Programming/Assembly

Syntax Types

For 32 bit (x86) assembly, there are two main syntax types. AT&T is mostly used in Unix environments, while Intel is mostly used in MS-DOS and Windows.
The differences are as follows:

	AT&T	Intel
Signs	Instructions need size definition suffix (see #Instruction Sizes). Values need % prefix for registers, and $ prefix for constants. Ex:%eax	Automatically detects size and type of value. Signs are not needed. Ex:eax
Value Order	Source first, destination second. Ex:mov $5, %eax	Destination first, source second. Ex:mov eax, 5
Value Size	Size suffix (see #Instruction Sizes) must be added to instruction. Ex:addl %eax, %ebx	Size automatically derived from register used. In instances where size is ambiguous, must use a size keyword (byte, word, dword, qword). Ex:add eax, ebx
Effective Address	Uses general memory address syntax. Ex:(%ebx, %ecx, 4)	Uses arithmetic expressions in square brackets. Ex:[ebx + ecx*4]

Registers

The following registers exist in 64 and 32 bit assembly.

								Stack Pointer								Stack Base Pointer								Accumulator								Base								Counter								Data								Source								Destination
64 Bit								RSP								RBP								RAX								RBX								RCX								RDX								RSI								RDI
32 Bit												ESP								EBP								EAX								EBX								ECX								EDX								ESI								EDI
16 Bit														SP								BP								AX								BX								CX								DX								SI								DI
8 Bit															SPL								BPL							AH	AL							BH	BL							CH	CL							DH	DL								SIL								DIL

The following registers only exist in 64 bit assembly.

								Temp 1								Temp 2								Temp 3								Temp 4								Temp 5								Temp 6								Temp 7								Temp 8
64 Bit								R8								R9								R10								R11								R12								R13								R14								R15
32 Bit												R8D								R9D								R10D								R11D								R12D								R13D								R14D								R15D
16 Bit														R8W								R9W								R10W								R11W								R12W								R13W								R14W								R15W
8 Bit															R8B								R9B								R10B								R11B								R12B								R13B								R14B								R15B

In-depth details of how assembly register and function calling should work: https://www.cs.princeton.edu/courses/archive/spring11/cos217/lectures/15AssemblyFunctions.pdf

Instruction Sizes

In 64 bit assembly, some assembly instructions will have letters appended to the end of the instruction, indicating the size of data being referenced. The letters are the following:

• Byte (b) - A one-byte (8 bit) value.
• Word (w) - A two-byte (16 bit) value.
• DoubleWord (l) - A four-byte (32 bit) value.
• QuadWord (q) - A eight-byte (64 bit) value.

Instructions

• mov <a>, - Copies data location from one to the other.