Transcript Introduction to Assembly Programming

Introduction to Assembly
Programming
Natawut Nupairoj
Assembly Language
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Outline
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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 = v[k];
v[k] = v[k+1];
v[k+1] = temp;
}
•High level: C / Java / Pascal
•Low level: Assembly / Bytecode
•Machine Language
C Compiler
swap:
muli $2, $5, 4
add $2, $4, $2
lw
$15, 0($2)
...
Natawut Nupairoj
Assembler
000010001101101100110000
000010001101101100110000
000010001101101100110000
000010001101101100110000
...
Assembly Language
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When to Use Assembly
• When speed and size matter !
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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
CPU
Input
A
L
U
MEMORY
Output
Register
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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 ?
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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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Assembly Language
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Instruction Formats (Cont’)
• Limited number of operands per instruction:
r5 = r1 + 8 - r2 + r3
add %r1, 8, %r1
sub %r1, %r2, %r1
add %r1, %r3, %r5
Natawut Nupairoj
! r1 = r1 + 8
! r1 = r1 - r2
! 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
Assembler
Object
File
Object
File
Natawut Nupairoj
Assembly Language
Libraries
Linker
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.
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Assembly Language
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