First pass of assembler
This document discusses the first pass of an assembler. It begins by defining an assembler as a language processor that converts assembly language to machine language. It then describes the different types of assemblers, focusing on single-pass and two-pass assemblers. For two-pass assemblers, it outlines the tasks of the analysis and synthesis phases in the first and second passes respectively. These include separating symbols, building symbol tables, performing label and literal processing, and constructing intermediate code in the first pass and then generating the target program in the second pass. The document provides an example of intermediate code format and walks through converting an example assembly program to intermediate code using the first pass of a two-pass assembler.
First pass of assembler
- 1. FIRST PASS OF ASSEMBLER ACTIVE LEARNING ASSIGNMENT FOR THE SUBJECT “SYSTEMS PROGRAMMING” PREPARED BY: HEMANT H. CHETWANI (130410107010 – TY CE-II)
- 2. What is Assembler ? An Assembler is a language processor that converts an assembly language program into a machine language program. To perform this conversion, it has to analyze the source program, determine which symbols used in the program correspond to which data or instruction, and use this information while synthesizing a target program. The organization of an assembler shows how it structures the various analysis and synthesis tasks.
- 3. Types of Assembler (According to it’s Pass structure) 2. Two pass assembler 1. Single Pass Assembler
- 4. 1. Single Pass Assembler ALP is converted into a target program on a statement by statement basis. Analysis & synthesis both tasks are done within a single pass only…
- 5. Two pass assembler 1st PASS Analysis Phase 2nd PASS Synthesis Phase
- 6. Tasks of Analysis Phase 1. Separate label, opcode & operand 2. Build the symbol table 3. Perform LC processing 4. Construct IC Analysis
- 7. Tasks of Synthesis phase 1. Obtain the machine opcode corresponding to the mnemonic 2. Obtain the address of a memory operand from symbol table 3. Synthesize the machine instruction Synthesis
- 8. Design of a two pass assembler 1. Separate label, opcode & operand 2. Builds the symbol table 3. Perform LC processing 4. Construct Intermediate Code 1st pass
- 11. Pass 1 Pass 2 Source Program Target Program Data Structures Intermediate Code
- 12. 1st Pass Constructs Intermediate Code 1. Data structures (symbol table) 2. Intermediate form of source program
- 13. Data Structures • Table of mnemonic Opcodes and related infoOPTAB • Contains symbol name, addressSYMTAB • Table of literals used in the programLITTAB • Table of information concerning literal poolsPOOLTAB
- 14. Opcode Table
- 15. Class IS DS AD Mnemonic info (Machine Opcode, Inst Length) Mnemonic info ID of a routine
- 16. Symbol Table
- 17. Literal Table
- 18. Pool Table
- 20. Example MOVER AREG, A Which information do we need to convert this instruction in to its equivalent intermediate code??? 1. CLASSES 2. CODES
- 21. (Statement Class, Opcode) Statement Class IS (Imperative stmt) DS (Declarative stmt) AD (Assembler Directives)
- 24. MOVER AREG,A (IS, 04) (1)(S, 01)
- 25. Example Program
- 26. PASS-1 Algorithm
- 31. Example START 200 X DS 4 L1 MOVER AREG,Y SUB AREG,Z MOVEM AREG,W W EQU X+2 L2 PRINT W ORIGIN X-5 Z DC ‘9’ ORIGIN L2+1 STOP Y DC ‘7’ END LC 200 204 205 206 207 195 208 209
- 32. Example START 200 X DS 4 L1 MOVER AREG,Y SUB AREG,Z MOVEM AREG,W W EQU X+2 L2 PRINT W ORIGIN X-5 Z DC ‘9’ ORIGIN L2+1 STOP Y DC ‘7’ END (AD,01)(C,200) (DL,02)(C,04) (IS,04)(1)(S,01) (IS,02)(1)(S,02) (IS,05)(1)(S,03) (AD,04) (IS,10)(S,03) (AD,03) (DL,01)(L,01) (AD,03) (AD,00) (DL,01)(L,02) (AD,02)
- 33. SYMTAB SYMBOL ADDRESS LENGTH X 200 4 L1 204 1 W 202 1 L2 207 1 Z 195 1 Y 209 1
- 34. LIKEWISE... WE CAN GENERATE ALL THE TABLES THAT WE NEED USING FIRST PASS OF ASSEMBLER