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

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Message-ID: <20250222084112.23eb2856@pumpkin>
Date: Sat, 22 Feb 2025 08:41:12 +0000
From: David Laight <david.laight.linux@...il.com>
To: Willy Tarreau <w@....eu>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>, Jan Engelhardt
 <ej@...i.de>, "H. Peter Anvin" <hpa@...or.com>, Greg KH
 <gregkh@...uxfoundation.org>, Boqun Feng <boqun.feng@...il.com>, Miguel
 Ojeda <miguel.ojeda.sandonis@...il.com>, Christoph Hellwig
 <hch@...radead.org>, rust-for-linux <rust-for-linux@...r.kernel.org>, David
 Airlie <airlied@...il.com>, linux-kernel@...r.kernel.org,
 ksummit@...ts.linux.dev
Subject: Re: C aggregate passing (Rust kernel policy)

On Sat, 22 Feb 2025 07:37:30 +0100
Willy Tarreau <w@....eu> wrote:

...
> Update: I found in my code a comment suggesting that it works when using
> -freg-struct (which is in fact -freg-struct-return) which works both on
> i386 and ARM.

The problem is that you need it to be an __attribute__(()) so it can
be per-function without breaking ABI.

> I just didn't remember about this and couldn't find it when
> looking at gcc docs.

I can never find anything in there either.
And then I wish they say when it was introduced.

	David