caution against ptr-to-int transmutes #95547
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| r? @scottmcm (rust-highfive has picked a reviewer for you, use r? to override) |
rust-highfive added the S-waiting-on-review 
RalfJung force-pushed the ptr-int-transmutes branch from a7b204c to dd85a76 Compare This was referenced Apr 2, 2022
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| Since I don't think this is making any new promises and it being "preferrable" to avoid @bors r+ rollup We have lots of time to tweak the messaging before even going to beta, if anyone else has strong feelings. |
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bors added S-waiting-on-bors 
bors added a commit to rust-lang-ci/rust that referenced this pull request Apr 5, 2022
Rollup of 8 pull requests Successful merges: - rust-lang#88025 (ScmCredentials netbsd implementation.) - rust-lang#95473 (track individual proc-macro expansions in the self-profiler) - rust-lang#95547 (caution against ptr-to-int transmutes) - rust-lang#95585 (Explain why `&T` is cloned when `T` is not `Clone`) - rust-lang#95591 (Use revisions to track NLL test output (part 1)) - rust-lang#95663 (diagnostics: give a special note for unsafe fn / Fn/FnOnce/FnMut) - rust-lang#95673 (:arrow_up: rust-analyzer) - rust-lang#95681 (resolve: Fix resolution of empty paths passed from rustdoc) Failed merges: r? `@ghost` `@rustbot` modify labels: rollup
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I don't know how strong of a statement we want to make here, but I am very concerned that the current docs could be interpreted as saying that ptr-to-int transmutes are just as okay as transmuting
*mut Tinto an&mut T.Examples like this show that ptr-to-int transmutes are deeply suspicious -- they are either UB, or they don't round-trip properly, or we have to basically say that
transmutewill actively look for pointers and do all the things a ptr-to-int cast does (which includes a global side-effect of marking the pointed-to allocation as 'exposed').Another alternative might be to simply not talk about them... but we do want people to use casts rather than transmutes for this.
Cc @rust-lang/lang