std: improve safety documentation in UNIX stack overflow code by joboet · Pull Request #162132 · rust-lang/rust

joboet · 2026-09-01T15:12:24Z

The UNIX stack overflow handling code was only partially documented, and applied #![forbid(unsafe_op_in_unsafe_fn)] inconsistently. Also, the existing safety documentation wasn't very clear on the assumptions made by std and the reasoning behind those assumptions. I've tried to rectify all that here by adding some unsafe, removing some unsafe and writing a lot of comments. There are no functional changes however, I'll get started on those once this is merged.

rustbot · 2026-09-01T15:12:30Z

r? @ChrisDenton

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ChrisDenton

I think this is much clearer to read, thanks.

I do wonder if it'd be worth creating small wrappers for some of the trivially safe functions if they're used more than a couple of times.

View changes since this review

joboet · 2026-09-02T10:30:01Z

I do wonder if it'd be worth creating small wrappers for some of the trivially safe functions if they're used more than a couple of times.

That sounds like a good idea. I think I'll defer that to a follow-up PR though, unless you think otherwise?

ChrisDenton · 2026-09-03T00:00:57Z

This is definitely an improvement on its own so I'm happy to accept this as-is

@bors r+

rust-bors · 2026-09-03T00:01:00Z

📌 Commit 7394cc6 has been approved by ChrisDenton

It is now in the queue for this repository.

…sDenton std: improve safety documentation in UNIX stack overflow code The UNIX stack overflow handling code was only partially documented, and applied `#![forbid(unsafe_op_in_unsafe_fn)]` inconsistently. Also, the existing safety documentation wasn't very clear on the assumptions made by `std` and the reasoning behind those assumptions. I've tried to rectify all that here by adding some `unsafe`, removing some `unsafe` and writing a lot of comments. There are no functional changes however, I'll get started on those once this is merged.

Rollup of 29 pull requests Successful merges: - #161694 (add `Complex` ABI run-make test) - #162014 (Move more `rustdoc-html` tests using `--test` into the right folder) - #162164 (Revert "Implement Debug for C-like enums with a concatenated string") - #160564 (volatile: allow accesses to non-AM memory to trap) - #161579 (suggest calling a fn item used as the iterator of a `for` loop) - #162044 (coverage: Resolve spans to file-coordinates in a separate step) - #162120 (Introduce `PerOwnerLoweringState`) - #162132 (std: improve safety documentation in UNIX stack overflow code) - #162151 (Test itanium mangling of `f16` and `f128`) - #162162 (Don't special-case `!` in stability checks anymore) - #162181 (Remove wrong UnusedBraces lint for iterator loop in edition 2024 ) - #162187 (Rename `thir::ExprKind::Use` to `ValueExpr`) - #158401 (mgca: Don't ICE when evaluating ValTrees that contain error constants) - #159873 (fuchsia: Add safestack as a supported sanitizer for x86_64 fuchsia) - #161847 (Preserve visibility in nested macro import suggestions) - #161951 (Windows: add fallback if `canonicalize` fails) - #161972 (Improve tests for `#[track_caller]` in async) - #162008 (Render the `box` pattern removal diagnostic more actionable & remove `box` expression recovery) - #162065 (std: don't reference `libc::O_NOFOLLOW` on VxWorks in `set_perm_nofollow`) - #162076 (docs(num): clarify conditions under which error occurs in `impl TryFrom<int> for int`) - #162152 (Revert "retrieve supported GCC targets from the sysroot") - #162153 (Prefer `LLVMGetVersion` for runtime info) - #162168 (fix ICE in project_goals/inherent) - #162171 (Explain LoongArch f16 NaN-boxing in inline asm) - #162173 (fix supposedly unreachable `bug!` being reachable) - #162180 (remove outdated next-solver FIXMEs) - #162191 (core: mark float `ClampBounds` methods as `#[inline]`) - #162195 (docs(time): clarify exact seconds for week and day) - #162199 (docs(time): clarify exact seconds for hour and minute)

…uwer Rollup of 25 pull requests Successful merges: - #161694 (add `Complex` ABI run-make test) - #162014 (Move more `rustdoc-html` tests using `--test` into the right folder) - #162164 (Revert "Implement Debug for C-like enums with a concatenated string") - #160564 (volatile: allow accesses to non-AM memory to trap) - #161579 (suggest calling a fn item used as the iterator of a `for` loop) - #162044 (coverage: Resolve spans to file-coordinates in a separate step) - #162120 (Introduce `PerOwnerLoweringState`) - #162132 (std: improve safety documentation in UNIX stack overflow code) - #162151 (Test itanium mangling of `f16` and `f128`) - #162162 (Don't special-case `!` in stability checks anymore) - #162181 (Remove wrong UnusedBraces lint for iterator loop in edition 2024 ) - #162187 (Rename `thir::ExprKind::Use` to `ValueExpr`) - #158401 (mgca: Don't ICE when evaluating ValTrees that contain error constants) - #159873 (fuchsia: Add safestack as a supported sanitizer for x86_64 fuchsia) - #161135 (Add `f16` and `f128` inline ASM support for PowerPC) - #161847 (Preserve visibility in nested macro import suggestions) - #161972 (Improve tests for `#[track_caller]` in async) - #162008 (Render the `box` pattern removal diagnostic more actionable & remove `box` expression recovery) - #162065 (std: don't reference `libc::O_NOFOLLOW` on VxWorks in `set_perm_nofollow`) - #162076 (docs(num): clarify conditions under which error occurs in `impl TryFrom<int> for int`) - #162111 (Update mailmap for Will Crichton and Petr Hosek) - #162152 (Revert "retrieve supported GCC targets from the sysroot") - #162153 (Prefer `LLVMGetVersion` for runtime info) - #162168 (fix ICE in project_goals/inherent) - #162171 (Explain LoongArch f16 NaN-boxing in inline asm)

Rollup merge of #162132 - joboet:safe_stack_overflow, r=ChrisDenton std: improve safety documentation in UNIX stack overflow code The UNIX stack overflow handling code was only partially documented, and applied `#![forbid(unsafe_op_in_unsafe_fn)]` inconsistently. Also, the existing safety documentation wasn't very clear on the assumptions made by `std` and the reasoning behind those assumptions. I've tried to rectify all that here by adding some `unsafe`, removing some `unsafe` and writing a lot of comments. There are no functional changes however, I'll get started on those once this is merged.

rust-timer · 2026-09-03T20:04:09Z

Note

This PR was benchmarked as part of triage of its containing rollup: triage URL.

Finished benchmarking commit (6d17148): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

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Bootstrap: missing data
Artifact size: 401.86 MiB -> 401.08 MiB (-0.20%)

…uwer Rollup of 25 pull requests Successful merges: - rust-lang/rust#161694 (add `Complex` ABI run-make test) - rust-lang/rust#162014 (Move more `rustdoc-html` tests using `--test` into the right folder) - rust-lang/rust#162164 (Revert "Implement Debug for C-like enums with a concatenated string") - rust-lang/rust#160564 (volatile: allow accesses to non-AM memory to trap) - rust-lang/rust#161579 (suggest calling a fn item used as the iterator of a `for` loop) - rust-lang/rust#162044 (coverage: Resolve spans to file-coordinates in a separate step) - rust-lang/rust#162120 (Introduce `PerOwnerLoweringState`) - rust-lang/rust#162132 (std: improve safety documentation in UNIX stack overflow code) - rust-lang/rust#162151 (Test itanium mangling of `f16` and `f128`) - rust-lang/rust#162162 (Don't special-case `!` in stability checks anymore) - rust-lang/rust#162181 (Remove wrong UnusedBraces lint for iterator loop in edition 2024 ) - rust-lang/rust#162187 (Rename `thir::ExprKind::Use` to `ValueExpr`) - rust-lang/rust#158401 (mgca: Don't ICE when evaluating ValTrees that contain error constants) - rust-lang/rust#159873 (fuchsia: Add safestack as a supported sanitizer for x86_64 fuchsia) - rust-lang/rust#161135 (Add `f16` and `f128` inline ASM support for PowerPC) - rust-lang/rust#161847 (Preserve visibility in nested macro import suggestions) - rust-lang/rust#161972 (Improve tests for `#[track_caller]` in async) - rust-lang/rust#162008 (Render the `box` pattern removal diagnostic more actionable & remove `box` expression recovery) - rust-lang/rust#162065 (std: don't reference `libc::O_NOFOLLOW` on VxWorks in `set_perm_nofollow`) - rust-lang/rust#162076 (docs(num): clarify conditions under which error occurs in `impl TryFrom<int> for int`) - rust-lang/rust#162111 (Update mailmap for Will Crichton and Petr Hosek) - rust-lang/rust#162152 (Revert "retrieve supported GCC targets from the sysroot") - rust-lang/rust#162153 (Prefer `LLVMGetVersion` for runtime info) - rust-lang/rust#162168 (fix ICE in project_goals/inherent) - rust-lang/rust#162171 (Explain LoongArch f16 NaN-boxing in inline asm)

rustbot assigned ChrisDenton Sep 1, 2026

rustbot added O-unix Operating system: Unix-like S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Sep 1, 2026

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std: improve safety documentation in UNIX stack overflow code

7394cc6

joboet force-pushed the safe_stack_overflow branch from 0340a0f to 7394cc6 Compare September 1, 2026 18:08

ChrisDenton reviewed Sep 1, 2026

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Comment thread library/std/src/sys/pal/unix/stack_overflow.rs

Comment thread library/std/src/sys/pal/unix/stack_overflow.rs

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-review Status: Awaiting review from the assignee but also interested parties. labels Sep 3, 2026

Zalathar mentioned this pull request Sep 3, 2026

Rollup of 29 pull requests #162221

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JonathanBrouwer mentioned this pull request Sep 3, 2026

Rollup of 25 pull requests #162229

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rust-bors Bot merged commit 92e0f00 into rust-lang:main Sep 3, 2026
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rustbot added this to the 1.100.0 milestone Sep 3, 2026

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std: improve safety documentation in UNIX stack overflow code - #162132

std: improve safety documentation in UNIX stack overflow code#162132
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