汇编源码系列之showmem

来源:岁月联盟 编辑:zhu 时间:2009-03-11

  这个都是过去DOS时代的汇编源码,虽然已经过去了,但是对于学习汇编还是有帮助的,汇编语言只是程序员一门基础语言,大多人掌握即可,不一定要深入研究.......

;************************************************************************
;*
;*   SHOWMEM (C) 1997 RonSoft.                    *
;*                                   *
;*   A little utility thats shows what's in a given mem position.  *
;*   Usage:                             *
;*   Showmem <segment,offset/startaddress>              *
;*   Where segment and offset are 16 bit hexadecimal values or    *
;*   a single 32 bit value.                     *
;*   Just like this:                         *
;*   Showmem 00000000 or Showmem 0.                 *
;*                                   *
;*   Ronald Nordberg.                        *
;*   Silverv刧en 3                          *
;*   907 50 Ume?                          *
;*   Sweden                             *
;*   christine.martinson@swipnet.se                 *
;*   http://home2.swipnet.se/~w-20064                *
;*                                   *
;*   THIS IS ALL PUBLIC DOMAIN FREEWARE.               *
;*   LET EM KNOW IF YOU USE MY CODE.                 *
;*                                   *
;************************************************************************
                    ;some euqates for readability
kbd       equ   16h       ;keyboard irq
msdos      equ   21h       ;MSDOS irq
reset      equ   0dh       ;disk reset
dfopen     equ   0fh       ;open disk file
dfclose     equ   10h       ;close disk file
searchf     equ   11h       ;search first
searchn     equ   12h       ;search next
seqread     equ   14h       ;sequential disk read
seqwrite    equ   15h       ;   "    " write
setdta     equ   1ah       ;set disk transfer area address
createf     equ   3ch       ;create file with handle
openf      equ   3dh       ;open file with handle
closef     equ   3eh       ;close file with handle
readf      equ   3fh       ;read from file with handle
writef     equ   40h       ;write to file with handle
setfp      equ   42h       ;set file pointer
allocmem    equ   48h       ;allocate memory
freemem     equ   49h       ;free memory
changebs    equ   4ah       ;change block size
findfirst    equ   4eh       ;find first file
exit      equ   4c00h      ;msdos exit
[BITS 16]                ;NASM stuff
[ORG 0x100]
s1:
    mov   ax,cs          ;get code segment
    mov   ds,ax          ;use it now
    mov   [comseg],ds       ;save it there    
    mov   si,0080h        ;DOS command line page 0
    lodsb              ;load size of command line
    cmp   al,0          ;anything on command line ?
    jbe   usage          ;noo, show usage
    cbw               ;extend AL to AX
    xchg  bx,ax          ;swap size to bx for indexing
    mov   byte [bx si],0     ;null terminate command line
    call  parse          ;parse command line
    jmp   main          ;go on with main
usage: mov   bx,utext        ;pointer usage text
    jmp   errout         ;skip this
main:
    mov   si,inbuff        ;check for valid HEX input
    mov   bx,errt1        ;proper text
ishex: lodsb              ;get the char
    cmp   al,'0'
    jb   errout
    and   al,0dfh         ;force UPPERCASE
    cmp   al,'F'         ;>F ?
    ja   errout         ;yeahh, dump this
    loop  ishex
    call  hexbin         ;make hex bin
                    ;start address now in EDX
    mov   ax,dx          ;get low word (segment)
    mov   es,ax          ;start segment
    shr   edx,16         ;shift in offset
    mov   di,dx          ;start offset
dopage:
    push  es           ;save registers
    push  di
    push  ds
    push  si
    mov   ax,es
    mov   ds,ax          ;make ds=es
    mov   si,di          ;and si=di
    
    call  showpage        ;show it
    
    pop   si           ;restore registers
    pop   ds
    pop   di
    pop   es
    add   di,512         ;adjust memory position
    ;xor   ah,ah         ;wait for ANY key
    ;int   kbd
    
    mov   bx,text         ;show message
    call  write
    mov   ah,0          ;wanna see next screen ?
    int   kbd           ;chek out keyboard buffer
    and   al,0DFh         ;force UPPER CASE
    cmp   al,"Q"         ;wanna quit ?
    je   quit          ;yeahh
    jmp   dopage
errout:
    call  write
quit: 
    mov   ax,exit
    int   msdos
;***********************************************************
;*   Convert ascii hex to 32 bit binary
;*   Input = command line buffer, output EDX
;***********************************************************
hexbin:
    mov   si,inbuff        ;pointer command line buffer
    xor   edx,edx         ;clear binary output
aschexbin:
    lodsb
    cmp   al,'0'         ;< 0
    jb   notasc         ;yes invalid character
    cmp   al,'9'         ;<= 9
    jbe   astrip         ;yes, strip high 4 bits
    and   al,05fh         ;force upper case
    cmp   al,'A'         ;< ascii A
    jb   notasc         ;yes, invalid character
    cmp   al,'F'         ;> ascii F
    ja   notasc         ;yes, invalid character
    add   al,9          ;ok, add 9 for strip
astrip:
    and   al,0fh         ;strip high 4 bits
    mov   cx,4          ;set shift count
    shl   edx,cl         ;rotate EDX 4 bits
    xor   ah,ah          ;zero out AH
    cbw
    add   edx,eax         ;add digit to value
    jmp   aschexbin        ;continue
notasc: ret
;*********************************************************************
;*   Format and show the stuff in a "sector"
;*   Input SI
;*********************************************************************
showpage:
    mov   cx,32          ;32*16=512
arow:  push  cx
    mov   di,outline       ;output buffer
    mov   cx,16          ;process 16 bytes
hexrow: push  cx
    lodsb              ;load al with byte
    mov   dl,al          ;get value
    mov   cx,2          ;2 nibbles
chexb: push  cx           ;save that
    mov   cl,4          ;4 bits
    rol   dl,cl          ;rotate source left
    mov   al,dl          ;move digit into AL
    and   al,15          ;clear high nibble
    daa               ;adjust AL if A through F
    add   al,240         ;bump the carry
    adc   al,40h         ;convert HEX to ASCII
    stosb              ;copy to buffer
    pop   cx           ;get digit counter
    loop  chexb          ;next digit
    mov   al,32          ;copy a SPACE
    stosb
    pop   cx           ;restore loop counter
    loop  hexrow         ;loop on
    mov   al,32          ;copy 2 spaces
    stosb
    stosb
    sub   si,16          ;adjust source back
    mov   cx,16          ;copy ASCII bytes
cccp:  lodsb
    cmp   al,32          ;< SPACE ?
    jb   noa           ;yeahh, skip it
    stosb              ;no, store in buffer
    jmp   next
noa:  mov   al,'.'
    stosb
next  loop  cccp 
    mov   al,13
    stosb
    mov   al,10
    stosb
    mov   al,0          ;null terminate line
    stosb
    mov   bx,outline       ;show the line
    call  write
    pop   cx
    cmp   cx,17
    jne   nopause
    push  ds
    mov   ax,cs
    mov   ds,ax
    mov   bx,text1
    call  write
    pop   ds
    xor   ah,ah
    int   kbd
nopause:
    loop  arow          ;next 16 bytes
    ret
;************************************************************************'
;*   Convert bin WORD to HEX ascii. Input DX. Result in Numbuff   *
;************************************************************************
binhex: pusha   
    mov   di,numbuff       ;destination buffer
    mov   dx,[count]       ;binary number
    mov   cx,4          ;four nibbles
convhex:
    push  cx           ;save counter
    mov   cl, 4          ;4 bits
    rol   dx, cl         ;rotate source left
    mov   al, dl         ;move digit into AL
    and   al, 15         ;clear high nibble
    daa               ;adjust AL if A through F
    add   al, 240         ;bump the carry
    adc   al, 40h         ;convert HEX to ASCII
    stosb              ;copy to buffer
    pop   cx           ;get digit counter
    loop  convhex         ;next digit
    mov   al,32          ;copy a space
    stosb
    mov   al,0          ;null terminate
    stosb
    popa
    ret
;*************************************************************************
;*    Writes out the NULL terminated text supplied in BX.       *
;*    OR writes out data,BX and size,CX if called at lwrite.     *
;*************************************************************************
write: pusha
    mov   si,bx          ;copy to SI
    mov   cx,0          ;clear count
wloop: lodsb              ;load AL with SI
    cmp   al,0          ;end of line ?
    je   lwrite          ;yeahh
    inc   cx           ;no, incrase byte count
    jmp   wloop          ;test next byte
lwrite: mov   dx,bx          ;text address in DX
    mov   bx,1          ;filehandle standard output = 1
    mov   ah,writef        ;MS-DOS writefile with handle is 040
    int   msdos          ;write buffer to standard output
    popa
    ret               ;done
;*************************************************************************
;*   My kind of command line parsing. It just checks if there飐
;*   any blankspaces between the options. The parameters ends up
;*   in the inbuff separated by 0:s, binary zeroes.
;*************************************************************************
parse:
    mov   di,inbuff        ;our buffer
ifspc: cmp   byte [si],32      ;leading space ?
    jne   nospc          ;noo
    inc   si           ;yeahh, dump that
    jmp   ifspc          ;check next
nospc: mov   cx,1          ;were here, so we got one arg
copy1: lodsb              ;load byte SI to AL
    cmp   al,0          ;0 ?(end of line)
    je   done          ;yeahh
    cmp   al,32          ;SPACE ?
    je   cop2          ;yeah
    stosb              ;noo, move AL to DI, incrase DI
    jmp   copy1          ;go on
cop2:  mov   byte [di],0       ;null terminate
    add   cx,1
    inc   di           ;dump that byte(SPACE)
    jmp   copy1          ;back
done:  mov   byte [di],0       ;null terminate
    ret               ;return
;*************************** DATA STUFF **********************************
XMS_SEGMENT   dw 0
XMS_OFFSET   dw 0
inbuff     times 64 dw 0      ;128 byte command line buffer
outline     times 40 dw 0      ;buffer output line
numbuff     times 7 dw 0      ;word ascii number buffer
comseg     dw 0
count      dw 0
bcount     dw 0
acount     dw 0
;outbuff     times 512 db 0
utext      db   'Showmem (C) 1997 RonSoft.',13,10
        db   'Usage: Showmem [start address].',13,10
        db   'Start address = Hexadecimal.',13,10,0
text:      db   13,10,'Q = Quit. Any key = Next page.',13,10,0
text1:     db   13,10,'Any Key = Next 256 Bytes.',13,10,0
errt1:     db   'That address is not hexadecimal.',13,10,0
s2:
END

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