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execom.asm
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Assembly Source File
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1988-03-19
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15KB
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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
