System Software

1
System Software

• Bryan Duggan

2
Overview of this Section

• Languages
• Assemblers
• Compilers
• Function
• Components
• Interpreters
• The JVM
• Compiled versus Interpreted systems

3
GENERATIONS OF APPLICATION PROGRAMMING LANGUAGES

• 1st. Since 1940s. MACHINE LANGUAGE binary code
• 2nd. Since early 50s. ASSEMBLY LANGUAGE
  mnemonics for numeric code
• 3rd. Since mid 50s. HIGH-LEVEL LANGUAGES
• 4th. Since late 70s. MODERN APPLICATION
  PACKAGES
• 5th. Object oriented programming languages.

4
Types of Application Programming Languages
5
Examples of Commands in Different Levels of
Languages
6
We have a problem ?
7
Options 1. Speaker learns English 2. Class
learns Chinese 3. Use a translator
8
Now, here is the solution !
Talks Chinese
Understands English
Speaker
Translator
Class
Translates Chinese to English
9
Interpreters and Compilers
Writes High Level Language
Understands Machine Language
Programmer (Human)
Interpreter/ Compiler
Computer (machine)
Translates High Level Language to Machine Language
10
The Language Translation Process

• Compiler
• Interpreter
• Assembler

Source Program
Language Translation Process
Written in BASIC, COBOL, etc.
11
Assembler

• Small ratio between the statements in the
  language and the machine code instructions
• Instructions consist of bit patterns, some are
  operator some are operand
• Could write programs like this
• complicated
• error prone
• time consuming
• Assembly language uses symbols (mnemonics)
  instead of bit patterns
• E.g. ADD may translate as 100
• Programs must be translated from mnemonics to bit
  patterns
• Different assembler for each processor
• No abstraction
• Parses symbols and translates into machine code
• Two passes

12

• Linker
• Many source modules can be linked together in the
  same executable program.
• Symbols defined in one module can be accessed in
  another
• Saves time
• Libraries
• Loader
• Loads the linker output into memory
• Transfers control to the start address of the
  program
• Bootstrap loader loads the loader

13
Compilation

• A compiler is more complicated than an assembler
• one high-level instruction can correspond to
  several machine instructions. Ex. x (y3) / z
• fancier data structures. Ex.
• arrays address calculations must be done for
  references to array elements
• records similar to arrays, but less regular
• Procedures/subroutines/functions/methods - must
  write machine language code to
• copy input parameter values
• save return address
• start executing at beginning of procedure code
• copy output parameter values at end of procedure
• set PC to return address

14
Functions of a compiler?

• Lexical analysis Break up strings of characters
  into logical components, called tokens, and
  discard comments, spaces, etc.
• Parsing Decide how tokens are related.Ex. Sum
  55.32 is an arithmetic expression, and total
  sum 55.32 is an assignment statement.
• Code generation Generate machine instructions
  for each high-level instruction.
• Important to optimize the generated code. Ex.
• 1. X Y Z
• 2. W X Z
• After line 1, X and Z are already in registers,
  so dont load the registers for line 2
• The resulting machine language program, called
  object code, is written to disk.
• Object code is then linked into an executable

15
Components of a compiler

• Syntax checker
• Checks the code for errors
• Can be integrated into an IDE, or standalone
• Provides feedback of errors
• lexical analyser
• Lexical analysis Break up strings of characters
  into logical components, called tokens, and
  discard comments, spaces, etc.
• Parsing Decide how tokens are related.Ex. Sum
  55.32 is an arithmetic expression, and total
  sum 55.32 is an assignment statement.
• code generator
• Generate machine instructions for each high-level
  instruction.
• Linker
• Links all the compiled modules together into a
  standalone program

16
Compiler Generation
Line 3 push ebp mov ebp, esp push ecx mov DW
ORD PTR ebp-4, -858993460 ccccccccH Line
6 mov DWORD PTR _iebp, 0 jmp SHORT
L578 L579 mov eax, DWORD PTR
_iebp add eax, 1 mov DWORD PTR _iebp,
eax L578 cmp DWORD PTR _iebp, 10
0000000aH jge SHORT L580 Line 7 mov ecx,
DWORD PTR _iebp push ecx push OFFSET
FLATSG581 call _printf add esp, 8 Line
8 jmp SHORT L579 L580 Line 9 add esp,
4 cmp ebp, esp call __chkesp mov esp,
ebp pop ebp ret 0 _main ENDP _TEXT ENDS END

• include ltstdio.hgt
• main()
• int i
• for (i 0 i lt 10 i )
• printf("d", i)

17
Issues

• Different machine languages
• Machine languages are incompatible

18
Interpreters vs. Compilers

• Interpreter
• Converts one line of high level language to
  machine language and then performs it.
• Compiler
• Converts entire program to machine language code
  the machine language can then be executed.
• A compiler defines a translation from one
  programming language to another,usually so that
  the program can be efficiently interpreted
• An interpreter defines a program evaluator

19
The Java Solution - Write Once, Run Anywhere
Java Code (High Level)
Byte Code (can be understood by JVM)
JVM for Machine 1
Machine 1
Java Compiler
Translates BC to ML for Machine 2
Translates Java Code to Byte Code
JVM for Machine 2
Machine 2
BC - Byte Code ML - Machine Language JVM - Java
Virtual Machine
Translates BC to ML for Machine 2
20
Java programs

• javac - The Java compiler
• javac HelloWorld.javaproduces HelloWorld.class
• java - The JVM
• java HelloWorldruns HelloWorld.class in the JVM.

21
Summary

• Compiler/Interpreter translates high level
  language to machine language
• Interpreter translates line by line
• Compiler translates entire program at once
• Java code compiles to intermediate byte code
  using javac, then JVM interprets byte code (java).

22
Just-In-Time

• In the Java programming language and environment,
  a just-in-time (JIT) compiler is a program that
  turns Java bytecode (a program that contains
  instructions that must be interpreted) into
  instructions that can be sent directly to the
  processor.

23
Advantages Disadvantages of Interpreted Java
and Compiled C