Allow section override when using patchable-function-entries by pmur · Pull Request #157445 · rust-lang/rust

pmur · 2026-06-04T20:12:24Z

Sometimes it is necessary to group patchable function entrypoint records in distinct linker sections. This is the case for some bpf functions within the linux kernel which shouldn't be visible to ftrace.

Extend -Zpatchable-function-entry to accept an argument of the form prefix_nops,total_nops,record_section, which places all entry record into a user specified section.

Likewise, extend the patchable_function_entry attribute to accept an optional section="name" option to place a function into a specific section.

This is made possible by llvm attribute patchable-function-entry-section added in llvm 21.

rustbot · 2026-06-04T21:52:32Z

Some changes occurred in compiler/rustc_attr_parsing

cc @jdonszelmann, @JonathanBrouwer

Some changes occurred in compiler/rustc_hir/src/attrs

cc @jdonszelmann, @JonathanBrouwer

rustbot · 2026-06-04T21:52:34Z

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pmur · 2026-06-04T22:01:21Z

I think this is an important feature which we weren't aware of during the initial implementation of #123115.

Adding this should allow Rust to reduce the need to implement mcount or fentry (essentially x86 only) for compatibility within the linux kernel, and likely reduces the need for rust-lang/rfcs#3917.

pmur · 2026-06-17T14:56:53Z

@rustbot reroll

chenyukang · 2026-06-22T04:07:40Z

@rustbot reroll

mejrs

What are the rules for valid section names? This implementation accepts every string. Is #[patchable_function_entry(section = "")] valid? Can I use names with null bytes in them?

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rustbot · 2026-06-24T11:21:29Z

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

mejrs · 2026-06-24T11:24:28Z

+                sym::section => {
+                    // Duplicate entries are not allowed
+                    if section.is_some() {
+                        errored = true;


nit: usually we use Option<ErrorGuaranteed> for "has errored" variables. Feel free to implement it or not, at your option.

View changes since the review

Can that be done within the attribute parsing framework? I think I am constrained to the SingleAttributeParser trait.

Functions like duplicate_key return ErrorGuaranteed for this reason.

pmur · 2026-06-24T20:56:39Z

What are the rules for valid section names?

I think that gets punted to the assembler, and the targets object file format. For ELF, I think that is any nul terminated string.

mejrs · 2026-06-25T12:54:31Z

What are the rules for valid section names?

I think that gets punted to the assembler, and the targets object file format. For ELF, I think that is any nul terminated string.

So this would fail at the codegen stage? It makes for a better user experience to reject it earlier, similar to #155817

pmur · 2026-06-25T16:03:46Z

Updated to handle nul's more gracefully. llvm doesn't handle the inline nul gracefully.

rustbot · 2026-06-29T14:53:08Z

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.

mejrs

Thanks!

@bors r+ rollup

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rust-bors · 2026-06-29T15:19:37Z

📌 Commit c340e8a has been approved by mejrs

It is now in the queue for this repository.

Allow section override when using patchable-function-entries Sometimes it is necessary to group patchable function entrypoint records in distinct linker sections. This is the case for some bpf functions within the linux kernel which shouldn't be visible to ftrace. Extend `-Zpatchable-function-entry` to accept an argument of the form `prefix_nops,total_nops,record_section`, which places all entry record into a user specified section. Likewise, extend the `patchable_function_entry` attribute to accept an optional `section="name"` option to place a function into a specific section. This is made possible by llvm attribute `patchable-function-entry-section` added in llvm 21.

Rollup of 12 pull requests Successful merges: - #158073 (bootstrap: fix panic when repo path contains spaces by switching to CARGO_ENCODED_RUSTFLAGS) - #158169 (Fix debuginfo compression in bootstrap) - #158256 (Avoid parser panics bubbling out to proc macros) - #158375 (Support `DefKind::InlineConst` in `ConstKind::Unevaluated`) - #158417 (Avoid ICE when cfg_eval recovers no item from derive input) - #158556 (delegation: store child segment flag in `PathSegment`) - #158561 (Avoid building rustdoc for tests without doctests) - #158562 (Improve tracing of steps in bootstrap) - #157445 (Allow section override when using patchable-function-entries) - #158081 (trait-system: Recover deferred closure calls after errors) - #158327 (Move attribute and keyword docs from `std` to `core`) - #158468 (Include default-stability info in rustdoc JSON.)

Allow section override when using patchable-function-entries Sometimes it is necessary to group patchable function entrypoint records in distinct linker sections. This is the case for some bpf functions within the linux kernel which shouldn't be visible to ftrace. Extend `-Zpatchable-function-entry` to accept an argument of the form `prefix_nops,total_nops,record_section`, which places all entry record into a user specified section. Likewise, extend the `patchable_function_entry` attribute to accept an optional `section="name"` option to place a function into a specific section. This is made possible by llvm attribute `patchable-function-entry-section` added in llvm 21.

…uwer Rollup of 16 pull requests Successful merges: - #155722 (Introduce aarch64-unknown-linux-pauthtest target) - #156230 (tests: check wasm compiler_builtins object architecture) - #158073 (bootstrap: fix panic when repo path contains spaces by switching to CARGO_ENCODED_RUSTFLAGS) - #158169 (Fix debuginfo compression in bootstrap) - #158256 (Avoid parser panics bubbling out to proc macros) - #158375 (Support `DefKind::InlineConst` in `ConstKind::Unevaluated`) - #158556 (delegation: store child segment flag in `PathSegment`) - #158561 (Avoid building rustdoc for tests without doctests) - #158562 (Improve tracing of steps in bootstrap) - #157445 (Allow section override when using patchable-function-entries) - #158081 (trait-system: Recover deferred closure calls after errors) - #158327 (Move attribute and keyword docs from `std` to `core`) - #158468 (Include default-stability info in rustdoc JSON.) - #158564 (fix `-Z min-recursion-limit` unstable chapter name) - #158568 (llvm-wrapper: use accessors for private fields in LLVM 23+) - #158582 (Comment on needed RAM in huge-stacks.rs)

JonathanBrouwer · 2026-06-30T01:38:16Z

@bors try jobs=dist-x86_64-msvc

Allow section override when using patchable-function-entries try-job: dist-x86_64-msvc

…uwer Rollup of 7 pull requests Successful merges: - #158073 (bootstrap: fix panic when repo path contains spaces by switching to CARGO_ENCODED_RUSTFLAGS) - #158256 (Avoid parser panics bubbling out to proc macros) - #158561 (Avoid building rustdoc for tests without doctests) - #158562 (Improve tracing of steps in bootstrap) - #157445 (Allow section override when using patchable-function-entries) - #158327 (Move attribute and keyword docs from `std` to `core`) - #158591 (Fix spacing issue for unused parentheses lint)

rust-bors · 2026-06-30T04:34:39Z

☀️ Try build successful (CI)
Build commit: b51b1b6 (b51b1b640424281574727bc510e87d381ef1e3e5)
Base parent: 0966944 (096694416a41840709140eb0fd0ca193d1a3e6ba)

…uwer Rollup of 7 pull requests Successful merges: - #158073 (bootstrap: fix panic when repo path contains spaces by switching to CARGO_ENCODED_RUSTFLAGS) - #158256 (Avoid parser panics bubbling out to proc macros) - #158561 (Avoid building rustdoc for tests without doctests) - #158562 (Improve tracing of steps in bootstrap) - #157445 (Allow section override when using patchable-function-entries) - #158327 (Move attribute and keyword docs from `std` to `core`) - #158591 (Fix spacing issue for unused parentheses lint)

Rollup merge of #157445 - pmur:murp/extend-patchable, r=mejrs Allow section override when using patchable-function-entries Sometimes it is necessary to group patchable function entrypoint records in distinct linker sections. This is the case for some bpf functions within the linux kernel which shouldn't be visible to ftrace. Extend `-Zpatchable-function-entry` to accept an argument of the form `prefix_nops,total_nops,record_section`, which places all entry record into a user specified section. Likewise, extend the `patchable_function_entry` attribute to accept an optional `section="name"` option to place a function into a specific section. This is made possible by llvm attribute `patchable-function-entry-section` added in llvm 21.

…uwer Rollup of 7 pull requests Successful merges: - rust-lang/rust#158073 (bootstrap: fix panic when repo path contains spaces by switching to CARGO_ENCODED_RUSTFLAGS) - rust-lang/rust#158256 (Avoid parser panics bubbling out to proc macros) - rust-lang/rust#158561 (Avoid building rustdoc for tests without doctests) - rust-lang/rust#158562 (Improve tracing of steps in bootstrap) - rust-lang/rust#157445 (Allow section override when using patchable-function-entries) - rust-lang/rust#158327 (Move attribute and keyword docs from `std` to `core`) - rust-lang/rust#158591 (Fix spacing issue for unused parentheses lint)

pmur marked this pull request as ready for review June 4, 2026 21:52

rustbot added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Jun 4, 2026

rustbot removed the S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. label Jun 4, 2026

rustbot assigned jackh726 Jun 4, 2026

ojeda mentioned this pull request Jun 5, 2026

Rust unstable features needed for the kernel Rust-for-Linux/linux#2

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rustbot assigned chenyukang and unassigned jackh726 Jun 17, 2026

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pmur force-pushed the murp/extend-patchable branch from 8f7613b to c729ed3 Compare June 25, 2026 15:57

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pmur force-pushed the murp/extend-patchable branch from c729ed3 to 55b62aa Compare June 25, 2026 21:16

pmur force-pushed the murp/extend-patchable branch from a81de40 to c340e8a Compare June 29, 2026 14:53

mejrs approved these changes Jun 29, 2026

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Rollup of 12 pull requests #158570

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Rollup of 14 pull requests #158578

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rust-bors Bot pushed a commit that referenced this pull request Jun 30, 2026

Auto merge of #157445 - pmur:murp/extend-patchable, r=<try>

b51b1b6

Allow section override when using patchable-function-entries try-job: dist-x86_64-msvc

JonathanBrouwer mentioned this pull request Jun 30, 2026

Rollup of 7 pull requests #158595

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rust-bors Bot merged commit 86eb76f into rust-lang:main Jun 30, 2026
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rustbot added this to the 1.98.0 milestone Jun 30, 2026

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