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Subject[Patch 1/2] Improvements and minor fixes to HW Breakpoint interface
This patch brings a couple of changes to the HW Breakpoint infrastructure:

- Set/clear TIF_DEBUG task flag in <un>register_user_hw_breakpoint()
instead of being done by users of this interface (such as ptrace).

- Modify return code of hw_breakpoint_handler() to NOTIFY_STOP if
triggered due to lazy debug register switching.

Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
---
arch/x86/kernel/hw_breakpoint.c | 4 +++-
arch/x86/kernel/ptrace.c | 4 +---
kernel/hw_breakpoint.c | 16 +++++++++++++---
3 files changed, 17 insertions(+), 7 deletions(-)
Index: linux-2.6-tip.hbkpt/arch/x86/kernel/hw_breakpoint.c
===================================================================
--- linux-2.6-tip.hbkpt.orig/arch/x86/kernel/hw_breakpoint.c
+++ linux-2.6-tip.hbkpt/arch/x86/kernel/hw_breakpoint.c
@@ -346,8 +346,10 @@ 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);
/*
Index: linux-2.6-tip.hbkpt/arch/x86/kernel/ptrace.c
===================================================================
--- linux-2.6-tip.hbkpt.orig/arch/x86/kernel/ptrace.c
+++ linux-2.6-tip.hbkpt/arch/x86/kernel/ptrace.c
@@ -530,9 +530,7 @@ restore:
bp->info.len = len;
bp->info.type = type;
rc = register_user_hw_breakpoint(tsk, bp);
- if (!rc)
- set_tsk_thread_flag(tsk, TIF_DEBUG);
- else
+ if (rc)
kfree(bp);
}
} else
Index: linux-2.6-tip.hbkpt/kernel/hw_breakpoint.c
===================================================================
--- linux-2.6-tip.hbkpt.orig/kernel/hw_breakpoint.c
+++ linux-2.6-tip.hbkpt/kernel/hw_breakpoint.c
@@ -233,6 +233,8 @@ int register_user_hw_breakpoint(struct t
break;
}
}
+ if (!rc)
+ set_tsk_thread_flag(tsk, TIF_DEBUG);

spin_unlock_bh(&hw_breakpoint_lock);
return rc;
@@ -272,15 +274,23 @@ void unregister_user_hw_breakpoint(struc
struct hw_breakpoint *bp)
{
struct thread_struct *thread = &(tsk->thread);
- int i;
+ int i, pos = -1, clear_tsk_debug_counter = 0;

spin_lock_bh(&hw_breakpoint_lock);
for (i = 0; i < hbp_kernel_pos; i++) {
+ if (thread->hbp[i])
+ clear_tsk_debug_counter++;
if (bp == thread->hbp[i]) {
- __unregister_user_hw_breakpoint(i, tsk);
- break;
+ clear_tsk_debug_counter--;
+ pos = i;
}
}
+ if (pos >= 0)
+ __unregister_user_hw_breakpoint(pos, tsk);
+
+ if (!clear_tsk_debug_counter)
+ clear_tsk_thread_flag(tsk, TIF_DEBUG);
+
spin_unlock_bh(&hw_breakpoint_lock);
}
EXPORT_SYMBOL_GPL(unregister_user_hw_breakpoint);


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