Use &raw in A|Rc::as_ptr #73845

CAD97 · 2020-06-28T18:37:54Z

This PR uses &raw for offsetting *mut [A]RcInner<T> -> *mut T.

Additionally, this updates the implementation of Weak::as_ptr to support unsized T, though it does not yet relax the bounds of Weak::as_ptr/into_raw/from_raw to accept unsized T.

rust-highfive · 2020-06-28T18:37:56Z

r? @sfackler

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sfackler · 2020-06-28T19:03:18Z

r? @RalfJung

src/liballoc/rc.rs

CAD97 · 2020-06-30T16:49:16Z

Addressed the review comments (and in sync.rs as well, of course).

(I really need to figure out why format-on-save is not agreeing with ./x.py fmt....)

src/liballoc/rc.rs

Co-Authored-By: Ralf Jung <post@ralfj.de>

src/liballoc/rc.rs

RalfJung · 2020-07-03T10:42:37Z

Awesome, thanks a lot for enduring all these rounds of review. :)
@bors r+

bors · 2020-07-03T11:34:40Z

💔 Test failed - checks-actions

RalfJung · 2020-07-03T12:17:27Z

Second network failure in a row? Cc @rust-lang/infra
@bors retry

RalfJung · 2020-07-03T12:18:58Z

Same failure in 2 other PRs.
@bors treeclosed=100

pietroalbini · 2020-07-03T13:00:06Z

Opened #73992 to track it, will ping GitHub.

@ghost

…arth Rollup of 12 pull requests Successful merges: - rust-lang#73140 (Fallback to xml.etree.ElementTree) - rust-lang#73670 (Add `format_args_capture` feature) - rust-lang#73693 (Use exhaustive match in const_prop.rs) - rust-lang#73845 (Use &raw in A|Rc::as_ptr) - rust-lang#73861 (Create E0768) - rust-lang#73881 (Standardize bibliographic citations in rustc API docs) - rust-lang#73925 (Improve comments from rust-lang#72617, as suggested by RalfJung) - rust-lang#73949 ([mir-opt] Fix mis-optimization and other issues with the SimplifyArmIdentity pass) - rust-lang#73984 (Edit docs for rustc_data_structures::graph::scc) - rust-lang#73985 (Fix "getting started" link) - rust-lang#73997 (fix typo) - rust-lang#73999 (Bump mingw-check CI image from Ubuntu 16.04 to 18.04.) Failed merges: - rust-lang#74000 (add `lazy_normalization_consts` feature gate) r? @ghost

....to allow use with unsized T. This is a follow-up to rust-lang#73845, which did the impl work required to be able to relax these bounds.

@RalfJung

Allow Weak::as_ptr and friends for unsized T Relaxes `impl<T> Weak<T>` to `impl<T: ?Sized> Weak<T>` for the methods `rc::Weak::as_ptr`, `into_raw`, and `from_raw`. Follow-up to rust-lang#73845, which did most of the impl work to make these functions work for `T: ?Sized`. We still have to adjust the implementation of `Weak::from_raw` here, however, because I missed a use of `ptr.is_null()` previously. This check was necessary when `into`/`from_raw` were first implemented, as `into_raw` returned `ptr::null()` for dangling weak. However, we now just (wrapping) offset dangling weaks' pointers the same as nondangling weak, so the null check is no longer necessary (or even hit). (I can submit just 17a928f as a separate PR if desired.) As a nice side effect, moves the `fn is_dangling` definition closer to `Weak::new`, which creates the dangling weak. This technically stabilizes that "something like `align_of_val_raw`" is possible to do. However, I believe the part of the functionality required by these methods here -- specifically, getting the alignment of a pointee from a pointer where it may be dangling iff the pointee is `Sized` -- is uncontroversial enough to stabilize these methods without a way to implement them on stable Rust. r? @RalfJung, who reviewed rust-lang#73845. ATTN: This changes (relaxes) the (input) generic bounds on stable fn!

Allow Weak::as_ptr and friends for unsized T Relaxes `impl<T> Weak<T>` to `impl<T: ?Sized> Weak<T>` for the methods `rc::Weak::as_ptr`, `into_raw`, and `from_raw`. Follow-up to rust-lang#73845, which did most of the impl work to make these functions work for `T: ?Sized`. We still have to adjust the implementation of `Weak::from_raw` here, however, because I missed a use of `ptr.is_null()` previously. This check was necessary when `into`/`from_raw` were first implemented, as `into_raw` returned `ptr::null()` for dangling weak. However, we now just (wrapping) offset dangling weaks' pointers the same as nondangling weak, so the null check is no longer necessary (or even hit). (I can submit just 17a928f as a separate PR if desired.) As a nice side effect, moves the `fn is_dangling` definition closer to `Weak::new`, which creates the dangling weak. This technically stabilizes that "something like `align_of_val_raw`" is possible to do. However, I believe the part of the functionality required by these methods here -- specifically, getting the alignment of a pointee from a pointer where it may be dangling iff the pointee is `Sized` -- is uncontroversial enough to stabilize these methods without a way to implement them on stable Rust. r? `@RalfJung,` who reviewed rust-lang#73845. ATTN: This changes (relaxes) the (input) generic bounds on stable fn!

RalfJung · 2020-12-26T22:25:54Z

src/liballoc/sync.rs

@@ -2279,13 +2292,6 @@ unsafe fn data_offset<T: ?Sized>(ptr: *const T) -> isize {
    unsafe { data_offset_align(align_of_val(&*ptr)) }


oops this line should have been align_of_val_raw now, right?

But I doubt that that's enough to fix #80365.

Yes, it definitely should have been. I don't know how I missed this one 🙃

This was missed in rust-lang#73845 when switching to use the raw operators. Fixes rust-lang#80365

Use raw version of align_of in rc data_offset This was missed in rust-lang#73845 when switching to use the raw operators. Fixes rust-lang#80365

CAD97 added 3 commits June 28, 2020 14:21

Use raw_ref_op in A|Rc::as_ptr

db539c6

Do not require ptr validity in rc::data_offset

e4bdf47

Use impl for Weak::as_ptr that works for unsized T

d8a9c61

rust-highfive assigned sfackler Jun 28, 2020

rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Jun 28, 2020

rust-highfive assigned RalfJung and unassigned sfackler Jun 28, 2020

RalfJung reviewed Jun 29, 2020

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CAD97 force-pushed the weak-as-unsized-ptr branch from dce66a3 to b581b39 Compare June 30, 2020 16:51

CAD97 added 3 commits June 30, 2020 15:01

Clarify safety comment for A|Rc::as_ptr

fc3dc72

Fix invalid pointer deref in Weak::as_ptr

0aecf3c

Clarify when rc::data_offset is safe

aed88e1

CAD97 force-pushed the weak-as-unsized-ptr branch from b581b39 to aed88e1 Compare June 30, 2020 19:03

RalfJung reviewed Jul 1, 2020

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CAD97 and others added 2 commits July 1, 2020 15:05

Apply documentation review suggestions

ac40d1e

Co-Authored-By: Ralf Jung <post@ralfj.de>

Simplify Weak::as_ptr impl

98789ac

CAD97 force-pushed the weak-as-unsized-ptr branch from 31f8489 to 98789ac Compare July 1, 2020 19:06

RalfJung reviewed Jul 1, 2020

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Reclarify safety comments in Weak::as_ptr

7498cad

RalfJung reviewed Jul 2, 2020

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Note Weak.ptr never dangles sooner

1b5ac57

CAD97 force-pushed the weak-as-unsized-ptr branch from 0db0dcb to 1b5ac57 Compare July 2, 2020 21:08

bors added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Jul 3, 2020

bors 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 Jul 3, 2020

pietroalbini mentioned this pull request Jul 3, 2020

Failed to clone the index on CI #73992

Closed

Manishearth mentioned this pull request Jul 4, 2020

Rollup of 12 pull requests #74019

Merged

bors merged commit 9a659c5 into rust-lang:master Jul 4, 2020

CAD97 deleted the weak-as-unsized-ptr branch July 4, 2020 05:02

CAD97 added a commit to CAD97/rust that referenced this pull request Jul 4, 2020

Relax bounds of rc::Weak::as_ptr and friends

207c52d

....to allow use with unsized T. This is a follow-up to rust-lang#73845, which did the impl work required to be able to relax these bounds.

CAD97 mentioned this pull request Jul 4, 2020

?Sized bounds for rc::Weak::as_ptr and friends #74022

Closed

RalfJung mentioned this pull request Jul 8, 2020

Support T: ?Sized in Weak::new() #50513

Closed

CAD97 mentioned this pull request Jul 8, 2020

Allow Weak::as_ptr and friends for unsized T #74160

Merged

RalfJung mentioned this pull request Jul 11, 2020

Tracking issue for RFC 2582, &raw [mut | const] $place (raw_ref_op) #64490

Closed

3 tasks

RalfJung mentioned this pull request Jul 27, 2020

Tracking Issue for raw_ref_macros #73394

Closed

3 tasks

SNCPlay42 mentioned this pull request Dec 25, 2020

UB inside Weak::as_ptr #80365

Closed

RalfJung reviewed Dec 26, 2020

View reviewed changes

CAD97 mentioned this pull request Dec 26, 2020

Use raw version of align_of in rc data_offset #80398

Merged

CAD97 added a commit to CAD97/rust that referenced this pull request Dec 26, 2020

Use raw version of align_of in rc data_offset

eeed311

This was missed in rust-lang#73845 when switching to use the raw operators. Fixes rust-lang#80365

cuviper added this to the 1.46 milestone May 2, 2024

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Use &raw in A|Rc::as_ptr #73845

Use &raw in A|Rc::as_ptr #73845

CAD97 commented Jun 28, 2020

rust-highfive commented Jun 28, 2020

sfackler commented Jun 28, 2020

CAD97 commented Jun 30, 2020 •

edited

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RalfJung commented Jul 3, 2020

bors commented Jul 3, 2020

RalfJung commented Jul 3, 2020

RalfJung commented Jul 3, 2020

pietroalbini commented Jul 3, 2020

RalfJung Dec 26, 2020

CAD97 Dec 26, 2020

		@@ -2279,13 +2292,6 @@ unsafe fn data_offset<T: ?Sized>(ptr: *const T) -> isize {
		unsafe { data_offset_align(align_of_val(&*ptr)) }

Use &raw in A|Rc::as_ptr #73845

Use &raw in A|Rc::as_ptr #73845

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CAD97 commented Jun 28, 2020

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CAD97 commented Jun 30, 2020 •

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