[win][arm64] Disable MSVC Linker 'Arm Hazard' warning #140758

dpaoliello · 2025-05-07T18:09:52Z

While trying to get the aarch64-msvc build working correctly (#140136), I observed the following test failure:

  = note: main.main.d17f5fbe6225cf88-cgu.0.rcgu.o : fatal error LNK1322: cannot avoid potential ARM hazard (Cortex-A53 MPCore processor bug #843419) in section 0x57; please consider using compiler option /Gy if it was not used

This is warning of a code sequence that triggers a bug in Cortex-A53 processors: https://developer.arm.com/documentation/epm048406/latest

However, since Windows 10 isn't supported on the Cortex-A53, this warning is not required, so it can be suppressed using the undocumented /arm64hazardfree flag.

rustbot · 2025-05-07T18:09:57Z

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rustbot · 2025-05-07T18:09:59Z

These commits modify compiler targets.
(See the Target Tier Policy.)

jieyouxu

undocumented /arm64hazardfree flag.

Incredible. Feel free to r=me with or without the commit nit.

compiler/rustc_target/src/spec/targets/aarch64_pc_windows_msvc.rs

jieyouxu · 2025-05-07T18:58:53Z

r? jieyouxu

dpaoliello · 2025-05-07T19:04:07Z

@bors r=jieyouxu rollup

bors · 2025-05-07T19:04:10Z

@dpaoliello: 🔑 Insufficient privileges: Not in reviewers

bors · 2025-05-07T19:04:10Z

@dpaoliello: 🔑 Insufficient privileges: not in try users

jieyouxu · 2025-05-07T19:05:15Z

Oops
@bors r+ rollup

bors · 2025-05-07T19:05:17Z

📌 Commit 75ca6c6 has been approved by jieyouxu

It is now in the queue for this repository.

[win][arm64] Disable MSVC Linker 'Arm Hazard' warning While trying to get the aarch64-msvc build working correctly (rust-lang#140136), I observed the following test failure: From <rust-lang#140136 (comment)> ``` = note: main.main.d17f5fbe6225cf88-cgu.0.rcgu.o : fatal error LNK1322: cannot avoid potential ARM hazard (Cortex-A53 MPCore processor bug #843419) in section 0x57; please consider using compiler option /Gy if it was not used ``` This is warning of a code sequence that triggers a bug in Cortex-A53 processors: <https://developer.arm.com/documentation/epm048406/latest> However, since Windows 10 isn't supported on the Cortex-A53, this warning is not required, so it can be suppressed using the undocumented `/arm64hazardfree` flag.

Rollup of 15 pull requests Successful merges: - rust-lang#138736 (Sanitizers target modificators) - rust-lang#140260 (Only prefer param-env candidates if they remain non-global after norm) - rust-lang#140523 (Better error message for late/early lifetime param mismatch) - rust-lang#140579 (Remove estebank from automated review assignment) - rust-lang#140641 (detect additional uses of opaques after writeback) - rust-lang#140711 (Do not discard constraints on overflow if there was candidate ambiguity) - rust-lang#140716 (Improve `-Zremap-path-scope` tests with dependency) - rust-lang#140755 ([win][arm64] Disable various DebugInfo tests that don't work on Arm64 Windows) - rust-lang#140756 ([arm64] Pointer auth test should link with C static library statically) - rust-lang#140758 ([win][arm64] Disable MSVC Linker 'Arm Hazard' warning) - rust-lang#140759 ([win][arm64] Disable std::fs tests that require symlinks) - rust-lang#140762 (rustdoc-json: Remove newlines from attributes) - rust-lang#140764 (style: Never break within a nullary function call `func()` or a unit literal `()`) - rust-lang#140769 (Add `DefPathData::OpaqueLifetime` to avoid conflicts for remapped opaque lifetimes) - rust-lang#140773 (triagebot: Better message for changes to `tests/rustdoc-json`) r? `@ghost` `@rustbot` modify labels: rollup

[win][arm64] Disable MSVC Linker 'Arm Hazard' warning While trying to get the aarch64-msvc build working correctly (rust-lang#140136), I observed the following test failure: From <rust-lang#140136 (comment)> ``` = note: main.main.d17f5fbe6225cf88-cgu.0.rcgu.o : fatal error LNK1322: cannot avoid potential ARM hazard (Cortex-A53 MPCore processor bug #843419) in section 0x57; please consider using compiler option /Gy if it was not used ``` This is warning of a code sequence that triggers a bug in Cortex-A53 processors: <https://developer.arm.com/documentation/epm048406/latest> However, since Windows 10 isn't supported on the Cortex-A53, this warning is not required, so it can be suppressed using the undocumented `/arm64hazardfree` flag.

…iaskrgr Rollup of 7 pull requests Successful merges: - rust-lang#140716 (Improve `-Zremap-path-scope` tests with dependency) - rust-lang#140732 (make it possible to run in-tree rustfmt with `x run rustfmt`) - rust-lang#140736 (trait selection: check `&` before suggest remove deref) - rust-lang#140755 ([win][arm64] Disable various DebugInfo tests that don't work on Arm64 Windows) - rust-lang#140756 ([arm64] Pointer auth test should link with C static library statically) - rust-lang#140758 ([win][arm64] Disable MSVC Linker 'Arm Hazard' warning) - rust-lang#140759 ([win][arm64] Disable std::fs tests that require symlinks) r? `@ghost` `@rustbot` modify labels: rollup

…iaskrgr Rollup of 5 pull requests Successful merges: - rust-lang#140736 (trait selection: check `&` before suggest remove deref) - rust-lang#140755 ([win][arm64] Disable various DebugInfo tests that don't work on Arm64 Windows) - rust-lang#140756 ([arm64] Pointer auth test should link with C static library statically) - rust-lang#140758 ([win][arm64] Disable MSVC Linker 'Arm Hazard' warning) - rust-lang#140759 ([win][arm64] Disable std::fs tests that require symlinks) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of rust-lang#140758 - dpaoliello:armhazard, r=jieyouxu [win][arm64] Disable MSVC Linker 'Arm Hazard' warning While trying to get the aarch64-msvc build working correctly (rust-lang#140136), I observed the following test failure: From <rust-lang#140136 (comment)> ``` = note: main.main.d17f5fbe6225cf88-cgu.0.rcgu.o : fatal error LNK1322: cannot avoid potential ARM hazard (Cortex-A53 MPCore processor bug #843419) in section 0x57; please consider using compiler option /Gy if it was not used ``` This is warning of a code sequence that triggers a bug in Cortex-A53 processors: <https://developer.arm.com/documentation/epm048406/latest> However, since Windows 10 isn't supported on the Cortex-A53, this warning is not required, so it can be suppressed using the undocumented `/arm64hazardfree` flag.

bgw · 2025-05-12T23:02:13Z

We enable rust-lld on windows-arm64 using

[target.aarch64-pc-windows-msvc]
linker = "rust-lld"

https://github.com/vercel/next.js/blob/f7c274328f193be99d182ced0f869334c8b0afdb/.cargo/config.toml#L37-L38

I think this PR might've broken rust-lld, because now we're seeing:

note: rust-lld: error: could not open '/arm64hazardfree': no such file or directory

dpaoliello · 2025-05-13T16:55:08Z

I think this PR might've broken rust-lld, because now we're seeing:
note: rust-lld: error: could not open '/arm64hazardfree': no such file or directory

Ugh, we might need to try -arm64hazardfree, is that something that you can do from your side or would you need a PR to the Rust Compiler?

dpaoliello · 2025-05-13T21:09:05Z

Reproduced the issue locally and confirmed that using a dash fixes it.

Fix: #140977

[win] Use a dash instead of slash for linker to avoid breaking lld rust-lang#140758 added the `/arm64hazardfree` linker arg for aarch64-pc-windows-msvc, unfortunately this breaks linking with `lld` as it 1) doesn't understand the arguments and 2) assumes that unknown args that start with `/` are input files. Fix is to use a dash for the arg: `-arm64hazardfree` r? `@wesleywiser`

[win][arm64] Remove 'Arm64 Hazard' undocumented MSVC option and instead disable problematic test PR rust-lang#140758 added the undocumented `/arm64hazardfree` MSVC linker flag to work around a test failure where LLVM generated code that would trip a hazard in an outdated ARM processor. Adding this flag caused issues with LLD, as it doesn't recognize it. Rethinking the issue, using the undocumented flag seems like the incorrect solution: there's no guarantee that the flag won't be removed in the future, or change its meaning. Instead, I've disabled the problematic test for Arm64 Windows and have filed a bug with the MSVC team to have the check removed: <https://developercommunity.microsoft.com/t/Remove-checking-for-and-fixing-Cortex-A/10905134> This PR supersedes rust-lang#140977 r? `@jieyouxu`

[win][arm64] Remove 'Arm64 Hazard' undocumented MSVC option and instead disable problematic test PR rust-lang#140758 added the undocumented `/arm64hazardfree` MSVC linker flag to work around a test failure where LLVM generated code that would trip a hazard in an outdated ARM processor. Adding this flag caused issues with LLD, as it doesn't recognize it. Rethinking the issue, using the undocumented flag seems like the incorrect solution: there's no guarantee that the flag won't be removed in the future, or change its meaning. Instead, I've disabled the problematic test for Arm64 Windows and have filed a bug with the MSVC team to have the check removed: <https://developercommunity.microsoft.com/t/Remove-checking-for-and-fixing-Cortex-A/10905134> This PR supersedes rust-lang#140977 r? ``@jieyouxu``

[win][arm64] Remove 'Arm64 Hazard' undocumented MSVC option and instead disable problematic test PR rust-lang#140758 added the undocumented `/arm64hazardfree` MSVC linker flag to work around a test failure where LLVM generated code that would trip a hazard in an outdated ARM processor. Adding this flag caused issues with LLD, as it doesn't recognize it. Rethinking the issue, using the undocumented flag seems like the incorrect solution: there's no guarantee that the flag won't be removed in the future, or change its meaning. Instead, I've disabled the problematic test for Arm64 Windows and have filed a bug with the MSVC team to have the check removed: <https://developercommunity.microsoft.com/t/Remove-checking-for-and-fixing-Cortex-A/10905134> This PR supersedes rust-lang#140977 r? ```@jieyouxu```

Rollup merge of rust-lang#141045 - dpaoliello:noarmhazard, r=jieyouxu [win][arm64] Remove 'Arm64 Hazard' undocumented MSVC option and instead disable problematic test PR rust-lang#140758 added the undocumented `/arm64hazardfree` MSVC linker flag to work around a test failure where LLVM generated code that would trip a hazard in an outdated ARM processor. Adding this flag caused issues with LLD, as it doesn't recognize it. Rethinking the issue, using the undocumented flag seems like the incorrect solution: there's no guarantee that the flag won't be removed in the future, or change its meaning. Instead, I've disabled the problematic test for Arm64 Windows and have filed a bug with the MSVC team to have the check removed: <https://developercommunity.microsoft.com/t/Remove-checking-for-and-fixing-Cortex-A/10905134> This PR supersedes rust-lang#140977 r? ```@jieyouxu```

rustbot assigned estebank May 7, 2025

rustbot added 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. labels May 7, 2025

jieyouxu approved these changes May 7, 2025

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compiler/rustc_target/src/spec/targets/aarch64_pc_windows_msvc.rs Outdated Show resolved Hide resolved

rustbot assigned jieyouxu and unassigned estebank May 7, 2025

[win][arm64] Disable MSVC Linker 'Arm Hazard' warning

75ca6c6

dpaoliello force-pushed the armhazard branch from c217269 to 75ca6c6 Compare May 7, 2025 19:02

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 May 7, 2025

Zalathar mentioned this pull request May 8, 2025

Rollup of 15 pull requests #140777

Closed

matthiaskrgr mentioned this pull request May 8, 2025

Rollup of 7 pull requests #140788

Closed

matthiaskrgr mentioned this pull request May 8, 2025

Rollup of 5 pull requests #140797

Merged

bors merged commit 54f1da4 into rust-lang:master May 8, 2025
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rustbot added this to the 1.88.0 milestone May 8, 2025

dpaoliello deleted the armhazard branch May 8, 2025 18:21

dpaoliello mentioned this pull request May 13, 2025

[win] Use a dash instead of slash for linker to avoid breaking lld #140977

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dpaoliello mentioned this pull request May 15, 2025

[win][arm64] Remove 'Arm64 Hazard' undocumented MSVC option and instead disable problematic test #141045

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