glibc/sysdeps/unix/bsd/i386/vfork.S

/* Copyright (C) 1993, 1994, 1995, 1997, 2002 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, write to the Free
   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
   02111-1307 USA.  */

#include <sysdep.h>

/* Since vfork shares the address space between the parent and child,
   we must take care to avoid the child unwinding the stack frame and
   clobbering it for the parent.  */

.text
ENTRY (__vfork)
	popl scratch		/* Save the return PC in a register.  */
	DO_CALL (vfork, 0)	/* Do the system call.  */
	pushl scratch		/* Put the return PC back on the stack.  */
	jb syscall_error	/* Branch if error.  */
	/* R1 is now 0 for the parent and 1 for the child.  Decrement it to
	   make it -1 (all bits set) for the parent, and 0 (no bits set)
	   for the child.  Then AND it with R0, so the parent gets
	   R0&-1==R0, and the child gets R0&0==0.  */
	decl r1
	andl r1, r0
	ret
libc_hidden_def (__vfork)

weak_alias (__vfork, vfork)