x86-64 ASM - Registers

Registers in Intel

There are 16 “general” registers and one instruction pointer for the next instruction to execute. On x86-64, registers are 64 bits wide.

As we got to higher bit processors, and started extending registers, we still make the old register accessible as sub registers.

Register Usage Conventions

Register	Recommended Usage
RAX	Function return values
RBX	Base pointer to data section
RCX	Counter for string and loop operations
RDX	I/O Pointer
RSI	Source index pointer for string operations
RDI	Destination index pointer for string operations
RSP	Stack pointer
RBP	Stack frame base pointer
RSI	Instruction pointer