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Added ability for kernel to load files from disk and execute them

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This commit is contained in:
Xnoe 2021-08-29 17:09:08 +01:00
parent 3e288a821e
commit fa15c6f6d9
Signed by: xnoe
GPG Key ID: 45AC398F44F0DAFE
1 changed files with 222 additions and 3 deletions
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225
kernel.asm
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@ -2,6 +2,39 @@
mov ax, 2000h
mov ds, ax
pop ax
mov byte [bootdisk], al
; Set up kernel specifics
; Root Directory Entries will be at 2000h:2000h
; FAT1 will be at 2000h:4000h
mov ax, 2000h
mov es, ax
mov bx, 2000h
mov ah, 2
mov al, 16
mov cl, 20
mov ch, 0
mov dh, 0
mov dl, [bootdisk]
; Load sectors 20 through 36 to 2000h:2000h
int 13h
mov ax, 2000h
mov es, ax
mov bx, 4000h
mov ah, 2
mov al, 9
mov cl, 2
mov ch, 0
mov dh, 0
mov dl, [bootdisk]
; Load sectors 2 through 11 to 2000h:4000h
int 13h
push msg
call print
@ -9,6 +42,15 @@ cmd_loop:
push cmd_prompt
call print
; Clear command buffer
mov al, 0
mov di, user_cmd
mov cx, 64
clear_loop:
stosb
loop clear_loop
push user_cmd
push 64
call readline
@ -28,6 +70,44 @@ cmd_loop:
rep cmpsb
je cmd_clear
; If the user hasn't run a command we should determine if they're trying to run a program.
; Decode input to filename
push user_cmd
call decode_filename
; Search for file
mov si, ax
call file_exists
; If it doesn't exist jump to error
cmp ax, 0
je handle_error
; If the file exists load it at 3000h:0
push ax
push 0
push 3000h
call load_file
; Make a call to 3000h:0
call 3000h:0
; We've now returned.
; Recover ds
mov ax, 2000h
mov ds, ax
mov es, ax
; jmp $
; Loop
jmp cmd_loop
handle_error:
push cmd_err
call print
@ -64,13 +144,17 @@ cmd_clear:
data:
msg db "Kernel OK!", 13, 10, 0
cmd_prompt db ">>> ", 0
cmd_err db "Bad Command!", 13, 10, 13, 10, 0
cmd_err db "Bad Command or filename!", 13, 10, 13, 10, 0
cmd_help_text db "help"
cmd_clear_text db "clear"
newline db 13, 10, 0
bootdisk db 0
program_two db "HELLO BIN"
user_cmd:
@ -92,7 +176,7 @@ print_loop:
jmp print_loop
print_exit:
pop bp
ret
ret 2
; readline(max length, buffer)
readline:
@ -145,4 +229,139 @@ readline_backspace:
readline_exit:
pop bp
ret
ret 4
file_exists:
push si
mov bp, sp
mov cx, 256 ; Hardcode the amount of entries for now
mov ax, ds
mov es, ax
mov ax, 0
file_exists_loop:
pop si ; Get value in to si
push si ; Keep track of original value
xchg cx, dx
mov di, 2000h ; Root Entries is at 2000h:2000h
add di, ax
mov cx, 11
rep cmpsb
je file_exists_found
add ax, 32
xchg cx, dx
loop file_exists_loop
file_exists_not_found:
mov ax, 0
pop si
ret
file_exists_found:
mov ax, [es:di+0fh]
pop si
ret
; loadfile(segment, offset, initsector)
load_file:
push bp
mov bp, sp
mov ax, word [bp + 4]
mov word [_load_segment], ax
mov ax, word [bp + 6]
mov word [_load_pointer], ax
mov ax, word [bp + 8]
mov word [_load_cluster], ax
mov ax, word [_load_segment]
mov es, ax
load_file_loop:
mov bx, word [_load_pointer]
mov al, byte [_load_cluster]
add al, 34
mov cl, al
mov al, 1
mov ah, 2
mov ch, 0
mov dh, 0
mov dl, byte [bootdisk]
int 13h
add word [_load_pointer], 512
mov si, word [_load_cluster]
shl si, 1
add si, 4000h
; add si, 1
cmp word [ds:si], 0ffffh
je load_file_loaded
add word [_load_cluster], 1
jmp load_file_loop
load_file_loaded:
pop bp
ret 6
_load_pointer dw 0
_load_cluster dw 0
_load_segment dw 0
decode_filename:
push bp
mov bp, sp
push word [bp + 4]
; First we want to clear the buffer with 0x20s
mov al, 20h
mov cx, 11
mov di, _decode_buffer
decode_clear_loop:
stosb
loop decode_clear_loop
pop si
mov cx, 8
mov bx, 0
decode_filename_loop:
lodsb
cmp al, "."
je decode_filename_stage2
mov byte [_decode_buffer+bx], al
inc bx
loop decode_filename_loop
decode_filename_stage2:
mov bx, 8
mov cx, 3
; add si, 1
decode_filename_stage2_loop:
lodsb
cmp al, 0
je decode_filename_final
mov byte [_decode_buffer+bx], al
inc bx
loop decode_filename_stage2_loop
decode_filename_final:
pop bp
mov ax, _decode_buffer
ret 2
_decode_buffer:
times 11 db 0