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

Jeremy Fitzhardinge
2006-12-20T19:22:28Z

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.

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;