linux-kernel - Re: [PATCH] fix for futex_wait signal stack corruption

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Date:	Tue, 4 Dec 2007 14:43:29 -0800 (PST)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Steven Rostedt <rostedt@...dmis.org>
cc:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	David Holmes - Sun Microsystems <David.Holmes@....COM>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] fix for futex_wait signal stack corruption

On Tue, 4 Dec 2007, Steven Rostedt wrote:
> 
> Seems that arg3 is not used here and since the timer is 64 bits, we can
> store the bottom 32 bits in arg2 and the top in arg3 (this will work for
> both 32 and 64 bit archs).

Yes. That should work fine.

The restart logic sometimes results in odd calling conventions, and quite 
frankly, we could just change how "restart_block" looks too. There is 
nothing that says that it has to be

	unsigned long arg0, arg1, arg2, arg3

and that particular layout was just picked on a whim. The only issue is:

 - we don't want the restart block to be *too* large, since it's part of 
   the thread info.
 - but we need to have enough room for all the system calls that want to 
   use the restart block, and preferably in a reasonable format.

So far, using "unsigned long" has been good enough, in that it's big 
enough for a pointer and all normal arguments, but if something really 
deeply wants another format or a guaranteed 64-bit word regardless of 
architecture, we could make one or more of the arguments be "u64" instead.

But in this case, since there is already unused argument space, I think 
that doing the "32 high bits + 32 low bits" is probably the best option.

			Linus
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