From: Kent Overstreet <kent.overstreet@linux.dev>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: comex <comexk@gmail.com>,
"Dr. David Alan Gilbert" <dave@treblig.org>,
"Philipp Stanner" <pstanner@redhat.com>,
"Boqun Feng" <boqun.feng@gmail.com>,
rust-for-linux <rust-for-linux@vger.kernel.org>,
linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
llvm@lists.linux.dev, "Miguel Ojeda" <ojeda@kernel.org>,
"Alex Gaynor" <alex.gaynor@gmail.com>,
"Wedson Almeida Filho" <wedsonaf@gmail.com>,
"Gary Guo" <gary@garyguo.net>,
"Björn Roy Baron" <bjorn3_gh@protonmail.com>,
"Benno Lossin" <benno.lossin@proton.me>,
"Andreas Hindborg" <a.hindborg@samsung.com>,
"Alice Ryhl" <aliceryhl@google.com>,
"Alan Stern" <stern@rowland.harvard.edu>,
"Andrea Parri" <parri.andrea@gmail.com>,
"Will Deacon" <will@kernel.org>,
"Peter Zijlstra" <peterz@infradead.org>,
"Nicholas Piggin" <npiggin@gmail.com>,
"David Howells" <dhowells@redhat.com>,
"Jade Alglave" <j.alglave@ucl.ac.uk>,
"Luc Maranget" <luc.maranget@inria.fr>,
"Paul E. McKenney" <paulmck@kernel.org>,
"Akira Yokosawa" <akiyks@gmail.com>,
"Daniel Lustig" <dlustig@nvidia.com>,
"Joel Fernandes" <joel@joelfernandes.org>,
"Nathan Chancellor" <nathan@kernel.org>,
"Nick Desaulniers" <ndesaulniers@google.com>,
kent.overstreet@gmail.com,
"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
"Marco Elver" <elver@google.com>,
"Mark Rutland" <mark.rutland@arm.com>,
"Thomas Gleixner" <tglx@linutronix.de>,
"Ingo Molnar" <mingo@redhat.com>,
"Borislav Petkov" <bp@alien8.de>,
"Dave Hansen" <dave.hansen@linux.intel.com>,
x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
"Catalin Marinas" <catalin.marinas@arm.com>,
linux-arm-kernel@lists.infradead.org,
linux-fsdevel@vger.kernel.org
Subject: Re: [WIP 0/3] Memory model and atomic API in Rust
Date: Wed, 27 Mar 2024 15:41:16 -0400 [thread overview]
Message-ID: <bjorlxatlpzjlh6dfulham3u4mqsfqt7ir5wtayacaoefr2r7x@lmfcqzcobl3f> (raw)
In-Reply-To: <CAHk-=wgQy+FRKjO_BvZgZN56w6-+jDO8p-Mt=X=zM70CG=CVBQ@mail.gmail.com>
On Wed, Mar 27, 2024 at 12:07:26PM -0700, Linus Torvalds wrote:
> On Wed, 27 Mar 2024 at 11:51, Kent Overstreet <kent.overstreet@linux.dev> wrote:
> >
> > On Wed, Mar 27, 2024 at 09:16:09AM -0700, comex wrote:
> > > Meanwhile, Rust intentionally lacks strict aliasing.
> >
> > I wasn't aware of this. Given that unrestricted pointers are a real
> > impediment to compiler optimization, I thought that with Rust we were
> > finally starting to nail down a concrete enough memory model to tackle
> > this safely. But I guess not?
>
> Strict aliasing is a *horrible* mistake.
>
> It's not even *remotely* "tackle this safely". It's the exact
> opposite. It's completely broken.
>
> Anybody who thinks strict aliasing is a good idea either
>
> (a) doesn't understand what it means
>
> (b) has been brainwashed by incompetent compiler people.
>
> it's a horrendous crock that was introduced by people who thought it
> was too complicated to write out "restrict" keywords, and that thought
> that "let's break old working programs and make it harder to write new
> programs" was a good idea.
Strict aliasing is crap in C and C++ because we started out with
unrestricetd pointers, and it just doesn't work in C and C++ with the
realities of the kind of code we have to write, and we never got any
kind of a model that would have made it workable. Never mind trying to
graft that onto existing codebases...
(Restrict was crap too... no scoping, nothing but a single f*cking
keyword? Who ever thought _that_ was going to work?)
_But_: the lack of any aliasing guarantees means that writing through
any pointer can invalidate practically anything, and this is a real
problem. A lot of C programmers have stockholm syndrome when it comes to
this, we end up writing a lot of code in weirdly baroque and artificial
styles to partially work around this when we care about performance -
saving things into locals because at least the _stack_ generally can't
alias to avoid forced reloads, or passing and returning things by
reference instead of by value when that's _not the semantics we want_
because otherwise the compiler is going to do an unnecessary copy -
again, that's fundamentally because of aliasing.
next prev parent reply other threads:[~2024-03-27 19:41 UTC|newest]
Thread overview: 76+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-03-22 23:38 [WIP 0/3] Memory model and atomic API in Rust Boqun Feng
2024-03-22 23:38 ` [WIP 1/3] rust: Introduce atomic module Boqun Feng
2024-03-22 23:52 ` Andrew Lunn
2024-03-23 0:03 ` Boqun Feng
2024-03-23 19:13 ` Miguel Ojeda
2024-03-23 19:30 ` Boqun Feng
2024-03-23 9:58 ` Alice Ryhl
2024-03-23 14:10 ` Andrew Lunn
2024-03-23 19:09 ` Miguel Ojeda
2024-03-26 5:56 ` Trevor Gross
2024-03-22 23:38 ` [WIP 2/3] rust: atomic: Add ARM64 fetch_add_relaxed() Boqun Feng
2024-03-22 23:38 ` [WIP 3/3] rust: atomic: Add fetch_sub_release() Boqun Feng
2024-03-22 23:57 ` [WIP 0/3] Memory model and atomic API in Rust Kent Overstreet
2024-03-23 0:12 ` Linus Torvalds
2024-03-23 0:21 ` Kent Overstreet
2024-03-23 0:36 ` Linus Torvalds
2024-03-23 2:07 ` Kent Overstreet
2024-03-23 2:26 ` Boqun Feng
2024-03-23 2:33 ` Kent Overstreet
2024-03-23 2:57 ` Boqun Feng
2024-03-23 3:10 ` Kent Overstreet
2024-03-23 3:51 ` Boqun Feng
2024-03-23 4:16 ` Kent Overstreet
2024-03-25 13:56 ` Philipp Stanner
2024-03-25 17:44 ` Linus Torvalds
2024-03-25 18:59 ` Kent Overstreet
2024-03-25 19:44 ` Linus Torvalds
2024-03-25 21:14 ` Kent Overstreet
2024-03-25 21:37 ` Boqun Feng
2024-03-25 22:09 ` Kent Overstreet
2024-03-25 22:38 ` Boqun Feng
2024-03-25 23:02 ` Kent Overstreet
2024-03-25 23:41 ` Boqun Feng
2024-03-26 0:05 ` Dr. David Alan Gilbert
2024-03-26 0:36 ` Kent Overstreet
2024-03-26 1:35 ` Dr. David Alan Gilbert
2024-03-26 3:28 ` Kent Overstreet
2024-03-26 2:51 ` Boqun Feng
2024-03-26 3:49 ` Linus Torvalds
2024-03-26 14:35 ` Dr. David Alan Gilbert
2024-03-27 16:16 ` comex
2024-03-27 18:50 ` Kent Overstreet
2024-03-27 19:07 ` Linus Torvalds
2024-03-27 19:41 ` Kent Overstreet [this message]
2024-03-27 20:45 ` Linus Torvalds
2024-03-27 21:41 ` Kent Overstreet
2024-03-27 22:57 ` Linus Torvalds
2024-03-27 23:35 ` Kent Overstreet
2024-03-27 21:21 ` Boqun Feng
2024-03-27 21:49 ` Kent Overstreet
2024-03-27 22:26 ` Boqun Feng
2024-03-27 21:56 ` comex
2024-03-27 22:02 ` comex
2024-04-05 17:13 ` Philipp Stanner
2024-04-08 16:02 ` Matthew Wilcox
2024-04-08 16:55 ` Paul E. McKenney
2024-04-08 17:03 ` Matthew Wilcox
2024-04-08 18:47 ` Paul E. McKenney
2024-04-09 0:58 ` Kent Overstreet
2024-04-09 4:47 ` Paul E. McKenney
2024-04-08 17:01 ` Linus Torvalds
2024-04-08 18:14 ` Al Viro
2024-04-08 20:05 ` Linus Torvalds
2024-03-23 21:40 ` comex
2024-03-24 15:22 ` Alan Stern
2024-03-24 17:37 ` comex
2024-03-23 0:15 ` Boqun Feng
2024-03-23 0:49 ` Boqun Feng
2024-03-23 1:42 ` Kent Overstreet
2024-03-23 14:29 ` Andrew Lunn
2024-03-23 14:41 ` Boqun Feng
2024-03-23 14:55 ` Boqun Feng
2024-03-25 10:44 ` Mark Rutland
2024-03-25 20:59 ` Boqun Feng
2024-04-09 10:50 ` Peter Zijlstra
2024-04-16 18:12 ` Boqun Feng
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