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Date: Thu, 27 May 2010 16:20:44 +1000
From: Paul Mackerras <paulus@samba.org>
To: "K.Prasad" <prasad@linux.vnet.ibm.com>
Subject: Re: [Patch 3/4] PPC64-HWBKPT: Handle concurrent alignment interrupts
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On Tue, May 25, 2010 at 02:44:35PM +0530, K.Prasad wrote:

> An alignment interrupt may intervene between a DSI/hw-breakpoint exception
> and the single-step exception. Enable the alignment interrupt (through
> modifications to emulate_single_step()) to notify the single-step exception
> handler for proper restoration of hw-breakpoints.
> 
> Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
> ---
>  arch/powerpc/kernel/traps.c |    7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
> 
> Index: linux-2.6.ppc64_test/arch/powerpc/kernel/traps.c
> ===================================================================
> --- linux-2.6.ppc64_test.orig/arch/powerpc/kernel/traps.c
> +++ linux-2.6.ppc64_test/arch/powerpc/kernel/traps.c
> @@ -602,7 +602,7 @@ void RunModeException(struct pt_regs *re
>  
>  void __kprobes single_step_exception(struct pt_regs *regs)
>  {
> -	regs->msr &= ~(MSR_SE | MSR_BE);  /* Turn off 'trace' bits */
> +	clear_single_step(regs);
>  
>  	if (notify_die(DIE_SSTEP, "single_step", regs, 5,
>  					5, SIGTRAP) == NOTIFY_STOP)
> @@ -621,10 +621,7 @@ void __kprobes single_step_exception(str
>   */
>  static void emulate_single_step(struct pt_regs *regs)
>  {
> -	if (single_stepping(regs)) {
> -		clear_single_step(regs);
> -		_exception(SIGTRAP, regs, TRAP_TRACE, 0);
> -	}
> +	single_step_exception(regs);
>  }

We still need the if (single_stepping(regs)) in emulate_single_step.
We don't want to send the process a SIGTRAP every time it gets an
alignment interrupt. :)

Paul.