/*-
 * Copyright (c) 1990 The Regents of the University of California.
 * 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.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS 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 REGENTS 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.
 *
 * $FreeBSD: src/sys/i386/i386/exception.s,v 1.65.2.3 2001/08/15 01:23:49 peter Exp $
 */

#include <machine/asmacros.h>
#include <machine/segments.h>
#include <machine/lock.h>
#include <machine/psl.h>
#include <machine/trap.h>

#include "assym.s"

        .text

        .globl  lwkt_switch_return

/*
 * This function is what cpu_heavy_restore jumps to after a new process
 * is created.  The LWKT subsystem switches while holding a critical
 * section and we maintain that abstraction here (e.g. because
 * cpu_heavy_restore needs it due to PCB_*() manipulation), then get out of
 * it before calling the initial function (typically fork_return()) and/or
 * returning to user mode.
 *
 * The MP lock is not held at any point but the critcount is bumped
 * on entry to prevent interruption of the trampoline at a bad point.
 *
 * This is effectively what td->td_switch() returns to.  It 'returns' the
 * old thread in %eax and since this is not returning to a td->td_switch()
 * call from lwkt_switch() we must handle the cleanup for the old thread
 * by calling lwkt_switch_return().
 *
 * fork_trampoline(%rax:otd, %rbp:func, %r12:arg)
 */
ENTRY(fork_trampoline)
        movq    %rax,%rdi
        call    lwkt_switch_return
        movq    PCPU(curthread),%rax
        decl    TD_CRITCOUNT(%rax)

        /*
         * cpu_set_fork_handler intercepts this function call to
         * have this call a non-return function to stay in kernel mode.
         *
         * initproc has its own fork handler, start_init(), which DOES
         * return.
         *
         * %rbx - chaining function (typically fork_return)
         * %r12 -> %rdi (argument)
         * frame-> %rsi (trap frame)
         *
         *   void (func:rbx)(arg:rdi, trapframe:rsi)
         */
        movq    %rsp, %rsi              /* pass trapframe by reference */
        movq    %r12, %rdi              /* arg1 */
        call    *%rbx                   /* function */

        /* cut from syscall */

        call    splz

        /*
         * Return via doreti to handle ASTs.
         *
         * trapframe is at the top of the stack.
         */
        MEXITCOUNT
        pushq   $0              /* if_vec */
        movq    %rsp,%rdi       /* pass by reference */
        call    go_user
        /* NOT REACHED */
END(fork_trampoline)