linux-kernel - Re: [PATCH] x86-64: remove unnecessary ptregs call stubs

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Date:	Thu, 19 Jun 2008 15:32:22 +0100
From:	"Jan Beulich" <jbeulich@...ell.com>
To:	"Ingo Molnar" <mingo@...e.hu>, "Andi Kleen" <andi@...stfloor.org>
Cc:	"the arch/x86 maintainers" <x86@...nel.org>, <tglx@...utronix.de>,
	<linux-kernel@...r.kernel.org>, <hpa@...or.com>
Subject: Re: [PATCH] x86-64: remove unnecessary ptregs call stubs

>>> Andi Kleen <andi@...stfloor.org> 19.06.08 14:50 >>>
>Ingo Molnar wrote:
>> * Jan Beulich <jbeulich@...ell.com> wrote:
>> 
>>> A few of the ptregs call stubs are superfluous these days - the called 
>>> functions don't have a trailing 'struct pt_regs *' parameter anymore.
>> 
>> applied to tip/x86/cleanups - thanks Jan.
>
>Just want to point out that not having a pt_regs * argument is not necessarily
>sufficient for not needing a ptregs stub. Some code also accesses ptregs directly
>through the stack top from get_thread_info() and might assume a full one. That said I *think*
>it's ok for sigsuspend et.al. as in Jan's patch, but I haven't audited the complete code paths
>in question that they never do that.
>
>Would be good to clarify that in the commit log.

Looking at both the source and disassembly of sys_rt_sigsuspend() and
sys32_sigsuspend(), I cannot see anything pt_regs related. All these
functions call are copy_from_user(), spin_lock_irq(), recalc_sigpending(),
and schedule(), and besides that they just update some global and task
state.

Jan

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