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/*
*
* Trampoline.S Derived from Setup.S by Linus Torvalds
*
* 4 Jan 1997 Michael Chastain: changed to gnu as.
* 15 Sept 2005 Eric Biederman: 64bit PIC support
*
* Entry: CS:IP point to the start of our code, we are
* in real mode with no stack, but the rest of the
* trampoline page to make our stack and everything else
* is a mystery.
*
* On entry to trampoline_start, the processor is in real mode
* with 16-bit addressing and 16-bit data. CS has some value
* and IP is zero. Thus, data addresses need to be absolute
* (no relocation) and are taken with regard to r_base.
*
* With the addition of trampoline_level4_pgt this code can
* now enter a 64bit kernel that lives at arbitrary 64bit
* physical addresses.
*
* If you work on this file, check the object module with objdump
* --full-contents --reloc to make sure there are no relocation
* entries.
*/
#include <linux/linkage.h>
#include <linux/init.h>
#include <asm/pgtable_types.h>
#include <asm/page_types.h>
#include <asm/msr.h>
#include <asm/segment.h>
#include <asm/processor-flags.h>
#include "realmode.h"
.text
.code16
.balign PAGE_SIZE
ENTRY(trampoline_start)
cli # We should be safe anyway
wbinvd
LJMPW_RM(1f)
1:
mov %cs, %ax # Code and data in the same place
mov %ax, %ds
mov %ax, %es
mov %ax, %ss
movl $0xA5A5A5A5, trampoline_status
# write marker for master knows we're running
# Setup stack
movl $rm_stack_end, %esp
call verify_cpu # Verify the cpu supports long mode
testl %eax, %eax # Check for return code
jnz no_longmode
/*
* GDT tables in non default location kernel can be beyond 16MB and
* lgdt will not be able to load the address as in real mode default
* operand size is 16bit. Use lgdtl instead to force operand size
* to 32 bit.
*/
lidtl tr_idt # load idt with 0, 0
lgdtl tr_gdt # load gdt with whatever is appropriate
movw $__KERNEL_DS, %dx # Data segment descriptor
# Enable protected mode
movl $X86_CR0_PE, %eax # protected mode (PE) bit
movl %eax, %cr0 # into protected mode
# flush prefetch and jump to startup_32
ljmpl $__KERNEL32_CS, $pa_startup_32
no_longmode:
hlt
jmp no_longmode
#include "../kernel/verify_cpu.S"
.section ".text32","ax"
.code32
.balign 4
ENTRY(startup_32)
movl %edx, %ss
addl $pa_real_mode_base, %esp
movl %edx, %ds
movl %edx, %es
movl %edx, %fs
movl %edx, %gs
movl pa_tr_cr4, %eax
movl %eax, %cr4 # Enable PAE mode
# Setup trampoline 4 level pagetables
movl $pa_trampoline_pgd, %eax
movl %eax, %cr3
# Set up EFER
movl pa_tr_efer, %eax
movl pa_tr_efer + 4, %edx
movl $MSR_EFER, %ecx
wrmsr
# Enable paging and in turn activate Long Mode
movl $(X86_CR0_PG | X86_CR0_WP | X86_CR0_PE), %eax
movl %eax, %cr0
/*
* At this point we're in long mode but in 32bit compatibility mode
* with EFER.LME = 1, CS.L = 0, CS.D = 1 (and in turn
* EFER.LMA = 1). Now we want to jump in 64bit mode, to do that we use
* the new gdt/idt that has __KERNEL_CS with CS.L = 1.
*/
ljmpl $__KERNEL_CS, $pa_startup_64
.section ".text64","ax"
.code64
.balign 4
ENTRY(startup_64)
# Now jump into the kernel using virtual addresses
jmpq *tr_start(%rip)
.section ".rodata","a"
# Duplicate the global descriptor table
# so the kernel can live anywhere
.balign 16
.globl tr_gdt
tr_gdt:
.short tr_gdt_end - tr_gdt - 1 # gdt limit
.long pa_tr_gdt
.short 0
.quad 0x00cf9b000000ffff # __KERNEL32_CS
.quad 0x00af9b000000ffff # __KERNEL_CS
.quad 0x00cf93000000ffff # __KERNEL_DS
tr_gdt_end:
.bss
.balign PAGE_SIZE
GLOBAL(trampoline_pgd) .space PAGE_SIZE
.balign 8
GLOBAL(trampoline_header)
tr_start: .space 8
GLOBAL(tr_efer) .space 8
GLOBAL(tr_cr4) .space 4
END(trampoline_header)
#include "trampoline_common.S"
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