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Clarify (un)signed-ness of pointers for comparisons #77497

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gamozolabs opened this issue Oct 3, 2020 · 1 comment · Fixed by #136364
Closed

Clarify (un)signed-ness of pointers for comparisons #77497

gamozolabs opened this issue Oct 3, 2020 · 1 comment · Fixed by #136364
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A-docs Area: Documentation for any part of the project, including the compiler, standard library, and tools A-raw-pointers Area: raw pointers, MaybeUninit, NonNull C-enhancement Category: An issue proposing an enhancement or a PR with one. T-lang Relevant to the language team, which will review and decide on the PR/issue.

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@gamozolabs
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It seems currently pointer comparisons, ala. (foo as *const u32) > (bar as *const u32). Emits an unsigned comparison. I looked a little bit to see if this was documented somewhere and I didn't see anything super obvious.

Is this something that is defined behavior, and if it is, could we clarify it in the primitive pointer type documentation? This can be relevant especially in many kernel designs when there are "negative" addresses in the kernel and "positive" in user-space.

Thanks!
-B
@gamozolabs gamozolabs changed the title Clarify (un)signed-ness of pointers Clarify (un)signed-ness of pointers for comparisons Oct 3, 2020
@jonas-schievink jonas-schievink added A-raw-pointers Area: raw pointers, MaybeUninit, NonNull C-enhancement Category: An issue proposing an enhancement or a PR with one. T-lang Relevant to the language team, which will review and decide on the PR/issue. labels Oct 3, 2020
@RalfJung
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RalfJung commented Oct 5, 2020

Yes, pointers are definitely treated as unsigned integers for inequality comparisons. There is no such thing as a "negative address", just an address >= 0xF0000000[00000000].

@Enselic Enselic added the A-docs Area: Documentation for any part of the project, including the compiler, standard library, and tools label Dec 6, 2024
@hkBst hkBst mentioned this issue Jan 31, 2025
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@bors bors closed this as completed in 15a5f5f Feb 1, 2025
rust-timer added a commit to rust-lang-ci/rust that referenced this issue Feb 1, 2025
@rust-timer
Unrolled build for rust-lang#136364
d38d22f 
Rollup merge of rust-lang#136364 - hkBst:ptr_cmp_docs, r=tgross35

document that ptr cmp is unsigned

Fixes rust-lang#77497
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A-docs Area: Documentation for any part of the project, including the compiler, standard library, and tools A-raw-pointers Area: raw pointers, MaybeUninit, NonNull C-enhancement Category: An issue proposing an enhancement or a PR with one. T-lang Relevant to the language team, which will review and decide on the PR/issue.
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document that ptr cmp is unsigned hkBst/rust
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@Enselic @RalfJung @jonas-schievink @gamozolabs