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

Frederik Deweerdt
2006-12-20T20:44:06Z

On Wed, Dec 20, 2006 at 11:21:50AM -0800, Jeremy Fitzhardinge wrote:
> Frederik Deweerdt wrote:
> > 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.
> >
>
> Thanks Frederik; that's exactly the kind of thing I thought it might
> be. I wonder if there's some way we can make this more robust
> though... Does this work for you? I did a slightly larger cleanup
> which should make it less fragile and more comprehensible.
>
It works too, thanks. BTW, I wondered if the "case GS:" in getreg() made
sense now?

Frederik
> J
>
> diff -r e775f6e42258 arch/i386/kernel/ptrace.c
> --- a/arch/i386/kernel/ptrace.c Tue Dec 19 10:32:40 2006 -0800
> +++ b/arch/i386/kernel/ptrace.c Wed Dec 20 11:18:56 2006 -0800
> @@ -45,7 +45,7 @@
> /*
> * Offset of eflags on child stack..
> */
> -#define EFL_OFFSET ((EFL-2)*4-sizeof(struct pt_regs))
> +#define EFL_OFFSET offsetof(struct pt_regs, eflags)
>
> static inline struct pt_regs *get_child_regs(struct task_struct *task)
> {
> @@ -54,24 +54,24 @@ static inline struct pt_regs *get_child_
> }
>
> /*
> - * this routine will get a word off of the processes privileged stack.
> - * the offset is how far from the base addr as stored in the TSS.
> - * this routine assumes that all the privileged stacks are in our
> + * This routine will get a word off of the processes privileged stack.
> + * the offset is bytes into the pt_regs structure on the stack.
> + * This routine assumes that all the privileged stacks are in our
> * data space.
> */
> static inline int get_stack_long(struct task_struct *task, int offset)
> {
> unsigned char *stack;
>
> - stack = (unsigned char *)task->thread.esp0;
> + stack = (unsigned char *)task->thread.esp0 - sizeof(struct pt_regs);
> stack += offset;
> return (*((int *)stack));
> }
>
> /*
> - * this routine will put a word on the processes privileged stack.
> - * the offset is how far from the base addr as stored in the TSS.
> - * this routine assumes that all the privileged stacks are in our
> + * This routine will put a word on the processes privileged stack.
> + * the offset is bytes into the pt_regs structure on the stack.
> + * This routine assumes that all the privileged stacks are in our
> * data space.
> */
> static inline int put_stack_long(struct task_struct *task, int offset,
> @@ -79,7 +79,7 @@ static inline int put_stack_long(struct
> {
> unsigned char * stack;
>
> - stack = (unsigned char *) task->thread.esp0;
> + stack = (unsigned char *)task->thread.esp0 - sizeof(struct pt_regs);
> stack += offset;
> *(unsigned long *) stack = data;
> return 0;
> @@ -114,7 +114,7 @@ static int putreg(struct task_struct *ch
> }
> if (regno > ES*4)
> regno -= 1*4;
> - put_stack_long(child, regno - sizeof(struct pt_regs), value);
> + put_stack_long(child, regno, value);
> return 0;
> }
>
> @@ -137,7 +137,6 @@ static unsigned long getreg(struct task_
> default:
> if (regno > ES*4)
> regno -= 1*4;
> - regno = regno - sizeof(struct pt_regs);
> retval &= get_stack_long(child, regno);
> }
> return retval;
>
> -
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