119 lines
3 KiB
NASM
119 lines
3 KiB
NASM
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TITLE KERNSTUB - Assembly stub program for KERNEL.EXE
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.xlist
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?DF = 1
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SWAPPRO = 0
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include cmacros.inc
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; NOTE: This code is always assembled in real mode, so it'll run on any machine.
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;
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PMODE32=0
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include newexe.inc
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include protect.inc
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ifdef WOW
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include vint.inc
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endif
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.list
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createSeg _TEXT,CODE,PARA,PUBLIC,CODE
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createSeg STACK,STACK,PARA,STACK,STACK
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sBegin STACK
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DB 128 DUP (?)
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stacktop LABEL BYTE
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sEnd STACK
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sBegin CODE
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assumes CS,CODE
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assumes DS,CODE
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KERNSTUB PROC FAR
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push cs
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pop ds
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mov si,codeOFFSET stacktop
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add si,1FFh
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and si,not 1FFh
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cmp cs:[si].ne_magic,NEMAGIC
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je @F
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jmp ksfail
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@@:
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mov ax,ds
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cli
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mov ss,ax
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mov sp,si
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sti
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mov bx,ds:[si].ne_autodata ; Get number of automatic DS
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dec bx
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jl ksg11 ; Continue if no DS
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shl bx,1
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shl bx,1
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shl bx,1
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.errnz 8 - SIZE new_seg
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add bx,ds:[si].ne_segtab ; DS:BX -> seg. tab. entry for DS
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mov ax,ds:[si+bx].ns_sector ; Compute paragraph address of DS
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cmp ds:[si].ne_align,0
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jne ksg10
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mov ds:[si].ne_align,NSALIGN ; in DI
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ksg10:
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mov cx,ds:[si].ne_align ; Convert sectors to paragraphs
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sub cx,4
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shl ax,cl
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mov di,cs ; Add to paragraph address of old
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sub di,20h ; exe header
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add di,ax
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ksg11:
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push cx
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mov bx,word ptr cs:[si].ne_csip+2 ; Get number of CS
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dec bx
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jl ksfail ; Error if no CS
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shl bx,1
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shl bx,1
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shl bx,1
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.errnz 8 - SIZE new_seg
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add bx,cs:[si].ne_segtab ; DS:BX -> seg. tab. entry for CS
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mov ax,cs:[si+bx].ns_sector ; Compute paragraph address of CS
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mov cx,cs:[si].ne_align ; Convert sectors to paragraphs
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sub cx,4
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shl ax,cl
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pop bx
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mov dx,cs ; Add to paragraph address of old
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sub dx,20h ; exe header
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add dx,ax
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push dx ; Push far address of start proc
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push word ptr cs:[si].ne_csip
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mov ds,di ; DS:0 points to automatic DS
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mov cx,si ; CX = file offset of new header
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add cx,200h
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jmp short ksgo
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org 0A0h
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ksgo:
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;!!! The old CS selector should be freed up at some point!
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mov ax, "KO"
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ret ; FAR return to start proc
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ksfail:
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call ks1
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DB 'KERNSTUB: Error during boot',13,10,'$'
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ks1: pop dx
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push cs
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pop ds ; DS:DX -> error message
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mov ah,9 ; Print error message
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int 21h
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mov ax,4C01h ; Terminate program, exit code = 1
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int 21h
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KERNSTUB ENDP
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sEnd CODE
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END KERNSTUB
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