Support `u128`/`i128` c-variadic arguments by folkertdev · Pull Request #155429 · rust-lang/rust

folkertdev · 2026-04-17T10:39:17Z

The restriction on u128 is kind of arbitrary, so let's see what it would take to support it.

folkertdev · 2026-04-17T10:40:44Z

@bors try jobs=dist-various-1,dist-various-2,aarch64-apple,x86_64-mingw-1

Support `u128`/`i128` c-variadic arguments try-job: dist-various-1 try-job: dist-various-2 try-job: aarch64-apple try-job: x86_64-mingw-1

folkertdev · 2026-04-17T13:28:53Z

@bors try jobs=dist-various-1,dist-various-2,aarch64-apple,x86_64-mingw-1

Support `u128`/`i128` c-variadic arguments try-job: dist-various-1 try-job: dist-various-2 try-job: aarch64-apple try-job: x86_64-mingw-1

rust-bors · 2026-04-17T16:19:42Z

💔 Test for d3bd26f failed: CI. Failed job:

try - aarch64-apple (web logs, enhanced plaintext logs)

folkertdev · 2026-04-17T20:45:36Z

@bors try jobs=dist-various-1,dist-various-2,aarch64-apple,x86_64-mingw-1

Support `u128`/`i128` c-variadic arguments try-job: dist-various-1 try-job: dist-various-2 try-job: aarch64-apple try-job: x86_64-mingw-1

rust-bors · 2026-04-18T00:04:36Z

☀️ Try build successful (CI)
Build commit: d505291 (d50529125c96155f22b48fab34b00ab49c79dcad, parent: f29256dd1420dc681bf4956e3012ffe9eccdc7e7)

folkertdev · 2026-04-21T17:43:28Z

+            Primitive::Int(integer, _) => match integer {
+                Integer::I8 | Integer::I16 => unreachable!(),
+                Integer::I32 | Integer::I64 => { /* fall through */ }
+                Integer::I128 => return Align::EIGHT,


It has custom behavior, the va_arg implementation for powerpc64 is here

https://github.com/llvm/llvm-project/blob/c7eea85b8046660f0a1fd4a1c5c41b44475f8caf/clang/lib/CodeGen/Targets/PPC.cpp#L998

and it uses the implementation here

https://github.com/llvm/llvm-project/blob/c7eea85b8046660f0a1fd4a1c5c41b44475f8caf/clang/lib/CodeGen/Targets/PPC.cpp#L765

The logic falls through to the last line for i128, returning 8. For f128 it curiously does use an alignment of 16, so I've just added that already because it would be easy to miss down the line.

View changes since the review

That's Weird. Kinda almost want to ask if that's intentional. I suppose this is currently correct, at least...? ...but does gcc agree...?

GCC does agree, see https://godbolt.org/z/eW3daf7rG. 24 is added to the pointer, with an alignment of 16 you'd expect to see 32 to be added. 24 = 8 (for the u32 plus padding) + 16 (for the i128).

Ah thanks for digging that up! Such a weird assembly language, to notate immediate adds with their own instruction and use juxtaposition for addition...

workingjubilee

r? workingjubilee

Thanks! I'm going to cogitate on this a little now that I've absorbed it and raised what half-formed thoughts of concerns I have and had those addressed insofar as they were addressable, and will approve-approve this later this night or tomorrow assuming l'esprit d'escalier does not come up with a more material problem. Feel free to ping if it's like Thursday/Friday and it's still waiting on r+, shouldn't be even that long.

View changes since this review

workingjubilee

I think this is the only extra thing I'd like to record, since clang also mentions "welllll, this isn't in the psABI buuuuut..." and someone might apply the impl without checking the compiler code and then at some point we encounter hilarity and bug reports and etc.

View changes since this review

On platforms where `clang` defines `__int128`.

rustbot · 2026-07-01T22:32:09Z

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

folkertdev · 2026-07-01T22:33:57Z

r=you when CI is green?

workingjubilee · 2026-07-02T01:56:37Z

@bors r+

rust-bors · 2026-07-02T01:56:40Z

📌 Commit 68d7148 has been approved by workingjubilee

It is now in the queue for this repository.

@ghost

…ingjubilee Support `u128`/`i128` c-variadic arguments The restriction on `u128` is kind of arbitrary, so let's see what it would take to support it. r? @ghost

Rollup of 3 pull requests Successful merges: - #155429 (Support `u128`/`i128` c-variadic arguments) - #158669 (Remove `src/tools/test-float-parse/Cargo.lock`) - #158674 (library: Polish transmute's `split_at_stdlib` example)

rust-bors · 2026-07-02T04:27:58Z

⌛ Testing commit 68d7148 with merge d3b0bac...

Workflow: https://github.com/rust-lang/rust/actions/runs/28565410648

@ghost

Support `u128`/`i128` c-variadic arguments The restriction on `u128` is kind of arbitrary, so let's see what it would take to support it. r? @ghost

jhpratt · 2026-07-02T04:29:09Z

yielding to rollup

@bors yield

rust-bors · 2026-07-02T04:29:12Z

Auto build was cancelled. Cancelled workflows:

https://github.com/rust-lang/rust/actions/runs/28565410648

The next pull request likely to be tested is #158678.

Rollup of 3 pull requests Successful merges: - #155429 (Support `u128`/`i128` c-variadic arguments) - #158669 (Remove `src/tools/test-float-parse/Cargo.lock`) - #158674 (library: Polish transmute's `split_at_stdlib` example)

@ghost

…ingjubilee Support `u128`/`i128` c-variadic arguments The restriction on `u128` is kind of arbitrary, so let's see what it would take to support it. r? @ghost

Rollup of 4 pull requests Successful merges: - #155429 (Support `u128`/`i128` c-variadic arguments) - #158669 (Remove `src/tools/test-float-parse/Cargo.lock`) - #158674 (library: Polish transmute's `split_at_stdlib` example) - #158682 (Avoid delayed bug for disabled on_type_error arguments)

@ghost

…ingjubilee Support `u128`/`i128` c-variadic arguments The restriction on `u128` is kind of arbitrary, so let's see what it would take to support it. r? @ghost

Rollup of 5 pull requests Successful merges: - #155429 (Support `u128`/`i128` c-variadic arguments) - #158627 (Simplify option-iterator flattening in the compiler) - #158669 (Remove `src/tools/test-float-parse/Cargo.lock`) - #158674 (library: Polish transmute's `split_at_stdlib` example) - #158682 (Avoid delayed bug for disabled on_type_error arguments)