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Support u128/i128 c-variadic arguments#155429

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folkertdev:c-variadic-i128
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Support u128/i128 c-variadic arguments#155429
folkertdev wants to merge 2 commits into
rust-lang:mainfrom
folkertdev:c-variadic-i128

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@folkertdev folkertdev commented Apr 17, 2026 •
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The restriction on u128 is kind of arbitrary, so let's see what it would take to support it.

r? @ghost

@rustbot rustbot added A-LLVM Area: Code generation parts specific to LLVM. Both correctness bugs and optimization-related issues. 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. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Apr 17, 2026
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folkertdev commented Apr 17, 2026

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

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rust-bors Bot pushed a commit that referenced this pull request Apr 17, 2026
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Auto merge of #155429 - folkertdev:c-variadic-i128, r=<try>
896022a 
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 folkertdev force-pushed the c-variadic-i128 branch 2 times, most recently from 3f2ff65 to 5e8c8b5 Compare April 17, 2026 13:27
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folkertdev commented Apr 17, 2026

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

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

💔 Test for d3bd26f failed: CI. Failed job:

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folkertdev commented Apr 17, 2026

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

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rust-bors Bot pushed a commit that referenced this pull request Apr 17, 2026
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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
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rust-bors Bot commented Apr 18, 2026

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

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folkertdev commented Apr 21, 2026
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Comment thread library/core/src/ffi/va_list.rs Outdated
Comment on lines +359 to +383
crate::cfg_select! {
target_pointer_width = "32" => {
// GCC says <https://gcc.gnu.org/onlinedocs/gcc-15.2.0/gcc/_005f_005fint128.html>
//
// > There is no support in GCC for expressing an integer constant of type __int128 for targets
// > with long long integer less than 128 bits wide.
}
target_env = "msvc" => {
// Per https://learn.microsoft.com/en-us/cpp/cpp/data-type-ranges?view=msvc-170, __int128 is
// not recognized by msvc.
}
any(
target_arch = "x86_64",
target_arch = "aarch64",
target_arch = "riscv64",
target_arch = "loongarch64",
target_arch = "s390x",
target_arch = "powerpc64"
) => {
unsafe impl VaArgSafe for i128 {}
unsafe impl VaArgSafe for u128 {}
}
_ => {
}
}
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@folkertdev folkertdev Apr 21, 2026 •
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cc @Amanieu @joshtriplett @workingjubilee thoughts on this as an initial set of targets to support i128 varargs on?

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Comment thread compiler/rustc_codegen_llvm/src/va_arg.rs Outdated
Comment thread compiler/rustc_codegen_llvm/src/va_arg.rs
Primitive::Int(integer, _) => match integer {
Integer::I8 | Integer::I16 => unreachable!(),
Integer::I32 | Integer::I64 => { /* fall through */ }
Integer::I128 => return Align::EIGHT,
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@folkertdev folkertdev Apr 21, 2026 •
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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.

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Comment thread library/core/src/ffi/va_list.rs
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rustbot commented Apr 25, 2026

tgross35 is currently at their maximum review capacity.
They may take a while to respond.

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folkertdev commented Apr 25, 2026

may as well

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

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rust-bors Bot pushed a commit that referenced this pull request Apr 25, 2026
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Auto merge of #155429 - folkertdev:c-variadic-i128, r=<try>
9d4c015 
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 commented Apr 25, 2026
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Comment thread compiler/rustc_codegen_llvm/src/va_arg.rs Outdated
) -> &'ll Value {
if layout.layout.align.abi > src_align {
let tmp = bx.alloca(layout.layout.size(), layout.layout.align().abi);
let tmp = bx.alloca_with_ty(layout);
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@folkertdev folkertdev Apr 25, 2026 •
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Using a typed alloca solves an issue with the memcpy not being optimized out, see llvm/llvm-project#194158. Normally rust type erases allocas (e.g. [16 x i8]) and that confuses LLVM apparently.

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💔 Test for 9d4c015 failed: CI. Failed job:

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folkertdev commented Apr 25, 2026

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

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rust-bors Bot pushed a commit that referenced this pull request Apr 25, 2026
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Auto merge of #155429 - folkertdev:c-variadic-i128, r=<try>
aee82fa 
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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rust-bors Bot commented Apr 25, 2026

☀️ Try build successful (CI)
Build commit: aee82fa (aee82fa5d127ed3da73b856690b5b55cbfd0efd3, parent: 9838411cb723b60dc62b1625751075c4d933b992)

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@folkertdev folkertdev force-pushed the c-variadic-i128 branch 2 times, most recently from 2db94a6 to 7d2a6d2 Compare April 26, 2026 17:01
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rustbot commented May 29, 2026

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.

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folkertdev commented May 29, 2026

didn't realize I had never pushed/marked as ready.

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@rustbot rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels May 29, 2026
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A-LLVM Area: Code generation parts specific to LLVM. Both correctness bugs and optimization-related issues. A-run-make Area: port run-make Makefiles to rmake.rs F-c_variadic `#![feature(c_variadic)]` 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. T-libs Relevant to the library team, which will review and decide on the PR/issue.

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