Registers

8 registers with names and 8 registers with numbers:
- rax, rbx, rcx, rdx, rsi, rdi, rsp, rbp
- r8, r9, r10, r11, r12, r13, r14, r15
Prefixes
- r prefix is for 64-bit
- e is for 32-bit (eax, ebx, exc, etc.)
- no prefix is used for 16-bit or 2 byte- registers (ax, bx, cx, etc.)
- h and l suffix is used for 8-bits, where h is for higher 8-bit and l is for lower 8-bit.

Fig 1.1 - Register Prefix

Caller and Callee Saved

Caller saved (or must be preserved by the caller — the caller can expect the values to be changed after a function or system call). These are also called as call-clobbered registers.

rax, rcx, rdx, r8-r11

Callee saved (the function must store and restore these registers, the caller can expect them to be unchanged)

rbx, rbp, rdi, rsi, rsp, r12-r15

Fig 1.2 - Caller and Callee Saved Registers

Source - System V ABI Document