Difference between revisions of "Assembly"

Revision as of 02:03, 21 May 2012

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Introduction

• assembler - An assembler is a program that compiles human-readable operations into instructions interpreted by the processor
• linker - A linker is a program that combines the compiled assembly objects into a binary. 'ld' is the standard linker on Linux platforms.

Compilers such as GCC/CC do both operations dynamically.

• Assemble-time: Assembly & operands -> Opcode Sequence
• Link-time: Flat binary of opcode sequence -> executable file format for OS
• Runtime: Opcode Sequence -> hardware gates (may interact with ram etc)

Binary

• counting
• endianness
• nybble - An uncommon unit of memory equivalent to 4 bits.
• byte - A byte is a unit of memory equivalent to 8 bits.
• word
• dword
• qword

Number handling

• signed - Signed values are required to represent negative numbers. Most languages by default assume values are signed. The range of numbers it can assign extends from -1 downwards, depending on the data type.
• unsigned - Despite not being able to assign negative numbers, unsigned values are particularly advantageous for positive ranges. The memory that would have been applied assigning a negative range is instead added to the positive range, giving you twice as many positive numbers.
• 2's compliment

Data storage

• register
• pointer
• sub-register
• cpu flag registers
• architecture-specific registers

Memory Addressing

• stack pointer
• instruction pointer
• base pointer
• addressing mode
• index

Instructions

Syntaxes

• Intel (dest, src)
• ATT (src, dest)

Data manipulation basic primitives

• mov
• push
• pop

Basic arithmetic

• add
• sub
• div
• mul

Bitwise mathematics operators

• and
• not
• or
• xor

Shifts and rotations

• shl
• shr
• rol
• ror

Control flow operators

• cmp
• jmp
• call
• ret

Taking it further

• kernel interrupt
• architecture
• operating system