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>

arch/powerpc/include/asm/processor.h

@@ -219,6 +219,7 @@ struct thread_struct {
 #endif /* CONFIG_HAVE_HW_BREAKPOINT */
 #endif
 	unsigned long	dabr;		/* Data address breakpoint register */
+	unsigned long	trap_nr;	/* last trap # on this thread */
 #ifdef CONFIG_ALTIVEC
 	/* Complete AltiVec register set */
 	vector128	vr[32] __attribute__((aligned(16)));

arch/powerpc/kernel/process.c

@@ -258,6 +258,7 @@ void do_send_trap(struct pt_regs *regs, unsigned long address,
 {
 	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 @@ void do_dabr(struct pt_regs *regs, unsigned long address,
 {
 	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;

arch/powerpc/kernel/traps.c

@@ -251,6 +251,7 @@ void _exception(int signr, struct pt_regs *regs, int code, unsigned long addr)
 	if (arch_irqs_disabled() && !arch_irq_disabled_regs(regs))
 		local_irq_enable();
 
+	current->thread.trap_nr = code;
 	memset(&info, 0, sizeof(info));
 	info.si_signo = signr;
 	info.si_code = code;

arch/powerpc/mm/fault.c

@@ -133,6 +133,7 @@ static int do_sigbus(struct pt_regs *regs, unsigned long address)
 	up_read(&current->mm->mmap_sem);
 
 	if (user_mode(regs)) {
+		current->thread.trap_nr = BUS_ADRERR;
 		info.si_signo = SIGBUS;
 		info.si_errno = 0;
 		info.si_code = BUS_ADRERR;