chapter 11 implementing an assembler and a linker using c++ and java
TRANSCRIPT
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Chapter 11
Implementing an Assembler and a Linker Using C++ and Java
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An assembler must handle
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Assembler pseudocode—pass 1
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Pass 2
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Symbol tableHow to implement?
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Relationship of opcode index (position of its mnemonic in an
alphabetized table) and the opcode
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Computing an opcode from its table index
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Opcode table in Java
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Implement the symbol table using the SymbolTable class
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Assembler should check for duplicate labels when making an entry into the symbol table.
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Text files
Contain ASCII codes exclusively.
A “.mas” file is an example of a text file.
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Binary files
• Do not contain ASCII codes exclusively.
• “.mob” and “.mac” files are binary files.
• No translation of end-of-line markers occurs during input or output of binary files.
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Creates text file.
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Creates binary file
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Creates text file
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Creates binary file
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Binary input file in Java
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Binary input file in C++
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Reading the input text file
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Creating an R entry
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assemble method in Assembler class constructs machine word
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Constructing the machine word requires shifting. For example,
for a 4-bit opcode:
Machine_word = (short)(opcode <<12) | operand_value;
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To handle endian problem (e.g., if assembler written in Java and linker in C++ on a PC).
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Using reverseOrder
Use
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Linker should detect these errors
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As linker loads modules, it keeps track of its module’s starting address
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Implement the P, E, R, and S tables using classes.
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Implement the text buffer using a class.
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Linker pseudocode—phase 1
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Processing modules from a library