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]

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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