lkml.org 
[lkml]   [2009]   [May]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
SubjectRe: [Patch 1/2] Improvements and minor fixes to HW Breakpoint interface
On Wed, 20 May 2009, K.Prasad wrote:

> --- linux-2.6-tip.hbkpt.orig/arch/x86/kernel/hw_breakpoint.c
> +++ linux-2.6-tip.hbkpt/arch/x86/kernel/hw_breakpoint.c
> @@ -296,6 +296,19 @@ void arch_flush_thread_hw_breakpoint(str
>
> /*
> * Handle debug exception notifications.
> + *
> + * Return value is either NOTIFY_STOP or NOTIFY_DONE as explained below.
> + *
> + * NOTIFY_DONE returned if one of the following conditions is true.
> + * i) When the causative address is from user-space and the exception
> + * is a valid one i.e. not triggered a result of lazy debug register
--------------------^----^ missing ',' characters
---------------------------------------^ missing "as"

> + * switching
> + * ii) When there are more bits than trap<n> set in DR6 register (such
> + * as BD, BS or BT) indicating that more than one debug condition is
> + * met and requires some more action in do_debug().
> + *
> + * NOTIFY_STOP returned for all other cases
> + *
> */
> int __kprobes hw_breakpoint_handler(struct die_args *args)
> {
> @@ -346,8 +359,10 @@ int __kprobes hw_breakpoint_handler(stru
> * or due to the delay between updates of hbp_kernel_pos
> * and this_hbp_kernel.
> */
> - if (!bp)
> + if (!bp) {
> + rc = NOTIFY_STOP;
> continue;
> + }
>
> (bp->triggered)(bp, args->regs);

This is the same mistake as before. If rc had previously been set to
NOTIFY_DONE then you will unconditionally change it back to
NOTIFY_STOP. You should make the code do what the comment says, set rc
to NOTIFY_DONE when a non-NULL user breakpoint occurs:

if (i >= hbp_kernel_pos) {
bp = per_cpu(this_hbp_kernel[i], cpu);
} else {
bp = current->thread.hbp[i];
if (bp)
rc = NOTIFY_DONE;
}
/*
* bp can be NULL due to lazy debug register switching
* or due to the delay between updates of hbp_kernel_pos
* and this_hbp_kernel.
*/
if (!bp)
continue;

(bp->triggered)(bp, args->regs);


The rest of the changes are okay.

Alan Stern



\
 
 \ /
  Last update: 2009-05-20 16:07    [W:0.094 / U:0.032 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site