sparc64: Properly truncate pt_regs framepointer in perf callback.

For 32-bit processes, we save the full 64-bits of the regs in pt_regs.

But unlike when the userspace actually does load and store
instructions, the top 32-bits don't get automatically truncated by the
cpu in kernel mode (because the kernel doesn't execute with PSTATE_AM
address masking enabled).

So we have to do it by hand.
Reported-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

arch/sparc/kernel/perf_event.c

@@ -1337,7 +1337,7 @@ static void perf_callchain_user_32(struct pt_regs *regs,
 	callchain_store(entry, PERF_CONTEXT_USER);
 	callchain_store(entry, regs->tpc);
 
-	ufp = regs->u_regs[UREG_I6];
+	ufp = regs->u_regs[UREG_I6] & 0xffffffffUL;
 	do {
 		struct sparc_stackf32 *usf, sf;
 		unsigned long pc;