[Patch 3/5] PPC64-HWBKPT: Handle concurrent alignment interrupts

["K.Prasad" <prasad@linux.vnet.ibm.com>]

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.

[The need to invoke single-step handler after alignment interrupt pointed out
by Paul Mackerras <paulus@samba.org>]

Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
---
 arch/powerpc/kernel/traps.c |    8 +++-----
 1 file changed, 3 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 +621,8 @@ 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);
-	}
+	if (single_stepping(regs))
+		single_step_exception(regs);
 }
 
 static inline int __parse_fpscr(unsigned long fpscr)