🧩 Two-Pass Assembler in C

A complete two-pass assembler built in ANSI C, designed to translate assembly code for a custom CPU architecture.
This project was developed as part of the *System Programming Lab * course at the University.

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🚀 Overview

The assembler reads .as source files, performs two passes over the code, expands macros, builds symbol tables, resolves labels, and generates machine-level output files:

• .ob — object code
• .ent — entries
• .ext — external references

It supports all standard directives (.data, .string, .struct, .extern, .entry) and implements strong validation and error handling for both passes.

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⚙️ Features

• Two-Pass Compilation:
  First pass builds symbol tables and detects syntax errors.
  Second pass encodes instructions and resolves references.
• Macro Preprocessor:
  Expands user-defined macros before assembly (.am files).
• Symbol & Label Management:
  Handles .entry and .extern directives with relocation support.
• Machine Code Generation:
  Outputs 10-bit word binary code to .ob, .ent, and .ext files.
• Error Handling:
  Detects invalid labels, directives, addressing modes, and memory references.
• Modular Design:
  Split into modules — lexer, parser, code generator, and utilities.

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🧱 Project Structure

assembler/
│── main.c
│── preprocessor.c
│── parser.c
│── assembler.c
│── codegen.c
│── utils.c
│── include/
│   ├── assembler.h
│   ├── globals.h
│── Makefile

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🧩 Example Usage

make
./assembler file1.as file2.as

Input:

MAIN: mov r3, LENGTH
LOOP: jmp END

Output files:

file.ob
file.ent
file.ext

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🧠 Tech Stack

C (ANSI), Makefile, File I/O, Custom ISA, Macro Preprocessor, Data Structures

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📜 License

System Programming Lab