Add original unix v6

source/s4/execv.s

@@ -0,0 +1,31 @@
+/ C library -- execv
+
+/ execv(file, argv);
+/
+/ where argv is a vector argv[0] ... argv[x], 0
+/ last vector element must be 0
+/
+/ The _exectrap flags is used by the debugger and causes
+/ a trace trap on the first instruction of the executed instruction
+/ to give a chance to set breakpoints.
+
+.globl	_execv, cerror
+.comm	__exectrap,2
+rtt	= 6
+
+_execv:
+	mov	r5,-(sp)
+	mov	sp,r5
+	mov	4(r5),0f
+	mov	6(r5),0f+2
+	tst	__exectrap
+	beq	1f
+	mov	$170020,-(sp)	/ t-bit
+	mov	$1f,-(sp)
+	rtt
+1:
+	sys	0; 9f
+	jmp	cerror
+.data
+9:
+	sys	exec; 0:..; ..