boot.s

   1 # boot.s
   2 #
   3 # bootstrap assembly stub to setup the processor
   4 # and call the kernel main function
   5 ################################################
   6
   7 # declare multiboot header
   8
   9 .set ALIGN,    1<<0
  10 .set MEMINFO,  1<<1
  11 .set FLAGS,    ALIGN | MEMINFO
  12 .set MAGIC,    0x1BADB002
  13 .set CHECKSUM, -(MAGIC + FLAGS)
  14
  15 .section .multiboot
  16 .align 4
  17 .long MAGIC
  18 .long FLAGS
  19 .long CHECKSUM
  20
  21 # set up a temporary stack
  22
  23 .section .bootstrap_stack
  24 stack_bottom:
  25 .skip 16384 # 16 KiB
  26 stack_top:
  27
  28 # we are now ready to start working
  29
  30 .section .text
  31 .global _start
  32 .type _start, @function
  33 _start:
  34
  35         # we are now in kernel mode.
  36         # next, set up the actual stack
  37         movl $stack_top, %esp
  38
  39         # then jump in the actual kernel
  40         call kmain
  41
  42         # if we ever return from the kernel, we put the cpu in an idle loop
  43         cli
  44         hlt
  45 .Lloop:
  46         jmp .Lloop
  47
  48 # useful for debugging, call tracing etc
  49 .size _start, . - _start