linux-kernel - Re: [WIP 0/3] Memory model and atomic API in Rust

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Date: Wed, 27 Mar 2024 15:02:41 -0700
From: comex <comexk@...il.com>
To: Boqun Feng <boqun.feng@...il.com>
Cc: Kent Overstreet <kent.overstreet@...ux.dev>,
 Linus Torvalds <torvalds@...ux-foundation.org>,
 "Dr. David Alan Gilbert" <dave@...blig.org>,
 Philipp Stanner <pstanner@...hat.com>,
 rust-for-linux <rust-for-linux@...r.kernel.org>,
 linux-kernel@...r.kernel.org,
 linux-arch@...r.kernel.org,
 llvm@...ts.linux.dev,
 Miguel Ojeda <ojeda@...nel.org>,
 Alex Gaynor <alex.gaynor@...il.com>,
 Wedson Almeida Filho <wedsonaf@...il.com>,
 Gary Guo <gary@...yguo.net>,
 Björn Roy Baron <bjorn3_gh@...tonmail.com>,
 Benno Lossin <benno.lossin@...ton.me>,
 Andreas Hindborg <a.hindborg@...sung.com>,
 Alice Ryhl <aliceryhl@...gle.com>,
 Alan Stern <stern@...land.harvard.edu>,
 Andrea Parri <parri.andrea@...il.com>,
 Will Deacon <will@...nel.org>,
 Peter Zijlstra <peterz@...radead.org>,
 Nicholas Piggin <npiggin@...il.com>,
 David Howells <dhowells@...hat.com>,
 Jade Alglave <j.alglave@....ac.uk>,
 Luc Maranget <luc.maranget@...ia.fr>,
 "Paul E. McKenney" <paulmck@...nel.org>,
 Akira Yokosawa <akiyks@...il.com>,
 Daniel Lustig <dlustig@...dia.com>,
 Joel Fernandes <joel@...lfernandes.org>,
 Nathan Chancellor <nathan@...nel.org>,
 Nick Desaulniers <ndesaulniers@...gle.com>,
 kent.overstreet@...il.com,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Marco Elver <elver@...gle.com>,
 Mark Rutland <mark.rutland@....com>,
 Thomas Gleixner <tglx@...utronix.de>,
 Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>,
 Dave Hansen <dave.hansen@...ux.intel.com>,
 x86@...nel.org,
 "H. Peter Anvin" <hpa@...or.com>,
 Catalin Marinas <catalin.marinas@....com>,
 linux-arm-kernel@...ts.infradead.org,
 linux-fsdevel@...r.kernel.org
Subject: Re: [WIP 0/3] Memory model and atomic API in Rust

> On Mar 27, 2024, at 2:56 PM, comex <comexk@...il.com> wrote:
> 
> Right.  When I said “strict aliasing” I meant type-based aliasing rules, which is what GCC calls “strict aliasing".  But Rust does have stricter aliasing rules than C in a different way.  Both mutable and immutable references are annotated with LLVM `noalias` by default, equivalent to C `restrict`.

…oops, this should say “reference-typed function parameters”.

> On Mar 27, 2024, at 2:49 PM, Kent Overstreet <kent.overstreet@...ux.dev> wrote:
> 
> That's not really a workable rule because in practice every data
> structure has unsafe Rust underneath. Strict aliasing would mean that
> unsafe Rust very much has to follow the aliasing rules too.

There have indeed been a lot of issues where some innocent-seeming piece of unsafe Rust turns out to violate the reference aliasing rules.  Miri helps (it’s a tool that can detect violations at runtime), and there have been attempts to loosen the rules where possible.  But it is definitely a case where Rust’s UB rules are more subtle than one would like.  At least it only applies to unsafe code.