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

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Message-Id: <200909111312.27497.arnd@arndb.de>
Date:	Fri, 11 Sep 2009 13:12:27 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Louis Rilling <Louis.Rilling@...labs.com>
Cc:	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>,
	Containers <containers@...ts.linux-foundation.org>,
	Nathan Lynch <nathanl@...tin.ibm.com>,
	linux-kernel@...r.kernel.org,
	"Eric W. Biederman" <ebiederm@...ssion.com>, hpa@...or.com,
	mingo@...e.hu, torvalds@...ux-foundation.org,
	Alexey Dobriyan <adobriyan@...il.com>,
	Pavel Emelyanov <xemul@...nvz.org>
Subject: Re: [RFC][v6][PATCH 8/9]: Define clone_with_pids() syscall

On Friday 11 September 2009, Louis Rilling wrote:
> On 11/09/09 12:31 +0200, Arnd Bergmann wrote:
> > 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.
> 
> AFAICS clone() actually needs all registers (see x86 copy_thread() for
> instance). Any variant of clone() will have this requirement.

Right, but that part (do_fork) is already handled in common code, which
function calls into architecture specific code.

The point I was making is that the sys_clone() and sys_clone_with_pids()
functions themselves only access the argument registers, the stack
pointer and pass those down to do_fork, along with pt_regs.

	Arnd <><
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