powerpc: Add trap_nr to thread_struct

Add thread_struct.trap_nr and use it to store the last exception
the thread experienced. In this patch, we populate the field at
various places where we force_sig_info() to the process.

This is also used in uprobes to determine if the probed instruction
caused an exception.

Signed-off-by: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 710f400..8e701a4 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -258,6 +258,7 @@
 {
 	siginfo_t info;
 
+	current->thread.trap_nr = signal_code;
 	if (notify_die(DIE_DABR_MATCH, "dabr_match", regs, error_code,
 			11, SIGSEGV) == NOTIFY_STOP)
 		return;
@@ -275,6 +276,7 @@
 {
 	siginfo_t info;
 
+	current->thread.trap_nr = TRAP_HWBKPT;
 	if (notify_die(DIE_DABR_MATCH, "dabr_match", regs, error_code,
 			11, SIGSEGV) == NOTIFY_STOP)
 		return;