const-eval: make misalignment a hard error #115524

RalfJung · 2023-09-04T07:26:33Z

It's been a future-incompat error (showing up in cargo's reports) since #104616, Rust 1.68, released in March. That should be long enough.

The question for the lang team is simply -- should we move ahead with this, making const-eval alignment failures a hard error? (It turns out some of them accidentally already were hard errors since #104616. But not all so this is still a breaking change. Crater found no regression.)

rustbot · 2023-09-04T07:26:38Z

r? @wesleywiser

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rustbot · 2023-09-04T07:26:41Z

Some changes occurred to the CTFE / Miri engine

cc @rust-lang/miri

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

The Miri subtree was changed

cc @rust-lang/miri

RalfJung · 2023-09-04T07:33:02Z

tests/ui/consts/const-eval/raw-pointer-ub.rs

+    let ptr = mem.as_ptr().byte_add(1);
+    let _val = *ptr; //~ERROR: evaluation of constant value failed
+    //~^NOTE: accessing memory with alignment 1, but alignment 4 is required
+};


Strangely this test is already a hard error on nightly... https://play.rust-lang.org/?version=nightly&mode=debug&edition=2021&gist=24a9a0f6ecadb7064178b092b4fab1a6

Ah, here's why:

rust/compiler/rustc_const_eval/src/interpret/place.rs

Lines 474 to 476 in 3ec4b3b

let align =

if M::enforce_alignment(self).should_check() { mplace.align } else { Align::ONE };

self.check_ptr_access_align(mplace.ptr, size, align, CheckInAllocMsg::DerefTest)?;

check_ptr_access_align will always check alignment, so this entirely circumvented the future-incompat machinery.

compiler/rustc_const_eval/src/const_eval/machine.rs

oli-obk · 2023-09-04T08:39:20Z

Should we crater it again just for impact analysis?

RalfJung · 2023-09-04T08:53:21Z

I don't even know of an example where this is a breaking change... So crater seems unnecessary to me.

RalfJung · 2023-09-04T09:09:30Z

This is a kind of funny FCP since it turns out the breaking change accidentally happened in #104616, we're now just removing some dead code.^^

oli-obk · 2023-09-04T09:09:56Z

r=me on the impl.

Nominating for T-lang team discussion. Don't know if you want to FCP this, as it's already in line with the const UB RFC (if your code exhibits UB at compile-time, but passes, we are allowed to break it later)

RalfJung · 2023-09-04T09:10:31Z

I'd say let's nominate, and then T-lang can decide if they want an FCP or not.

compiler/rustc_lint_defs/src/builtin.rs

RalfJung · 2023-09-04T13:40:05Z

Ah, the lint docs actually have an example of code that did trigger the lint. So this is a breaking change after all.

RalfJung · 2023-09-04T13:45:45Z

@bors try

bors · 2023-09-04T13:45:54Z

⌛ Trying commit 70db9968a8d128fde5d2fb656c7b4a62cf3c92be with merge bbf68c7b2a40f9417a5515b471f1ff6e35782bca...

bors · 2023-09-04T13:47:20Z

💔 Test failed - checks-actions

RalfJung · 2023-09-04T13:51:13Z

All jobs are failing with Error: Can't use 'tar -xzf' extract archive file: /home/runner/work/_actions/_temp_4fa9e092-7404-456e-a7a7-7f3b4643ea20/643dcc28-3f26-4cc7-ad85-3ef6e4c709eb.tar.gz. return code: 2, not just this PR.

don't UB on dangling ptr deref, instead check inbounds on projections This implements rust-lang/reference#1387 in Miri. See that PR for what the change is about. Detecting dangling references in `let x = &...;` is now done by validity checking only, so some tests need to have validity checking enabled. There is no longer inherently a "nodangle" check in evaluating the expression `&*ptr` (aside from the aliasing model). r? `@oli-obk` Blocked on: - rust-lang/reference#1387 - rust-lang#115524

RalfJung · 2023-09-29T08:26:26Z

@joshtriplett @pnkfelix @scottmcm friendly reminder that there's a checkbox waiting for you here. :)

rfcbot · 2023-10-03T18:18:52Z

🔔 This is now entering its final comment period, as per the review above. 🔔

traviscross · 2023-10-10T19:22:45Z

@rustbot labels -S-waiting-on-team

rfcbot · 2023-10-13T18:19:02Z

The final comment period, with a disposition to merge, as per the review above, is now complete.

As the automated representative of the governance process, I would like to thank the author for their work and everyone else who contributed.

This will be merged soon.

RalfJung · 2023-10-13T21:47:51Z

@bors r=wesleywiser

bors · 2023-10-13T21:47:53Z

📌 Commit bd33846 has been approved by wesleywiser

It is now in the queue for this repository.

bors · 2023-10-14T00:57:12Z

⌛ Testing commit bd33846 with merge 75a5dd0...

bors · 2023-10-14T02:44:12Z

☀️ Test successful - checks-actions
Approved by: wesleywiser
Pushing 75a5dd0 to master...

rust-timer · 2023-10-14T04:20:36Z

Finished benchmarking commit (75a5dd0): comparison URL.

Overall result: ❌ regressions - no action needed

@rustbot label: -perf-regression

Instruction count

This is a highly reliable metric that was used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	0.3%	[0.3%, 0.3%]	3
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	1.4%	[1.1%, 1.5%]	3
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	1.4%	[1.1%, 1.5%]	3

Cycles

This benchmark run did not return any relevant results for this metric.

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 627.259s -> 628.136s (0.14%)
Artifact size: 271.34 MiB -> 271.27 MiB (-0.02%)

don't UB on dangling ptr deref, instead check inbounds on projections This implements rust-lang/reference#1387 in Miri. See that PR for what the change is about. Detecting dangling references in `let x = &...;` is now done by validity checking only, so some tests need to have validity checking enabled. There is no longer inherently a "nodangle" check in evaluating the expression `&*ptr` (aside from the aliasing model). r? `@oli-obk` Based on: - rust-lang/reference#1387 - rust-lang#115524

don't UB on dangling ptr deref, instead check inbounds on projections This implements rust-lang/reference#1387 in Miri. See that PR for what the change is about. Detecting dangling references in `let x = &...;` is now done by validity checking only, so some tests need to have validity checking enabled. There is no longer inherently a "nodangle" check in evaluating the expression `&*ptr` (aside from the aliasing model). r? `@oli-obk` Based on: - rust-lang/reference#1387 - rust-lang/rust#115524

Pkgsrc changes: * Adjust patches and cargo checksums to new versions. * For an external LLVM, set dependency of llvm >= 16, in accordance with the upstream changes. * Mark that on NetBSD we now need >= 9.0, so 8.x is no longer supported. * On NetBSD/sparc64 10.x, we now need GCC 12 to build the embedded LLVM, which is version 17; apparently GCC 10.4 or 10.5 mis-compiles it, resulting in an illegal instruction fault during the build. Ref. rust-lang/rust#117231 Upstream changes: Version 1.75.0 (2023-12-28) ========================== - [Stabilize `async fn` and return-position `impl Trait` in traits.] (rust-lang/rust#115822) - [Allow function pointer signatures containing `&mut T` in `const` contexts.] (rust-lang/rust#116015) - [Match `usize`/`isize` exhaustively with half-open ranges.] (rust-lang/rust#116692) - [Guarantee that `char` has the same size and alignment as `u32`.] (rust-lang/rust#116894) - [Document that the null pointer has the 0 address.] (rust-lang/rust#116988) - [Allow partially moved values in `match`.] (rust-lang/rust#103208) - [Add notes about non-compliant FP behavior on 32bit x86 targets.] (rust-lang/rust#113053) - [Stabilize ratified RISC-V target features.] (rust-lang/rust#116485) Compiler -------- - [Rework negative coherence to properly consider impls that only partly overlap.] (rust-lang/rust#112875) - [Bump `COINDUCTIVE_OVERLAP_IN_COHERENCE` to deny, and warn in dependencies.] (rust-lang/rust#116493) - [Consider alias bounds when computing liveness in NLL.] (rust-lang/rust#116733) - [Add the V (vector) extension to the `riscv64-linux-android` target spec.] (rust-lang/rust#116618) - [Automatically enable cross-crate inlining for small functions] (rust-lang/rust#116505) - Add several new tier 3 targets: - [`csky-unknown-linux-gnuabiv2hf`] (rust-lang/rust#117049) - [`i586-unknown-netbsd`] (rust-lang/rust#117170) - [`mipsel-unknown-netbsd`] (rust-lang/rust#117356) Refer to Rust's [platform support page][platform-support-doc] for more information on Rust's tiered platform support. Libraries --------- - [Override `Waker::clone_from` to avoid cloning `Waker`s unnecessarily.] (rust-lang/rust#96979) - [Implement `BufRead` for `VecDeque<u8>`.] (rust-lang/rust#110604) - [Implement `FusedIterator` for `DecodeUtf16` when the inner iterator does.] (rust-lang/rust#110729) - [Implement `Not, Bit{And,Or}{,Assign}` for IP addresses.] (rust-lang/rust#113747) - [Implement `Default` for `ExitCode`.] (rust-lang/rust#114589) - [Guarantee representation of None in NPO] (rust-lang/rust#115333) - [Document when atomic loads are guaranteed read-only.] (rust-lang/rust#115577) - [Broaden the consequences of recursive TLS initialization.] (rust-lang/rust#116172) - [Windows: Support sub-millisecond sleep.] (rust-lang/rust#116461) - [Fix generic bound of `str::SplitInclusive`'s `DoubleEndedIterator` impl] (rust-lang/rust#100806) - [Fix exit status / wait status on non-Unix `cfg(unix)` platforms.] (rust-lang/rust#115108) Stabilized APIs --------------- - [`Atomic*::from_ptr`] (https://doc.rust-lang.org/stable/core/sync/atomic/struct.AtomicUsize.html#method.from_ptr) - [`FileTimes`] (https://doc.rust-lang.org/stable/std/fs/struct.FileTimes.html) - [`FileTimesExt`] (https://doc.rust-lang.org/stable/std/os/windows/fs/trait.FileTimesExt.html) - [`File::set_modified`] (https://doc.rust-lang.org/stable/std/fs/struct.File.html#method.set_modified) - [`File::set_times`] (https://doc.rust-lang.org/stable/std/fs/struct.File.html#method.set_times) - [`IpAddr::to_canonical`] (https://doc.rust-lang.org/stable/core/net/enum.IpAddr.html#method.to_canonical) - [`Ipv6Addr::to_canonical`] (https://doc.rust-lang.org/stable/core/net/struct.Ipv6Addr.html#method.to_canonical) - [`Option::as_slice`] (https://doc.rust-lang.org/stable/core/option/enum.Option.html#method.as_slice) - [`Option::as_mut_slice`] (https://doc.rust-lang.org/stable/core/option/enum.Option.html#method.as_mut_slice) - [`pointer::byte_add`] (https://doc.rust-lang.org/stable/core/primitive.pointer.html#method.byte_add) - [`pointer::byte_offset`] (https://doc.rust-lang.org/stable/core/primitive.pointer.html#method.byte_offset) - [`pointer::byte_offset_from`] (https://doc.rust-lang.org/stable/core/primitive.pointer.html#method.byte_offset_from) - [`pointer::byte_sub`] (https://doc.rust-lang.org/stable/core/primitive.pointer.html#method.byte_sub) - [`pointer::wrapping_byte_add`] (https://doc.rust-lang.org/stable/core/primitive.pointer.html#method.wrapping_byte_add) - [`pointer::wrapping_byte_offset`] (https://doc.rust-lang.org/stable/core/primitive.pointer.html#method.wrapping_byte_offset) - [`pointer::wrapping_byte_sub`] (https://doc.rust-lang.org/stable/core/primitive.pointer.html#method.wrapping_byte_sub) These APIs are now stable in const contexts: - [`Ipv6Addr::to_ipv4_mapped`] (https://doc.rust-lang.org/stable/core/net/struct.Ipv6Addr.html#method.to_ipv4_mapped) - [`MaybeUninit::assume_init_read`] (https://doc.rust-lang.org/stable/core/mem/union.MaybeUninit.html#method.assume_init_read) - [`MaybeUninit::zeroed`] (https://doc.rust-lang.org/stable/core/mem/union.MaybeUninit.html#method.zeroed) - [`mem::discriminant`] (https://doc.rust-lang.org/stable/core/mem/fn.discriminant.html) - [`mem::zeroed`] (https://doc.rust-lang.org/stable/core/mem/fn.zeroed.html) Cargo ----- - [Add new packages to `[workspace.members]` automatically.] (rust-lang/cargo#12779) - [Allow version-less `Cargo.toml` manifests.] (rust-lang/cargo#12786) - [Make browser links out of HTML file paths.] (rust-lang/cargo#12889) Rustdoc ------- - [Accept less invalid Rust in rustdoc.] (rust-lang/rust#117450) - [Document lack of object safety on affected traits.] (rust-lang/rust#113241) - [Hide `#[repr(transparent)]` if it isn't part of the public ABI.] (rust-lang/rust#115439) - [Show enum discriminant if it is a C-like variant.] (rust-lang/rust#116142) Compatibility Notes ------------------- - [FreeBSD targets now require at least version 12.] (rust-lang/rust#114521) - [Formally demote tier 2 MIPS targets to tier 3.] (rust-lang/rust#115238) - [Make misalignment a hard error in `const` contexts.] (rust-lang/rust#115524) - [Fix detecting references to packed unsized fields.] (rust-lang/rust#115583) - [Remove support for compiler plugins.] (rust-lang/rust#116412)

rustbot assigned wesleywiser Sep 4, 2023

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Sep 4, 2023

RalfJung commented Sep 4, 2023

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RalfJung force-pushed the misalign branch from c525c8c to bb2bd82 Compare September 4, 2023 07:37

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oli-obk added T-lang Relevant to the language team, which will review and decide on the PR/issue. needs-fcp This change is insta-stable, so needs a completed FCP to proceed. and removed T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Sep 4, 2023

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rfcbot added final-comment-period In the final comment period and will be merged soon unless new substantive objections are raised. and removed proposed-final-comment-period Proposed to merge/close by relevant subteam, see T-<team> label. Will enter FCP once signed off. labels Oct 3, 2023

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bors merged commit 75a5dd0 into rust-lang:master Oct 14, 2023
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This was referenced Oct 14, 2023

Print a backtrace in const eval if interrupted #111769

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See through aggregates in GVN #116270

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RalfJung deleted the misalign branch October 14, 2023 08:16

Veykril mentioned this pull request Oct 17, 2023

Pull upstream master 2023 10 17 ferrocene/ferrocene#54

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const-eval: make misalignment a hard error #115524

const-eval: make misalignment a hard error #115524

RalfJung commented Sep 4, 2023 •

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rust-timer commented Oct 14, 2023

	let align =
	if M::enforce_alignment(self).should_check() { mplace.align } else { Align::ONE };
	self.check_ptr_access_align(mplace.ptr, size, align, CheckInAllocMsg::DerefTest)?;

const-eval: make misalignment a hard error #115524

const-eval: make misalignment a hard error #115524

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Overall result: ❌ regressions - no action needed

Instruction count

Max RSS (memory usage)

Cycles

Binary size

RalfJung commented Sep 4, 2023 •

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RalfJung commented Sep 4, 2023 •

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