/*      $OpenBSD: tfork_thread.S,v 1.11 2023/12/10 16:45:51 deraadt Exp $ */
/*-
 * Copyright (c) 2000 Peter Wemm <peter@FreeBSD.org>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <machine/asm.h>

/*
 * With thanks to John Dyson for the original version of this.
 */

#include "SYS.h"

/*
 *                8      12     16         20
 * __tfork_thread(param, psize, start_fnc, start_arg);
 *
 * param:               Arguments to actual system call.
 * psize:               Other argument to pass to the actual kernel call.
 * start_fnc:           Address of thread function to call in child.
 * start_arg:           Argument to pass to the thread function in child.
 */

ENTRY(__tfork_thread)
        pushl   %ebp
        movl    %esp, %ebp
        pushl   %esi
        pushl   %edi

        /*
         * Save the thread info in esi and ebx
         */
        movl    16(%ebp), %esi  # get start thread address
        movl    20(%ebp), %edi  # get start argument

        /*
         * Prepare and execute the thread creation syscall
         */
        pushl   12(%ebp)        # push psize
        pushl   8(%ebp)         # push param
        pushl   $0              # slot for return address, ignored by kernel
        movl    $SYS___tfork, %eax
99:     int     $0x80
        PINSYSCALL(SYS___tfork, 99b)
        jb      2f

        /*
         * Check to see if we are in the parent or child
         */
        cmpl    $0, %eax
        jz      1f
        addl    $12, %esp
        popl    %edi
        popl    %esi
        movl    %ebp, %esp
        popl    %ebp
        ret
        .p2align 2

        /*
         * If we are in the child (new thread), then
         * set-up the call to the internal subroutine.  If it
         * returns, then call __threxit.
         */
1:
        xorl    %ebp, %ebp      # mark outermost frame
        subl    $4, %esp        # align stack
        andl    $~15, %esp
        addl    $4, %esp
        pushl   %edi            # push start argument
        call    *%esi
        addl    $4, %esp

        /*
         * Exit system call
         */
        pushl   $0              # NULL pointer argument to __threxit
        pushl   $0              # slot for return address, ignored by kernel
        movl    $SYS___threxit, %eax
98:     int     $0x80
        PINSYSCALL(SYS___threxit, 98b)
        int3

        /*
         * Branch here if the thread creation fails:
         */
2:
        addl    $12, %esp
        popl    %edi
        popl    %esi
        movl    %ebp, %esp
        popl    %ebp
        HANDLE_ERRNO()
        ret
END(__tfork_thread)