linux-kernel - Re: [RFC][v6][PATCH 8/9]: Define clone_with

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Date:	Fri, 11 Sep 2009 12:31:29 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, Oren Laadan <orenl@...columbia.edu>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Pavel Emelyanov <xemul@...nvz.org>,
	Andrew Morton <akpm@...l.org>, torvalds@...ux-foundation.org,
	mikew@...gle.com, mingo@...e.hu, hpa@...or.com,
	Nathan Lynch <nathanl@...tin.ibm.com>,
	Containers <containers@...ts.linux-foundation.org>,
	sukadev@...ibm.com
Subject: Re: [RFC][v6][PATCH 8/9]: Define clone_with_pids() syscall

On Thursday 10 September 2009, Sukadev Bhattiprolu wrote:
> Since this is a variant of clone() and clone is listed as a PTREGSCALL(),
> I pass in the pt_regs.
> 
> arch/x86/kernel/entry_32.S lists clone() under this comment:
> 
> /*
>  * System calls that need a pt_regs pointer.
>  */
> 
> Is there a guideline on what system calls use/need pt_regs ?

You need pt_regs if you access any registers from the user task
other than the argument registers. In case of clone(), this is
the user stack pointer.

The user_stack_pointer() function is relatively new, before this
you couldn't get the stack pointer out of pt_regs in a generic
way.

	Arnd <><
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