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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
#include <linux/init.h>
#include <linux/linkage.h>
#include <asm/segment.h>
#include <asm/pgtable_types.h>
#include <asm/page_types.h>
#include <asm/boot.h>
#include <asm/msr.h>
#include <asm/processor-flags.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 $(__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 (BP_scratch+4)(%esi), %esp
call 1f
1: popl %ebp
subl $1b, %ebp
/* setup a stack and make sure cpu supports long mode. */
movl $boot_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.
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
* 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 */
movl $(X86_CR4_PAE), %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
btsl $_EFER_LME, %eax
* 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 $(X86_CR0_PG | X86_CR0_PE), %eax /* Enable Paging and Protected mode */
movl %eax, %cr0
/* Jump from 32bit compatibility mode into 64bit mode. */
/* This isn't an x86-64 CPU so hang */
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.
.org 0x200
* 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
movl %eax, %fs
movl %eax, %gs
lldt %ax
movl $0x20, %eax
ltr %ax
* 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 LOAD_PHYSICAL_ADDR
* We cannot rely on the calculation done in 32-bit mode, since we
* may have been invoked via the 64-bit entry point.
/* Start with the delta to where the kernel will run at. */
leaq startup_32(%rip) /* - $startup_32 */, %rbp
movl BP_kernel_alignment(%rsi), %eax
decl %eax
addq %rax, %rbp
notq %rax
andq %rax, %rbp
/* Target address to relocate to for decompression */
leaq z_extract_offset(%rbp), %rbx
/* Set up the stack */
leaq boot_stack_end(%rbx), %rsp
/* Zero EFLAGS */
pushq $0
* Copy the compressed kernel to the end of our buffer
* where decompression in place becomes safe.
pushq %rsi
leaq (_bss-8)(%rip), %rsi
leaq (_bss-8)(%rbx), %rdi
movq $_bss /* - $startup_32 */, %rcx
shrq $3, %rcx
rep movsq
popq %rsi
* Jump to the relocated address.
leaq relocated(%rbx), %rax
jmp *%rax
* Clear BSS (stack is currently empty)
xorl %eax, %eax
leaq _bss(%rip), %rdi
leaq _ebss(%rip), %rcx
subq %rdi, %rcx
shrq $3, %rcx
rep stosq
* Adjust our own GOT
leaq _got(%rip), %rdx
leaq _egot(%rip), %rcx
cmpq %rcx, %rdx
jae 2f
addq %rbx, (%rdx)
addq $8, %rdx
jmp 1b
* Do the decompression, and jump to the new kernel..
pushq %rsi /* Save the real mode argument */
movq %rsi, %rdi /* real mode address */
leaq boot_heap(%rip), %rsi /* malloc area for uncompression */
leaq input_data(%rip), %rdx /* input_data */
movl $z_input_len, %ecx /* input_len */
movq %rbp, %r8 /* output target address */
call decompress_kernel
popq %rsi
* Jump to the decompressed kernel.
jmp *%rbp
.word gdt_end - gdt
.long gdt
.word 0
.quad 0x0000000000000000 /* NULL descriptor */
.quad 0x00af9a000000ffff /* __KERNEL_CS */
.quad 0x00cf92000000ffff /* __KERNEL_DS */
.quad 0x0080890000000000 /* TS descriptor */
.quad 0x0000000000000000 /* TS continued */
* Stack and heap for uncompression
.balign 4
.fill BOOT_HEAP_SIZE, 1, 0
.fill BOOT_STACK_SIZE, 1, 0
* Space for page tables (not in .bss so not zeroed)
.section ".pgtable","a",@nobits
.balign 4096
.fill 6*4096, 1, 0