[POWERPC] Save trap number in bad_stack

Save the trap number in the case of getting a bad stack in an exception
handler. It is sometimes useful to know what exception it was that caused
this to happen. Without this, no trap number is reported.

Signed-off-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/kernel/asm-offsets.c

@@ -139,6 +139,7 @@ int main(void)
 	DEFINE(PACA_SYSTEM_TIME, offsetof(struct paca_struct, system_time));
 	DEFINE(PACA_SLBSHADOWPTR, offsetof(struct paca_struct, slb_shadow_ptr));
 	DEFINE(PACA_DATA_OFFSET, offsetof(struct paca_struct, data_offset));
+	DEFINE(PACA_TRAP_SAVE, offsetof(struct paca_struct, trap_save));
 
 	DEFINE(SLBSHADOW_STACKVSID,
 	       offsetof(struct slb_shadow, save_area[SLB_NUM_BOLTED - 1].vsid));

arch/powerpc/kernel/head_64.S

@@ -278,8 +278,12 @@ exception_marker:
 	beq-	1f;							   \
 	ld	r1,PACAKSAVE(r13);	/* kernel stack to use		*/ \
 1:	cmpdi	cr1,r1,0;		/* check if r1 is in userspace	*/ \
-	bge-	cr1,bad_stack;		/* abort if it is		*/ \
-	std	r9,_CCR(r1);		/* save CR in stackframe	*/ \
+	bge-	cr1,2f;			/* abort if it is		*/ \
+	b	3f;							   \
+2:	li	r1,(n);			/* will be reloaded later	*/ \
+	sth	r1,PACA_TRAP_SAVE(r13);					   \
+	b	bad_stack;						   \
+3:	std	r9,_CCR(r1);		/* save CR in stackframe	*/ \
 	std	r11,_NIP(r1);		/* save SRR0 in stackframe	*/ \
 	std	r12,_MSR(r1);		/* save SRR1 in stackframe	*/ \
 	std	r10,0(r1);		/* make stack chain pointer	*/ \
@@ -940,6 +944,8 @@ bad_stack:
 	SAVE_2GPRS(7,r1)
 	SAVE_10GPRS(12,r1)
 	SAVE_10GPRS(22,r1)
+	lhz	r12,PACA_TRAP_SAVE(r13)
+	std	r12,_TRAP(r1)
 	addi	r11,r1,INT_FRAME_SIZE
 	std	r11,0(r1)
 	li	r12,0

include/asm-powerpc/paca.h

@@ -94,6 +94,7 @@ struct paca_struct {
 	u64 stab_rr;			/* stab/slb round-robin counter */
 	u64 saved_r1;			/* r1 save for RTAS calls */
 	u64 saved_msr;			/* MSR saved here by enter_rtas */
+	u16 trap_save;			/* Used when bad stack is encountered */
 	u8 soft_enabled;		/* irq soft-enable flag */
 	u8 hard_enabled;		/* set if irqs are enabled in MSR */
 	u8 io_sync;			/* writel() needs spin_unlock sync */