[SPARC64]: Add dummy PTRACE_PEEKUSR for gdb.

GDB uses a PTRACE_PEEKUSR call with offset 0 to see
if a thread is alive, so provide a success return for
this particular special case.

Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/arch/sparc64/kernel/ptrace.c b/arch/sparc64/kernel/ptrace.c
index eb93e9c..c910af5 100644
--- a/arch/sparc64/kernel/ptrace.c
+++ b/arch/sparc64/kernel/ptrace.c
@@ -244,6 +244,13 @@
 	}
 
 	switch(request) {
+	case PTRACE_PEEKUSR:
+		if (addr != 0)
+			pt_error_return(regs, EIO);
+		else
+			pt_succ_return(regs, 0);
+		goto out_tsk;
+
 	case PTRACE_PEEKTEXT: /* read word at location addr. */ 
 	case PTRACE_PEEKDATA: {
 		unsigned long tmp64;