Check for magic bytes before booting a disk's boot sector

This commit is contained in:
Ry 2023-03-04 18:14:14 -08:00
parent a4efa7e640
commit 9cfb010116

View File

@ -1,14 +1,26 @@
; disk booting routines ; disk booting routines
; these are only used during booting, they are not exposed via the jump table
; load the boot sector of disk 0 to 0x00000800 and jump to it ; load the boot sector of disk 0 to 0x00000800 and jump to it
; inputs: ; inputs:
; none ; none
; outputs: ; outputs:
; none (doesn't return) ; none (returns if disk 0 is not bootable)
start_boot_process: start_boot_process:
mov r0, 0x80003000 ; command to read a sector from disk 0 into memory ; read sector 0 to 0x800
mov r1, 0x80002000 ; command to set the location of the buffer mov r0, 0
mov r1, 0
mov r2, 0x00000800
call read_sector
; check for the bootable magic bytes
cmp [0x000009FC], 0x523C334C
ifnz ret
; now clean up and jump to the loaded binary
call boot_cleanup
mov rsp, SYSTEM_STACK ; reset stack pointer
mov r0, 0 ; booting from disk id 0
jmp 0x00000800
; read sector 0 to 0x800 ; read sector 0 to 0x800
out r1, 0x00000800 out r1, 0x00000800
@ -28,4 +40,37 @@ boot_cleanup:
mov r0, BACKGROUND_COLOR mov r0, BACKGROUND_COLOR
call fill_background call fill_background
movz.8 r0, 0
movz.8 r1, 0
movz.8 r2, 0
movz.8 r3, 0
movz.8 r4, 0
movz.8 r5, 0
movz.8 r6, 0
movz.8 r7, 0
movz.8 r8, 0
movz.8 r9, 0
movz.8 r10, 0
movz.8 r11, 0
movz.8 r12, 0
movz.8 r13, 0
movz.8 r14, 0
movz.8 r15, 0
movz.8 r16, 0
movz.8 r17, 0
movz.8 r18, 0
movz.8 r19, 0
movz.8 r20, 0
movz.8 r21, 0
movz.8 r22, 0
movz.8 r23, 0
movz.8 r24, 0
movz.8 r25, 0
movz.8 r26, 0
movz.8 r27, 0
movz.8 r28, 0
movz.8 r29, 0
movz.8 r30, 0
movz.8 r31, 0
ret ret