Fix passing/returning structs with the 64-bit SPARC ABI #142680

beetrees · 2025-06-18T15:11:25Z

Fixes the 64-bit SPARC part of #115609 by replacing the current implementation with a new implementation modelled on the RISC-V calling convention code (SPARC ABI reference).

Pinging sparcv9-sun-solaris target maintainers: @psumbera @kulikjak
Fixes #115336
Fixes #115399
Fixes #122620
Fixes #147883
r? @workingjubilee

rustbot · 2025-06-18T15:11:29Z

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beetrees · 2025-06-18T15:13:23Z

r? @bjorn3

beetrees · 2025-06-18T18:49:07Z

Note that there are currently two places that Clang and GCC disagree AFAIK:

Clang fails to correctly align 16-byte structs when passing them as arguments, whereas GCC correctly aligns them. As the specification states that the structs must be aligned, I've filed an Clang bug at Clang: 64-bit SPARC doesn't align struct arguments as required by ABI llvm/llvm-project#144709.
Clang passes floating point fields in packed structs in floating point register if the field is aligned within the argument as a whole, whereas GCC always passes packed structs in integer registers. The specification doesn't consider the existence of packed structs, however in my opinion Clang's interpretation seems more correct so that's what I've implemented in this PR. Issues for Rust, Clang and GCC.

psumbera · 2025-06-19T14:58:27Z

Thank you for doing this! My knowledge in this area is rather limited.

I was able to build latest Rust sources with your fix on top on Solaris 11.4 SPARC. Then I used this version to build Firefox on Solaris. There was no problem. Firefox also worked as expected.

I also tested some problematic cases which I was handling few years ago (https://github.com/psumbera/rust-sparc64-abi-tests). All seemed to be ok.

bjorn3 · 2025-07-03T11:23:02Z

I don't have time to properly review this right now.

r? compiler

bors · 2025-07-06T14:13:49Z

☔ The latest upstream changes (presumably #143521) made this pull request unmergeable. Please resolve the merge conflicts.

beetrees · 2025-07-06T14:45:16Z

Rebased

bors · 2025-07-22T22:48:52Z

☔ The latest upstream changes (presumably #144249) made this pull request unmergeable. Please resolve the merge conflicts.

wesleywiser · 2025-08-28T14:48:36Z

Hi @workingjubilee, are you still interested in reviewing this? If not, we can reroll for a different reviewer. Thanks!

tgross35 · 2025-09-05T02:17:41Z

Looks like there is a Clang fix in llvm/llvm-project#155829

tests/assembly-llvm/sparc-struct-abi.rs

compiler/rustc_target/src/callconv/sparc64.rs

tests/assembly-llvm/sparc-struct-abi.rs

compiler/rustc_target/src/callconv/sparc64.rs

workingjubilee · 2025-09-10T04:26:47Z

Sorry about that, currently in catchup mode so I am going to delegate, yes.

r? @tgross35

folkertdev · 2026-01-31T13:04:11Z

In @beetrees's absence, @tgross35 and I decided that we should move forward here to remove a blocker for f128, so I'll rebase and add some comments and this should be good to go.

folkertdev · 2026-01-31T13:08:06Z

compiler/rustc_target/src/callconv/sparc64.rs

+    let cast_target = match regs {
+        [Some(reg), None, ..] => CastTarget::from(reg),
+        _ => CastTarget::prefixed(regs, Uniform::new(Reg::i8(), Size::ZERO)),
+    };


I'm not entirely sure why the special-casing is, but the first case fits in a register no problem, while the second case requires some sort of larger struct that is cast.

folkertdev · 2026-02-02T23:59:15Z

@rustbot ready

tgross35

Two nits but LGTM, thanks for picking this up. Two comment requests below.

I believe you should technically make yourself the commit author since you're the one submitting it in its final form. Then add beetrees back via a Co-authored-by: trailer.

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tgross35 · 2026-02-09T11:25:44Z

compiler/rustc_target/src/callconv/sparc64.rs


-    arg.cast_to(Uniform::new(Reg::i64(), total));
+    let cast_target = match regs {
+        [Some(reg), None, ..] => CastTarget::from(reg),


Optional nit, sanity check

[Some(reg), None, rest @ ..] => { debug_assert!(rest.iter().all(|x| x.is_none()); CastTarget::from(reg) }

tgross35 · 2026-02-09T11:36:15Z

compiler/rustc_target/src/callconv/sparc64.rs

+    // sparc64-unknown-linux-{gnu,musl,uclibc} doesn't ignore ZSTs.
+    let passes_zsts = match cx.target_spec().os {
+        Os::Linux => matches!(cx.target_spec().env, Env::Gnu | Env::Musl | Env::Uclibc),
+        _ => false,
+    };


What makes this env-dependent? The only supported Linux env seems to be gnu at this time.

We have

sparc64-unknown-linux-gnu sparc64-unknown-netbsd sparc64-unknown-openbsd sparcv9-sun-solaris

so this only matches in if the os is linux, and it's a bit more general so that if a new target (e.g. musl) is added, it does the right thing from the start. There could, I suppose, be a linux env that does ignore ZSTs.

Why would it ever be coupled to the env though? I see that this exists across other arches but it seems a bit bogus.

Doing some archaeology, the pattern kind of follows:

65dabd6 which references the SPARC ABI

19b8408

e177207

More targets, grouping

Move ZST ABI handling to rustc_target #125854

The env had to be specified on Windows and it seems like others followed suit. I think this can just be deleted here, probably the same in the other places, under the assumption that we're not likely to get a nightmare env that breaks from the psABI (at least not on Linux).

tgross35 · 2026-02-10T06:14:37Z

@rustbot author

rustbot · 2026-02-10T10:39:55Z

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.

tgross35

Awesome, lgtm

View changes since this review

Co-authored-by: beetrees <b@beetr.ee>

folkertdev · 2026-02-10T20:48:58Z

@bors r=tgross35

rust-bors · 2026-02-10T20:49:01Z

📌 Commit c9b5c93 has been approved by tgross35

It is now in the queue for this repository.

@psumbera

… r=tgross35 Fix passing/returning structs with the 64-bit SPARC ABI Fixes the 64-bit SPARC part of rust-lang#115609 by replacing the current implementation with a new implementation modelled on the RISC-V calling convention code ([SPARC ABI reference](https://sparc.org/wp-content/uploads/2014/01/SCD.2.4.1.pdf.gz)). Pinging `sparcv9-sun-solaris` target maintainers: @psumbera @kulikjak Fixes rust-lang#115336 Fixes rust-lang#115399 Fixes rust-lang#122620 Fixes rust-lang#147883 r? @workingjubilee

@psumbera

… r=tgross35 Fix passing/returning structs with the 64-bit SPARC ABI Fixes the 64-bit SPARC part of rust-lang#115609 by replacing the current implementation with a new implementation modelled on the RISC-V calling convention code ([SPARC ABI reference](https://sparc.org/wp-content/uploads/2014/01/SCD.2.4.1.pdf.gz)). Pinging `sparcv9-sun-solaris` target maintainers: @psumbera @kulikjak Fixes rust-lang#115336 Fixes rust-lang#115399 Fixes rust-lang#122620 Fixes rust-lang#147883 r? @workingjubilee

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tgross35 mentioned this pull request Jun 19, 2025

The sparc64, riscv64, loongarch64 extern "C" fn ABIs are all wrong when aligned/packed structs are involved #115609

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Fix passing/returning structs with the 64-bit SPARC ABI

c9b5c93

Co-authored-by: beetrees <b@beetr.ee>

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Zalathar mentioned this pull request Feb 11, 2026

[EXPERIMENT] Rollup of 9 pull requests #152476

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Zalathar mentioned this pull request Feb 11, 2026

[EXPERIMENT] Rollup of 8 pull requests #152479

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