error on invalid macho section specifier by folkertdev · Pull Request #155065 · rust-lang/rust

folkertdev · 2026-04-09T20:11:02Z

The macho section specifier used by #[link_section = "..."] is more strict than e.g. the one for elf. LLVM will error when you get it wrong, which is easy to do if you're used to elf. So, provide some guidance for the simplest mistakes, based on the LLVM validation.

Currently compilation fails with an LLVM error, see https://godbolt.org/z/WoE8EdK1K.

The LLVM validation logic is at

https://github.com/llvm/llvm-project/blob/a0f0d6342e0cd75b7f41e0e6aae0944393b68a62/llvm/lib/MC/MCSectionMachO.cpp#L199-L203

LLVM validates the other components of the section specifier too, but it feels a bit fragile to duplicate those checks. If you get that far, hopefully the LLVM errors will be sufficient to get unstuck.

sidequest from #147811

r? JonathanBrouwer

specifically, is this the right place for this sort of validation? rustc_attr_parsing also does some validation.

rustbot · 2026-04-09T20:11:06Z

Some changes occurred in compiler/rustc_hir/src/attrs

cc @jdonszelmann, @JonathanBrouwer

Some changes occurred in compiler/rustc_passes/src/check_attr.rs

cc @jdonszelmann, @JonathanBrouwer

Some changes occurred in compiler/rustc_attr_parsing

cc @jdonszelmann, @JonathanBrouwer

folkertdev · 2026-04-09T20:14:59Z

just in case we're doing something weird that never got built or linked

@bors try jobs=aarch64-apple

error on invalid macho section specifier try-job: aarch64-apple

JonathanBrouwer · 2026-04-09T20:33:01Z

specifically, is this the right place for this sort of validation? rustc_attr_parsing also does some validation.

We're trying to move as many checks as possible to attribute parsing, with the "parse, don't validate" mentality, so if an attribute gets through parsing you can assume it is correct. Therefore I'd like this to be in the attribute parser

tests/ui/linkage-attr/link-section-macho.rs

rustbot · 2026-04-09T20:41:53Z

Reminder, once the PR becomes ready for a review, use @rustbot ready.

rust-bors · 2026-04-09T21:44:51Z

💔 Test for 3e6930f failed: CI. Failed job:

try - aarch64-apple (web logs, enhanced plaintext logs)

…, r=JonathanBrouwer error on invalid macho section specifier The macho section specifier used by `#[link_section = "..."]` is more strict than e.g. the one for elf. LLVM will error when you get it wrong, which is easy to do if you're used to elf. So, provide some guidance for the simplest mistakes, based on the LLVM validation. Currently compilation fails with an LLVM error, see https://godbolt.org/z/WoE8EdK1K. The LLVM validation logic is at https://github.com/llvm/llvm-project/blob/a0f0d6342e0cd75b7f41e0e6aae0944393b68a62/llvm/lib/MC/MCSectionMachO.cpp#L199-L203 LLVM validates the other components of the section specifier too, but it feels a bit fragile to duplicate those checks. If you get that far, hopefully the LLVM errors will be sufficient to get unstuck. --- sidequest from rust-lang#147811 r? JonathanBrouwer specifically, is this the right place for this sort of validation? `rustc_attr_parsing` also does some validation.

rustbot · 2026-04-12T12:48:03Z

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 · 2026-04-12T13:03:15Z

@bors try jobs=aarch64-apple

error on invalid macho section specifier try-job: aarch64-apple

bjorn3 · 2026-04-12T14:18:59Z

compiler/rustc_attr_parsing/src/attributes/link_attrs.rs

 pub(crate) struct LinkSectionParser;

+fn check_link_section_macho(name: Symbol) -> Result<(), InvalidMachoSectionReason> {
+    let mut parts = name.as_str().split(',').map(|s| s.trim());


View changes since the review

Does LLVM also trim? I don't trim in cg_clif when parsing section names.

I believe so

https://github.com/llvm/llvm-project/blob/a0f0d6342e0cd75b7f41e0e6aae0944393b68a62/llvm/lib/MC/MCSectionMachO.cpp#L191

rust-bors · 2026-04-12T14:23:46Z

💔 Test for 5c7f2d3 failed: CI. Failed job:

try - aarch64-apple (web logs, enhanced plaintext logs)

compiler/rustc_attr_parsing/src/session_diagnostics.rs

folkertdev · 2026-04-12T16:16:40Z

@bors try jobs=aarch64-apple

error on invalid macho section specifier try-job: aarch64-apple

rust-bors · 2026-04-12T18:29:32Z

💔 Test for b88cc98 failed: CI. Failed job:

try - aarch64-apple (web logs, enhanced plaintext logs)

rustbot · 2026-04-12T19:07:23Z

These commits modify tests/rustdoc-json.
rustdoc-json is a public (but unstable) interface.

Please ensure that if you've changed the output:

It's intentional.
The FORMAT_VERSION in src/librustdoc-json-types is bumped if necessary.

cc @aDotInTheVoid, @obi1kenobi

folkertdev · 2026-04-12T19:08:53Z

@bors try jobs=aarch64-apple

error on invalid macho section specifier try-job: aarch64-apple

folkertdev · 2026-04-12T19:10:51Z

btw there is some discussion at #t-lang > error on invalid macho section about whether we should FCW this first.

This change might break projects that use an invalid section specifier for a symbol that never gets linked. Currently LLVM's codegen would never see that symbol, but with this change rustc will error early.

rust-bors · 2026-04-12T22:02:43Z

☀️ Try build successful (CI)
Build commit: 6c29d2f (6c29d2f2952cde2f07cef44fa298d1b9180dd914, parent: dab8d9d1066c4c95008163c7babf275106ce3f32)

JonathanBrouwer

r=me if T-lang is happy

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rustbot added A-attributes Area: Attributes (`#[…]`, `#![…]`) 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 Apr 9, 2026

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Auto merge of #155065 - folkertdev:macho-section-specifier, r=<try>

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error on invalid macho section specifier try-job: aarch64-apple

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folkertdev force-pushed the macho-section-specifier branch from 35e0a3f to c90d31f Compare April 9, 2026 20:21

rustbot added the A-rustdoc-json Area: Rustdoc JSON backend label Apr 9, 2026

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rustbot 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 9, 2026

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folkertdev force-pushed the macho-section-specifier branch from c90d31f to 30b9c6e Compare April 9, 2026 22:49

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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-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Apr 10, 2026

JonathanBrouwer mentioned this pull request Apr 10, 2026

Rollup of 2 pull requests #155090

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folkertdev force-pushed the macho-section-specifier branch from a5691b8 to 896d75e Compare April 12, 2026 12:47

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Auto merge of #155065 - folkertdev:macho-section-specifier, r=<try>

5c7f2d3

error on invalid macho section specifier try-job: aarch64-apple

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folkertdev added 3 commits April 12, 2026 18:06

error on invalid macho section specifier

2a41d4d

fix usage of #[link_section] to be compatible with mach-o rules

0d36466

use cfg(target_object_format = "mach-o") to clean up tests

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folkertdev force-pushed the macho-section-specifier branch from 896d75e to 3f4778b Compare April 12, 2026 16:16

rustbot added the T-rustdoc-frontend Relevant to the rustdoc-frontend team, which will review and decide on the web UI/UX output. label Apr 12, 2026

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Auto merge of #155065 - folkertdev:macho-section-specifier, r=<try>

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error on invalid macho section specifier try-job: aarch64-apple

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fix rustdoc tests that assume elf

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folkertdev force-pushed the macho-section-specifier branch from 3f4778b to 7aeba4e Compare April 12, 2026 19:07

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Auto merge of #155065 - folkertdev:macho-section-specifier, r=<try>

6c29d2f

error on invalid macho section specifier try-job: aarch64-apple

JonathanBrouwer approved these changes Apr 13, 2026

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folkertdev added the I-lang-nominated Nominated for discussion during a lang team meeting. label Apr 13, 2026

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