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                         PATCH PROGRAM NOTE TO USER
       	        	       DECEMBER, 1979




	I.  Purpose

		The PATCH program allows the user to append a new segment
	of code to an existing RIO procedure file, or to modify bytes in
	any kind of file without program relinking.

	
	II. Operation

		The PATCH program has two modes of operation, PATCH and
	MODIFY, as described below.
	
	Example:	
		%PATCH
		#FILE PATCH 1.0
		#SELECT MODE:
		MODIFY (M OR m) OR PATCH (P or p)
		P

	III. PATCH mode

		The PATCH program stores a string of bytes at a given address
	in a program.  The length of the string of bytes is user-defined and
	must be less than or equal to 255 bytes.  The PATCH program stores
	a CALL instruction and as many NOP instructions as are needed to fill
	out the length supplied by the user.  The bytes replaced by this
	string become the first bytes in the new code segment.  In this way
	the user may move as many instructions as are needed to the new
	code segment.  PATCH creates a segment that starts at a user supplied
	address and contains the bytes taken from the original segment and
	any user supplied bytes.  When the user teminates the byte input
	PATCH writes the last segment and fixes the descriptor record to
	include the new segment.

		The user input for PATCH mode is as follows:
		

          1.  Procedure file name - A RIO procedure-type file.

		#PROCEDURE FILE NAME
		test_program

	  2.  CALL address (hex) - The address in the procedure where the 
	      call instruction is to be placed.

                #ADDRESS TO STORE CALL
		5A35

\f






				     - 2 -




	  3. PATCH address (hex) - The low address of the new segment.

		#ADDRESS FOR PATCH
		6E00

	  4. Number of bytes to be transferred to the new segment (decimal).

		#NUMBER OF BYTES TO MOVE OUT OF OLD SEGMENT
		NULL INPUT (CARRIAGE RETURN) SETS DEFAULT (=3)
		5

	  5. Code bytes (hex) - The bytes of data or code for the new 
	     program segment.

		#ENTER PATCH BYTES (ONE AT A TIME),
		NULL INPUT (CARRIAGE RETURN) TERMINATES INPUT
		FD
		21
		0B
		50
		CD
		03
		14
		C9

	IV.  MODIFY Mode

		In MODIFY mode, PATCH allows the user to replace existing
	bytes within a file (any type).  PATCH prompts the user for the
	record number to be modified (records index from 1), and the
	index into the record for the byte being modified (bytes also 
	index from 1).  PATCH then asks the user for the new byte value,
	inserts the new value in the record, and updates the file.  This
	mode of the PATCH  program operates in a loop so that multiple 
	bytes may be changed in a single session.

	NOTE:  The PATCH program replaces the original file with the new 
	       one.  If the user is uncertain about the changes, a 
	       backup copy of the original should be made.

	       The user input for MODIFY mode is as follows:

	  1.  File name to be modified - Any RIO file

		#MODIFY FILE NAME
		test_modify

\f



 



                                     - 3 -





	  2.  Record number to be modified (decimal) - The record
	      number (indexed from 1) that contains the byte to be
	      modified.

	    	#RECORD NUMBER
		1

	  3.  Byte position to be modified (decimal) - The position
	      (indexed from 1) in the specified record.

		#BYTE POSITION
		23

	  4.  New value for the byte (hex) 

		#NEW VALUE
		FF

	V.  I/O Unit Utilization

	  	Unit 1 - User input
		Unit 2 _ Console messages
		Unit 4 - File I/O