Re: Issue with custom Linux Bootloader
Posted: Fri Nov 21, 2008 8:50 am
I see my mistake with loading it from the Floppy.
Once I was able to load it from a Floppy, I was able to debug. The following is my changed code that can boot the Linux Kernel. All I can say is that with BOCHS I able to confirm that all the registers were set correctly. I tried this on my target and the kernel boots correctly.
Thanks for all the assistance, I can have a nice relaxing weekend
-Moffatt
Once I was able to load it from a Floppy, I was able to debug. The following is my changed code that can boot the Linux Kernel. All I can say is that with BOCHS I able to confirm that all the registers were set correctly. I tried this on my target and the kernel boots correctly.
Code: Select all
_TEXT32 SEGMENT PARA PUBLIC USE32 'CODE16'
ASSUME CS:_TEXT32, DS:NOTHING
org 0x0
;Disable the Interrupts before beginning
cli
; Reload CS with 16-bit value
; Try a jmp
db 0xea
dw 0x30 ; Hardcoded JUMP to known offset
dw PSEUDO_RM_CSEG
_TEXT32 Ends
_TEXT16 SEGMENT PARA PUBLIC USE16 'CODE16'
ASSUME CS:_TEXT16, DS:NOTHING
org 0x20
; Load the Segment Registers, with Segment Limit
mov ax, PSEUDO_RM_DSEG
mov ss, ax
mov ds, ax
mov es, ax
mov fs, ax
mov gs, ax
; Clear the PE flag in the CR0 register
mov eax, cr0 ; Get the current CR0
and al, NOT 1 ; Clear the PE bit to enable real mode
mov cr0, eax ; NOW WE'RE IN REALMODE!
; Reload CS with Real Mode value
; Try a jmp
db 0xea
dw 0x60 ; Hardcoded JUMP to known offset
dw 0x1000
org 0x50
;Change Bx to linux kernel segment
mov bx, LINUX_KERNEL_SEGMENT
mov ss, bx
mov sp, LINUX_SETUP_STACK
mov ds, bx
mov es, bx
mov fs, bx
mov gs, bx
;/* jump to start */
;/* ljmp */
; Always jump to LINUX_KERNEL_ENTRY_POINT
db 0xea
dw 0
dw LINUX_KERNEL_ENTRY_POINT
_TEXT16 ends
end
-Moffatt