linux-kernel - Re: [-mm patch] ptrace: Fix EFL_OFFSET value according to i386 pda changes (was Re: BUG on 2.6.20-rc1 when using gdb)

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Message-Id: <1166641335.4017.0.camel@r51.oakcourt.dyndns.org>
Date:	Wed, 20 Dec 2006 14:02:15 -0500
From:	"Andrew J. Barr" <andrew.james.barr@...il.com>
To:	Frederik Deweerdt <deweerdt@...e.fr>
Cc:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Andrew Morton <akpm@...l.org>, linux-kernel@...r.kernel.org,
	Jan Beulich <jbeulich@...ell.com>, Andi Kleen <ak@...e.de>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	walt <w41ter@...il.com>
Subject: Re: [-mm patch] ptrace: Fix EFL_OFFSET value according to i386 pda
	changes (was Re: BUG on 2.6.20-rc1 when using gdb)

On Wed, 2006-12-20 at 18:35 +0000, Frederik Deweerdt wrote:
> On Wed, Dec 20, 2006 at 03:21:53AM -0800, Jeremy Fitzhardinge wrote:
> > "walt" <w41ter@...il.com> reported a similar problem which he bisected
> > down to the PDA changeset which touches ptrace
> > (66e10a44d724f1464b5e8b5a3eae1e2cbbc2cca6).  I haven't managed to repo
> > the problem, but I guess there's something nasty going on in ptrace -
> > maybe its screwing up eflags on the stack or something.  Need to
> > double-check all the conversions from kernel<->usermode registers.  Hm,
> > wonder if its fixed with the %gs->%fs conversion patch applied?
> > 
> Hi Jeremy,
> 
> Same problems here with 2.6.20-rc1-mm1 (ie with the %gs->%fs patch).
> It seems to me that the problem comes from the EFL_OFFSET no longer
> beeing accurate.
> The following patch fixes the problem for me.

Me too. Thanks.

Andrew

> Regards,
> Frederik
> 
> Signed-off-by: Frederik Deweerdt <frederik.deweerdt@...il.com>
> 
> diff --git a/arch/i386/kernel/ptrace.c b/arch/i386/kernel/ptrace.c
> index 7f7d830..00d8a5a 100644
> --- a/arch/i386/kernel/ptrace.c
> +++ b/arch/i386/kernel/ptrace.c
> @@ -45,7 +45,7 @@
>  /*
>   * Offset of eflags on child stack..
>   */
> -#define EFL_OFFSET ((EFL-2)*4-sizeof(struct pt_regs))
> +#define EFL_OFFSET ((EFL-1)*4-sizeof(struct pt_regs))
>  
>  static inline struct pt_regs *get_child_regs(struct task_struct *task)
>  {
-
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