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pure asm blocks must terminate #1442

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merged 2 commits into from
Jan 27, 2024
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RalfJung
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@Amanieu am I correct in assuming that all other asm blocks (i.e, not marked pure), may loop infinitely?

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Amanieu commented Dec 26, 2023

Since non-pure asm blocks can do anything C FFI can do, yes, it's valid.

However I'm not sure that pure should be prevented from looping indefinitely. How is that different from it just taking a very long time to run?

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If they loop infinitely they can cannot be optimized away.

asm!("<infinite loop>", pure);
unreachable_unchecked();

It is my understanding that the compiler can remove this asm block, so this program must have UB. Our current docs do not explain where that UB comes from.

src/inline-assembly.md Outdated Show resolved Hide resolved
Co-authored-by: Amanieu d'Antras <amanieu@gmail.com>
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@ehuss we got an expert review; is anything else needed to land this?

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Thanks!

I'm going to go ahead and approve, but I'm a little uncomfortable with the process we've been using for defining assembly and its behavior. It feels very ad-hoc, without any oversight other than Amanieu. It's not that I don't trust @Amanieu (I trust him more than anyone else, and am very appreciative of his help), but that I think that having a very large surface area of Rust be defined by essentially one person without any discussion or broad feedback can lead to mistakes or disagreements or misunderstandings.

I don't know how else to handle this since I have difficulty getting the lang team to participate.

@ehuss ehuss added this pull request to the merge queue Jan 27, 2024
Merged via the queue into rust-lang:master with commit e848fbc Jan 27, 2024
1 check passed
GuillaumeGomez added a commit to GuillaumeGomez/rust that referenced this pull request Jan 30, 2024
Update books

## rust-lang/edition-guide

1 commits in bbffb074e16bef89772818b400b6c76a65eac126..baafacc6d8701269dab1e1e333f3547fb54b5a59
2024-01-18 18:44:06 UTC to 2024-01-18 18:44:06 UTC

- Update c-string literal stabilization release number. (rust-lang/edition-guide#289)

## rust-embedded/book

1 commits in 3f9df2b9885c6741365da2e12ed6662cd0e827d6..2e95fc2fd31d669947e993aa07ef10dc9828bee7
2024-01-29 07:19:07 UTC to 2024-01-29 07:19:07 UTC

- Mention generics in "optimizing dependencies" (rust-embedded/book#366)

## rust-lang/reference

3 commits in 8c77e8be9da1a9c70545556218d563c8d061f1fd..a0b119535e7740f68494c4f0582f7ad008b00ccd
2024-01-27 19:22:06 UTC to 2024-01-27 16:43:49 UTC

- Update C-String literals to reject NUL (rust-lang/reference#1450)
- pure asm blocks must terminate (rust-lang/reference#1442)
- String literal expressions (rust-lang/reference#1452)

## rust-lang/rust-by-example

4 commits in ddf5cb0e6ee54ba2dd84c8ca3e1314120014e20d..179256a445d6144f5f371fdefb993f48f33978b0
2024-01-22 12:21:42 UTC to 2024-01-20 23:10:42 UTC

- Updated first sentence of "parsing a string" in string.md (rust-lang/rust-by-example#1805)
- Update the rustdoc example to match best practice (rust-lang/rust-by-example#1804)
- Add reference to crates.io error handling crates (rust-lang/rust-by-example#1803)
- fix(str.md): avoid misunderstanding that there were only two string types (rust-lang/rust-by-example#1802)

## rust-lang/rustc-dev-guide

15 commits in 4af29d1a7f64f88a36539662c6a84fe1fbe6cde1..ec287e332777627185be4798ad22599ffe7b84aa
2024-01-28 22:45:18 UTC to 2024-01-15 17:44:49 UTC

- Upgrade actions to use Node.js v20 (rust-lang/rustc-dev-guide#1863)
- Fix some links (rust-lang/rustc-dev-guide#1865)
- Add link in salsa (rust-lang/rustc-dev-guide#1866)
- Clarify what rt.rs is. (rust-lang/rustc-dev-guide#1876)
- update link to rustc dependencies (rust-lang/rustc-dev-guide#1869)
- Followup to rust-lang#1862 (rust-lang/rustc-dev-guide#1864)
- Clarify debugging graph dependency (rust-lang/rustc-dev-guide#1862)
- Get diagnostics directly in `rustc-driver-getting-diagnostics` example (rust-lang/rustc-dev-guide#1857)
- Update examples (rust-lang/rustc-dev-guide#1856)
- Add a perf. bot command and a link to its help page (rust-lang/rustc-dev-guide#1855)
- Add some explanations for frequently used rustbot commands (rust-lang/rustc-dev-guide#1849)
- update some of the diagnostic translations info (rust-lang/rustc-dev-guide#1711)
- Document unsafety checking (rust-lang/rustc-dev-guide#1847)
- Remove outdated references to `-Z dump-mir-spanview` (rust-lang/rustc-dev-guide#1853)
- update old bootstrap docs (rust-lang/rustc-dev-guide#1852)
rust-timer added a commit to rust-lang-ci/rust that referenced this pull request Jan 30, 2024
Rollup merge of rust-lang#120467 - rustbot:docs-update, r=ehuss

Update books

## rust-lang/edition-guide

1 commits in bbffb074e16bef89772818b400b6c76a65eac126..baafacc6d8701269dab1e1e333f3547fb54b5a59
2024-01-18 18:44:06 UTC to 2024-01-18 18:44:06 UTC

- Update c-string literal stabilization release number. (rust-lang/edition-guide#289)

## rust-embedded/book

1 commits in 3f9df2b9885c6741365da2e12ed6662cd0e827d6..2e95fc2fd31d669947e993aa07ef10dc9828bee7
2024-01-29 07:19:07 UTC to 2024-01-29 07:19:07 UTC

- Mention generics in "optimizing dependencies" (rust-embedded/book#366)

## rust-lang/reference

3 commits in 8c77e8be9da1a9c70545556218d563c8d061f1fd..a0b119535e7740f68494c4f0582f7ad008b00ccd
2024-01-27 19:22:06 UTC to 2024-01-27 16:43:49 UTC

- Update C-String literals to reject NUL (rust-lang/reference#1450)
- pure asm blocks must terminate (rust-lang/reference#1442)
- String literal expressions (rust-lang/reference#1452)

## rust-lang/rust-by-example

4 commits in ddf5cb0e6ee54ba2dd84c8ca3e1314120014e20d..179256a445d6144f5f371fdefb993f48f33978b0
2024-01-22 12:21:42 UTC to 2024-01-20 23:10:42 UTC

- Updated first sentence of "parsing a string" in string.md (rust-lang/rust-by-example#1805)
- Update the rustdoc example to match best practice (rust-lang/rust-by-example#1804)
- Add reference to crates.io error handling crates (rust-lang/rust-by-example#1803)
- fix(str.md): avoid misunderstanding that there were only two string types (rust-lang/rust-by-example#1802)

## rust-lang/rustc-dev-guide

15 commits in 4af29d1a7f64f88a36539662c6a84fe1fbe6cde1..ec287e332777627185be4798ad22599ffe7b84aa
2024-01-28 22:45:18 UTC to 2024-01-15 17:44:49 UTC

- Upgrade actions to use Node.js v20 (rust-lang/rustc-dev-guide#1863)
- Fix some links (rust-lang/rustc-dev-guide#1865)
- Add link in salsa (rust-lang/rustc-dev-guide#1866)
- Clarify what rt.rs is. (rust-lang/rustc-dev-guide#1876)
- update link to rustc dependencies (rust-lang/rustc-dev-guide#1869)
- Followup to rust-lang#1862 (rust-lang/rustc-dev-guide#1864)
- Clarify debugging graph dependency (rust-lang/rustc-dev-guide#1862)
- Get diagnostics directly in `rustc-driver-getting-diagnostics` example (rust-lang/rustc-dev-guide#1857)
- Update examples (rust-lang/rustc-dev-guide#1856)
- Add a perf. bot command and a link to its help page (rust-lang/rustc-dev-guide#1855)
- Add some explanations for frequently used rustbot commands (rust-lang/rustc-dev-guide#1849)
- update some of the diagnostic translations info (rust-lang/rustc-dev-guide#1711)
- Document unsafety checking (rust-lang/rustc-dev-guide#1847)
- Remove outdated references to `-Z dump-mir-spanview` (rust-lang/rustc-dev-guide#1853)
- update old bootstrap docs (rust-lang/rustc-dev-guide#1852)
@RalfJung RalfJung deleted the asm-terminate branch May 26, 2024 07:35
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3 participants