Subject: Re: [PATCH] Enable hardware breakpoint upon re-registering

From: Michael Neuling <[email-masked]>
Date: Wed, 07 Nov 2012 07:53:26 +1100

Aravinda Prasad <[email-masked]> wrote:

> On powerpc, ptrace will disable hardware breakpoint request once the
> breakpoint is hit. It is the responsibility of the caller to set it
> again. However, when the caller sets the hardware breakpoint again
> using ptrace(PTRACE_SET_DEBUGREG, child_pid, 0, addr), the hardware
> breakpoint is not enabled.
> 
> While gdb's approach is to unregister and re-register the hardware
> breakpoint every time the breakpoint is hit - which is working fine,
> this could affect other programs trying to re-register hardware
> breakpoint without unregistering.
> 
> This patch enables hardware breakpoint if the caller is re-registering.
> 
> Signed-off-by: Aravinda Prasad <[email-masked]>

Passes my tests here and I don't think it'll break existing gdb.  So FWIW

Acked-by: Michael Neuling <[email-masked]>

Thanks!

> ---
>  arch/powerpc/kernel/ptrace.c |    4 ++++
>  1 files changed, 4 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/ptrace.c b/arch/powerpc/kernel/ptrace.c
> index 79d8e56..09371d0 100644
> --- a/arch/powerpc/kernel/ptrace.c
> +++ b/arch/powerpc/kernel/ptrace.c
> @@ -952,6 +952,10 @@ int ptrace_set_debugreg(struct task_struct *task, unsigned long addr,
>  		arch_bp_generic_fields(data &
>  					(DABR_DATA_WRITE | DABR_DATA_READ),
>  							&attr.bp_type);
> +
> +		/* Enable breakpoint */
> +		attr.disabled = false;
> +
>  		ret =  modify_user_hw_breakpoint(bp, &attr);
>  		if (ret) {
>  			ptrace_put_breakpoints(task);
> 
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