Outdated documentation with regards to `ptr::addr_of!` #83509

jfrimmel · 2021-03-26T06:39:48Z

Rust 1.51 was released yesterday and included the ptr::addr_of! macro. Its documentation talks about its usage in creating pointers to unaligned fields without the need for an intermediate reference:

However, &expr as *const _ creates a reference before casting it to a raw pointer, and that reference is subject to the same rules as all other references. This macro can create a raw pointer without creating a reference first.

Despite that, the documentation of ptr::write_unaligned states the following:

It is currently impossible to create raw pointers to unaligned fields of a packed struct.
Attempting to create a raw pointer to an unaligned struct field with an expression such as &packed.unaligned as *const FieldType creates an intermediate unaligned reference before converting that to a raw pointer. That this reference is temporary and immediately cast is inconsequential as the compiler always expects references to be properly aligned. As a result, using &packed.unaligned as *const FieldType causes immediate undefined behavior in your program.

The documentation of ptr::write_unaligned should be updated to reflect the new changes in the language.

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rustc --version --verbose:

rustc 1.51.0 (2fd73fabe 2021-03-23)
binary: rustc
commit-hash: 2fd73fabe469357a12c2c974c140f67e7cdd76d0
commit-date: 2021-03-23
host: x86_64-unknown-linux-gnu
release: 1.51.0
LLVM version: 11.0.1

and

rustc 1.53.0-nightly (07e0e2ec2 2021-03-24)
binary: rustc
commit-hash: 07e0e2ec268c140e607e1ac7f49f145612d0f597
commit-date: 2021-03-24
host: x86_64-unknown-linux-gnu
release: 1.53.0-nightly
LLVM version: 12.0.0

@rustbot modify labels: T-doc
@rustbot claim

The text was updated successfully, but these errors were encountered:

Update `ptr` docs with regards to `ptr::addr_of!` This updates the documentation since `ptr::addr_of!` and `ptr::addr_of_mut!` are now stable. One might remove the distinction between the sections `# On packed structs` and `# Examples`, as the old section on packed structs was primarily to prevent users of doing undefined behavior, which is not necessary anymore. Technically there is now wrong/outdated documentation on stable, but I don't think this is worth a point release 😉 Fixes rust-lang#83509. `@rustbot` modify labels: T-doc

Update `ptr` docs with regards to `ptr::addr_of!` This updates the documentation since `ptr::addr_of!` and `ptr::addr_of_mut!` are now stable. One might remove the distinction between the sections `# On packed structs` and `# Examples`, as the old section on packed structs was primarily to prevent users of doing undefined behavior, which is not necessary anymore. Technically there is now wrong/outdated documentation on stable, but I don't think this is worth a point release 😉 Fixes rust-lang#83509. ``@rustbot`` modify labels: T-doc

Update `ptr` docs with regards to `ptr::addr_of!` This updates the documentation since `ptr::addr_of!` and `ptr::addr_of_mut!` are now stable. One might remove the distinction between the sections `# On packed structs` and `# Examples`, as the old section on packed structs was primarily to prevent users of doing undefined behavior, which is not necessary anymore. Technically there is now wrong/outdated documentation on stable, but I don't think this is worth a point release 😉 Fixes rust-lang#83509. ```@rustbot``` modify labels: T-doc

Update `ptr` docs with regards to `ptr::addr_of!` This updates the documentation since `ptr::addr_of!` and `ptr::addr_of_mut!` are now stable. One might remove the distinction between the sections `# On packed structs` and `# Examples`, as the old section on packed structs was primarily to prevent users of doing undefined behavior, which is not necessary anymore. Technically there is now wrong/outdated documentation on stable, but I don't think this is worth a point release 😉 Fixes rust-lang#83509. ````@rustbot```` modify labels: T-doc

Update `ptr` docs with regards to `ptr::addr_of!` This updates the documentation since `ptr::addr_of!` and `ptr::addr_of_mut!` are now stable. One might remove the distinction between the sections `# On packed structs` and `# Examples`, as the old section on packed structs was primarily to prevent users of doing undefined behavior, which is not necessary anymore. Technically there is now wrong/outdated documentation on stable, but I don't think this is worth a point release 😉 Fixes rust-lang#83509. `````@rustbot````` modify labels: T-doc

Update `ptr` docs with regards to `ptr::addr_of!` This updates the documentation since `ptr::addr_of!` and `ptr::addr_of_mut!` are now stable. One might remove the distinction between the sections `# On packed structs` and `# Examples`, as the old section on packed structs was primarily to prevent users of doing undefined behavior, which is not necessary anymore. Technically there is now wrong/outdated documentation on stable, but I don't think this is worth a point release 😉 Fixes rust-lang#83509. ``````@rustbot`````` modify labels: T-doc

Update `ptr` docs with regards to `ptr::addr_of!` This updates the documentation since `ptr::addr_of!` and `ptr::addr_of_mut!` are now stable. One might remove the distinction between the sections `# On packed structs` and `# Examples`, as the old section on packed structs was primarily to prevent users of doing undefined behavior, which is not necessary anymore. Technically there is now wrong/outdated documentation on stable, but I don't think this is worth a point release 😉 Fixes rust-lang#83509. ```````@rustbot``````` modify labels: T-doc

Update `ptr` docs with regards to `ptr::addr_of!` This updates the documentation since `ptr::addr_of!` and `ptr::addr_of_mut!` are now stable. One might remove the distinction between the sections `# On packed structs` and `# Examples`, as the old section on packed structs was primarily to prevent users of doing undefined behavior, which is not necessary anymore. Technically there is now wrong/outdated documentation on stable, but I don't think this is worth a point release 😉 Fixes rust-lang#83509. ````````@rustbot```````` modify labels: T-doc

Update `ptr` docs with regards to `ptr::addr_of!` This updates the documentation since `ptr::addr_of!` and `ptr::addr_of_mut!` are now stable. One might remove the distinction between the sections `# On packed structs` and `# Examples`, as the old section on packed structs was primarily to prevent users of doing undefined behavior, which is not necessary anymore. Technically there is now wrong/outdated documentation on stable, but I don't think this is worth a point release 😉 Fixes rust-lang#83509. `````````@rustbot````````` modify labels: T-doc

jfrimmel added the C-bug Category: This is a bug. label Mar 26, 2021

rustbot assigned jfrimmel Mar 26, 2021

rustbot added the A-docs Area: documentation for any part of the project, including the compiler, standard library, and tools label Mar 26, 2021

jfrimmel mentioned this issue Mar 27, 2021

Update ptr docs with regards to ptr::addr_of! #83553

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bors closed this as completed in 722bebf May 5, 2021

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Outdated documentation with regards to `ptr::addr_of!` #83509

Outdated documentation with regards to `ptr::addr_of!` #83509

jfrimmel commented Mar 26, 2021 •

edited

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Outdated documentation with regards to ptr::addr_of! #83509

Outdated documentation with regards to ptr::addr_of! #83509

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jfrimmel commented Mar 26, 2021 • edited Loading

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Outdated documentation with regards to `ptr::addr_of!` #83509

Outdated documentation with regards to `ptr::addr_of!` #83509

jfrimmel commented Mar 26, 2021 •

edited

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