/* Copyright (C) 2005  David Decotigny
   Copyright (C) 2004  The KOS Team

   This program is free software; you can redistribute it and/or
   modify it under the terms of the GNU General Public License
   as published by the Free Software Foundation; either version 2
   of the License, or (at your option) any later version.
   
   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.
   
   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307,
   USA. 
*/
#include "segment.h"


/**
 * @file swintr_wrappers.S
 *
 * The SOS low-level handlers for the software interrupts. Currently
 * only 1 wrapper: that for the SOS syscalls.
 */
.file "swintr_wrappers.S"

.text

/* The address of the real "C" syscall function */
.extern sos_do_syscall

/** Update the kernel TSS in case we are switching to a thread in user
	mode in order to come back into the correct kernel stack */
.extern sos_cpu_context_update_kernel_tss

/* The address of the function to call to set back the user thread's
   MMU configuration upon return to user context */
.extern sos_thread_prepare_syscall_switch_back

.p2align 2, 0x90
.globl sos_syscall_wrapper
sos_syscall_wrapper:
.type sos_syscall_wrapper,@function
 
  /* Fake error code */
  pushl $0
  /* Backup the context */
  pushl %ebp
  movl %esp, %ebp
 
  pushl %edi
  pushl %esi
  pushl %edx
  pushl %ecx
  pushl %ebx
  pushl %eax
  subl  $2,%esp
  pushw %ss
  pushw %ds
  pushw %es
  pushw %fs
  pushw %gs

  /* Set correct kernel segment descriptors' value */
  movw $SOS_BUILD_SEGMENT_REG_VALUE(0, 0, SOS_SEG_KDATA), %di
  pushw %di ; popw %ds
  pushw %di ; popw %es
  pushw %di ; popw %fs
  pushw %di ; popw %gs

  /* Prepare the call to do_syscall */ 
  pushl %esp /* user_ctxt */
  pushl %eax /* syscall ID */

  call  sos_do_syscall
  /* Unallocate the stack used by the
     do_syscall arguments */
  addl  $8, %esp

  /* store the do_syscall return value into interrupted context */
  movl %eax, 12(%esp)

  /* Set the MMU configuration to that of the user thread's process */
  pushl %esp /* user_ctxt */
  call sos_thread_prepare_syscall_switch_back
  addl  $4, %esp /* Unallocate the stack */

  /* Prepare kernel TSS because we are switching back to a user
     thread: we make sure that we will come back into the kernel at a
     correct stack location */
  pushl %esp /* Pass the location of the context we are
  	        restoring to the function */
  call sos_cpu_context_update_kernel_tss
  addl $4, %esp

  /* Restore the user context */
  popw  %gs
  popw  %fs
  popw  %es
  popw  %ds
  popw  %ss
  addl  $2,%esp
  popl  %eax /* This is the return value of do_syscall (see above) */
  popl  %ebx
  popl  %ecx
  popl  %edx
  popl  %esi
  popl  %edi
 
  popl  %ebp
  /* Remove fake error code */
  addl $4, %esp
  iret