/*
 * 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)