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linux/arch/x86_64/boot/compressed/head.S
H. Peter Anvin 85414b693a Define zero-page offset 0x1e4 as a scratch field, and use it 
The relocatable kernel code needs a scratch field for the decompressor
to determine its own location.  It was using a location inside
struct screen_info; reserve a free location and document it as scratch
instead.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-07-12 10:55:54 -07:00

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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
*/
.code32
.text
#include <linux/linkage.h>
#include <asm/segment.h>
#include <asm/pgtable.h>
#include <asm/page.h>
#include <asm/msr.h>
.section ".text.head"
.code32
.globl startup_32
startup_32:
cld
cli
movl $(__KERNEL_DS), %eax
movl %eax, %ds
movl %eax, %es
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 (0x1e4+4)(%esi), %esp
call 1f
1: popl %ebp
subl $1b, %ebp
/* setup a stack and make sure cpu supports long mode. */
movl $user_stack_end, %eax
addl %ebp, %eax
movl %eax, %esp
call verify_cpu
testl %eax, %eax
jnz no_longmode
/* Compute the delta between where we were compiled to run at
* and where the code will actually run at.
*/
/* %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.
*/
#ifdef CONFIG_RELOCATABLE
movl %ebp, %ebx
addl $(LARGE_PAGE_SIZE -1), %ebx
andl $LARGE_PAGE_MASK, %ebx
#else
movl $CONFIG_PHYSICAL_START, %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 and align on a 4K boundary */
addl $(32768 + 18 + 4095), %ebx
andl $~4095, %ebx
/*
* Prepare for entering 64 bit mode
*/
/* Load new GDT with the 64bit segments using 32bit descriptor */
leal gdt(%ebp), %eax
movl %eax, gdt+2(%ebp)
lgdt gdt(%ebp)
/* Enable PAE mode */
xorl %eax, %eax
orl $(1 << 5), %eax
movl %eax, %cr4
/*
* Build early 4G boot pagetable
*/
/* Initialize Page tables to 0*/
leal pgtable(%ebx), %edi
xorl %eax, %eax
movl $((4096*6)/4), %ecx
rep stosl
/* Build Level 4 */
leal pgtable + 0(%ebx), %edi
leal 0x1007 (%edi), %eax
movl %eax, 0(%edi)
/* Build Level 3 */
leal pgtable + 0x1000(%ebx), %edi
leal 0x1007(%edi), %eax
movl $4, %ecx
1: movl %eax, 0x00(%edi)
addl $0x00001000, %eax
addl $8, %edi
decl %ecx
jnz 1b
/* Build Level 2 */
leal pgtable + 0x2000(%ebx), %edi
movl $0x00000183, %eax
movl $2048, %ecx
1: movl %eax, 0(%edi)
addl $0x00200000, %eax
addl $8, %edi
decl %ecx
jnz 1b
/* Enable the boot page tables */
leal pgtable(%ebx), %eax
movl %eax, %cr3
/* Enable Long mode in EFER (Extended Feature Enable Register) */
movl $MSR_EFER, %ecx
rdmsr
btsl $_EFER_LME, %eax
wrmsr
/* Setup for the jump to 64bit mode
*
* When the jump is performend we will be in long mode but
* in 32bit compatibility mode with EFER.LME = 1, CS.L = 0, CS.D = 1
* (and in turn EFER.LMA = 1). To jump into 64bit mode we use
* the new gdt/idt that has __KERNEL_CS with CS.L = 1.
* We place all of the values on our mini stack so lret can
* used to perform that far jump.
*/
pushl $__KERNEL_CS
leal startup_64(%ebp), %eax
pushl %eax
/* Enter paged protected Mode, activating Long Mode */
movl $0x80000001, %eax /* Enable Paging and Protected mode */
movl %eax, %cr0
/* Jump from 32bit compatibility mode into 64bit mode. */
lret
no_longmode:
/* This isn't an x86-64 CPU so hang */
1:
hlt
jmp 1b
#include "../../kernel/verify_cpu.S"
/* Be careful here startup_64 needs to be at a predictable
* address so I can export it in an ELF header. Bootloaders
* should look at the ELF header to find this address, as
* it may change in the future.
*/
.code64
.org 0x200
ENTRY(startup_64)
/* We come here either from startup_32 or directly from a
* 64bit bootloader. If we come here from a bootloader we depend on
* an identity mapped page table being provied that maps our
* entire text+data+bss and hopefully all of memory.
*/
/* Setup data segments. */
xorl %eax, %eax
movl %eax, %ds
movl %eax, %es
movl %eax, %ss
/* Compute the decompressed kernel start address. It is where
* we were loaded at aligned to a 2M boundary. %rbp contains the
* decompressed kernel start address.
*
* If it is a relocatable kernel then decompress and run the kernel
* from load address aligned to 2MB addr, otherwise decompress and
* run the kernel from CONFIG_PHYSICAL_START
*/
/* Start with the delta to where the kernel will run at. */
#ifdef CONFIG_RELOCATABLE
leaq startup_32(%rip) /* - $startup_32 */, %rbp
addq $(LARGE_PAGE_SIZE - 1), %rbp
andq $LARGE_PAGE_MASK, %rbp
movq %rbp, %rbx
#else
movq $CONFIG_PHYSICAL_START, %rbp
movq %rbp, %rbx
#endif
/* Replace the compressed data size with the uncompressed size */
movl input_len(%rip), %eax
subq %rax, %rbx
movl output_len(%rip), %eax
addq %rax, %rbx
/* Add 8 bytes for every 32K input block */
shrq $12, %rax
addq %rax, %rbx
/* Add 32K + 18 bytes of extra slack and align on a 4K boundary */
addq $(32768 + 18 + 4095), %rbx
andq $~4095, %rbx
/* Copy the compressed kernel to the end of our buffer
* where decompression in place becomes safe.
*/
leaq _end(%rip), %r8
leaq _end(%rbx), %r9
movq $_end /* - $startup_32 */, %rcx
1: subq $8, %r8
subq $8, %r9
movq 0(%r8), %rax
movq %rax, 0(%r9)
subq $8, %rcx
jnz 1b
/*
* Jump to the relocated address.
*/
leaq relocated(%rbx), %rax
jmp *%rax
.section ".text"
relocated:
/*
* Clear BSS
*/
xorq %rax, %rax
leaq _edata(%rbx), %rdi
leaq _end(%rbx), %rcx
subq %rdi, %rcx
cld
rep
stosb
/* Setup the stack */
leaq user_stack_end(%rip), %rsp
/* zero EFLAGS after setting rsp */
pushq $0
popfq
/*
* Do the decompression, and jump to the new kernel..
*/
pushq %rsi # Save the real mode argument
movq %rsi, %rdi # real mode address
leaq _heap(%rip), %rsi # _heap
leaq input_data(%rip), %rdx # input_data
movl input_len(%rip), %eax
movq %rax, %rcx # input_len
movq %rbp, %r8 # output
call decompress_kernel
popq %rsi
/*
* Jump to the decompressed kernel.
*/
jmp *%rbp
.data
gdt:
.word gdt_end - gdt
.long gdt
.word 0
.quad 0x0000000000000000 /* NULL descriptor */
.quad 0x00af9a000000ffff /* __KERNEL_CS */
.quad 0x00cf92000000ffff /* __KERNEL_DS */
gdt_end:
.bss
/* Stack for uncompression */
.balign 4
user_stack:
.fill 4096,4,0
user_stack_end:
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