Download A = B + 4

ITEC 352
Lecture 11
ISA - CPU
Review
• Questions?
• HW 2 due on Friday
• ISA
– Machine language
– Buses
– Memory
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Outline
• P1 is posted
• CPU
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Architectur
e
• Contains: Data Section and Control Unit
Data Section: Registers and ALU (they do the processing)
Control Unit: controls the processing.`
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CPU
• Registers
– One type of memory.
• Each register can usually store a word (there are some that store a
byte).
– They are few in number (usually range from 16 onwards to
something higher).
– Hence, they require fewer bits to represent their addresses.
• E.g., if we had 16 registers, we would only need 4 bits to address
them (contrast this with 32 bit memory).
– Hence, it is very fast memory.
• ALU: Arithmetic and Logic Unit: This implements a
variety of binary and unary operations. Examples: ADD,
MULTIPLY, AND, NOT, OR etc…
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ISA
definition
•
Every control unit is pre-programmed with a set of basic
instructions.
–
E.g.,
•
•
•
•
–
http://siyobik.info/main/reference
–
ARM processors (used in DROID and other mobile devices)
instruction set:
–
http://infocenter.arm.com/help/topic/com.arm.doc.qrc0001m/QRC0001_UAL.pdf
SUN SPARC instruction set (32 bit) (version 7)
http://www.cs.utexas.edu/users/novak/sparcv7.pdf
These basic instructions are called Instruction sets and the
architecture supporting the instruction set is refereed as
Instruction Set Architecture (ISA).
–
E.g., SUN SPARC Version 7 32 bit ISA
•
•
IA-32 (Intel 32 bit processor) instruction set:
ARM 11 ISA
NEXT: A second in the life of a program (from program to a process).
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Program to Process:
The process of compilation, linking and loading (overview)
A second (or
much less) in
the life of a
high-level
program
Program in
high level language
(e.g., C/C++/Java/ADA)
Libraries
(e.g., stdlib)
COMPILATION
Assembly code (Java is a
little different)
Assembly code
ASSEMBLY
Waiting (and happy)
to be executed
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Machine Code
Machine Code
LINKING
Combined machine
code
Compiler/OS
COMPILER
Program in
high level language
(e.g., C/C++/Java/ADA)
Libraries
(e.g., stdlib)
COMPILATION
Assembly code (Java is a
little different)
Assembly code
ASSEMBLY
Waiting (and happy)
to be executed
By the CPU
Operating System
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Machine Code
Machine Code
LINKING
Combined machine
code
Portability
• Java programs are compiled into “Java
bytecode”
– Java bytecode is analogous to an ISA.
• Depending on the specific CPU (Intel or
ARM etc.),
– Java’s bytecode is mapped to specific ISA.
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Program to
Process
A specific ISA can only execute the
instructions it supports.
•
E.g., to execute a Java program:
–
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It has to be finally translated into the specific
ISA.
Compilatio
n
• Consider the following harmless statement in a
high level language:
A=B+4
To compile this program in a high level language (say
Java), it must first reduce the statement to various
symbols in the language.
Symbols in the example statement:
Identifiers
Operators (delimiters)
A=B+4
This phase in compilation is called Lexical Analysis.
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constant
Lexical
Analysis (2)
• How does compiler store information about the symbols in a
statement ?
• Answer: Symbol table.
• Symbol table contains several records. Each record in the table
usually has the following information:
– Name of the symbol if it is an identifier (Stored as a String) or a key
word like “constant” if the symbol happens to be a contant value.
• E.., A, B
– Type of the identifier or constant. E.g., (integer , …)
• This value cannot be filled up during the lexical analysis. We will see
how this value is derived later.
– Scope of the identifier (if the identifier is a variable – what is its
scope). Remember scope from a previous slide.
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Lexical
Analysis (3)
• Example
– For the statement:
A=B+4
The compiler builds the symbol table:
Name
Type
Scope
Name: A
UNKNOWN
UNKNOWN
Name: B
UNKNOWN
UNKNOWN
CONST:4
UNKNOWN
UNKNOWN
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Static
Analysis
• Lexical analysis is done in parallel with syntactic
analysis. Here, the compiler checks to see if the
syntax of the statement is correct.
– For instance, in Java, the statement A = B + 4 is
incorrect, because at the end of the statement Java
expects a “semicolon”.
– We will not go into details of how it check the
syntax. Lets just assume it does.
• As part of these analysis, a brief step is the
building of a syntax tree.
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Syntax
tree
• A syntax tree captures the syntax of a statement. The
nodes of the tree are operators (or delimiters). The
leaves are the symbols.
=
+
Symbol table entry of B
Symbol table entry of 4
Symbol table entry of A
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Semantic
Analysis
• After determining the syntax is correct, the compiler does a semantic
analysis.
– Usually, in many programming languages this requires that the compiler
make a second pass across the program.
– THIS ALLOWS A PROGRAM TO USE VARIABLES OR FUNCTIONS
DEFINED LATER. This is called FORWARD REFERENCING
• In this phase, the compiler determines and check the types of
variables and functions. E.g.,
In A = B + 4, it determines the type of A and B (perhaps int A and int B) and
then checks to see if the statement is correct when A and B are ints).
E.g., if B is a String, the above statement will be incorrect – a
compilation error is thrown here.
– Also in this phase the compiler adds the remaining entries of the
symbol table
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Semantic
Analysis (2)
• After the type checking phase during
semantic analysis
Name
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Type
Scope
Name: A
int
scope of A
Name: B
int
scope of B
CONST :4
int
Code
Generation
• In this phase, the compiler generates the
assembly code.
– Usually, the compiler first converts the program (the
syntax tree) into an intermediate form of pseudo code
that closely parallels assembly.
– It then maps the pseudo code into assembly.
– This is because, assembly is specific to an
architecture – hence this step is not portable across
different machines. Converting to pseudo code
however is portable.
• Hence, compiler writers can simply port their compilers to
different OSes by changing this one last step.
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Code
generation
• The statement A = B + 4 is now generated into
specific ISA:
ld [B], %r1
add %r1, 4, %r2
st %r2, %r0, [A]
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Compilation: end of our discussion
• So far we looked at the process of compilation.
– For more information, you should take a course on
Compilers/Translators (offered sometimes in Spring by Dr. Okie)
(or) read a very popular textbook in Compilers called the
“Dragon Book”
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Summary
• Compiler:
– Programs are compiled into machine code
• Operating system:
– executes a program (program in execution is called a process).
– Execution starts when a user passes the program as an
argument to a “method/function call” called exec implemented
by the OS.
• Next how does the control unit interact with the OS?
– How does it execute the machine code that the OS wants it
to execute?
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Next.
• Once machine code is generated, linked
and loaded, it is executed by the CPU.
• Next: The all important: Fetch – execute
cycle.
– Defines how instructions are executed.
– Every commercial architecture out there (from
Intel to ARM) follows this cycle.
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