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

Andrew J. Barr
2006-12-20T19:02:22Z

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@gmail.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@gmail.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)
> {