Patchwork Enable hardware breakpoint upon re-registering

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Submitter Aravinda Prasad
Date Nov. 5, 2012, 8:15 a.m.
Message ID <20121105081527.29141.11384.stgit@aravinda>
Download mbox | patch
Permalink /patch/197161/
State Accepted
Commit a53fd61ac2f411745471c1c877d5e072fbbf0e5c
Delegated to: Benjamin Herrenschmidt
Headers show

Comments

Aravinda Prasad - Nov. 5, 2012, 8:15 a.m.
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 <aravinda@linux.vnet.ibm.com>
---
 arch/powerpc/kernel/ptrace.c |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)
Michael Neuling - Nov. 6, 2012, 8:53 p.m.
Aravinda Prasad <aravinda@linux.vnet.ibm.com> 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 <aravinda@linux.vnet.ibm.com>

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

Acked-by: Michael Neuling <mikey@neuling.org>

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);
> 
> _______________________________________________
> Linuxppc-dev mailing list
> Linuxppc-dev@lists.ozlabs.org
> https://lists.ozlabs.org/listinfo/linuxppc-dev
>

Patch

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);