linux/arch/x86_64/kernel/relocate_kernel.S

/*
 * relocate_kernel.S - put the kernel image in place to boot
 * Copyright (C) 2002-2005 Eric Biederman  <ebiederm@xmission.com>
 *
 * This source code is licensed under the GNU General Public License,
 * Version 2.  See the file COPYING for more details.
 */

#include <linux/linkage.h>

	/*
	 * Must be relocatable PIC code callable as a C function, that once
	 * it starts can not use the previous processes stack.
	 */
	.globl relocate_new_kernel
	.code64
relocate_new_kernel:
	/* %rdi page_list
	 * %rsi reboot_code_buffer
	 * %rdx start address
	 * %rcx page_table
	 * %r8  arg5
	 * %r9  arg6
	 */

	/* zero out flags, and disable interrupts */
	pushq $0
	popfq

	/* set a new stack at the bottom of our page... */
	lea   4096(%rsi), %rsp

	/* store the parameters back on the stack */
	pushq	%rdx /* store the start address */

	/* Set cr0 to a known state:
	 * 31 1 == Paging enabled
	 * 18 0 == Alignment check disabled
	 * 16 0 == Write protect disabled
	 * 3  0 == No task switch
	 * 2  0 == Don't do FP software emulation.
	 * 0  1 == Proctected mode enabled
	 */
	movq	%cr0, %rax
	andq	$~((1<<18)|(1<<16)|(1<<3)|(1<<2)), %rax
	orl	$((1<<31)|(1<<0)), %eax
	movq	%rax, %cr0

	/* Set cr4 to a known state:
	 * 10 0 == xmm exceptions disabled
	 * 9  0 == xmm registers instructions disabled
	 * 8  0 == performance monitoring counter disabled
	 * 7  0 == page global disabled
	 * 6  0 == machine check exceptions disabled
	 * 5  1 == physical address extension enabled
	 * 4  0 == page size extensions	disabled
	 * 3  0 == Debug extensions disabled
	 * 2  0 == Time stamp disable (disabled)
	 * 1  0 == Protected mode virtual interrupts disabled
	 * 0  0 == VME disabled
	 */

	movq	$((1<<5)), %rax
	movq	%rax, %cr4

	jmp 1f
1:

	/* Switch to the identity mapped page tables,
	 * and flush the TLB.
	*/
	movq	%rcx, %cr3

	/* Do the copies */
	movq	%rdi, %rcx 	/* Put the page_list in %rcx */
	xorq	%rdi, %rdi
	xorq	%rsi, %rsi
	jmp	1f

0:	/* top, read another word for the indirection page */

	movq	(%rbx), %rcx
	addq	$8,	%rbx
1:
	testq	$0x1,	%rcx  /* is it a destination page? */
	jz	2f
	movq	%rcx,	%rdi
	andq	$0xfffffffffffff000, %rdi
	jmp	0b
2:
	testq	$0x2,	%rcx  /* is it an indirection page? */
	jz	2f
	movq	%rcx,   %rbx
	andq	$0xfffffffffffff000, %rbx
	jmp	0b
2:
	testq	$0x4,	%rcx  /* is it the done indicator? */
	jz	2f
	jmp	3f
2:
	testq	$0x8,	%rcx  /* is it the source indicator? */
	jz	0b	      /* Ignore it otherwise */
	movq	%rcx,   %rsi  /* For ever source page do a copy */
	andq	$0xfffffffffffff000, %rsi

	movq	$512,   %rcx
	rep ; movsq
	jmp	0b
3:

	/* To be certain of avoiding problems with self-modifying code
	 * I need to execute a serializing instruction here.
	 * So I flush the TLB by reloading %cr3 here, it's handy,
	 * and not processor dependent.
	 */
	movq	%cr3, %rax
	movq	%rax, %cr3

	/* set all of the registers to known values */
	/* leave %rsp alone */

	xorq	%rax, %rax
	xorq	%rbx, %rbx
	xorq    %rcx, %rcx
	xorq    %rdx, %rdx
	xorq    %rsi, %rsi
	xorq    %rdi, %rdi
	xorq    %rbp, %rbp
	xorq	%r8,  %r8
	xorq	%r9,  %r9
	xorq	%r10, %r9
	xorq	%r11, %r11
	xorq	%r12, %r12
	xorq	%r13, %r13
	xorq	%r14, %r14
	xorq	%r15, %r15

	ret
relocate_new_kernel_end:

	.globl relocate_new_kernel_size
relocate_new_kernel_size:
	.quad relocate_new_kernel_end - relocate_new_kernel