[PATCH] alpha: Fix getxpid on alpha so it works for threads

While looking in the code I discovered that alpha has fallen behind because
it doesn't use sys_getppid.  The problem is that it doesn't follow the task
struct to the task_group_leader.
Acked-by: Richard Henderson <rth@twiddle.net>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/alpha/kernel/asm-offsets.c

@@ -28,6 +28,7 @@ void foo(void)
         DEFINE(TASK_GID, offsetof(struct task_struct, gid));
         DEFINE(TASK_EGID, offsetof(struct task_struct, egid));
         DEFINE(TASK_REAL_PARENT, offsetof(struct task_struct, real_parent));
+        DEFINE(TASK_GROUP_LEADER, offsetof(struct task_struct, group_leader));
         DEFINE(TASK_TGID, offsetof(struct task_struct, tgid));
         BLANK();
 

arch/alpha/kernel/entry.S

@@ -879,17 +879,19 @@ sys_getxpid:
 
 	/* See linux/kernel/timer.c sys_getppid for discussion
 	   about this loop.  */
-	ldq	$3, TASK_REAL_PARENT($2)
-1:	ldl	$1, TASK_TGID($3)
+	ldq	$3, TASK_GROUP_LEADER($2)
+	ldq	$4, TASK_REAL_PARENT($3)
+	ldl	$0, TASK_TGID($2)
+1:	ldl	$1, TASK_TGID($4)
 #ifdef CONFIG_SMP
-	mov	$3, $4
+	mov	$4, $5
 	mb
-	ldq	$3, TASK_REAL_PARENT($2)
-	cmpeq	$3, $4, $4
-	beq	$4, 1b
+	ldq	$3, TASK_GROUP_LEADER($2)
+	ldq	$4, TASK_REAL_PARENT($3)
+	cmpeq	$4, $5, $5
+	beq	$5, 1b
 #endif
 	stq	$1, 80($sp)
-	ldl	$0, TASK_TGID($2)
 	ret
 .end sys_getxpid