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...

@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

…uwer Rollup of 17 pull requests Successful merges: - #158510 (Enable `static_position_independent_executables` on all gnu and musl targets) - #158541 (Move `std::io::Write` to `core::io`) - #158899 (Fix `unaligned_volatile_store` by removing `MemFlags::UNALIGNED`) - #155429 (Support `u128`/`i128` c-variadic arguments) - #156370 (Reject linked dylib EII default overrides) - #157153 (allow `Allocator`s to be used as `#[global_allocator]`s) - #158535 (Support `#[track_caller]` on EII declarations) - #158617 (allow mGCA const arguments to fall back to anon consts) - #158645 (Fix splat ICEs and ban it in closures) - #158988 (Redo `TokenStreamIter`) - #158347 (Improve generic parameters handling for #[diagnostic::on_const]) - #158722 (delegation: do not always inherit `ConstArgHasType` predicates) - #158739 (view-types: HIR lowering) - #158883 (tests: fix enum-match.rs to handle LLVM 23) - #158886 (Add documentation for the `no_std` attribute) - #158951 (Merge three `MaxUniverse`s into one) - #158961 (Reapply "LLVM 23: Run AssignGUIDPass in some places")

@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

folkertdev · 2026-07-09T19:13:27Z

@bors r-

#159024 (comment)

rust-bors · 2026-07-09T19:13:34Z

This pull request was unapproved.

This PR was contained in a rollup (#159024), which was unapproved.

View changes since this unapproval

On platforms where `clang` defines `__int128`.

rustbot · 2026-07-09T19:48:28Z

Some changes occurred in src/tools/cargo

cc @ehuss

rust-bors · 2026-07-09T19:48:30Z

⚠️ A new commit de4f96e41055bc24ff31a85aa5fc01a806bb044d was pushed.

This PR was contained in a rollup (#159024), which was closed.

rustbot · 2026-07-09T19:48:30Z

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 · 2026-07-09T19:52:51Z

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

rust-bors · 2026-07-09T22:54:56Z

☀️ Try build successful (CI)
Build commit: b5658f2 (b5658f2c88ed3161e8ba8532a11712e0eac41763)
Base parent: 3664b37 (3664b37017c529cad0f0ed259769f15743c21a6a)

folkertdev · 2026-07-09T22:56:36Z

@bors r=workingjubilee iffy

rust-bors · 2026-07-09T22:56:39Z

📌 Commit 3ba3735 has been approved by workingjubilee

It is now in the queue for this repository.

folkertdev · 2026-07-09T23:22:43Z

hmm

@bors iffy

rust-bors · 2026-07-09T23:22:46Z

Unknown command "iffy". Run @bors help or go to https://bors.rust-lang.org/help to see available commands.

folkertdev · 2026-07-09T23:23:06Z

@bors rollup=iffy

tgross35 · 2026-07-10T11:23:31Z

Thank you @workingjubilee for taking over the review I never got to

taiki-e · 2026-07-11T06:02:50Z

+        #[cfg(not(any(target_arch = "wasm32", target_abi = "x32", target_pointer_width = "64")))]
+        compile_error!("unexpected target architecture for 128-bit c-variadic");


This broke AArch64 ILP32 targets (aarch64-unknown-linux-gnu_ilp32, aarch64_be-unknown-linux-gnu_ilp32, arm64_32-apple-watchos).

https://github.com/taiki-e/atomic-maybe-uninit/actions/runs/29137306574/job/86504296151#step:4:244

error: unexpected target architecture for 128-bit c-variadic --> /home/runner/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/ffi/va_list.rs:391:9 | 391 | compile_error!("unexpected target architecture for 128-bit c-variadic"); | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

(By the way, although they aren't builtin targets, similar ABIs exist for other architectures as well.)

It might make more sense to use something like any(target_arch = "wasm32", target_arch = "x86_64", all(target_pointer_width = "64", any(target_arch = "aarch64", ...))) for the cfg in cfg_select. (I use approach like that in my crates e.g., (atomic-maybe-uninit, portable-atomic).)

Can you make a PR for that? It's really just a backup check for us not providing the functionality where we can't guarantee it'll work.

Filed #159167.

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rust-bors Bot pushed a commit that referenced this pull request Apr 17, 2026

Auto merge of #155429 - folkertdev:c-variadic-i128, r=<try>

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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

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folkertdev force-pushed the c-variadic-i128 branch 2 times, most recently from 3f2ff65 to 5e8c8b5 Compare April 17, 2026 13:27

rust-bors Bot pushed a commit that referenced this pull request Apr 17, 2026

Auto merge of #155429 - folkertdev:c-variadic-i128, r=<try>

d3bd26f

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

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folkertdev force-pushed the c-variadic-i128 branch from 5e8c8b5 to bcf4cfa Compare April 17, 2026 14:52

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rust-bors Bot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Apr 17, 2026

folkertdev force-pushed the c-variadic-i128 branch from bcf4cfa to 8e7c3b1 Compare April 17, 2026 17:22

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rust-bors Bot pushed a commit that referenced this pull request Apr 17, 2026

Auto merge of #155429 - folkertdev:c-variadic-i128, r=<try>

d505291

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 force-pushed the c-variadic-i128 branch from 8e7c3b1 to d765f82 Compare April 21, 2026 17:18

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folkertdev force-pushed the c-variadic-i128 branch from d765f82 to 1b40600 Compare April 21, 2026 17:25

folkertdev commented Apr 21, 2026

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rust-bors Bot removed the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Jul 9, 2026

JonathanBrouwer mentioned this pull request Jul 9, 2026

Rollup of 17 pull requests #159007

Closed

This was referenced Jul 9, 2026

Rollup of 18 pull requests #159013

Closed

Rollup of 21 pull requests #159020

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Rollup of 21 pull requests #159024

Closed

Support u128/i128 c-variadic arguments

ab19077

On platforms where `clang` defines `__int128`.

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folkertdev added 3 commits July 9, 2026 21:51

c-variadic: add assembly test files

92d4098

c-variadic: fix i128 argument being misread on aarch64 msvc

acccc68

c-variadic: fix i128 argument being misread on arm64ec

3ba3735

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jhpratt mentioned this pull request Jul 10, 2026

Rollup of 7 pull requests #159057

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taiki-e reviewed Jul 11, 2026

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taiki-e mentioned this pull request Jul 12, 2026

c-variadic: Update cfg for 128-bit integers to fix build error on AArch64 ILP32 #159167

Merged

		#[cfg(not(any(target_arch = "wasm32", target_abi = "x32", target_pointer_width = "64")))]
		compile_error!("unexpected target architecture for 128-bit c-variadic");

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