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BOTOKILLER



Joined: 07 Jan 2011
Posts: 154
Location: Ukraine
BOTOKILLER
Hi everyone!!!
I've decided to rewrite the whole code so, that it becomes cleaner and more scalable, also try using paging. Well, I ran into a problem.
Code:
        USE16
        ORG 0h

        ;NOT ASSEMBLED!!!
        PRE_ASM_VAR:
        SSBL_Size equ 80h           ;should be like in MBR
        SSBL_Stack equ 20h          ;same
        Primary_CS equ 8h
        SDAq equ 0
        KERN_LOAD_Seg equ 0
        END_PRE_ASM_VARS:
        ;ASSEMBLED!!!

        jmp START


        DATASECT:

        DAP:                              ;DATA;REL
        DAP_Size             db 10h       ;0h  ;1h
        DAP_Res1             db 0         ;1h  ;2h
        DAP_Bytes2Transfer   db 1h        ;2h  ;3h
        DAP_Res2             db 0         ;3h  ;4h
        DAP_Buff_Addr1       dw 0h        ;4h  ;6h
        DAP_Buff_Addr2       dw 8000h     ;6h  ;8h
        DAP_LBA              dq 1h        ;8h  ;9h

        DAT_Disk_Num         db 80h       ;10h ;12h          number of device 80h-winchester
        DAT_Num_Of_Sects     dw 04h       ;11h ;13h          the number of 512byte sectors, that contain your kernel your kernel + 1

        END_DAP:

        GDT:
                dw GDT_ENDS + GDT_STARTS - 1h              ;size of GDT
                dd 0h                                       ;value to be inserted during execution
        GDT_STARTS:
        REC0:
                dq 0h

        REC1:
                dw 0FFFFh      ;Limit_0_15
                dw 00000h      ;Base_0_15
                db 00h         ;Base_16_23
                db 10011010b   ;||Present bit||Priviligies||1||Code-1, Data - 0||if want to execute from low levels - 1, else 0|| can write here? yes=1||0||
                db 11001111b   ;||Granularity||1||0||0||Limit 16-19||
                db 00h         ;Base_24_31

        REC2:
                dw 0FFFFh      ;Limit_0_15
                dw 00000h      ;Base_0_15
                db 00h         ;Base_16_23
                db 10010010b   ;||Present bit||Priviligies||1||Code-1, Data - 0||if want to execute from low levels - 1, else 0|| can write here? yes=1||0||
                db 11001111b   ;||Granularity||1||0||0||Limit 16-19||
                db 00h         ;Base_24_31


        GDT_ENDS:

        END_DATEASECT:

        START:

        SETREG_SSBL:
        xor eax, eax                       ;clean eax
        mov ax, cs                         ;ax = cs
        mov ds, ax                         ;ds = cs
        mov ss, ax                         ;ss = cs
        mov sp, (SSBL_Stack + SSBL_Size)*10h;stack points 256 bytes above end of SSBL
        shl eax, 4h                         ;get raw address of start of segment
        add eax, GDT_STARTS                 ;adding ofset of start of GDT
        mov dword [ds:GDT+2], eax          ;GDT offset ready
        mov bp, DATASECT                   ;base pointer = datasect
        ;well... thats all

        PMJMP:
        cli                                ;disable interrupts

        lea eax, [ds:GDT]
        lgdt [eax]

        mov ax, 2401h
        int 15h

        xor eax, eax
        mov ax, cs
        shl eax, 4h
        add eax, PMODE

        mov ebx, cr0
        or ebx, 1
        mov cr0, ebx

        jmp Primary_CS:eax  ;!!! HERE ERROR!!!

        USE32
        PMODE:


        FIN:
        times 2047d - FIN db 0h
        db 'F'        

    

I need to make a jump into protected mode code through address calculated in eax, but compiller doesnt lets me do it! Code is loaded right before EBDA and I dont know address where it is executed before compilation. How do I make that jump???

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NSOS


Last edited by BOTOKILLER on 25 Jul 2011, 13:06; edited 1 time in total
Post 25 Jul 2011, 11:30
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DJ Mauretto



Joined: 14 Mar 2007
Posts: 464
Location: Rome,Italy
DJ Mauretto
put the address in memory and make a jump Wink

Code:

Jmp  [16:32]
    

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Nil Volentibus Arduum Razz
Post 25 Jul 2011, 12:05
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BOTOKILLER



Joined: 07 Jan 2011
Posts: 154
Location: Ukraine
BOTOKILLER
Thats what i did:
Code:
        PMJMP:
        cli                                 ;disable interrupts

        xor eax, eax
        mov ax, cs
        shl eax, 4h
        add eax, PMODE
        mov [cs:JUMP_+2], eax

        lea eax, [ds:GDT]
        lgdt [eax]

        mov ax, 2401h
        int 15h

        mov ebx, cr0
        or ebx, 1
        mov cr0, ebx

        JUMP_:
        jmp pword Primary_CS:0h

                      

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NSOS
Post 25 Jul 2011, 13:07
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