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/*
* linux/boot/head.S
*
* Copyright (C) 1991, 1992, 1993 Linus Torvalds
*/
/*
* head.S contains the 32-bit startup code.
*
* NOTE!!! Startup happens at absolute address 0x00001000, which is also where
* the page directory will exist. The startup code will be overwritten by
* the page directory. [According to comments etc elsewhere on a compressed
* kernel it will end up at 0x1000 + 1Mb I hope so as I assume this. - AC]
*
* In SMP mode we keep this page safe. Really we ought to shuffle things and
* put the trampoline here. - AC. An SMP trampoline enters with %cx holding
* the stack base.
*
* Page 0 is deliberately kept safe, since System Management Mode code in
* laptops may need to access the BIOS data stored there. This is also
* useful for future device drivers that either access the BIOS via VM86
* mode.
*/
/*
* High loaded stuff by Hans Lermen & Werner Almesberger, Feb. 1996
*/
.text
#define __ASSEMBLY__
#include <linux/config.h>
#include <linux/linkage.h>
#include <asm/segment.h>
.globl startup_32
startup_32:
cld
cli
movl $(KERNEL_DS),%eax
mov %ax,%ds
mov %ax,%es
mov %ax,%fs
mov %ax,%gs
#ifdef __SMP__
orw %bx,%bx # What state are we in BX=1 for SMP
# 0 for boot
jz 2f # Initial boot
/*
* We are trampolining an SMP processor
*/
mov %ax,%ss
xorl %eax,%eax # Back to 0
mov %cx,%ax # SP low 16 bits
movl %eax,%esp
pushl 0 # Clear NT
popfl
ljmp $(KERNEL_CS), $0x100000 # Into C and sanity
2:
#endif
lss SYMBOL_NAME(stack_start),%esp
xorl %eax,%eax
1: incl %eax # check that A20 really IS enabled
movl %eax,0x000000 # loop forever if it isn't
cmpl %eax,0x100000
je 1b
/*
* Initialize eflags. Some BIOS's leave bits like NT set. This would
* confuse the debugger if this code is traced.
* XXX - best to initialize before switching to protected mode.
*/
pushl $0
popfl
/*
* Clear BSS
*/
xorl %eax,%eax
movl $ SYMBOL_NAME(_edata),%edi
movl $ SYMBOL_NAME(_end),%ecx
subl %edi,%ecx
cld
rep
stosb
/*
* Do the decompression, and jump to the new kernel..
*/
subl $16,%esp # place for structure on the stack
pushl %esp # address of structure as first arg
call SYMBOL_NAME(decompress_kernel)
orl %eax,%eax
jnz 3f
xorl %ebx,%ebx
ljmp $(KERNEL_CS), $0x100000
/*
* We come here, if we were loaded high.
* We need to move the move-in-place routine down to 0x1000
* and then start it with the buffer addresses in registers,
* which we got from the stack.
*/
3:
movl $move_routine_start,%esi
movl $0x1000,%edi
movl $move_routine_end,%ecx
subl %esi,%ecx
cld
rep
movsb
popl %esi # discard the address
popl %esi # low_buffer_start
popl %ecx # lcount
popl %edx # high_buffer_start
popl %eax # hcount
movl $0x100000,%edi
cli # make sure we don't get interrupted
ljmp $(KERNEL_CS), $0x1000 # and jump to the move routine
/*
* Routine (template) for moving the decompressed kernel in place,
* if we were high loaded. This _must_ PIC-code !
*/
move_routine_start:
rep
movsb
movl %edx,%esi
movl %eax,%ecx # NOTE: rep movsb won't move if %ecx == 0
rep
movsb
xorl %ebx,%ebx
/*
* Well, the kernel relies on %esp pointing into low mem,
* with the decompressor loaded high this is no longer true,
* so we set esp here.
*/
mov $0x90000,%esp
ljmp $(KERNEL_CS), $0x100000
move_routine_end:
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