root/entry.S

/*   */

   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
  30 multiboot_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
  45 entry:
  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

/*   */