boot/x86/stage3/e820.s

   1 ; Code for getting the BIOS E820 memory map
   2
   3 bits 16
   4
   5 ; Return: ECX - number of entries, DI - pointer to map
   6 get_e820_map:
   7         push eax
   8         push ebx
   9         push edx
  10         push esi
  11         push es
  12
  13         xor ax, ax
  14         mov es, ax
  15         push dword 1
  16         sub sp, 20
  17         xor si, si
  18         xor ebx, ebx
  19         mov edx, 0x534d4150
  20         mov eax, 0xe820
  21         mov ecx, 24
  22         mov di, sp
  23         int 0x15
  24         jc .no_e820
  25         cmp eax, 0x534d4150
  26         jne .unexpected
  27         inc si
  28         .loop:
  29                 push dword 1
  30                 sub sp, 20
  31                 mov di, sp
  32                 mov eax, 0xe820
  33                 mov ecx, 24
  34                 int 0x15
  35                 jc .carry_done
  36                 inc si
  37                 cmp ebx, 0
  38                 je .done
  39                 jmp .loop
  40         .carry_done:
  41                 add sp, 24
  42         .done:
  43                 movzx ecx, si
  44                 movzx edi, sp
  45                 mov ax, 24
  46                 mul si
  47                 add sp, ax
  48                 pop es
  49                 pop esi
  50                 pop edx
  51                 pop ebx
  52                 pop eax
  53                 ret
  54         .no_e820:
  55                 print no_e820
  56                 hlt
  57                 jmp $-1
  58         .unexpected
  59                 print e820_unexpected
  60                 call print_dword
  61                 hlt
  62                 jmp $-1
  63
  64 no_e820: db "BIOS does not support E820, cannot proceed!", 0xd, 0xa, 0
  65 e820_unexpected: db "Unexpected value in EAX after getting map entry: expected SMAP, got ", 0