New file to debug clobbers of "current".

arch/alpha/lib/dbg_current.S

+/*
+ * arch/alpha/lib/dbg_current.S
+ * Contributed by Richard Henderson (rth@cygnus.com)
+ *
+ * Trap if we find current not correct.
+ */
+
+#include <asm/pal.h>
+
+	.text
+	.set noat
+
+	.globl _mcount
+	.ent _mcount
+_mcount:
+	.frame $30, 0, $28, 0
+	.prologue 0
+
+	lda	$0, -0x4000($30)
+	cmpult	$8, $30, $1
+	cmpule	$0, $30, $2
+	and	$1, $2, $3
+	bne	$3, 1f
+
+	call_pal PAL_bugchk
+
+1:	ret	$31, ($28), 1
+
+	.end _mcount