Update to ar_archive_writer 0.5 #145721

dpaoliello · 2025-08-21T18:48:48Z

This updates ar_archive_writer to 0.5, which in turn was updated to match LLVM 20.1.8: rust-lang/ar_archive_writer#24

As part of this, I refactored part of SymbolWrapper.cpp to pull common code that I was about to duplicate again into a new function.

NOTE: ar_archive_writer does include a breaking change where it no longer supports mangling C++ mangled names for Arm64EC. Since we don't need the mangled name (it's not the "exported name" which we're trying to load from the external dll), I'm setting the import_name when building for Arm64EC to prevent error when failing to mangle.

r? @bjorn3

rustbot · 2025-08-21T18:48:54Z

Some changes occurred in compiler/rustc_codegen_ssa

cc @WaffleLapkin

These commits modify the Cargo.lock file. Unintentional changes to Cargo.lock can be introduced when switching branches and rebasing PRs.

If this was unintentional then you should revert the changes before this PR is merged.
Otherwise, you can ignore this comment.

bjorn3 · 2025-08-22T11:56:12Z

For the Rust project, this means that anyone using the raw-dylib feature will need to provide the Arm64EC mangled name for any C++ function when targeting Arm64EC

How would that actually work? If you just do #[link_name = "..."] it would be provided to both LLVM (which mangles it) and ar_archive_writer (which doesn't mangle it) To disable the name mangling on the LLVM side you have to use \x01, but ar_archive_writer doesn't handle that and it is an LLVM implementation detail that may not work with other backends anyway.

dpaoliello · 2025-08-22T16:41:50Z

For the Rust project, this means that anyone using the raw-dylib feature will need to provide the Arm64EC mangled name for any C++ function when targeting Arm64EC

How would that actually work? If you just do #[link_name = "..."] it would be provided to both LLVM (which mangles it) and ar_archive_writer (which doesn't mangle it) To disable the name mangling on the LLVM side you have to use \x01, but ar_archive_writer doesn't handle that and it is an LLVM implementation detail that may not work with other backends anyway.

Let's take the example from the LLVM bug I posted above: int Wrapper<X>::GetValue(void) const

For most arches this is mangled as ?GetValue@?$Wrapper@UA@@@@QEBAHXZ
But, for Arm64EC it is mangled as ?GetValue@?$Wrapper@UA@@@@$$hQEBAHXZ

So, with ar_archive_writer 0.4.2 writing #[link_name = "?GetValue@?$Wrapper@UA@@@@QEBAHXZ"] would generate an incorrect Arm64EC mangled name and so linking would fail. With 0.5.0, ar_archive_writer recognizes that it is not an Arm64EC mangled name and so raises an error.

There are cases where 0.4.2 got the Arm64EC mangling correct, and those will now raise an error.

bjorn3 · 2025-08-22T18:00:46Z

If you do #[link_name = "?GetValue@?$Wrapper@UA@@@@$$hQEBAHXZ"] as already mangled name, then LLVM would mangle it again when it codegens a call to this function, right? Or actually it turns out LLVM literally crashes when you try that currently: https://rust.godbolt.org/z/Y6aj635qc

dpaoliello · 2025-08-22T18:13:05Z

But if you use a simpler name where the old 0.4.2 algorithm happened to be correct, then it compiles correctly: https://rust.godbolt.org/z/dnhn64sqM but with 0.5.0 this will now raise an error.

bjorn3 · 2025-08-22T18:28:59Z

So basically before this PR there were cases where the name mangling was wrong for C++ on arm64ec when using raw-dylib and in those cases there was no workaround. And with this PR you simply can't correctly use C++ symbols with raw-dylib at all.

dpaoliello · 2025-08-22T22:06:14Z

Actually, the example that you provided works fine if you use raw-dylib: https://rust.godbolt.org/z/fofzhfs5G

I did some experiments with 0.4.2, and it did work correctly even with the incorrect Arm64EC mangling: turns out that we don't need the mangled name since the EXPORT_AS gets set to the unmangled name anyway. I'm going to make a slight change to ar_archive_writer that will allow us to avoid this error and continue to link against C++ mangled names.

dpaoliello · 2025-08-22T22:35:28Z

Ok, workaround in ar_archive_writer: rust-lang/ar_archive_writer#26

bors · 2025-08-27T16:58:51Z

☔ The latest upstream changes (presumably #145923) made this pull request unmergeable. Please resolve the merge conflicts.

rustbot · 2025-08-29T23:39:23Z

This PR was rebased onto a different master 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.

dpaoliello · 2025-08-29T23:43:06Z

@bjorn3 I've updated with the workaround I added in ar_archive_writer, and verified via our internal build pipeline that the workaround works.

bjorn3 · 2025-09-01T13:41:12Z

@bors r+

bors · 2025-09-01T13:41:15Z

📌 Commit 4daae65 has been approved by bjorn3

It is now in the queue for this repository.

bors · 2025-09-01T17:50:05Z

⌛ Testing commit 4daae65 with merge 7aef4be...

bors · 2025-09-01T20:55:38Z

☀️ Test successful - checks-actions
Approved by: bjorn3
Pushing 7aef4be to master...

github-actions · 2025-09-01T20:58:29Z

What is this?

This is an experimental post-merge analysis report that shows differences in test outcomes between the merged PR and its parent PR.

Comparing 154037f (parent) -> 7aef4be (this PR)

Test differences

Show 2 test diffs

2 doctest diffs were found. These are ignored, as they are noisy.

Test dashboard

Run

cargo run --manifest-path src/ci/citool/Cargo.toml -- \
    test-dashboard 7aef4bec4bec16cb6204d51eb633873e23b18771 --output-dir test-dashboard

And then open test-dashboard/index.html in your browser to see an overview of all executed tests.

Job duration changes

dist-x86_64-apple: 5796.5s -> 7384.2s (27.4%)
aarch64-apple: 5868.5s -> 7320.6s (24.7%)
dist-arm-linux-gnueabi: 4930.1s -> 5505.5s (11.7%)
dist-i586-gnu-i586-i686-musl: 5882.8s -> 5344.6s (-9.1%)
x86_64-gnu-stable: 7490.7s -> 6980.0s (-6.8%)
x86_64-gnu-llvm-19-1: 3595.9s -> 3365.6s (-6.4%)
dist-aarch64-msvc: 6022.0s -> 5668.6s (-5.9%)
dist-various-2: 2173.7s -> 2055.1s (-5.5%)
x86_64-gnu-llvm-20-1: 3485.4s -> 3309.7s (-5.0%)
aarch64-gnu: 7284.9s -> 6925.5s (-4.9%)

How to interpret the job duration changes?

Job durations can vary a lot, based on the actual runner instance
that executed the job, system noise, invalidated caches, etc. The table above is provided
mostly for t-infra members, for simpler debugging of potential CI slow-downs.

rust-timer · 2025-09-01T22:05:56Z

Finished benchmarking commit (7aef4be): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

Instruction count

This benchmark run did not return any relevant results for this metric.

Max RSS (memory usage)

Results (primary -3.5%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-3.5%	[-3.5%, -3.5%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-3.5%	[-3.5%, -3.5%]	1

Cycles

This benchmark run did not return any relevant results for this metric.

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 467.56s -> 469.026s (0.31%)
Artifact size: 388.51 MiB -> 388.37 MiB (-0.04%)

rustbot assigned bjorn3 Aug 21, 2025

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dpaoliello force-pushed the ar050 branch from 0e3d395 to bcf96fe Compare August 21, 2025 19:13

dpaoliello added 2 commits August 29, 2025 16:37

Update to ar_archive_writer 0.5.1

da8f230

Move to 0.50.1

4daae65

dpaoliello force-pushed the ar050 branch from bcf96fe to 4daae65 Compare August 29, 2025 23:39

dpaoliello changed the title ~~Update to ar_archive_writer 0.5.0~~ Update to ar_archive_writer 0.5 Aug 29, 2025

bors 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 1, 2025

bors added the merged-by-bors This PR was explicitly merged by bors. label Sep 1, 2025

bors merged commit 7aef4be into rust-lang:master Sep 1, 2025
11 checks passed

rustbot added this to the 1.91.0 milestone Sep 1, 2025

dpaoliello deleted the ar050 branch September 2, 2025 22:08

github-actions bot mentioned this pull request Sep 5, 2025

Toolchain upgrade to nightly-2025-09-02 flux-rs/flux#1260

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Update to ar_archive_writer 0.5 #145721

Update to ar_archive_writer 0.5 #145721

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dpaoliello commented Aug 21, 2025 •

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