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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]
*
* 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
#include <linux/linkage.h>
#include <asm/segment.h>
#include <asm/page.h>
.section ".text.head"
.globl startup_32
startup_32:
cld
cli
movl $(__BOOT_DS),%eax
movl %eax,%ds
movl %eax,%es
movl %eax,%fs
movl %eax,%gs
movl %eax,%ss
/* Calculate the delta between where we were compiled to run
* at and where we were actually loaded at. This can only be done
* with a short local call on x86. Nothing else will tell us what
* address we are running at. The reserved chunk of the real-mode
* data at 0x34-0x3f are used as the stack for this calculation.
* Only 4 bytes are needed.
*/
leal 0x40(%esi), %esp
call 1f
1: popl %ebp
subl $1b, %ebp
/* Compute the delta between where we were compiled to run at
* and where the code will actually run at.
*/
/* Start with the delta to where the kernel will run at. If we are
* a relocatable kernel this is the delta to our load address otherwise
* this is the delta to CONFIG_PHYSICAL start.
*/
#ifdef CONFIG_RELOCATABLE
movl %ebp, %ebx
#else
movl $(CONFIG_PHYSICAL_START - startup_32), %ebx
#endif
/* Replace the compressed data size with the uncompressed size */
subl input_len(%ebp), %ebx
movl output_len(%ebp), %eax
addl %eax, %ebx
/* Add 8 bytes for every 32K input block */
shrl $12, %eax
addl %eax, %ebx
/* Add 32K + 18 bytes of extra slack */
addl $(32768 + 18), %ebx
/* Align on a 4K boundary */
addl $4095, %ebx
andl $~4095, %ebx
/* Copy the compressed kernel to the end of our buffer
* where decompression in place becomes safe.
*/
pushl %esi
leal _end(%ebp), %esi
leal _end(%ebx), %edi
movl $(_end - startup_32), %ecx
std
rep
movsb
cld
popl %esi
/* Compute the kernel start address.
*/
#ifdef CONFIG_RELOCATABLE
leal startup_32(%ebp), %ebp
#else
movl $CONFIG_PHYSICAL_START, %ebp
#endif
/*
* Jump to the relocated address.
*/
leal relocated(%ebx), %eax
jmp *%eax
.section ".text"
relocated:
/*
* Clear BSS
*/
xorl %eax,%eax
leal _edata(%ebx),%edi
leal _end(%ebx), %ecx
subl %edi,%ecx
cld
rep
stosb
/*
* Setup the stack for the decompressor
*/
leal stack_end(%ebx), %esp
/*
* Do the decompression, and jump to the new kernel..
*/
movl output_len(%ebx), %eax
pushl %eax
pushl %ebp # output address
movl input_len(%ebx), %eax
pushl %eax # input_len
leal input_data(%ebx), %eax
pushl %eax # input_data
leal _end(%ebx), %eax
pushl %eax # end of the image as third argument
pushl %esi # real mode pointer as second arg
call decompress_kernel
addl $20, %esp
popl %ecx
#if CONFIG_RELOCATABLE
/* Find the address of the relocations.
*/
movl %ebp, %edi
addl %ecx, %edi
/* Calculate the delta between where vmlinux was compiled to run
* and where it was actually loaded.
*/
movl %ebp, %ebx
subl $CONFIG_PHYSICAL_START, %ebx
/*
* Process relocations.
*/
1: subl $4, %edi
movl 0(%edi), %ecx
testl %ecx, %ecx
jz 2f
addl %ebx, -__PAGE_OFFSET(%ebx, %ecx)
jmp 1b
2:
#endif
/*
* Jump to the decompressed kernel.
*/
xorl %ebx,%ebx
jmp *%ebp
.bss
.balign 4
stack:
.fill 4096, 1, 0
stack_end:
|
