Document 1114
SID and DEBUG
04/13/92
BK

                        SID AND THE DEBUG PATCH


Often software manufacturers will have to make changes to their software
after it has been released to customers.  Usually these are very small
changes to the instructions that make up the software, sometimes only
affecting 1 or 2 bytes out of the entire program.  Since the changes are so
small, they can often be  completed  by  the customer by following a patch
listing  from  the manufacturer. These patch listings depend on the use of
DEBUG.  A typical patch listing will look something like this:

1) COPY BROKFILE.EXE BROKFILE.SAV
2) DEBUG BROKFILE.EXE
3) -S 100 L FFFF B2 01 7C 56 8B 1E
4) -E xxxx:yyyy 91 92 93 94 88 1F
5) -W
6) -Q

DR  DOS  6.0  has a similar utility called  SID.  While  the function of
the two applications is the same, the actual commands are a little
different. Below is the typical listing  with  the purpose of each step
explained and the SID equivalent  described. The format in each step
explained here is:

DEBUG COMMAND LINE

          GENERAL COMMENTS AND CLARIFICATION

                                   EQUIVALENT SID COMMAND LINE


1) COPY BROKFILE.EXE BROKFILE.BAK

          Just in case things do not go as planned, make a  back-
up.

                              (same command)
2) DEBUG BROKFILE.EXE

          DEBUG is loading and reading the  subject file into
          memory. To accomplish this in SID, type SID at the
          command line and then use the R command to read the
          subject file into memory starting at memory offset
          address 100. SID will display the starting and ending
          address of the file in memory in a SEGMENT:OFFSET
          format. Note these addresses.

                                   SID
                                   #RBROKFILE.EXE,100

3) -S 100 L FFFF B2 01 7C 56 8B 1E
          DEBUG is searching from the offset address 100 to
          the last address of FFFF (a hexadecimal number) for the
          pattern of bytes listed (B2 01 7C 56 8B 1E B8). this is
          a pattern that is unique to the area or areas of the
          file that need to be changed. DEBUG will return the
          addresses of the desired patterns in a SEGMENT:OFFSET
          format like 2345:1DF5. The specific values returned
          will vary. There may be more than one found. The patch
          listing will usually refer to these values as
          'xxxx:yyyy'.
               The  SID SR command is very similar. Some  of  the
          arguments are separated with commas instead of  spaces.
          The  address  or  addresses that  contain  the  desired
          pattern will be returned in the same xxxx:yyyy  format.
          Record the addresses returned.
                                   #SR100,FFFF,B2 01 7c 56 8B  1E

4) -E xxxx:yyyy 91 92 93 94 88 1F

          DEBUG is entering new values for the bytes in memory.
          This is how the software is actually changed. The
          xxxx:yyyy is the address at which the new values should
          be added. The following numbers are the new values
          themselves. In SID, use the S command and specify where
          the new values should start.
               SID  will  display that starting address  and  the
          current  value  in memory and be waiting  for  the  new
          value. Enter the first value listed after xxxx:yyyy  in
          the -E command line of the patch listing. Press  Enter.
          SID  will  now show the next address  and  its  current
          value and be waiting for the new value. Enter the  next
          value  in  the -E command line. Continue  entering  the
          remaining  values.  After the last value has  been  en-
          tered, SID will display the next address and be waiting
          for  a new value. Simply enter a '.' and  press  ENTER.
          SID will return to its '#' prompt.
                                        #Sxxxx:yyyy
                                        xxxx:yyyy B2 91
                                        xxxx:yyyz 01 92
                                        xxxx:yyya 7C 93
                                        xxxx:yyyb 56 94
                                        xxxx:yyyb 8B 88
                                        xxxx:yyyb 1E 1F
                                        xxxx:yyyb 22 .
                                        #

5) -W

          The update version of the software is written from
          memory to the original file name. In SID use the
          W command followed by the filename.

                                        #WBROKFILE.EXE

6) -Q
          You're done. Quit. SID's command is the same.

                                        #Q
On  the  next page is a sample of what this patch  process  would
look like in SID.

[DR DOS] C:\MYFILES>SID
--------------------------------------------------
*** Symbolic Instruction Debugger ***  Release 3.2
      Copyright (c) 1983,1984,1985,1988,1990,1991
    Digital Research, Inc. All Rights Reserved
--------------------------------------------------

#RBROKFILE.EXE,100
  Start      End
1056:0100 2056:7BF2
#SR100,FFFF,B2 01 7C 56 8B 1E
1056:2344
#S1056:2344
1056:2344 B2 91
1056:2345 01 92
1056:2346 7C 93
1056:2347 56 94
1056:2348 8B 88
1056:2349 1E 1F
1056:234A B8 .
#WBROKFILE.EXE
#Q

[DR DOS] C:\MYFILES>