CS 2734 Computer Organization II

Do the following prior to the laboratory.

• Create a separate directory and download the following programs:
  • The assembler.c main program.
  • The assembler.h include file.
  • The symbol.o object file containing the symbol table implementation.
  • The assemblyErrors.c source file containing error handling utility routines.
  • The Makefile makefile.

• Copy the opcodes.c file from your laboratory 6 directory.

• Copy the parse.c file from your laboratory 7 directory.

• Perform a make to be sure that you have downloaded the programs correctly.

• Write the code for Pass 1 and put it in assembler.c:
  • If the number of command line arguments is incorrect, output a Usage message and exit.
  • Use the command line argument as a filename. Open the file for reading.
  • Read the file one line at a time until end-of-file using fgets.

  • Keep a location_counter and a line_counter as you process the input file. Also keep a count of the number of errors encountered.

  • Echo the input line to standard output and parse each line:
    • If the line starts with an opcode, determine whether the operand is a numeric, a literal, or an error. If it is a literal, insert it in the symbol table as SYMBOL_ONLY.
    • If the line starts with a valid label, insert it in the symbol table as BOTH.
    • If the line starts with a directive, determine whether the operand is a numeric or an error. If it is numeric, update the location counter.

    After you have parsed the line, output the outcome of the parse and any error messages.

  • When you have finished processing the entire file, output the symbol table by calling outputSymbolTable described below.

• The symbol.o file contains the following library routines to implement a symbol table object.

  •    assemblyErrorType getSymbolValue(const char *s, int *val);
       /* If s is a symbol with a defined value, put its associated value
          into *val and return NO_ERROR.  Otherwise return the
          appropriate error code:
               SYMBOL_UNDEFINED - s is not in the symbol table 
               VALUE_UNDEFINED - s is in the table but its value is undefined
       */
    

  •     assemblyErrorType insertSymbolTable(const char *s,
                               symbolInsertionType insert,  int val);
      /* Insert s in the symbol table.  Possible types of insertion
         include:
            VALUE_ONLY - assign a value to a symbol that is already in
                         the table. 
            SYMBOL_ONLY - if the symbol is already in the table, take
                         no action.  If the symbol is not in the table
                         insert it and assign its value to be undefined
            BOTH -   The val parameter
         contains the value of the symbol for the first and third
         types of insertion.      
    
         
    
         The possible error types are:
            SYMBOL_UNDEFINED - tried to insert VALUE_ONLY for symbol
                               not in the table
            DUPLICATE_VALUE - tried to insert a value for a symbol
                              that has been already defined
            STORAGE_ERROR - couldn't malloc space for the symbol 
            UNKNOWN_INSERTION - insert was not one of three values
                             indicated above
       */
    

  •    void outputSymbolTable (FILE *fp)
       /* Write the symbol table to the file fp.  */
    

Implementation Notes:

• If there are too many tokens on a line, indicate an error (e,g.)

        PUSH 5
        LODD 100 500
  

• For lines that are valid instructions you should print the hex opcode returned from checkopcode.

• Be sure to strip off the colon before inserting labels in the symbol table.

• If the line starts with a valid label, the value inserted into the symbol table is the location.

• Some opcodes don't have operands.

• You may assume that labels must be on a line by themselves.

Revision Date: 3/7/97