linux-kernel - Re: [RFC][v7][PATCH 8/9]: Define clone2() syscall

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Date:	Wed, 30 Sep 2009 19:59:40 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Arjan van de Ven <arjan@...radead.org>,
	Roland McGrath <roland@...hat.com>,
	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>, mingo@...e.hu,
	Alexey Dobriyan <adobriyan@...il.com>,
	Pavel Emelyanov <xemul@...nvz.org>, linux-api@...r.kernel.org,
	kosaki.motohiro@...fujitsu.com
Subject: Re: [RFC][v7][PATCH 8/9]: Define clone2() syscall

On Wednesday 30 September 2009, Linus Torvalds wrote:
> Umm. I don't think that is possible.
> 
> You need architecture-specific code to even get access to all registers to 
> copy and get a signal-handler-compatible stack frame. See for example 
> arch/alpha/kernel/entry.S with the switch-stack thing etc.  I don't think 
> there is any way to make that even remotely architecture-neutral.

Right, you still need to save all the registers from the entry code.
I was under the wrong assumption that task_pt_regs(current)
would give the full register set on all architectures.

However, I'd still hope that a new system call can be defined in
a way that you only need to have an assembly wrapper to save
the full pt_regs, but no arch specific code to get the syscall arguments
out of that again. In do_clone(), you need a pointer to pt_regs and
the user stack pointer, but that can be generated from
user_stack_pointer(regs).

Does task_pt_regs(current) give the right pointer on all architectures
or do we also need to pass the regs into the syscall?

	Arnd <><
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