/*	@(#)vfork.s	0.0	SCCS id keyword	*/
/ C library -- vfork

/ pid = vfork();
/
/ pid == 0 in child process; pid == -1 means error return
/ in child, parents id is in par_uid if needed
/
/ Since the parent and child share the stack, the return
/ address for the parent would be overwritten by the child.
/ Therefore, save the return address in r1 and "return"
/ by a jump indirect.

.globl	_vfork, _par_uid
.globl	__ovno
.comm	_errno,2

_vfork:
	mov	(sp)+,r1		/ save return address
	mov	__ovno,savov		/ save __ovno for parent
	sys	vfork
		br 1f			/ child returns here; if no vfork 
					/    syscall, parent returns here also.

	bec	2f			/ parent returns here
0:	mov	r0,_errno		/ vfork failed; can't use cerror
	mov	$-1,r0
	jmp	(r1)			/ "return" to saved location

1:	/ child:
	bes	0b			/ check error here also
					/    (in case no vfork syscall)
	mov	r0,_par_uid
	clr	r0
2:
	mov	savov,__ovno		/ restore ovno in case child switched
	jmp	(r1)			/ "return" to saved location

.bss
savov:	.=.+2