User defined trap handling routine is called with calls instruction.

A message is printed if there is no routine at all.

mach/vax4/libem/trp.s

@@ -2,7 +2,7 @@
 .globl	.trp
 
 .trp:
-	movl	r0,-(sp)
+	pushl	r0
 	movl	8(sp),r0
 	movl	4(sp),8(sp)
 	movl	(sp)+,(sp)
@@ -13,14 +13,40 @@
 	rsb
 L1:
 	pushr	$017776		# save registers
-	movl	r0,-(sp)	# trapnumber on stack
+	pushl	r0		# trapnumber on stack
 	movl	.trppc,r0
-	beql	L2		#is there a user defined traphandler?
+	beql	L2		# is there a user defined traphandler?
 	clrl	.trppc
-	jsb	(r0)		#if so, call it
-	tstl	(sp)+
-	popr	$017776		#restore registers
+	calls	$1,(r0)		# if so, call it
+	popr	$017776		# restore registers
 	movl	(sp)+,r0
 	rsb
+
+.set	write,4
+
 L2:
+	# Put the (octal) trapnumber in the zeroes in Lemes[].
+
+	movl	$Lemesend-1,r1	# Addres after last '0'.
+	movl	$5,r2		# Max number of digits.
+	movl	(sp),r0		# Trap number in r0.
+L3:
+	bicw2	$0177770,r0	# Lower 3 bits form lower octal digit.
+	bisb2	r0,-(r1)	# Put them in the '0'.
+	ashl	$-3,r0,r0	# Shift the 3 bits off.
+	sobgtr	r2,L3
+	movl	ap,r2
+	movl	$Lwr,ap
+	chmk	$write
+	movl	r2,ap
 	bpt
+.data
+Lemes:
+.byte 'E,'r,'r,' ,'0,'0,'0,'0,'0,0xa
+Lemesend:
+.align 2
+Lwr:
+.long 3			# 3 arguments.
+.long 2			# File descriptor 2.
+.long Lemes		# Address of character buffer.
+.long Lemesend - Lemes	# Number of characters to write.