xref: /illumos-gate/usr/src/lib/libc/amd64/sys/vforkx.S (revision 5d9d9091f564c198a760790b0bfa72c44e17912b)

/*
 * 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)
	movq	%rdi, %r8		/* flags */
	jmp	0f
	ENTRY_NP(vfork)
	xorq	%r8, %r8		/* flags = 0 */
0:
	popq	%r9			/* save return %rip in %r9 */
	pushq	%r8			/* save the flags on the stack */
	movl	$MASKSET3, %r8d		/* block all signals */
	movl	$MASKSET2, %ecx
	movl	$MASKSET1, %edx
	movl	$MASKSET0, %esi
	movl	$SIG_SETMASK, %edi
	__SYSCALL(lwp_sigmask)

	popq	%rsi			/* fetch flags from the stack */
	movl	$2, %edi
	__SYSCALL(forksys)		/* vforkx(flags) */
	jae 	1f

	/* reconstruct stack before jumping to __cerror */
	pushq	%r9
	movq	%rax, %r9		/* save the vfork() error number */

	movl	%fs:UL_SIGMASK+12, %r8d	/* reinstate signals */
	movl	%fs:UL_SIGMASK+8, %ecx
	movl	%fs:UL_SIGMASK+4, %edx
	movl	%fs:UL_SIGMASK, %esi
	movl	$SIG_SETMASK, %edi
	__SYSCALL(lwp_sigmask)

	movq	%r9, %rax		/* restore the vfork() error number */
	jmp	__cerror

1:
	/*
	 * 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	%fs: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	%fs:UL_VFORK, %edx
	addl	$1, %edx		/* curthread->ul_vfork++; */
3:
	movl	%edx, %fs:UL_VFORK
	/*
	 * Clear the schedctl interface in both parent and child.
	 * (The child might have modified the parent.)
	 */
	xorq	%rdx, %rdx
	movq	%rdx, %fs:UL_SCHEDCTL
	movq	%rdx, %fs:UL_SCHEDCTL_CALLED
	pushq	%rax			/* save the vfork() return value */

	movl	%fs:UL_SIGMASK+12, %r8d	/* reinstate signals */
	movl	%fs:UL_SIGMASK+8, %ecx
	movl	%fs:UL_SIGMASK+4, %edx
	movl	%fs:UL_SIGMASK, %esi
	movl	$SIG_SETMASK, %edi
	__SYSCALL(lwp_sigmask)

	popq	%rax			/* restore the vfork() return value */
	jmp	*%r9			/* jump back to the caller */
	SET_SIZE(vfork)
	SET_SIZE(vforkx)