1# The xv6 kernel starts executing in this file. This file is linked with 2# the kernel C code, so it can refer to kernel symbols such as main(). 3# The boot block (bootasm.S and bootmain.c) jumps to entry below. 4 5# Multiboot header, for multiboot boot loaders like GNU Grub. 6# http://www.gnu.org/software/grub/manual/multiboot/multiboot.html 7# 8# Using GRUB 2, you can boot xv6 from a file stored in a 9# Linux file system by copying kernel or kernelmemfs to /boot 10# and then adding this menu entry: 11# 12# menuentry "xv6" { 13# insmod ext2 14# set root='(hd0,msdos1)' 15# set kernel='/boot/kernel' 16# echo "Loading ${kernel}..." 17# multiboot ${kernel} ${kernel} 18# boot 19# } 20 21#include "asm.h" 22#include "memlayout.h" 23#include "mmu.h" 24#include "param.h" 25 26# Multiboot header. Data to direct multiboot loader. 27.p2align 2 28.text 29.globl multiboot_header 30multiboot_header: 31 #define magic 0x1badb002 32 #define flags 0 33 .long magic 34 .long flags 35 .long (-magic-flags) 36 37# By convention, the _start symbol specifies the ELF entry point. 38# Since we haven't set up virtual memory yet, our entry point is 39# the physical address of 'entry'. 40.globl _start 41_start = V2P_WO(entry) 42 43# Entering xv6 on boot processor, with paging off. 44.globl entry 45entry: 46 # Turn on page size extension for 4Mbyte pages 47 movl %cr4, %eax 48 orl $(CR4_PSE), %eax 49 movl %eax, %cr4 50 # Set page directory 51 movl $(V2P_WO(entrypgdir)), %eax 52 movl %eax, %cr3 53 # Turn on paging. 54 movl %cr0, %eax 55 orl $(CR0_PG|CR0_WP), %eax 56 movl %eax, %cr0 57 58 # Set up the stack pointer. 59 movl $(stack + KSTACKSIZE), %esp 60 61 # Jump to main(), and switch to executing at 62 # high addresses. The indirect call is needed because 63 # the assembler produces a PC-relative instruction 64 # for a direct jump. 65 mov $main, %eax 66 jmp *%eax 67 68.comm stack, KSTACKSIZE 69