cppkernel/kernel.asm at main · Ccode-archives/cppkernel · GitHub

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;nasm directive - 32 bit
bits 32
section .text
        ;multiboot spec
        align 4
        dd 0x1BADB002            ;magic
        dd 0x00                  ;flags
        dd - (0x1BADB002 + 0x00) ;checksum. m+f+c should be zero

global start
global read_port
global write_port
global load_idt
global kbhandler

extern kmain	        ;kmain is defined in the cpp file


  gdt:

  gdt_null:
  dq 0

  gdt_code:
  dw 0FFFFh
  dw 0

  db 0
  db 10011010b
  db 11001111b
  db 0

  gdt_data:
  dw 0FFFFh
  dw 0

  db 0
  db 10010010b
  db 11001111b
  db 0

  gdt_end:

  gdt_desc:
   dw gdt_end - gdt - 1
   dd gdt


; Read and write borrowed from lisse (https://github.com/InsaneMiner/Lisse)
read_port:
	mov edx, [esp + 4]
			;al is the lower 8 bits of eax
	in al, dx	;dx is the lower 16 bits of edx
	ret
write_port:
	mov   edx, [esp + 4]
	mov   al, [esp + 4 + 4]
	out   dx, al
	ret

load_idt:
	mov edx, [esp + 4]
	lidt [edx]
	sti
	ret

start:
  cli 			;block interrupts
  lgdt [gdt_desc]
  jmp 0x0008:fix_cs
  fix_cs:
  mov ax, 0x0010
  mov ds, ax
  mov es, ax
  mov fs, ax
  mov gs, ax
  mov ss, ax
  mov esp, stack_space	;set stack pointer
  call kmain
  jmp $		 	;halt the CPU

section .bss
resb 8192
stack_space: