linux-kernel - Re: [GIT PULL] pidfd updates

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Message-ID: <CAHk-=whdwStxVMiqQAKMJdYEF+mrxgqxvj1rFgbRw-9Rptavsg@mail.gmail.com>
Date:   Fri, 28 Apr 2023 11:26:39 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     David Laight <David.Laight@...lab.com>
Cc:     Christian Brauner <brauner@...nel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [GIT PULL] pidfd updates

On Fri, Apr 28, 2023 at 1:40 AM David Laight <David.Laight@...lab.com> wrote:
>
> It is definitely architecture dependant.
> x86-64 and arm-64 will return two 64bit values in registers.
> x86-32 and arm-32 return two 32bit values on stack.

Yes, but I think the "return value in two registers" is the generic
thing. At least gcc has very special code to deal with a two-register
return value.

And yes, those registers will then obviously be different sizes on
different architectures, but a tuple like a '(ptr,fd)' thing will fit
regardless.

We very much do depend on this kind of pattern generating reasonable
code in some parts of the kernel.

               Linus