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Assembly Source File | 1988-03-19 | 14.8 KB | 313 lines

Title EXECOM: convert an .EXE file to a .COM file comment ! EXECOM 1.1 Copyright (c) 1988 Thomas G. Hanlin III 1712 Maple Hill Pl. Alexandria VA 22152 Note: This was assembled with the excellent OPTASM assembler. Slight modifications may be needed in the way of JMP pointers, MOV size pointers, and so forth if you're using MASM (yuck). ! Sseg segment byte stack 'prog' ; dummy stack segment Sseg ends Cseg segment byte public 'prog' assume cs:Cseg, ds:Cseg, ss:Sseg org 100h MAIN proc far xor dx,dx ; number of parms mov cx,dx mov EXITCODE,cl ; assume no errors mov cl,ds:[0080h] ; get parm length jcxz Inform ; inform 'em if no parms mov si,0081h cld ScanParms: lodsb ; get a command-line char cmp al," " ; is it a space? jbe ScanLoop2 ; yes, ignore it mov di,offset OUTFILE ; assume output file name inc dx ; increment parm number cmp dx,2 ; check it ja Inform ; too large, inform 'em je SaveFileName ; default OUTFILE is ok mov di,offset INFILE ; input file name (string) SaveFileName: stosb ; store a char of the filename dec cx ; are we done yet? jz ScanDone ; yes, exit lodsb ; get another char cmp al," " ; is it blank? ja SaveFileName ; no, must be a filename chr ScanLoop2: loop ScanParms ; keep looking for parms ScanDone: or dx,dx ; any parms? jz Inform ; no, inform 'em dec dx ; only one parm? jnz ChangeExts ; no, go change extensions mov si,offset INFILE ; input file name mov di,offset OUTFILE ; output file name DupeFile: lodsb ; get an input char or al,al ; is it null? jz ChangeExts ; yes, done- change exts stosb ; store char in output name jmp DupeFile ; keep on truckin' Inform: mov dx,offset INFORMATION mov ah,9 int 21h mov EXITCODE,255 jmp Abort ChangeExts: mov si,offset INFILE ; input file name Change1: lodsb ; get a char or al,al ; are we done? jz AddExtIn1 ; yes, needs extension cmp al,"." ; is it a period? jne Change1 ; no, keep looking ChangeExt2: mov si,offset OUTFILE ; output file name Change2: lodsb ; get a char or al,al ; are we done? jz AddExtIn2 ; yes, needs extension cmp al,"." ; is it a period? jne Change2 ; no, keep looking lodsw ; is the extension ".EXE"? cmp ax,"XE" ; jne OpenFiles ; no, go open the files lodsb ; cmp al,"E" ; jne OpenFiles ; no, go open the files sub si,3 ; pretend there's no ext AddExtIn2: dec si ; move back to the first null mov di,si mov ax,"C." ; install a ".COM"... stosw ; ...file extension mov ax,"MO" ; stosw ; jmp OpenFiles AddExtIn1: dec si ; move back to the first null mov di,si mov ax,"E." ; install an ".EXE"... stosw ; ...file extension mov ax,"EX" ; stosw ; jmp ChangeExt2 ;------------------- Everything's set up, let's open the files ---------------- OpenFiles: mov ax,3D00h ; open file for read mov dx,offset INFILE ; input file name int 21h jnc InputOpenOk mov bl,1 jmp ErrVector InputOpenOk: mov INHANDLE,ax ; save input file handle mov bx,ax mov ah,3Fh ; read from file mov cx,24 ; 24 bytes mov dx,offset LASTBYTE ; data buffer int 21h jnc ReadOk mov bl,9 jmp ErrVector ReadOk: mov si,dx mov di,offset EXE_SIG movsw ; set EXE_SIG movsw ; set EXE_EXCESS movsw ; set EXE_PAGES movsw ; set EXE_RELOCCOUNT movsw ; set EXE_HDRSIZE add si,4 movsw ; set EXE_SS movsw ; set EXE_SP add si,2 movsw ; set EXE_IP movsw ; set EXE_CS mov bl,3 ; default error code cmp EXE_SIG,"ZM" ; is the signature ok? jne ErrVector ; nope, error inc bl ; inc error code cmp EXE_RELOCCOUNT,0 ; any relocations needed? jne ErrVector ; yes, error inc bl ; inc error code cmp EXE_SS,0 ; is there a defined SS? jne ErrVector ; yes, error cmp EXE_SP,0 ; is there a defined SP? jne ErrVector ; yes, error inc bl ; inc error code cmp EXE_CS,0 ; is there a defined CS? jne ErrVector ; yes, error inc bl ; inc error code cmp EXE_IP,0 ; is the IP = 0? je ChecksOk ; yes, it's ok cmp EXE_IP,0100h ; is the IP = 0100h? jne ErrVector ; no, error ChecksOk: mov bx,EXE_HDRSIZE mov cl,4 shl bx,cl ; CodeStart in BX **** mov ax,EXE_PAGES dec ax mov cx,512 mul cx sub ax,bx sbb dx,0 ; CodeSize in DX:AX *** mov cx,EXE_EXCESS jcxz NoDribble add ax,cx jmp GotCodeSize NoDribble: add ax,512 GotCodeSize: adc dx,0 or dx,dx ; is it too large? jz CheckIP ; no, keep on truckin' mov bl,8 ErrVector: jmp ErrorExit CheckIP: push ax cmp EXE_IP,0100h ; is IP right for .COM files? je IPok ; yes... mov dx,offset WARNING mov ah,9 ; display warning message int 21h IPok: mov dx,bx ; CodeStart xor cx,cx add dx,EXE_IP adc cx,cx mov bx,INHANDLE mov ax,4200h ; move file ptr from start int 21h mov ah,3Ch ; create file for write mov dx,offset OUTFILE ; output file name xor cx,cx ; normal file attribute int 21h pop si jnc OutputOpenOk mov bl,2 jmp ErrVector OutputOpenOk: mov OUTHANDLE,ax ; save output file handle sub si,EXE_IP ; ignore IP bytes mov dx,offset LASTBYTE ; buffer location mov cx,32 * 1024 ; buffer size: 32K ; ----------------- Just copy the code from the EXE to the COM file ----------- WriteLoop: or si,si jz Done cmp si,cx ja ReadBlock mov cx,si ReadBlock: mov ah,3Fh ; read from file mov bx,INHANDLE int 21h jc ReadError mov ah,40h ; write to file mov bx,OUTHANDLE int 21h jc WriteError sub si,cx jmp WriteLoop ReadError: mov bl,9 jmp ErrorExit0 WriteError: mov bl,10 ;---------------------------- Error exit handler ------------------------------ ErrorExit0: push bx mov ah,3Eh ; close a file mov bx,OUTHANDLE ; ...output file int 21h pop bx ErrorExit: mov EXITCODE,bl mov ah,9 ; display error message mov dx,offset FATALERR ; "Fatal error: " int 21h mov si,offset CANTOPEN ; first error message CheckErr: dec bl ; is it the error msg we want? jz GotError ; yes, got it FindErr: lodsb ; get a char cmp al,"$" ; end of message? jne FindErr ; no, keep looking jmp CheckErr ; see if it's the right one GotError: mov dx,si ; pointer to error message ErrDone: mov ah,9 int 21h cmp EXITCODE,1 ; did we open the input file? je Abort ; no, don't close or delete Done: mov ah,3Eh ; close a file mov bx,INHANDLE ; input file int 21h cmp EXITCODE,0 ; successful conversion? jnz Abort ; no, just exit mov ah,41h ; delete file mov dx,offset INFILE ; ...the original input file int 21h Abort: mov ah,4Ch ; terminate program mov al,EXITCODE ; error exit code int 21h MAIN endp WARNING db "WARNING: The default IP is not 0100h.",13,10 db "The output file will not be executable.",13,10,"$" FATALERR db "Fatal error: $" CANTOPEN db "Unable to open input file",13,10,"$" CANTMAKE db "Unable to create output file",13,10,"$" BADSIG db "Input file is not a valid .EXE file",13,10,"$" RELITEMS db "There are items requiring relocation",13,10,"$" BADSTACK db "A stack is defined",13,10,"$" BADCSEG db "A code segment is defined",13,10,"$" BADCOFS db "The code offset is neither 0 nor 0100h",13,10,"$" TOOBIG db "File is too large (.COM would be over 64K)",13,10,"$" CANTREAD db "Unable to read input file",13,10,"$" CANTWRITE db "Unable to write to output file",13,10,"$" INFORMATION db "EXECOM 1.1 Copyright (c) 1988 Thomas G. Hanlin III",13,10 db " Purpose: converts an .EXE file to a .COM file.",13,10 db " Format : EXECOM inputfile[.EXE] [outputfile[.COM]]",13,10 db "$" INHANDLE dw ? OUTHANDLE dw ? EXE_SIG dw ? ; EXE signature EXE_EXCESS dw ? ; bytes in excess of the 512b EXE_PAGES count EXE_PAGES dw ? ; code size, in 512b pages EXE_RELOCCOUNT dw ? ; count of items in the relocation table EXE_HDRSIZE dw ? ; header size, in 16b paragraphs EXE_SS dw ? ; default SS EXE_SP dw ? ; default SP EXE_IP dw ? ; default IP EXE_CS dw ? ; default CS EXITCODE db ? ; program error exit code INFILE db 80 dup (0) ; input file name OUTFILE db 80 dup (0) ; output file name LASTBYTE db ? ; final data byte, used as start of file buffer area Cseg ends end MAIN