linux-kernel - Re: C aggregate passing (Rust kernel policy)

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Message-ID: <rps5yviwyghhalaqmib3seqj62efzweixiqwb5wglzor4gk75n@oxki5lhsvhrf>
Date: Thu, 27 Feb 2025 15:22:20 -0500
From: Kent Overstreet <kent.overstreet@...ux.dev>
To: Ralf Jung <post@...fj.de>
Cc: Ventura Jack <venturajack85@...il.com>, 
	Miguel Ojeda <miguel.ojeda.sandonis@...il.com>, Gary Guo <gary@...yguo.net>, torvalds@...ux-foundation.org, 
	airlied@...il.com, boqun.feng@...il.com, david.laight.linux@...il.com, ej@...i.de, 
	gregkh@...uxfoundation.org, hch@...radead.org, hpa@...or.com, ksummit@...ts.linux.dev, 
	linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org
Subject: Re: C aggregate passing (Rust kernel policy)

On Thu, Feb 27, 2025 at 08:45:09PM +0100, Ralf Jung wrote:
> Hi,
> 
> > > > If C was willing to break code as much as Rust, it would be easier to
> > > > clean up C.
> > > 
> > > Is that true? Gcc updates do break code.
> > 
> > Surely not as much as Rust, right? From what I hear from users
> > of Rust and of C, some Rust developers complain about
> > Rust breaking a lot and being unstable, while I instead
> > hear complaints about C and C++ being unwilling to break
> > compatibility.
> 
> Stable Rust code hardly ever breaks on a compiler update. I don't know which
> users you are talking about here, and it's hard to reply anything concrete
> to such a vague claim that you are making here. I also "hear" lots of
> things, but we shouldn't treat hear-say as facts.
> *Nightly* Rust features do break regularly, but nobody has any right to
> complain about that -- nightly Rust is the playground for experimenting with
> features that we know are no ready yet.

It's also less important to avoid ever breaking working code than it was
20 years ago: more of the code we care about is open source, everyone is
using source control, and with so much code on crates.io it's now
possible to check what the potential impact would be.

This is a good thing as long as it's done judiciously, to evolve the
language towards stronger semantics and fix safety issues in the
cleanest way when found.