add recursion test, add noops for branch delay slots

lib/runtime.asm

@@ -23,6 +23,7 @@ _start:
 
 	# call main
 	jal main
+	nop
 
 	# exit
 	move	$a0, $v0

test/masm/fncall.asm

@@ -11,6 +11,7 @@ result:
 	move	$t0, $a0
 	move	$v0, $t0
 	jr	$ra
+	nop
 
 main:
 	# save ra on stack
@@ -20,6 +21,7 @@ main:
 	# set return to 17
 	li	$a0, 17
 	jal	result
+	nop
 
 	# pop ra from stack
 	lw	$ra, 0($sp)
@@ -27,3 +29,4 @@ main:
 
 	# return result
 	jr	$ra
+	nop

test/masm/fpe.asm

@@ -15,3 +15,4 @@ main:
 	# return
 	li	$v0, 0
 	jr	$ra
+	nop

test/masm/hello.asm

@@ -24,3 +24,4 @@ main:
 	# return 1
 	li	$v0, 0
 	jr	$ra
+	nop

test/masm/recursion.asm

@@ -0,0 +1,41 @@
+# Copyright (c) 2024 Freya Murphy
+
+# file: recursion.asm
+# test: should recurse sum n..0 numbers
+
+.text
+.align 2
+.globl main
+
+main:
+	# init $a0
+	li	$a0, 5
+
+sum:
+	# save stack
+	addiu	$sp, $sp, -8
+	sw	$ra, 0($sp)
+	sw	$s0, 4($sp)
+
+	# load n from a0
+	move	$s0, $a0
+
+	# skip if n is zero
+	li	$v0, 0
+	beq	$s0, $zero, add
+	nop
+	jal	sum
+	addi	$a0, $s0, -1
+
+add:
+	# n = n + returned
+	add	$v0, $s0, $v0
+
+	# restore stack
+	lw	$ra, 0($sp)
+	lw	$s0, 4($sp)
+	addiu	$sp, $sp, 8
+
+	# return
+	jr	$ra
+	nop

test/masm/segv.asm

@@ -13,3 +13,4 @@ main:
 	# return
 	li	$v0, 0
 	jr	$ra
+	nop

test/out/fpe

@@ -12,4 +12,4 @@ $v1:	0x00000000 $t3:	0x00000000 $s3:	0x00000000 $k1:	0x00000000
 $a0:	0x00000000 $t4:	0x00000000 $s4:	0x00000000 $gp:	0x00000000
 $a1:	0x00000000 $t5:	0x00000000 $s5:	0x00000000 $sp:	0x10001000
 $a2:	0x00000000 $t6:	0x00000000 $s6:	0x00000000 $fp:	0x00000000
-$a3:	0x00000000 $t7:	0x00000000 $s7:	0x00000000 $ra:	0x0040001c
+$a3:	0x00000000 $t7:	0x00000000 $s7:	0x00000000 $ra:	0x00400024

test/out/recursion.status

@@ -0,0 +1 @@
+15

test/out/segv

@@ -12,4 +12,4 @@ $v1:	0x00000000 $t3:	0x00000000 $s3:	0x00000000 $k1:	0x00000000
 $a0:	0x00000000 $t4:	0x00000000 $s4:	0x00000000 $gp:	0x00000000
 $a1:	0x00000000 $t5:	0x00000000 $s5:	0x00000000 $sp:	0x10001000
 $a2:	0x00000000 $t6:	0x00000000 $s6:	0x00000000 $fp:	0x00000000
-$a3:	0x00000000 $t7:	0x00000000 $s7:	0x00000000 $ra:	0x00400018
+$a3:	0x00000000 $t7:	0x00000000 $s7:	0x00000000 $ra:	0x00400020