linux-kernel - Re: [PATCH] x86_64 ia32 syscall restart fix

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Message-ID: <20080229155207.GC27248@elte.hu>
Date:	Fri, 29 Feb 2008 16:52:07 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Roland McGrath <roland@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86_64 ia32 syscall restart fix


* Roland McGrath <roland@...hat.com> wrote:

> The code to restart syscalls after signals depends on checking for a 
> negative orig_ax, and for particular negative -ERESTART* values in ax. 
> These fields are 64 bits and for a 32-bit task they get zero-extended. 
> The syscall restart behavior is lost, a regression from a native 
> 32-bit kernel and from 64-bit tasks' behavior.  This patch fixes the 
> problem by doing sign-extension where it matters.  For orig_ax, the 
> only time the value should be -1 but winds up as 0x0ffffffff is via a 
> 32-bit ptrace call.  So the patch changes ptrace to sign-extend the 
> 32-bit orig_eax value when it's stored; it doesn't change the checks 
> on orig_ax, though it uses the new current_syscall() inline to better 
> document the subtle importance of the used of signedness there.  The 
> ax value is stored a lot of ways and it seems hard to get them all 
> sign-extended at their origins.  So for that, we use the 
> current_syscall_ret() to sign-extend it only for 32-bit tasks at the 
> time of the -ERESTART* comparisons.

thanks, applied.

	Ingo
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