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142 lines
3.0 KiB
142 lines
3.0 KiB
/*
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* linux/boot/head.S
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*
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* Copyright (C) 1991, 1992, 1993 Linus Torvalds
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*
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* $Id: head.S,v 1.3 2001/04/20 00:59:28 ak Exp $
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*/
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/*
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* head.S contains the 32-bit startup code.
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*
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* NOTE!!! Startup happens at absolute address 0x00001000, which is also where
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* the page directory will exist. The startup code will be overwritten by
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* the page directory. [According to comments etc elsewhere on a compressed
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* kernel it will end up at 0x1000 + 1Mb I hope so as I assume this. - AC]
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*
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* Page 0 is deliberately kept safe, since System Management Mode code in
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* laptops may need to access the BIOS data stored there. This is also
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* useful for future device drivers that either access the BIOS via VM86
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* mode.
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*/
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/*
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* High loaded stuff by Hans Lermen & Werner Almesberger, Feb. 1996
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*/
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.code32
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.text
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#include <linux/linkage.h>
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#include <asm/segment.h>
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.code32
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.globl startup_32
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startup_32:
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cld
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cli
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movl $(__KERNEL_DS),%eax
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movl %eax,%ds
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movl %eax,%es
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movl %eax,%fs
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movl %eax,%gs
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lss stack_start,%esp
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xorl %eax,%eax
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1: incl %eax # check that A20 really IS enabled
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movl %eax,0x000000 # loop forever if it isn't
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cmpl %eax,0x100000
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je 1b
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/*
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* Initialize eflags. Some BIOS's leave bits like NT set. This would
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* confuse the debugger if this code is traced.
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* XXX - best to initialize before switching to protected mode.
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*/
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pushl $0
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popfl
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/*
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* Clear BSS
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*/
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xorl %eax,%eax
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movl $_edata,%edi
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movl $_end,%ecx
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subl %edi,%ecx
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cld
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rep
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stosb
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/*
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* Do the decompression, and jump to the new kernel..
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*/
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subl $16,%esp # place for structure on the stack
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movl %esp,%eax
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pushl %esi # real mode pointer as second arg
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pushl %eax # address of structure as first arg
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call decompress_kernel
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orl %eax,%eax
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jnz 3f
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addl $8,%esp
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xorl %ebx,%ebx
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ljmp $(__KERNEL_CS), $0x100000
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/*
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* We come here, if we were loaded high.
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* We need to move the move-in-place routine down to 0x1000
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* and then start it with the buffer addresses in registers,
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* which we got from the stack.
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*/
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3:
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movl %esi,%ebx
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movl $move_routine_start,%esi
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movl $0x1000,%edi
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movl $move_routine_end,%ecx
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subl %esi,%ecx
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addl $3,%ecx
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shrl $2,%ecx
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cld
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rep
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movsl
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popl %esi # discard the address
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addl $4,%esp # real mode pointer
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popl %esi # low_buffer_start
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popl %ecx # lcount
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popl %edx # high_buffer_start
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popl %eax # hcount
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movl $0x100000,%edi
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cli # make sure we don't get interrupted
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ljmp $(__KERNEL_CS), $0x1000 # and jump to the move routine
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/*
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* Routine (template) for moving the decompressed kernel in place,
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* if we were high loaded. This _must_ PIC-code !
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*/
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move_routine_start:
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movl %ecx,%ebp
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shrl $2,%ecx
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rep
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movsl
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movl %ebp,%ecx
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andl $3,%ecx
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rep
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movsb
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movl %edx,%esi
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movl %eax,%ecx # NOTE: rep movsb won't move if %ecx == 0
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addl $3,%ecx
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shrl $2,%ecx
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rep
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movsl
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movl %ebx,%esi # Restore setup pointer
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xorl %ebx,%ebx
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ljmp $(__KERNEL_CS), $0x100000
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move_routine_end:
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/* Stack for uncompression */
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.align 32
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user_stack:
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.fill 4096,4,0
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stack_start:
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.long user_stack+4096
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.word __KERNEL_DS
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