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    SubjectRe: [-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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    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)
    > {
    -
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