sys/platform/vkernel64/x86_64/fork_tramp.s

   1 /*-
   2  * Copyright (c) 1990 The Regents of the University of California.
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  * 3. Neither the name of the University nor the names of its contributors
  14  *    may be used to endorse or promote products derived from this software
  15  *    without specific prior written permission.
  16  *
  17  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  18  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  19  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  20  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  21  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  22  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  23  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  24  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  25  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  26  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  27  * SUCH DAMAGE.
  28  *
  29  * $FreeBSD: src/sys/i386/i386/exception.s,v 1.65.2.3 2001/08/15 01:23:49 peter Exp $
  30  */
  31
  32 #include <machine/asmacros.h>
  33 #include <machine/segments.h>
  34 #include <machine/lock.h>
  35 #include <machine/psl.h>
  36 #include <machine/trap.h>
  37
  38 #include "assym.s"
  39
  40         .text
  41
  42         .globl  lwkt_switch_return
  43
  44 /*
  45  * This function is what cpu_heavy_restore jumps to after a new process
  46  * is created.  The LWKT subsystem switches while holding a critical
  47  * section and we maintain that abstraction here (e.g. because
  48  * cpu_heavy_restore needs it due to PCB_*() manipulation), then get out of
  49  * it before calling the initial function (typically fork_return()) and/or
  50  * returning to user mode.
  51  *
  52  * The MP lock is not held at any point but the critcount is bumped
  53  * on entry to prevent interruption of the trampoline at a bad point.
  54  *
  55  * This is effectively what td->td_switch() returns to.  It 'returns' the
  56  * old thread in %eax and since this is not returning to a td->td_switch()
  57  * call from lwkt_switch() we must handle the cleanup for the old thread
  58  * by calling lwkt_switch_return().
  59  *
  60  * fork_trampoline(%rax:otd, %rbp:func, %r12:arg)
  61  */
  62 ENTRY(fork_trampoline)
  63         movq    %rax,%rdi
  64         call    lwkt_switch_return
  65         movq    PCPU(curthread),%rax
  66         decl    TD_CRITCOUNT(%rax)
  67
  68         /*
  69          * cpu_set_fork_handler intercepts this function call to
  70          * have this call a non-return function to stay in kernel mode.
  71          *
  72          * initproc has its own fork handler, start_init(), which DOES
  73          * return.
  74          *
  75          * %rbx - chaining function (typically fork_return)
  76          * %r12 -> %rdi (argument)
  77          * frame-> %rsi (trap frame)
  78          *
  79          *   void (func:rbx)(arg:rdi, trapframe:rsi)
  80          */
  81         movq    %rsp, %rsi              /* pass trapframe by reference */
  82         movq    %r12, %rdi              /* arg1 */
  83         call    *%rbx                   /* function */
  84
  85         /* cut from syscall */
  86
  87         call    splz
  88
  89         /*
  90          * Return via doreti to handle ASTs.
  91          *
  92          * trapframe is at the top of the stack.
  93          */
  94         MEXITCOUNT
  95         pushq   $0              /* if_vec */
  96         movq    %rsp,%rdi       /* pass by reference */
  97         call    go_user
  98         /* NOT REACHED */
  99 END(fork_trampoline)