usr/src/lib/libc/vax/sys/Ovfork.s

/*
 * Copyright (c) 1983 Regents of the University of California.
 * All rights reserved.  The Berkeley software License Agreement
 * specifies the terms and conditions for redistribution.
 */

#ifndef lint
static char sccsid[] = "@(#)Ovfork.s    5.2 (Berkeley) %G%";
#endif not lint

/*
 * @(#)vfork.s  4.1 (Berkeley) 12/21/80
 * C library -- vfork
 */

/*
 * pid = vfork();
 *
 * r1 == 0 in parent process, r1 == 1 in child process.
 * r0 == pid of child in parent, r0 == pid of parent in child.
 *
 * trickery here, due to keith sklower, uses ret to clear the stack,
 * and then returns with a jump indirect, since only one person can return
 * with a ret off this stack... we do the ret before we vfork!
 */

        .set    vfork,66
.globl  _vfork

_vfork:
        .word   0x0000
        movl    16(fp),r2
        movab   here,16(fp)
        ret
here:
        chmk    $vfork
        bcc     vforkok
        jmp     verror
vforkok:
        tstl    r1              # child process ?
        bneq    child   # yes
        bcc     parent          # if c-bit not set, fork ok
.globl  _errno
verror:
        movl    r0,_errno
        mnegl   $1,r0
        jmp     (r2)
child:
        clrl    r0
parent:
        jmp     (r2)