blob: 67a655a39ce43d3da454b7fd8f230b70d8a9c6bc [file] [log] [blame]
* 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
#include <linux/init.h>
#include <linux/linkage.h>
#include <asm/segment.h>
#include <asm/page_types.h>
#include <asm/boot.h>
#include <asm/asm-offsets.h>
* Test KEEP_SEGMENTS flag to see if the bootloader is asking
* us to not reload segments
testb $(1<<6), BP_loadflags(%esi)
jnz 1f
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 0x1e4 (defined as a scratch field) are used as the stack
* for this calculation. Only 4 bytes are needed.
leal (BP_scratch+4)(%esi), %esp
call 1f
1: popl %ebp
subl $1b, %ebp
* %ebp contains the address we are loaded at by the boot loader and %ebx
* contains the address where we should move the kernel image temporarily
* for safe in-place decompression.
movl %ebp, %ebx
movl BP_kernel_alignment(%esi), %eax
decl %eax
addl %eax, %ebx
notl %eax
andl %eax, %ebx
/* Target address to relocate to for decompression */
addl $z_extract_offset, %ebx
/* Set up the stack */
leal boot_stack_end(%ebx), %esp
/* Zero EFLAGS */
pushl $0
* Copy the compressed kernel to the end of our buffer
* where decompression in place becomes safe.
pushl %esi
leal (_bss-4)(%ebp), %esi
leal (_bss-4)(%ebx), %edi
movl $(_bss - startup_32), %ecx
shrl $2, %ecx
rep movsl
popl %esi
* Jump to the relocated address.
leal relocated(%ebx), %eax
jmp *%eax
* Clear BSS (stack is currently empty)
xorl %eax, %eax
leal _bss(%ebx), %edi
leal _ebss(%ebx), %ecx
subl %edi, %ecx
shrl $2, %ecx
rep stosl
* Adjust our own GOT
leal _got(%ebx), %edx
leal _egot(%ebx), %ecx
cmpl %ecx, %edx
jae 2f
addl %ebx, (%edx)
addl $4, %edx
jmp 1b
* Do the decompression, and jump to the new kernel..
leal z_extract_offset_negative(%ebx), %ebp
/* push arguments for decompress_kernel: */
pushl %ebp /* output address */
pushl $z_input_len /* input_len */
leal input_data(%ebx), %eax
pushl %eax /* input_data */
leal boot_heap(%ebx), %eax
pushl %eax /* heap area */
pushl %esi /* real mode pointer */
call decompress_kernel
addl $20, %esp
* Find the address of the relocations.
leal z_output_len(%ebp), %edi
* Calculate the delta between where vmlinux was compiled to run
* and where it was actually loaded.
movl %ebp, %ebx
jz 2f /* Nothing to be done if loaded at compiled addr. */
* Process relocations.
1: subl $4, %edi
movl (%edi), %ecx
testl %ecx, %ecx
jz 2f
addl %ebx, -__PAGE_OFFSET(%ebx, %ecx)
jmp 1b
* Jump to the decompressed kernel.
xorl %ebx, %ebx
jmp *%ebp
* Stack and heap for uncompression
.balign 4
.fill BOOT_HEAP_SIZE, 1, 0
.fill BOOT_STACK_SIZE, 1, 0