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Commit 06532a67 authored by K.Prasad's avatar K.Prasad Committed by Paul Mackerras
Browse files

powerpc, hw_breakpoint: Enable hw-breakpoints while handling intervening signals 



A signal delivered between a hw_breakpoint_handler() and the
single_step_dabr_instruction() will not have the breakpoint active
while the signal handler is running -- the signal delivery will
set up a new MSR value which will not have MSR_SE set, so we
won't get the signal step interrupt until and unless the signal
handler returns (which it may never do).

To fix this, we restore the breakpoint when delivering a signal --
we clear the MSR_SE bit and set the DABR again.  If the signal
handler returns, the DABR interrupt will occur again when the
instruction that we were originally trying to single-step gets
re-executed.

[Paul Mackerras <paulus@samba.org> pointed out the need to do this.]

Signed-off-by: default avatarK.Prasad <prasad@linux.vnet.ibm.com>
Signed-off-by: default avatarPaul Mackerras <paulus@samba.org>
parent 2538c2d0

arch/powerpc/include/asm/hw_breakpoint.h

+3 −0
Original line number Diff line number Diff line
@@ -65,9 +65,12 @@ static inline void hw_breakpoint_disable(void) 
{

	set_dabr(0);

}

extern void thread_change_pc(struct task_struct *tsk, struct pt_regs *regs);



#else	/* CONFIG_HAVE_HW_BREAKPOINT */

static inline void hw_breakpoint_disable(void) { }

static inline void thread_change_pc(struct task_struct *tsk,

					struct pt_regs *regs) { }

#endif	/* CONFIG_HAVE_HW_BREAKPOINT */

#endif	/* __KERNEL__ */

#endif	/* _PPC_BOOK3S_64_HW_BREAKPOINT_H */

arch/powerpc/kernel/hw_breakpoint.c

+18 −0
Original line number Diff line number Diff line
@@ -174,6 +174,24 @@ int arch_validate_hwbkpt_settings(struct perf_event *bp) 
	return 0;

}



/*

 * Restores the breakpoint on the debug registers.

 * Invoke this function if it is known that the execution context is

 * about to change to cause loss of MSR_SE settings.

 */

void thread_change_pc(struct task_struct *tsk, struct pt_regs *regs)

{

	struct arch_hw_breakpoint *info;



	if (likely(!tsk->thread.last_hit_ubp))

		return;



	info = counter_arch_bp(tsk->thread.last_hit_ubp);

	regs->msr &= ~MSR_SE;

	set_dabr(info->address | info->type | DABR_TRANSLATION);

	tsk->thread.last_hit_ubp = NULL;

}



/*

 * Handle debug exception notifications.

 */

arch/powerpc/kernel/signal.c

+3 −0
Original line number Diff line number Diff line
@@ -11,6 +11,7 @@ 


#include <linux/tracehook.h>

#include <linux/signal.h>

#include <asm/hw_breakpoint.h>

#include <asm/uaccess.h>

#include <asm/unistd.h>
@@ -149,6 +150,8 @@ static int do_signal_pending(sigset_t *oldset, struct pt_regs *regs) 
	if (current->thread.dabr)

		set_dabr(current->thread.dabr);

#endif

	/* Re-enable the breakpoints for the signal stack */

	thread_change_pc(current, regs);



	if (is32) {

        	if (ka.sa.sa_flags & SA_SIGINFO)