implement `VaArgSafe` for `f128` by folkertdev · Pull Request #161424 · rust-lang/rust

folkertdev · 2026-08-20T19:35:14Z

On some platforms, especially when long double is IEEE f128 on the platform.

folkertdev · 2026-08-20T20:43:02Z

@bors try jobs=test-various,aarch64-apple-,-gnu-nopt-,x86_64-mingw-,aarch64-msvc-*,arm-android

implement `VaArgSafe` for `f128` try-job: test-various try-job: aarch64-apple-* try-job: *-gnu-nopt-* try-job: x86_64-mingw-* try-job: aarch64-msvc-* try-job: arm-android

folkertdev

r? tgross35

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rust-bors · 2026-08-20T23:24:56Z

💔 Test for c9719b5 failed: CI. Failed job:

try - i686-gnu-nopt-1 (web logs, enhanced plaintext logs)

folkertdev · 2026-08-21T19:09:37Z

@bors try jobs=test-various,aarch64-apple-,-gnu-nopt-,x86_64-mingw-,aarch64-msvc-*,arm-android

implement `VaArgSafe` for `f128` try-job: test-various try-job: aarch64-apple-* try-job: *-gnu-nopt-* try-job: x86_64-mingw-* try-job: aarch64-msvc-* try-job: arm-android

rust-bors · 2026-08-21T21:40:25Z

☀️ Try build successful (CI)
Build commit: d5f25c2 (d5f25c2d0c850c37c152ae4a21b215d1c6f7960a)
Base parent: a872286 (a872286d0a1873caec0291ed4304de3170adbe16)

folkertdev · 2026-08-22T11:03:00Z

@rustbot ready

tgross35 · 2026-09-17T01:55:47Z

+        // Clang 23 hits https://github.com/llvm/llvm-project/issues/217747.
+        all(target_arch = "x86", not(target_vendor = "apple"), not(target_env = "msvc")),
+        // PowerPC requires VSX - only little endian has it enabled by default.
+        all(target_arch = "powerpc64", target_endian = "little"),


Can this just use target_feature="vsx"?

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I changed it, though core is built without vsx so in practice the result is the same.

I thought there may have been talks about an elfv2 BE target that requires VSX and thus could have it, but I may be misremembering

tgross35 · 2026-09-17T02:35:25Z

+
+#ifdef f128
+    assert(test_rust(check_list_f128, (f128)-42.0, 0xAAAAAAAA, (f128)-INFINITY) == 0);
+#endif


It would be better to load a literal for MAX since INFINITY only exercises the top 16 bits. E.g.:

union cvt128 { struct { #if defined(__BYTE_ORDER__) && (__BYTE_ORDER__ == __ORDER_BIG_ENDIAN__) uint64_t lo, hi; #else uint64_t hi, lo; #endif } i; _Float128 f; }; union cvt128 f128_max; f128_max.i.hi = 0x7ffeffffffffffff; f128_max.i.lo = 0xffffffffffffffff; assert(test_rust(check_list_f128, (f128)-42.0, 0xAAAAAAAA, f128_max.f) == 0);

Kind of annoying that llvm/llvm-project#97335 is still open and we can't just use __FLT128_MAX__.

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tgross35 · 2026-09-17T03:05:03Z

+// Implement `VaArgSafe` for 128-bit integers on targets where either:
+//
+// - clang provides `__float128`
+// - `long double` is IEEE f128 on the platform.
+//
+// When updating this cfg, also update the tests to match. Currently this condition
+// is duplicated in:
+//
+// - tests/ui/c-variadic/roundtrip.rs
+// - tests/run-make/c-link-to-rust-va-list-fn/checkrust.rs


I checked against https://c.godbolt.org/z/7WGxKeq9v and everything seems to match up, with the exception of PPC64le. Unless I'm doing something wrong, it seems like Clang doesn't support it but GCC does? If that's accurate, the comment should be updated.

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Clang requires the -mfloat128 option for __float128 on PowerPC.

rustbot · 2026-09-17T15:41:00Z

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 · 2026-09-17T12:31:02Z

+        // Clang 23 hits https://github.com/llvm/llvm-project/issues/217747.
+        all(target_arch = "x86", not(target_vendor = "apple"), not(target_env = "msvc")),
+        // PowerPC requires VSX - only little endian has it enabled by default.
+        all(target_arch = "powerpc64", target_endian = "little"),


I changed it, though core is built without vsx so in practice the result is the same.

folkertdev · 2026-09-17T17:49:54Z

+        #[unsafe(no_mangle)]
+        pub static RUST_HAS_F128: c_int = 1;


This is needed on powerpc64 where (at least my) GCC does have f128 support but our baseline does not.

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tgross35

LGTM!

@bors r+

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rust-bors · 2026-09-17T19:31:10Z

📌 Commit 454d69a has been approved by tgross35

It is now in the queue for this repository.

folkertdev · 2026-09-17T19:41:21Z

This will clash with making VaArgSafe unstable again. I'll just rebase when that merges and put it back in the queue then

@bors r-

rust-bors · 2026-09-17T19:41:26Z

This pull request was unapproved.

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rust-bors · 2026-09-18T01:17:25Z

☔ The latest upstream changes (presumably #162909) made this pull request unmergeable. Please resolve the merge conflicts by rebasing.

folkertdev added the F-c_variadic `#![feature(c_variadic)]` label Aug 20, 2026

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folkertdev commented Aug 20, 2026

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Comment thread library/core/src/ffi/va_list.rs

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

rustbot assigned tgross35 Aug 20, 2026

folkertdev marked this pull request as ready for review August 20, 2026 21:52

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 Aug 20, 2026

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folkertdev force-pushed the va-arg-f128 branch from fdb79cb to 8a4f680 Compare August 21, 2026 19:05

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folkertdev commented Aug 21, 2026

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Comment thread library/core/src/ffi/va_list.rs

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 Aug 22, 2026

tgross35 reviewed Aug 25, 2026

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Comment thread library/core/src/ffi/va_list.rs

folkertdev force-pushed the va-arg-f128 branch from 8a4f680 to 4947d1f Compare August 25, 2026 16:10

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This was referenced Aug 28, 2026

C interop: f80, f128 and c_longdouble rust-lang/goals#701

Open

c-variadic: use emit_ptr_va_arg for va_arg on sparc #160660

Merged

beetrees requested changes Sep 3, 2026

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Comment thread library/core/src/ffi/va_list.rs Outdated

Comment thread tests/run-make/c-link-to-rust-va-list-fn/test.c Outdated

Comment thread library/core/src/ffi/va_list.rs

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folkertdev force-pushed the va-arg-f128 branch from c04a2f3 to 3d04167 Compare September 3, 2026 19:25

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folkertdev force-pushed the va-arg-f128 branch from 3d04167 to a70355d Compare September 4, 2026 11:22

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tgross35 reviewed Sep 17, 2026

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folkertdev force-pushed the va-arg-f128 branch from a70355d to 5aa1fbe Compare September 17, 2026 15:40

folkertdev force-pushed the va-arg-f128 branch from 5aa1fbe to 5c2154a Compare September 17, 2026 15:51

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implement VaArgSafe for f128

454d69a

folkertdev force-pushed the va-arg-f128 branch from 5c2154a to 454d69a Compare September 17, 2026 17:06

folkertdev commented Sep 17, 2026

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tgross35 approved these changes Sep 17, 2026

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rust-bors Bot 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 Sep 17, 2026

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-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Sep 17, 2026

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