path: root/sysdeps/standalone/i386/start.S

/* Copyright (C) 1994, 1997 Free Software Foundation, Inc.
   Contributed by Joel Sherrill (jsherril@redstone-emh2.army.mil),
     On-Line Applications Research Corporation.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library 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
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, write to the Free
   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
   02111-1307 USA.  */

/*  entry.s
 *
 *  This file contains the entry point for the application.
 *  The name of this entry point is compiler dependent.
 *  It jumps to the BSP which is responsible for performing
 *  all initialization.
 *
 */

	.data
	.global  _Do_Load_IDT
	.global  _Do_Load_GDT

	.text
	      .global  start                  # GNU default entry point
	.global  _establish_stack

	.global   _bsp_start
	.global   _load_segments
	.global   __exit

start:
	nop
	cli                             # DISABLE INTERRUPTS!!!
#
#  Load the segment registers
#
#  NOTE: Upon return, gs will contain the segment descriptor for
#        a segment which maps directly to all of physical memory.
#
	jmp     _load_segments          # load board dependent segments

#
#  Set up the stack
#

_establish_stack:

	movl    $stack_end,%esp         # set stack pointer
	movl    $stack_end,%ebp         # set base pointer

#
#  Zero out the BSS segment
#
zero_bss:
	cld                             # make direction flag count up
	movl    $_end,%ecx              # find end of .bss
	movl    $_bss_start,%edi        # edi = beginning of .bss
	subl    %edi,%ecx               # ecx = size of .bss in bytes
	shrl    $2,%ecx                 # size of .bss in longs
	xorl    %eax,%eax               # value to clear out memory
	repne                           # while ecx != 0
	stosl                           #   clear a long in the bss

#
#  Set the C heap information for malloc
#
	movl    $heap_size,___C_heap_size    # set ___C_heap_size
	movl    $heap_memory,___C_heap_start # set ___C_heap_start

#
#  Copy the Global Descriptor Table to our space
#

	sgdt    _Original_GDTR          # save original GDT
	movzwl  _Original_GDTR_limit,%ecx # size of GDT in bytes; limit
					  #   is 8192 entries * 8 bytes per

	# make ds:esi point to the original GDT

	movl    _Original_GDTR_base,%esi
	push    %ds                     # save ds
	movw    %gs,%ax
	movw    %ax,%ds

	# make es:edi point to the new (our copy) GDT
	movl    $_Global_descriptor_table,%edi

	rep
	movsb                            # copy the GDT (ds:esi -> es:edi)

	pop     %ds                      # restore ds

	# Build and load new contents of GDTR
	movw    _Original_GDTR_limit,%ecx # set new limit
	movw    %cx,_New_GDTR_limit

	push    $_Global_descriptor_table
	push    %es
	call    _Logical_to_physical
	addl    $6,%esp
	movl    %eax,_New_GDTR_base      # set new base

	cmpb    $0,_Do_Load_GDT          # Should the new GDT be loaded?
	je      no_gdt_load              # NO, then branch
	lgdt    _New_GDTR                # load the new GDT
no_gdt_load:

#
#  Copy the Interrupt Descriptor Table to our space
#

	sidt    _Original_IDTR          # save original IDT
	movzwl  _Original_IDTR_limit,%ecx # size of IDT in bytes; limit
					  #   is 256 entries * 8 bytes per


	# make ds:esi point to the original IDT
	movl    _Original_IDTR_base,%esi

	push    %ds                     # save ds
	movw    %gs,%ax
	movw    %ax,%ds

	# make es:edi point to the new (our copy) IDT
	movl    $_Interrupt_descriptor_table,%edi

	rep
	movsb                            # copy the IDT (ds:esi -> es:edi)
	pop     %ds                      # restore ds

	# Build and load new contents of IDTR
	movw    _Original_IDTR_limit,%ecx # set new limit
	movw    %cx,_New_IDTR_limit

	push    $_Interrupt_descriptor_table
	push    %es
	call    _Logical_to_physical
	addl    $6,%esp
	movl    %eax,_New_IDTR_base      # set new base

	cmpb    $0,_Do_Load_IDT          # Should the new IDT be loaded?
	je      no_idt_load              # NO, then branch
	lidt    _New_IDTR                # load the new IDT
no_idt_load:

#
#  Initialize the i387.
#
#  Using the NO WAIT form of the instruction insures that if
#  it is not present the board will not lock up or get an
#  exception.
#

	fninit                           # MUST USE NO-WAIT FORM

	call    __Board_Initialize       # initialize the board

	pushl   $0                       # envp = NULL
	pushl   $0                       # argv = NULL
	pushl   $0                       # argc = NULL
	call    ___libc_init             # initialize the library and
					 #   call main
	addl    $12,%esp

	pushl   $0                       # argc = NULL
	call    __exit                   # call the Board specific exit
	addl     $4,%esp

#
#  Clean up
#


	.global  _Bsp_cleanup

	.global   _return_to_monitor

_Bsp_cleanup:
	cmpb    $0,_Do_Load_IDT          # Was the new IDT loaded?
	je      no_idt_restore           # NO, then branch
	lidt    _Original_IDTR           # restore the new IDT
no_idt_restore:

	cmpb    $0,_Do_Load_GDT          # Was the new GDT loaded?
	je      no_gdt_restore           # NO, then branch
	lgdt    _Original_GDTR           # restore the new GDT
no_gdt_restore:
	jmp     _return_to_monitor

#
#  void *Logical_to_physical(
#     rtems_unsigned16  segment,
#     void             *address
#  );
#
#  Returns thirty-two bit physical address for segment:address.
#

	.global  _Logical_to_physical

.set SEGMENT_ARG, 4
.set ADDRESS_ARG, 8

_Logical_to_physical:

	xorl    %eax,%eax                # clear eax
	movzwl  SEGMENT_ARG(%esp),%ecx   # ecx = segment value
	movl    $_Global_descriptor_table,%edx # edx = address of our GDT
	addl    %ecx,%edx                # edx = address of desired entry
	movb    7(%edx),%ah              # ah = base 31:24
	movb    4(%edx),%al              # al = base 23:16
	shll    $16,%eax                 # move ax into correct bits
	movw    2(%edx),%ax              # ax = base 0:15
	movl    ADDRESS_ARG(%esp),%ecx   # ecx = address to convert
	addl    %eax,%ecx                # ecx = physical address equivalent
	movl    %ecx,%eax                # eax = ecx
	ret

#
#  void *Physical_to_logical(
#     rtems_unsigned16  segment,
#     void             *address
#  );
#
#  Returns thirty-two bit physical address for segment:address.
#

	.global  _Physical_to_logical

#.set SEGMENT_ARG, 4
#.set ADDRESS_ARG, 8   -- use sets from above

_Physical_to_logical:

	xorl    %eax,%eax                # clear eax
	movzwl  SEGMENT_ARG(%esp),%ecx   # ecx = segment value
	movl    $_Global_descriptor_table,%edx # edx = address of our GDT
	addl    %ecx,%edx                # edx = address of desired entry
	movb    7(%edx),%ah              # ah = base 31:24
	movb    4(%edx),%al              # al = base 23:16
	shll    $16,%eax                 # move ax into correct bits
	movw    2(%edx),%ax              # ax = base 0:15
	movl    ADDRESS_ARG(%esp),%ecx   # ecx = address to convert
	subl    %eax,%ecx                # ecx = logical address equivalent
	movl    %ecx,%eax                # eax = ecx
	ret


/*
 *  Data Declarations.  Start with a macro which helps declare space.
 */

	.bss

#define DECLARE_SPACE(_name,_space,_align) \
	  .globl   _name ; \
	  .align   _align ; \
_name##:  .space _space

#define DECLARE_LABEL(_name) \
	  .globl   _name ; \
_name##:

#define DECLARE_PTR(_name) DECLARE_SPACE(_name,4,2)
#define DECLARE_U32(_name) DECLARE_SPACE(_name,4,2)
#define DECLARE_U16(_name) DECLARE_SPACE(_name,2,1)

/*
 *  Require environment stuff
 */

DECLARE_LABEL(_environ)
DECLARE_PTR(environ)

DECLARE_LABEL(_errno)
DECLARE_U32(errno)

/*
 *  Miscellaneous Variables used to restore the CPU state.
 *
 *  Start with a macro to declare the space for the contents of
 *  a Descriptor Table register.
 */

#define DECLARE_DTR_SPACE(_name) \
	  .global   _name ; \
	  .align    4 ; \
_name##:  ; \
_name##_limit:  .space 2  ; \
_name##_base:   .space 4

DECLARE_SPACE(_Interrupt_descriptor_table,256*8,4)
DECLARE_SPACE(_Global_descriptor_table,8192*8,4)

DECLARE_DTR_SPACE(_Original_IDTR)
DECLARE_DTR_SPACE(_New_IDTR)
DECLARE_DTR_SPACE(_Original_GDTR)
DECLARE_DTR_SPACE(_New_GDTR)

DECLARE_SPACE(_Physical_base_of_ds,4,4)
DECLARE_SPACE(_Physical_base_of_cs,4,4)

/*
 *  Stack Size and Space
 */

	.set stack_size, 0x20000

DECLARE_SPACE(stack_memory,stack_size,4)
DECLARE_LABEL(stack_end)