1 files changed, 127 insertions, 0 deletions
diff --git a/kernel/boot.s b/kernel/boot.s
new file mode 100644
index 0000000..be68109
--- /dev/null
+++ b/kernel/boot.s
@@ -0,0 +1,127 @@
+global kboot
+extern kmain
+
+; Multiboot header
+section .mboothdr
+mboot_hdr:
+  align 4
+  dd 0x1BADB002
+  dd 0x00
+  dd - (0x1BADB002 + 0x00)
+
+section .text
+
+kboot:
+  cli
+  call flush_gdt
+  call flush_idt
+  call kmain
+  cli
+  hlt
+
+gdt:
+  ; null descriptor
+  dq 0
+  ; kernel code segment
+  dw 0xFFFF ; limit (bits 0-15)
+  dw 0x0000 ; base (bits 0-15)
+  db 0x00   ; base (bits 16-23)
+  db 0x9A   ; access byte
+  db 0xCF   ; flags / limit (bits 16-19)
+  db 0x00   ; base (bits 24-31)
+  ; kernel data segment
+  dw 0xFFFF
+  dw 0x0000
+  db 0x00
+  db 0x92
+  db 0xCF
+  db 0x00
+  ; userspace code segment
+  dw 0xFFFF
+  dw 0x0000
+  db 0x00
+  db 0xFA
+  db 0xCF
+  db 0x00
+  ; userspace data segment
+  dw 0xFFFF
+  dw 0x0000
+  db 0x00
+  db 0xF2
+  db 0xCF
+  db 0x00
+
+gdtp:
+  dw ($-gdt-1)
+  dd gdt
+
+flush_gdt:
+  push ebp
+  mov ebp, esp
+  lgdt [gdtp]
+  mov ax, 0x10
+  mov ds, ax
+  mov es, ax
+  mov fs, ax
+  mov gs, ax
+  mov ss, ax
+  jmp 0x08:.end
+.end:
+  pop ebp
+  ret
+
+idt:
+  times (256*8) db 0
+
+idtp:
+  dw ($-idt-1)
+  dd idt
+
+int_handler:
+  iret
+
+flush_idt:
+  push ebp
+  mov ebp, esp
+  mov ecx, 256
+  mov edx, idt
+.loop:
+  mov eax, int_handler
+  mov [edx], ax
+  mov word [edx+2], 0x08
+  mov byte [edx+4], 0
+  mov byte [edx+5], 0x8E
+  shr eax, 16
+  mov [edx+6], ax
+  add edx, 8
+  dec ecx
+  jz .end
+  jmp .loop
+.end:
+  lidt [idtp]
+  call pic_init
+  sti
+  pop ebp
+  ret
+
+pic_init:
+  push ebp
+  mov ebp, esp
+  mov al, 0x11
+  out 0x20, al
+  out 0xA0, al
+  mov al, 0x20
+  out 0x21, al
+  out 0xA1, al
+  mov al, 0x04
+  out 0x21, al
+  mov al, 0x02
+  out 0xA1, al
+  mov al, 0x01
+  out 0x21, al
+  out 0xA1, al
+  mov al, 0xFF
+  out 0x21, al
+  out 0xA1, al
+  pop ebp
+  ret