test passing a `VaList` from rust to C #143397

folkertdev · 2025-07-03T19:36:28Z

Have C define various functions that take a ... or va_list as an argument, and call them from rust. As far as I can see, this just wasn't actually tested before.

In particular this tests a difference between rust VaList and C va_list where C uses array-to-pointer decay, but rust cannot.

I've locally tested this for

x86_64-unknown-linux-gnu
aarch64-unknown-linux-gnu
s390x-unknown-linux-gnu
powerpc64-unknown-linux-gnu
powerpc64le-unknown-linux-gnu

The latter 2 use an opaque pointer, the first 3 use a single-element array.

cc @beetrees if you see anything incorrect here

r? @workingjubilee

rustbot · 2025-07-03T19:36:32Z

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

rustbot · 2025-07-03T19:36:35Z

This PR modifies run-make tests.

cc @jieyouxu

tests/run-make/c-link-to-rust-va-list-fn/checkrust.rs

RalfJung · 2025-07-04T12:36:04Z

@bors2 try jobs=aarch64-gnu,x86_64-msvc-,x86_64-apple-

rust-bors · 2025-07-04T12:36:09Z

⌛ Trying commit a956428 with merge 69400e8…

To cancel the try build, run the command @bors2 try cancel.

… r=<try> test passing a `VaList` from rust to C Have C define various functions that take a `...` or `va_list` as an argument, and call them from rust. As far as I can see, this just wasn't actually tested before. In particular this tests a difference between rust `VaList` and C `va_list` where C uses array-to-pointer decay, but rust cannot. I've locally tested this for - `x86_64-unknown-linux-gnu` - `aarch64-unknown-linux-gnu` - `s390x-unknown-linux-gnu` - `powerpc64-unknown-linux-gnu` - `powerpc64le-unknown-linux-gnu` The latter 2 use an opaque pointer, the first 3 use a single-element array. cc `@beetrees` if you see anything incorrect here r? `@workingjubilee` try-job: aarch64-gnu try-job: x86_64-msvc-* try-job: x86_64-apple-*

RalfJung · 2025-07-04T12:41:50Z

Ah dang, forgot aarch64-apple...
@bors2 cancel

rust-bors · 2025-07-04T12:41:52Z

Unknown command "cancel".

RalfJung · 2025-07-04T12:42:18Z

@bors2 try jobs=x86_64-msvc-,x86_64-apple-,aarch64-apple

rust-bors · 2025-07-04T12:42:21Z

⌛ Trying commit a956428 with merge 037db17…

(The previously running try build was automatically cancelled.)

To cancel the try build, run the command @bors2 try cancel.

… r=<try> test passing a `VaList` from rust to C Have C define various functions that take a `...` or `va_list` as an argument, and call them from rust. As far as I can see, this just wasn't actually tested before. In particular this tests a difference between rust `VaList` and C `va_list` where C uses array-to-pointer decay, but rust cannot. I've locally tested this for - `x86_64-unknown-linux-gnu` - `aarch64-unknown-linux-gnu` - `s390x-unknown-linux-gnu` - `powerpc64-unknown-linux-gnu` - `powerpc64le-unknown-linux-gnu` The latter 2 use an opaque pointer, the first 3 use a single-element array. cc `@beetrees` if you see anything incorrect here r? `@workingjubilee` try-job: x86_64-msvc-* try-job: x86_64-apple-* try-job: aarch64-apple

rust-bors · 2025-07-04T13:52:32Z

💔 Test failed

CI ❌

RalfJung · 2025-07-04T14:26:31Z

macOS is not happy:

2025-07-04T13:51:46.4617680Z === STDERR ===
2025-07-04T13:51:46.4617930Z test.c:66:22: error: ISO C requires a named parameter before '...'
2025-07-04T13:51:46.4618260Z size_t test_variadic(...) {
2025-07-04T13:51:46.4618490Z                      ^
2025-07-04T13:51:46.4618820Z test.c:68:18: warning: second argument to 'va_start' is not the last named parameter [-Wvarargs]
2025-07-04T13:51:46.4619210Z     va_start(ap, 0);
2025-07-04T13:51:46.4619400Z                  ^
2025-07-04T13:51:46.4619620Z 1 warning and 1 error generated.
2025-07-04T13:51:46.4619860Z ------------------------------------------

Not all our tooling is recent enough for C23.

RalfJung · 2025-07-04T15:42:07Z

@bors2 try jobs=x86_64-msvc-*,x86_64-apple-*,aarch64-apple

rust-bors · 2025-07-04T15:42:11Z

⌛ Trying commit a3277a1 with merge f1d78fc…

To cancel the try build, run the command @bors2 try cancel.

… r=<try> test passing a `VaList` from rust to C Have C define various functions that take a `...` or `va_list` as an argument, and call them from rust. As far as I can see, this just wasn't actually tested before. In particular this tests a difference between rust `VaList` and C `va_list` where C uses array-to-pointer decay, but rust cannot. I've locally tested this for - `x86_64-unknown-linux-gnu` - `aarch64-unknown-linux-gnu` - `s390x-unknown-linux-gnu` - `powerpc64-unknown-linux-gnu` - `powerpc64le-unknown-linux-gnu` The latter 2 use an opaque pointer, the first 3 use a single-element array. cc `@beetrees` if you see anything incorrect here r? `@workingjubilee` try-job: x86_64-msvc-* try-job: x86_64-apple-* try-job: aarch64-apple

rust-bors · 2025-07-04T18:14:02Z

☀️ Try build successful (CI)
Build commit: f1d78fc (f1d78fcc4b1c2cca5eacc790284a3a135265e3a7, parent: 556d20a834126d2d0ac20743b9792b8474d6d03c)

RalfJung · 2025-07-04T19:28:36Z

Looks like a good baseline to have before any refactors, thanks. :)

@bors r+

bors · 2025-07-04T19:28:38Z

📌 Commit a3277a1 has been approved by RalfJung

It is now in the queue for this repository.

Rollup of 11 pull requests Successful merges: - #142440 (`tests/ui`: A New Order [14/N]) - #143040 (Add `const Rem`) - #143086 (Update poison.rs to fix the typo (sys->sync)) - #143202 (`tests/ui`: A New Order [18/N]) - #143296 (`tests/ui`: A New Order [21/N]) - #143297 (`tests/ui`: A New Order [22/N]) - #143299 (`tests/ui`: A New Order [24/N]) - #143300 (`tests/ui`: A New Order [25/N]) - #143397 (test passing a `VaList` from rust to C) - #143410 (Block SIMD in transmute_immediate; delete `OperandValueKind`) - #143452 (Fix CLI completion check in `tidy`) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of #143397 - folkertdev:test-variadic-call-from-rust-to-c, r=RalfJung test passing a `VaList` from rust to C Have C define various functions that take a `...` or `va_list` as an argument, and call them from rust. As far as I can see, this just wasn't actually tested before. In particular this tests a difference between rust `VaList` and C `va_list` where C uses array-to-pointer decay, but rust cannot. I've locally tested this for - `x86_64-unknown-linux-gnu` - `aarch64-unknown-linux-gnu` - `s390x-unknown-linux-gnu` - `powerpc64-unknown-linux-gnu` - `powerpc64le-unknown-linux-gnu` The latter 2 use an opaque pointer, the first 3 use a single-element array. cc `@beetrees` if you see anything incorrect here r? `@workingjubilee`

rustbot assigned workingjubilee Jul 3, 2025

rustbot added A-run-make Area: port run-make Makefiles to rmake.rs 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 Jul 3, 2025

beetrees suggested changes Jul 3, 2025

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tests/run-make/c-link-to-rust-va-list-fn/checkrust.rs Outdated Show resolved Hide resolved

folkertdev force-pushed the test-variadic-call-from-rust-to-c branch from 6ef0403 to a956428 Compare July 3, 2025 20:53

test rust calling a C C-variadic function

a3277a1

folkertdev force-pushed the test-variadic-call-from-rust-to-c branch from a956428 to a3277a1 Compare July 4, 2025 15:28

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 Jul 4, 2025

beetrees mentioned this pull request Jul 4, 2025

Rework c_variadic #141980

Open

workingjubilee mentioned this pull request Jul 5, 2025

Rollup of 11 pull requests #143473

Merged

bors merged commit 5b509e6 into rust-lang:master Jul 5, 2025
11 checks passed

rustbot added this to the 1.90.0 milestone Jul 5, 2025

RalfJung mentioned this pull request Jul 23, 2025

stabilize c-style varargs for system, sysv64, win64, efiapi, aapcs #144066

Open

test passing a VaList from rust to C #143397

test passing a VaList from rust to C #143397

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folkertdev commented Jul 3, 2025

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test passing a `VaList` from rust to C #143397

test passing a `VaList` from rust to C #143397