2025-07-04 03:10:55 +02:00
|
|
|
// vim: et:sw=12:ts=12:sts=12
|
|
|
|
|
|
|
|
|
|
.global _start
|
|
|
|
|
.text
|
2025-07-04 04:02:05 +02:00
|
|
|
.code16
|
2025-07-04 03:10:55 +02:00
|
|
|
|
2025-07-04 15:29:41 +02:00
|
|
|
_start: cli
|
|
|
|
|
cld
|
|
|
|
|
|
2025-07-04 15:51:51 +02:00
|
|
|
// we keep our text and data close to each other
|
|
|
|
|
xor %ax, %ax
|
2025-07-04 04:02:05 +02:00
|
|
|
mov %ax, %ds
|
|
|
|
|
|
2025-07-04 15:51:51 +02:00
|
|
|
mov $msg_start, %si
|
2025-07-04 15:29:41 +02:00
|
|
|
call print
|
|
|
|
|
|
2025-07-04 15:51:51 +02:00
|
|
|
mov $msg_a20, %si
|
|
|
|
|
call print
|
2025-07-04 15:29:41 +02:00
|
|
|
call enable_a20
|
|
|
|
|
|
2025-07-04 15:51:51 +02:00
|
|
|
mov $msg_unreal, %si
|
2025-07-04 04:02:05 +02:00
|
|
|
call print
|
2025-07-04 15:51:51 +02:00
|
|
|
call unreal
|
2025-07-04 15:29:41 +02:00
|
|
|
|
2025-07-04 15:51:51 +02:00
|
|
|
mov $msg_fin, %si
|
|
|
|
|
call print
|
2025-07-04 04:02:05 +02:00
|
|
|
1: hlt
|
|
|
|
|
jmp 1b
|
|
|
|
|
|
2025-07-04 15:29:41 +02:00
|
|
|
enable_a20: // TODO more thorough implementation
|
|
|
|
|
inb $0x92, %al
|
|
|
|
|
or $2, %al
|
|
|
|
|
outb %al, $0x92
|
|
|
|
|
ret
|
|
|
|
|
|
2025-07-04 15:51:51 +02:00
|
|
|
unreal: push %ds
|
|
|
|
|
lgdt gdt_ptr
|
|
|
|
|
|
|
|
|
|
mov %cr0, %eax
|
|
|
|
|
or $0x01, %al
|
2025-07-04 15:29:41 +02:00
|
|
|
mov %eax, %cr0
|
2025-07-04 15:51:51 +02:00
|
|
|
ljmp $0x8, $1f
|
|
|
|
|
|
|
|
|
|
1: mov $0x10, %cx
|
|
|
|
|
mov %cx, %ds
|
2025-07-04 15:29:41 +02:00
|
|
|
|
2025-07-04 15:51:51 +02:00
|
|
|
and $0xFE, %al
|
|
|
|
|
mov %eax, %cr0
|
|
|
|
|
ljmp $0x0, $2f
|
|
|
|
|
|
|
|
|
|
2: pop %ds
|
|
|
|
|
ret
|
|
|
|
|
|
2025-07-04 15:29:41 +02:00
|
|
|
print: xor %bx, %bx
|
2025-07-04 04:02:05 +02:00
|
|
|
|
|
|
|
|
1: lodsb
|
|
|
|
|
or %al, %al
|
|
|
|
|
jz 2f
|
2025-07-04 03:10:55 +02:00
|
|
|
mov $0x0E, %ah
|
|
|
|
|
int $0x10
|
|
|
|
|
jmp 1b
|
2025-07-04 04:02:05 +02:00
|
|
|
|
2025-07-04 15:29:41 +02:00
|
|
|
2: ret
|
|
|
|
|
|
|
|
|
|
gdt: // entry 0: null descriptor
|
|
|
|
|
.word 0
|
|
|
|
|
.word 0
|
|
|
|
|
.byte 0
|
|
|
|
|
.byte 0
|
|
|
|
|
.byte 0
|
|
|
|
|
.byte 0
|
|
|
|
|
// entry 1: code segment
|
|
|
|
|
.word 0xFFFF
|
|
|
|
|
.word 0
|
|
|
|
|
.byte 0
|
|
|
|
|
.byte 0b10011010
|
|
|
|
|
.byte 0x8F
|
|
|
|
|
.byte 0
|
|
|
|
|
// entry 2: data segment
|
|
|
|
|
.word 0xFFFF
|
|
|
|
|
.word 0
|
|
|
|
|
.byte 0
|
|
|
|
|
.byte 0b10010010
|
|
|
|
|
.byte 0x8F
|
|
|
|
|
.byte 0
|
|
|
|
|
.set gdt_size, .-gdt
|
|
|
|
|
gdt_ptr: .word gdt_size-1
|
|
|
|
|
.long gdt
|
2025-07-04 04:02:05 +02:00
|
|
|
|
2025-07-04 15:51:51 +02:00
|
|
|
msg_start: .asciz "Netboot via fernlader v1 ...\r\n"
|
|
|
|
|
msg_a20: .asciz " * Enabling A20\r\n"
|
|
|
|
|
msg_unreal: .asciz " * Unreal Mode\r\n"
|
|
|
|
|
msg_fin: .asciz "Finished.\r\n"
|
