; assumptions about the starting envionment
cpu 8086
org 0x0000

_startup:
  xor ax, ax ; trash ax
  mov ax, cs
  cmp ax, 0x0000 ; MBR or NBP, CS=0000 IP=7C00
  je .mbr
  cmp ax, 0x07C0 ;  MBR on weird BIOS, CS=07C0 IP=0000
  je .mbr
.dos:
  ; ROP because call only works on immediate or memory
  mov ax, cs
  push ax ; return CS
  mov ax, .dosret
  add ax, 0x0100
  push ax ; return IP
  mov ax, cs
  add ax, 0x0010
  push ax ; main CS
  mov ax, main
  push ax ; main IP
  retf
.dosret:
  int 0x20
  jmp .halt
.mbr:
  push si ; index of partition table entry
  push ds ; segment for ^
  push dx ; dl might contain drive number
  push bx ; possible offset for pxeenv+ struct
  push es ; segment for ^

  mov ax, 0x0050
  mov es, ax
  mov di, 0x0000

  xor ax, ax
  mov ds, ax
  mov si, 0x7C00

  mov cx, _reloc_end
  rep movsb

  call 0x0050:main
.halt:
  hlt
  jmp .halt

main:
  mov ax, cs
  mov ds, ax

  call heap_init
  call ivt_backup
  call debug_init

  int 0x2E

  retf

%include "heap.asm"
%include "intr.asm"
%include "debug.asm"
%include "kprintf.asm"

_reloc_end:

align 16
heap: