boot/x86/stage3/e820.s

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