linux-kernel - Re: [microblaze-linux] [RESEND PATCH v2] microblaze: Fix clone syscall

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Date:	Mon, 29 Jul 2013 02:41:08 -0400
From:	Rich Felker <dalias@...ifal.cx>
To:	Michal Simek <michal.simek@...inx.com>
Cc:	linux-kernel@...r.kernel.org, James Hogan <james.hogan@...tec.com>,
	Kees Cook <keescook@...omium.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Oleg Nesterov <oleg@...hat.com>, dholsgrove@...inx.com,
	Al Viro <viro@...IV.linux.org.uk>,
	microblaze-uclinux@...e.uq.edu.au,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [microblaze-linux] [RESEND PATCH v2] microblaze: Fix clone
 syscall

On Mon, Jul 29, 2013 at 08:22:56AM +0200, Michal Simek wrote:
> Microblaze was assign to CLONE_BACKWARDS type where
> parent tid was passed via 3rd argument.
> Microblaze glibc is using 4th argument for it.
> 
> Create new CLONE_BACKWARDS3 type where stack_size is passed
> via 3rd argument, parent thread id pointer via 4th,
> child thread id pointer via 5th and tls value as 6th
> argument
> 
> Inconsistency was introduced by this patch:
> "microblaze: switch to generic fork/vfork/clone"
> (sha1: f3268edbe6fe0ce56e62c6d6b14640aeb04864b7)

I still don't think this is clear. I would suggest language like:

==
Fix inadvertent breakage in the clone syscall ABI for Microblaze
that was introduced in this patch:

    "microblaze: switch to generic fork/vfork/clone"
    (sha1: f3268edbe6fe0ce56e62c6d6b14640aeb04864b7)

The Microblaze syscall ABI for clone takes the parent tid address in
the 4th argument; the third argument slot is used for the stack size.
The incorrectly-used CLONE_BACKWARDS type assigned parent tid to the
3rd slot.

This commit restores the original ABI so that existing userspace libc
code will work correctly.
==

And maybe add something about which versions were affected by the
breakage.

Rich
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