First pass of assembler

System Programming - Assembler's First Pass.

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)

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 1 st PASS Analysis Phase 2 nd 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 1 st pass

9. Generates Target Program (Machine Code) 2 nd Pass

10. Pass 1 Pass 2 Source Program Target Program Data Structures Intermediate Code

11. 1 st Pass Constructs Intermediate Code 1. Data structures (symbol table) 2. Intermediate form of source program

12. Data Structures

13. Opcode Table

14. Class IS DS AD Mnemonic info (Machine Opcode , Inst Length) Mnemonic info ID of a routine

15. Symbol Table

16. Literal Table

17. Pool Table

18. Intermediate Code Format

19. Example MOVER AREG , A Which information do we need to convert this instruction in to its equivalent intermediate code??? 1. CLASSES 2. CODES

20. (Statement Class, Opcode) Statement Class IS (Imperative stmt) DS (Declarative stmt) AD (Assembler Directives)

21. (Operand Class, Code) Operand Class C (Constant) L (Literal) S (Symbol )

22. Classes & Opcodes

23. MOVER AREG,A (IS, 04) (1)(S, 01)

24. Example Program

25. PASS-1 Algorithm

26. 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

27. 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)

28. SYMTAB SYMBOL ADDRESS LENGTH X 200 4 L1 204 1 W 202 1 L2 207 1 Z 195 1 Y 209 1

29. LIKEWISE... WE CAN GENERATE ALL THE TABLES THAT WE NEED USING FIRST PASS OF ASSEMBLER