linux-kernel - RE: [PATCH] sparc: make copy

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Message-ID: <05247c8b0e31420a9e6e7a43831212ff@AcuMS.aculab.com>
Date:   Thu, 18 Feb 2021 15:28:35 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     "'Dmitry V. Levin'" <ldv@...linux.org>,
        "David S. Miller" <davem@...emloft.net>
CC:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        Alexey Gladkov <gladkov.alexey@...il.com>,
        Gleb Fotengauer-Malinovskiy <glebfm@...linux.org>,
        Anatoly Pugachev <matorola@...il.com>,
        "sparclinux@...r.kernel.org" <sparclinux@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] sparc: make copy_thread honor pid namespaces

From: Dmitry V. Levin
> Sent: 17 February 2021 08:00
> 
> On sparc, fork and clone syscalls have an unusual semantics of
> returning the pid of the parent process to the child process.

Isn't that just broken?
The application expects fork() to return 0 in the child.
libc would have to do horrid things to convert the result.

It could be comparing against the saved 'current pid' in
order to save a system call for the first ppid() call.
But that isn't ever going to work if it is possible to
create a child in a different pid namespace.

FWIW the test program ought to use syscall() to get the pid
and ppid - rather than relying on any optimisations in libc.

	David

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