xref: /titanic_50/usr/src/lib/libc/i386/sys/vforkx.s (revision bdf0047c9427cca40961a023475891c898579c37)

/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */

/*
 * Copyright 2010 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

	.file	"vforkx.s"

#include "SYS.h"
#include <assym.h>

/*
 * pid = vforkx(flags);
 * syscall trap: forksys(2, flags)
 *
 * pid = vfork();
 * syscall trap: forksys(2, 0)
 *
 * From the syscall:
 * %edx == 0 in parent process, %edx = 1 in child process.
 * %eax == pid of child in parent, %eax == pid of parent in child.
 *
 * The child gets a zero return value.
 * The parent gets the pid of the child.
 */

/*
 * The child of vfork() will execute in the parent's address space,
 * thereby changing the stack before the parent runs again.
 * Therefore we have to be careful how we return from vfork().
 * Pity the poor debugger developer who has to deal with this kludge.
 *
 * We block all blockable signals while performing the vfork() system call
 * trap.  This enables us to set curthread->ul_vfork safely, so that we
 * don't end up in a signal handler with curthread->ul_vfork set wrong.
 */

	ENTRY_NP(vforkx)
	movl	4(%esp), %eax		/* flags */
	jmp	0f
	ENTRY_NP(vfork)
	xorl	%eax, %eax		/* flags = 0 */
0:
	popl	%ecx			/* save return %eip in %ecx */
	pushl	%eax			/* flags */
	pushl	$MASKSET3		/* block all signals */
	pushl	$MASKSET2
	pushl	$MASKSET1
	pushl	$MASKSET0
	pushl	$SIG_SETMASK
	pushl	%ecx
	__SYSCALLINT(lwp_sigmask)
	addl	$24, %esp

	pushl	$2
	pushl	%ecx
	__SYSCALLINT(forksys)		/* vforkx(flags) */
	jae 	1f

	/* reconstruct stack before jumping to __cerror */
	addl	$12, %esp
	pushl	%ecx
	pushl	%eax			/* save the vfork() error number */

	pushl	%gs:UL_SIGMASK+12	/* reinstate signals */
	pushl	%gs:UL_SIGMASK+8
	pushl	%gs:UL_SIGMASK+4
	pushl	%gs:UL_SIGMASK
	pushl	$SIG_SETMASK
	pushl	%ecx
	__SYSCALLINT(lwp_sigmask)
	addl	$24, %esp

	popl	%eax			/* restore the vfork() error number */
	jmp	__cerror

1:
	addl	$12, %esp
	/*
	 * To determine if we are (still) a child of vfork(), the child
	 * increments curthread->ul_vfork by one and the parent decrements
	 * it by one.  If the result is zero, then we are not a child of
	 * vfork(), else we are.  We do this to deal with the case of
	 * a vfork() child calling vfork().
	 */
	cmpl	$0, %edx
	jne	2f
	movl	%gs:UL_VFORK, %edx
	cmpl	$0, %edx		/* don't let it go negative */
	je	3f
	subl	$1, %edx		/* curthread->ul_vfork--; */
	jmp	3f
2:
	xorl	%eax, %eax		/* zero the return value in the child */
	movl	%gs:UL_VFORK, %edx
	addl	$1, %edx		/* curthread->ul_vfork++; */
3:
	movl	%edx, %gs:UL_VFORK
	/*
	 * Clear the schedctl interface in both parent and child.
	 * (The child might have modified the parent.)
	 */
	xorl	%edx, %edx
	movl	%edx, %gs:UL_SCHEDCTL
	movl	%edx, %gs:UL_SCHEDCTL_CALLED
	pushl	%eax			/* save the vfork() return value */

	pushl	%gs:UL_SIGMASK+12	/* reinstate signals */
	pushl	%gs:UL_SIGMASK+8
	pushl	%gs:UL_SIGMASK+4
	pushl	%gs:UL_SIGMASK
	pushl	$SIG_SETMASK
	pushl	%ecx
	__SYSCALLINT(lwp_sigmask)
	addl	$24, %esp

	popl	%eax			/* restore the vfork() return value */
	jmp	*%ecx			/* jump back to the caller */
	SET_SIZE(vfork)
	SET_SIZE(vforkx)