions) - rust-lang/rust#148770 (implement `feature(c_variadic_naked_functions)`) - rust-lang/rust#148780 (fix filecheck typos in tests) - rust-lang/rust#148819 (Remove specialized warning for removed target) - rust-lang/rust#148830 (miri subtree update) - rust-lang/rust#148833 (Update rustbook dependencies) - rust-lang/rust#148834 (fix(rustdoc): Color doctest errors) - rust-lang/rust#148841 (Remove more `#[must_use]` from portable-simd) r? `@ghost` `@rustbot` modify labels: rollup

…ked-functions, r=tiif stabilize `c_variadic_naked_functions` tracking issue: rust-lang#148767 reference PR: rust-lang/reference#2321 # Stabilization report ## Summary Stabilize the ability to use `#[unsafe(naked)]` functions to define c-variadic functions. These c-variadic naked functions accept the same set of ABIs as c-variadic foreign functions, this set is larger than what we currently accept for c-variadic definitions. ```rust #[unsafe(naked)] unsafe extern "aapcs" fn variadic_aapcs(_: f64, _: ...) -> f64 { core::arch::naked_asm!( r#" sub sp, sp, rust-lang#12 stmib sp, {{r2, r3}} vmov d0, r0, r1 add r0, sp, rust-lang#4 vldr d1, [sp, rust-lang#4] add r0, r0, rust-lang#15 bic r0, r0, rust-lang#7 vadd.f64 d0, d0, d1 add r1, r0, rust-lang#8 str r1, [sp] vldr d1, [r0] vadd.f64 d0, d0, d1 vmov r0, r1, d0 add sp, sp, rust-lang#12 bx lr "#, ) } ``` ## Accepted ABIs The set of accepted ABIs is the same as for c-variadic foreign functions, defined as rule [`items.extern.variadic.conventions`](https://doc.rust-lang.org/nightly/reference/items/external-blocks.html?highlight=externblo#r-items.extern.variadic.conventions): - `"aapcs"` - `"C"` - `"cdecl"` - `"efiapi"` - `"system"` - `"sysv64"` - `"win64"` And their corresponding `-unwind` variants. Given that naked functions desugar to a block of module assembly and a foreign definition, it makes sense to support the same set as source-level foreign definitions. For c-variadic definitions we only accept `"C"` and `"C-unwind"`. ## Multiple c-variadic ABIs in the same program LLVM supports c-variadic calls of different ABIs in the same program. We test both an arm and x86 configuration - https://github.com/rust-lang/rust/blob/771916f9028e7fe56d2685f2c4f698de5d7d6a45/tests/ui/c-variadic/same-program-multiple-abis-arm.rs - https://github.com/rust-lang/rust/blob/771916f9028e7fe56d2685f2c4f698de5d7d6a45/tests/ui/c-variadic/same-program-multiple-abis-x86_64.rs Note that GCC, Clang and LLVM do not support c-variadic definitions of multiple ABIs: the `va_start`, `va_arg` etc. macros are always expanded using the default C calling convention. Clang and GCC reject a variable argument list on definitions that use a non-default calling convention. ## History - [#t-lang > C-variadic naked functions](https://rust-lang.zulipchat.com/#narrow/channel/213817-t-lang/topic/C-variadic.20naked.20functions/with/554593886) - rust-lang#148770 The stabilization report of `feature(c_variadic)` mentions this feature: - rust-lang#155697 ## Unresolved questions None.

Rollup merge of #159746 - folkertdev:stabilize-c-variadic-naked-functions, r=tiif stabilize `c_variadic_naked_functions` tracking issue: #148767 reference PR: rust-lang/reference#2321 # Stabilization report ## Summary Stabilize the ability to use `#[unsafe(naked)]` functions to define c-variadic functions. These c-variadic naked functions accept the same set of ABIs as c-variadic foreign functions, this set is larger than what we currently accept for c-variadic definitions. ```rust #[unsafe(naked)] unsafe extern "aapcs" fn variadic_aapcs(_: f64, _: ...) -> f64 { core::arch::naked_asm!( r#" sub sp, sp, #12 stmib sp, {{r2, r3}} vmov d0, r0, r1 add r0, sp, #4 vldr d1, [sp, #4] add r0, r0, #15 bic r0, r0, #7 vadd.f64 d0, d0, d1 add r1, r0, #8 str r1, [sp] vldr d1, [r0] vadd.f64 d0, d0, d1 vmov r0, r1, d0 add sp, sp, #12 bx lr "#, ) } ``` ## Accepted ABIs The set of accepted ABIs is the same as for c-variadic foreign functions, defined as rule [`items.extern.variadic.conventions`](https://doc.rust-lang.org/nightly/reference/items/external-blocks.html?highlight=externblo#r-items.extern.variadic.conventions): - `"aapcs"` - `"C"` - `"cdecl"` - `"efiapi"` - `"system"` - `"sysv64"` - `"win64"` And their corresponding `-unwind` variants. Given that naked functions desugar to a block of module assembly and a foreign definition, it makes sense to support the same set as source-level foreign definitions. For c-variadic definitions we only accept `"C"` and `"C-unwind"`. ## Multiple c-variadic ABIs in the same program LLVM supports c-variadic calls of different ABIs in the same program. We test both an arm and x86 configuration - https://github.com/rust-lang/rust/blob/771916f9028e7fe56d2685f2c4f698de5d7d6a45/tests/ui/c-variadic/same-program-multiple-abis-arm.rs - https://github.com/rust-lang/rust/blob/771916f9028e7fe56d2685f2c4f698de5d7d6a45/tests/ui/c-variadic/same-program-multiple-abis-x86_64.rs Note that GCC, Clang and LLVM do not support c-variadic definitions of multiple ABIs: the `va_start`, `va_arg` etc. macros are always expanded using the default C calling convention. Clang and GCC reject a variable argument list on definitions that use a non-default calling convention. ## History - [#t-lang > C-variadic naked functions](https://rust-lang.zulipchat.com/#narrow/channel/213817-t-lang/topic/C-variadic.20naked.20functions/with/554593886) - #148770 The stabilization report of `feature(c_variadic)` mentions this feature: - #155697 ## Unresolved questions None.

folkertdev added 3 commits November 9, 2025 14:35

propagate function attributes in ast visitor

568c6ed

add feature(c_variadic_naked_functions)

ebd173f

use feature(c_variadic_naked_functions) in tests

9129b90

folkertdev added A-naked Area: `#[naked]`, prologue and epilogue-free, functions, https://git.io/vAzzS F-c_variadic `#![feature(c_variadic)]` labels Nov 9, 2025

rustbot assigned workingjubilee Nov 9, 2025

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Nov 9, 2025

folkertdev mentioned this pull request Nov 9, 2025

Tracking Issue for c_variadic_naked_functions #148767

Open

7 tasks

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Nov 11, 2025

Zalathar mentioned this pull request Nov 11, 2025

Rollup of 13 pull requests #148844

Closed

Zalathar mentioned this pull request Nov 11, 2025

Rollup of 12 pull requests #148845

Closed

Zalathar mentioned this pull request Nov 12, 2025

Rollup of 16 pull requests #148851

Merged

bors merged commit 60b2068 into rust-lang:main Nov 12, 2025
11 checks passed

rustbot added this to the 1.93.0 milestone Nov 12, 2025

folkertdev mentioned this pull request Dec 4, 2025

Tracking issue for RFC 2137: Support defining C-compatible variadic functions in Rust (c_variadic) #44930

Closed

4 tasks

folkertdev mentioned this pull request Jul 22, 2026

stabilize c_variadic_naked_functions #159746

Merged

Navigation Menu

Uh oh!

Uh oh!

implement `feature(c_variadic_naked_functions)` - #148770