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

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Message-ID: <51EF78BB.8000503@monstr.eu>
Date:	Wed, 24 Jul 2013 08:48:27 +0200
From:	Michal Simek <monstr@...str.eu>
To:	Rich Felker <dalias@...ifal.cx>
CC:	Michal Simek <michal.simek@...inx.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	James Hogan <james.hogan@...tec.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	linux-kernel@...r.kernel.org, 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>,
	Kees Cook <keescook@...omium.org>
Subject: Re: [microblaze-linux] [RESEND PATCH] microblaze: Fix clone syscall

Hi Rich,

On 07/24/2013 07:55 AM, Rich Felker wrote:
> On Wed, Jul 24, 2013 at 07:34:07AM +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
> 
> I believe this also affects us in musl. What is the motivation for
> making a configure option that results in there being two incompatible
> syscall ABIs for the same arch?
> This sounds like a really bad idea...

This patch fixes bug which was introduced by Al's patch where he moved
clone implementation from microblaze folder to generic location.
It means I am not creating two incompatible syscalls ABIs but fixing
broken one.

> And how was glibc successfuly using a form that mismatched the
> existing kernel? Did nobody ever use/test it?

We are running LTP syscall tests and there is not LTP test which
was able to find out this mismatch in clone. That's why I haven't
figure it out at that time and ACKed that origin patch.

In my email you can see that I have also asked about tools which should be used
for kernel API testing.

> I think the broken
> userspace software that was already failing to work due to this
> mismatch should simply be fixed rather than adding incompatible kernel
> ABI variants.

The incompatibility is between glibc register setup and the kernel sys_clone
register expectation which doesn't match right now.

Thanks,
Michal



-- 
Michal Simek, Ing. (M.Eng), OpenPGP -> KeyID: FE3D1F91
w: www.monstr.eu p: +42-0-721842854
Maintainer of Linux kernel - Microblaze cpu - http://www.monstr.eu/fdt/
Maintainer of Linux kernel - Xilinx Zynq ARM architecture
Microblaze U-BOOT custodian and responsible for u-boot arm zynq platform



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