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Roland McGrath
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323
sysdeps/standalone/i386/start.S
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323
sysdeps/standalone/i386/start.S
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/* Copyright (C) 1994 Free Software Foundation, Inc.
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Contributed by Joel Sherrill (jsherril@redstone-emh2.army.mil),
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On-Line Applications Research Corporation.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Library General Public License as
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published by the Free Software Foundation; either version 2 of the
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License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Library General Public License for more details.
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You should have received a copy of the GNU Library General Public
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License along with the GNU C Library; see the file COPYING.LIB. If
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not, write to the Free Software Foundation, Inc., 675 Mass Ave,
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Cambridge, MA 02139, USA. */
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/* entry.s
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*
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* This file contains the entry point for the application.
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* The name of this entry point is compiler dependent.
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* It jumps to the BSP which is responsible for performing
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* all initialization.
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*
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*/
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.data
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.global _Do_Load_IDT
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.global _Do_Load_GDT
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.text
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.global start # GNU default entry point
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.global _establish_stack
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.global _bsp_start
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.global _load_segments
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.global __exit
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start:
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nop
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cli # DISABLE INTERRUPTS!!!
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#
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# Load the segment registers
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#
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# NOTE: Upon return, gs will contain the segment descriptor for
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# a segment which maps directly to all of physical memory.
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#
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jmp _load_segments # load board dependent segments
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#
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# Set up the stack
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#
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_establish_stack:
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movl $stack_end,%esp # set stack pointer
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movl $stack_end,%ebp # set base pointer
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#
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# Zero out the BSS segment
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#
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zero_bss:
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cld # make direction flag count up
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movl $_end,%ecx # find end of .bss
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movl $_bss_start,%edi # edi = beginning of .bss
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subl %edi,%ecx # ecx = size of .bss in bytes
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shrl $2,%ecx # size of .bss in longs
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xorl %eax,%eax # value to clear out memory
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repne # while ecx != 0
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stosl # clear a long in the bss
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#
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# Set the C heap information for malloc
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#
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movl $heap_size,___C_heap_size # set ___C_heap_size
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movl $heap_memory,___C_heap_start # set ___C_heap_start
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#
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# Copy the Global Descriptor Table to our space
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#
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sgdt _Original_GDTR # save original GDT
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movzwl _Original_GDTR_limit,%ecx # size of GDT in bytes; limit
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# is 8192 entries * 8 bytes per
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# make ds:esi point to the original GDT
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movl _Original_GDTR_base,%esi
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push %ds # save ds
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movw %gs,%ax
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movw %ax,%ds
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# make es:edi point to the new (our copy) GDT
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movl $_Global_descriptor_table,%edi
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rep
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movsb # copy the GDT (ds:esi -> es:edi)
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pop %ds # restore ds
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# Build and load new contents of GDTR
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movw _Original_GDTR_limit,%ecx # set new limit
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movw %cx,_New_GDTR_limit
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push $_Global_descriptor_table
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push %es
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call _Logical_to_physical
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addl $6,%esp
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movl %eax,_New_GDTR_base # set new base
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cmpb $0,_Do_Load_GDT # Should the new GDT be loaded?
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je no_gdt_load # NO, then branch
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lgdt _New_GDTR # load the new GDT
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no_gdt_load:
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#
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# Copy the Interrupt Descriptor Table to our space
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#
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sidt _Original_IDTR # save original IDT
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movzwl _Original_IDTR_limit,%ecx # size of IDT in bytes; limit
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# is 256 entries * 8 bytes per
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# make ds:esi point to the original IDT
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movl _Original_IDTR_base,%esi
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push %ds # save ds
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movw %gs,%ax
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movw %ax,%ds
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# make es:edi point to the new (our copy) IDT
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movl $_Interrupt_descriptor_table,%edi
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rep
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movsb # copy the IDT (ds:esi -> es:edi)
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pop %ds # restore ds
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# Build and load new contents of IDTR
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movw _Original_IDTR_limit,%ecx # set new limit
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movw %cx,_New_IDTR_limit
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push $_Interrupt_descriptor_table
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push %es
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call _Logical_to_physical
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addl $6,%esp
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movl %eax,_New_IDTR_base # set new base
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cmpb $0,_Do_Load_IDT # Should the new IDT be loaded?
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je no_idt_load # NO, then branch
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lidt _New_IDTR # load the new IDT
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no_idt_load:
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#
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# Initialize the i387.
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#
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# Using the NO WAIT form of the instruction insures that if
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# it is not present the board will not lock up or get an
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# exception.
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#
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fninit # MUST USE NO-WAIT FORM
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call __Board_Initialize # initialize the board
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pushl $0 # envp = NULL
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pushl $0 # argv = NULL
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pushl $0 # argc = NULL
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call ___libc_init # initialize the library and
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# call main
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addl $12,%esp
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pushl $0 # argc = NULL
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call __exit # call the Board specific exit
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addl $4,%esp
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#
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# Clean up
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#
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.global _Bsp_cleanup
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.global _return_to_monitor
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_Bsp_cleanup:
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cmpb $0,_Do_Load_IDT # Was the new IDT loaded?
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je no_idt_restore # NO, then branch
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lidt _Original_IDTR # restore the new IDT
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no_idt_restore:
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cmpb $0,_Do_Load_GDT # Was the new GDT loaded?
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je no_gdt_restore # NO, then branch
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lgdt _Original_GDTR # restore the new GDT
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no_gdt_restore:
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jmp _return_to_monitor
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#
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# void *Logical_to_physical(
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# rtems_unsigned16 segment,
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# void *address
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# );
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#
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# Returns thirty-two bit physical address for segment:address.
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#
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.global _Logical_to_physical
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.set SEGMENT_ARG, 4
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.set ADDRESS_ARG, 8
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_Logical_to_physical:
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xorl %eax,%eax # clear eax
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movzwl SEGMENT_ARG(%esp),%ecx # ecx = segment value
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movl $_Global_descriptor_table,%edx # edx = address of our GDT
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addl %ecx,%edx # edx = address of desired entry
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movb 7(%edx),%ah # ah = base 31:24
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movb 4(%edx),%al # al = base 23:16
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shll $16,%eax # move ax into correct bits
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movw 2(%edx),%ax # ax = base 0:15
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movl ADDRESS_ARG(%esp),%ecx # ecx = address to convert
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addl %eax,%ecx # ecx = physical address equivalent
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movl %ecx,%eax # eax = ecx
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ret
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#
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# void *Physical_to_logical(
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# rtems_unsigned16 segment,
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# void *address
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# );
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#
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# Returns thirty-two bit physical address for segment:address.
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#
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.global _Physical_to_logical
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#.set SEGMENT_ARG, 4
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#.set ADDRESS_ARG, 8 -- use sets from above
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_Physical_to_logical:
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xorl %eax,%eax # clear eax
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movzwl SEGMENT_ARG(%esp),%ecx # ecx = segment value
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movl $_Global_descriptor_table,%edx # edx = address of our GDT
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addl %ecx,%edx # edx = address of desired entry
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movb 7(%edx),%ah # ah = base 31:24
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movb 4(%edx),%al # al = base 23:16
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shll $16,%eax # move ax into correct bits
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movw 2(%edx),%ax # ax = base 0:15
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movl ADDRESS_ARG(%esp),%ecx # ecx = address to convert
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subl %eax,%ecx # ecx = logical address equivalent
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movl %ecx,%eax # eax = ecx
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ret
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/*
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* Data Declarations. Start with a macro which helps declare space.
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*/
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.bss
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#define DECLARE_SPACE(_name,_space,_align) \
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.globl _name ; \
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.align _align ; \
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_name##: .space _space
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#define DECLARE_LABEL(_name) \
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.globl _name ; \
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_name##:
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#define DECLARE_PTR(_name) DECLARE_SPACE(_name,4,2)
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#define DECLARE_U32(_name) DECLARE_SPACE(_name,4,2)
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#define DECLARE_U16(_name) DECLARE_SPACE(_name,2,1)
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/*
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* Require environment stuff
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*/
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DECLARE_LABEL(_environ)
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DECLARE_PTR(environ)
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DECLARE_LABEL(_errno)
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DECLARE_U32(errno)
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/*
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* Miscellaneous Variables used to restore the CPU state.
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*
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* Start with a macro to declare the space for the contents of
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* a Descriptor Table register.
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*/
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#define DECLARE_DTR_SPACE(_name) \
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.global _name ; \
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.align 4 ; \
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_name##: ; \
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_name##_limit: .space 2 ; \
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_name##_base: .space 4
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DECLARE_SPACE(_Interrupt_descriptor_table,256*8,4)
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DECLARE_SPACE(_Global_descriptor_table,8192*8,4)
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DECLARE_DTR_SPACE(_Original_IDTR)
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DECLARE_DTR_SPACE(_New_IDTR)
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DECLARE_DTR_SPACE(_Original_GDTR)
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DECLARE_DTR_SPACE(_New_GDTR)
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DECLARE_SPACE(_Physical_base_of_ds,4,4)
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DECLARE_SPACE(_Physical_base_of_cs,4,4)
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/*
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* Stack Size and Space
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*/
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.set stack_size, 0x20000
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DECLARE_SPACE(stack_memory,stack_size,4)
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DECLARE_LABEL(stack_end)
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