79315836 - Fix OPs kernel.asm

MichaelPetch

Dec 29th, 2024 (edited)

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[org 0x8000]
[bits 16]
jmp short start
gdt_start:
dq 0x0000000000000000
dq 0x00CF9A000000FFFF
dq 0x00CF92000000FFFF
dq 0x00CF92000000FFFF
gdt_end:
gdt_descriptor:
dw gdt_end - gdt_start - 1
dd gdt_start
print:
push si
push ax
push bx
.loop:
lodsb
or al, al
jz .done
mov ah, 0x0E
mov bh, 0
int 0x10
jmp .loop
.done:
pop bx
pop ax
pop si
ret
start:
cli
xor ax, ax ; Set ES=DS=0
mov es, ax
mov ds, ax
mov ss, ax ; Set SS:SP (stackpointer) to 0x0000:0x7c00
; Will grow down beneath bootloader
mov sp, 0x7c00
mov si, start_sixteen
call print
in al, 0x64
.wait_ibe:
test al, 0x02
jnz .wait_ibe
mov al, 0xD1
out 0x64, al
.wait_ibe2:
in al, 0x64
test al, 0x02
jnz .wait_ibe2
mov al, 0xDF
out 0x60, al
first_sixteen:
cli
lgdt [gdt_descriptor]
mov eax, cr0
or eax, 1
mov cr0, eax
jmp dword 0x08:.afterstart
[bits 32]
.afterstart:
mov ax, 0x10
mov ds, ax
mov es, ax
mov fs, ax
mov gs, ax
mov ss, ax
mov esp, 0x7c00 ; Set protected mode stack to 0x7c00
; Initialize the entire BSS area to zero
mov ecx, _bss_end-_bss_start ; Length of region in ECX
xor eax, eax ; AL=0 (also used for rep stos)
mov edi, _bss_start ; Offset of BSS region
rep stosb ; Set ECX bytes of data at ES:[EDI] to AL(0)
; Remember parameters are passed right to left. Push in opposite order
; Setup exception 0 (div by zero)
push 0x8E ; Attribute for 32-bit interrupt gate (enabled)
push 0x08 ; Kernel code selector (from GDT)
push isr_divby0 ; Handler for exception
push 0x00 ; div by 0 (arithmetic error) is exception 0x00
call isg
add esp, 4*4 ; Remove the 4 parameters
; Setup exception 6 (invalid opcode)
push 0x8E ; Attribute for 32-bit interrupt gate (enabled)
push 0x08 ; Kernel code selector (from GDT)
push isr_invopcode ; Handler for invalid opcode
push 0x06 ; Invalid code is exception 0x06
call isg
add esp, 4*4 ; Remove the 4 parameters
call imake ; Set IDTR (via lidt)
; Cause invalid opcode exception
; ud2
; Cause division by 0 exception
xor ax, ax
div al
cli
.hltloop:
hlt
jmp .hltloop ; Infinite loop
isr_divby0:
; Replace with a proper interrupt/exception handler
hlt ; Inifinite loop
iret
isr_invopcode:
; Replace with a proper interrupt/exception handler
hlt ; Inifinite loop
iret
i686IDTLoad:
mov eax, [esp + 4]
lidt [eax]
ret
; void isg (uint32_t entrynum, void *handler, uint16_t selector, uint8_t attribs)
; Setup interrupt gate entrynum in the IDT with given handler function, selector, and attributes
;
; Parameters pushed on stack
;
isg:
push ebp
mov ebp, esp
sub esp, 8
mov edx, dword [ebp+10H]
mov eax, dword [ebp+14H]
mov word [ebp-4H], dx
mov byte [ebp-8H], al
mov eax, dword [ebp+0CH]
mov edx, eax
mov eax, dword [ebp+8H]
mov word [IDT+eax*8], dx
mov eax, dword [ebp+8H]
movzx edx, word [ebp-4H]
mov word [IDT+2H+eax*8], dx
mov eax, dword [ebp+8H]
mov byte [IDT+4H+eax*8], 0
mov eax, dword [ebp+8H]
movzx edx, byte [ebp-8H]
mov byte [IDT+5H+eax*8], dl
mov eax, dword [ebp+0CH]
shr eax, 16
mov edx, eax
mov eax, dword [ebp+8H]
mov word [IDT+6H+eax*8], dx
nop
leave
ret
; void ieg (uint32_t entrynum)
; Enable interrupt gate for entrynum in the IDT
;
; Parameters pushed on stack
;
ieg:
push ebp
mov ebp, esp
mov eax, dword [ebp+8H]
movzx eax, byte [IDT+5H+eax*8]
or eax, 0FFFFFF80H
mov edx, eax
mov eax, dword [ebp+8H]
mov byte [IDT+5H+eax*8], dl
nop
pop ebp
ret
; void idg (uint32_t entrynum)
; Disable interrupt gate for entrynum in the IDT
;
; Parameters pushed on stack
;
idg:
push ebp
mov ebp, esp
mov eax, dword [ebp+8H]
movzx eax, byte [IDT+5H+eax*8]
and eax, 7FH
mov edx, eax
mov eax, dword [ebp+8H]
mov byte [IDT+5H+eax*8], dl
nop
pop ebp
ret
imake:
push IDTDescriptor ; Argument 1 is address of IDT record
call i686IDTLoad
pop eax ; Remove arguments
ret
IDTDescriptor:
dw IDT_SIZE - 1
dd IDT
start_prog:
mov al, 2
mov ax, 1004
mov [Xval], eax
mov ax, 700
mov [Yval], eax
mov ax, 10
mov [Wval], eax
mov ax, 20
mov [Hval], eax
lea si, [PySpr]
call draw_spr
.halt:
cli
hlt
draw_spr:
xor edx, edx
mov ecx, [Hval]
draw_sprite:
mov eax, [Yval]
mov ebx, 1024
mul ebx
add eax, [Xval]
add edi, eax
push ecx
mov ecx, [Wval]
draw_pixels:
mov al, [si]
cmp al, 5
je skip_pixel_2
cld
movsb
jmp skip_pixel
skip_pixel_2:
inc edi
skip_pixel:
inc si
loop draw_pixels
pop ecx
mov eax, [Yval]
inc eax
mov [Yval], eax
loop draw_sprite
ret
start_sixteen: db 'KERNAL START', 0x0D, 0x0A, 0
Xval dd 0
Yval dd 0
Wval dd 0
Hval dw 0
PySpr db 5,5,5,2,2,2,2,5,5,5
db 5,5,2,2,2,2,2,2,5,5
db 5,2,2,2,2,2,2,2,2,5
db 2,2,2,2,2,2,2,2,2,2
db 5,8,8,8,8,8,8,8,8,5
db 5,8,15,0,8,8,0,15,8,5
db 5,8,8,8,8,8,8,8,8,5
db 5,8,8,0,0,0,0,8,8,5
db 5,5,8,8,8,8,8,8,5,5
db 2,2,2,2,2,2,2,2,2,2
db 2,2,2,2,2,2,2,2,2,2
db 2,5,2,2,2,2,2,2,5,2
db 2,5,2,2,2,2,2,2,5,2
db 2,5,2,2,2,2,2,2,5,2
db 8,5,2,2,2,2,2,2,5,8
db 5,5,6,6,6,6,6,6,5,5
db 5,5,6,6,5,5,6,6,5,5
db 5,5,6,6,5,5,6,6,5,5
db 5,5,6,6,5,5,6,6,5,5
db 5,7,7,7,5,5,7,7,7,5
section .bss
_bss_start:
IDT resq 256 ; Create an IDT with 256 entries
IDT_SIZE equ $-IDT
_bss_end:

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