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@xxxxxxxxx> 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@xxxxxxxxx>

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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