Introduction to Assembly Programming

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Introduction to Assembly Programming
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Outline

• What is assembly ?
• How does it look like ?
• Type of instructions.
• Assembler and other tools.

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What is Assembly ?

• Symbolic representation of machine language.
• opcodes
• operands
• labels
• More readable to human (not computer).
• add A, B 1000111000010110
• Easy to translate to machine language.

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Level of Languages

• swap(int v, int k)
• int temp
• temp vk
• vk vk1
• vk1 temp
• swap
• muli 2, 5, 4
• add 2, 4, 2
• lw 15, 0(2)
• ...

• High level C / Java / Pascal
• Low level Assembly / Bytecode
• Machine Language

C Compiler

• 000010001101101100110000
• 000010001101101100110000
• 000010001101101100110000
• 000010001101101100110000
• ...

Assembler
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When to Use Assembly

• When speed and size matter !
• Equipment that must response very quickly.
• Embedded devices.
• Device driver.
• When the resource is limited.
• When we use the specialized instructions
• 3D graphic library
• When there is no compiler !

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When to Use Assembly

• When you want to understand internal architecture
  of a CPU !
• Complex Instruction Set Computers (CISC)
• Intel x86, Intel Pentium, etc.
• Reduce Instruction Set Computers (RISC)
• DEC Alpha, Sun SPARC, HP P/A, MIPS, Pentium
  II/III/4, etc.
• Very-Large Instruction Word (VLIW)
• Intel Itanium (Pentium 4), Transmeta Crusoe.
• Pentium II/III/4 are special cases
• Outside CICS, inside RISC.

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Drawbacks of Assembly

• Machine-dependent
• must be rewritten on another computer
  architecture.
• not portable.
• Longer codes to write.
• Difficult to read and understand.

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Inside Computer
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Instruction Formats

• Different CPUs, different formats.
• Something in common
• opcode instruction
• What is the command ?
• Arithmetic
• Branch
• operand perform that command on ?
• What is the data ?
• registers
• memory
• constant

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Example adding two numbers

• Sparc r2 r0 r1
• add r0, r1, r2
• MIPS s2 s0 s1
• add s2, s0, s1
• IBM 370 R1 R1 R2
• AR R1, R2

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Instruction Formats (Cont)

• Limited number of operands per instruction
• r5 r1 8 - r2 r3
• add r1, 8, r1 ! r1 r1 8
• sub r1, r2, r1 ! r1 r1 - r2
• add r1, r3, r5 ! r5 r1 r3

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Translation Process

• Assembler
• translate assembly to a binary code.
• check syntax.
• produce an object file (not executable).
• Linker
• combine one or more object files.
• resolve references to other object files /
  libraries.
• produce an executable program.

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Translation Process (Cont)
Assembly Program
Object File
Libraries
Assembler
Object File
Linker
Object File
Executable File
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Other Tools

• Debugger
• trace assembly program.
• run a program in a step-by-step fashion.
• can display values of memory and registers.
• Profiler
• estimate time that a program spends in each
  subroutine.
• find the one with the longest time, optimize it.