Difference between revisions of "Assembly"

Revision as of 01:17, 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 assigned to the negative range is instead added to the positive range (twice as many positive numbers).
• 2's compliment

Data storage

• register - A location where memory can be stored temporarily. A register has the bit-width of a cpu's bit description. So for 32 bit systems, a register is 32 bits (4 bytes or a doubleword, also called long) whereas on a 64 bit system a register is 64 bits in length (8 bytes or a qword).
• pointer - An address that points to another location in memory
• sub-register - A portion of another register always divisible by 8 bits in size
• cpu flag registers
• architecture-specific registers

Memory Addressing

• stack pointer - A pointer that points to a location on the stack
• 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 - i386, i686, x86_64
• operating system