寄存器多的一塌糊涂：16 个 8 位通用寄存器、16 个 16 位通用寄存器、16 个 32 位通用寄存器、16 个 64 位通用寄存器，8 个 MM/FP 64 位寄存器，16 个 XMM 128 位寄存器……
下面的文字摘自 《AMD64 Architecture Programmer’s Manual Volume 1: Application Programming》
The AMD64 architecture introduces these new features:
- Register Extensions (see Figure 1-1 on page 2):
- 8 new general-purpose registers (GPRs).
- All 16 GPRs are 64 bits wide.
- 8 new 128-bit XMM registers.
- Uniform byte-register addressing for all GPRs.
- A new instruction prefix (REX) accesses the extended registers.
- Long Mode (see Table 1-1 on page 3):
- Up to 64 bits of virtual address.
- 64-bit instruction pointer (RIP).
- New instruction-pointer-relative data-addressing mode.
- Flat address space.
下面是寄存器图示和说明，均摘自 AMD64 程序员手册:
In 64-bit mode, eight new GPRs are added to the eight legacy
GPRs, all 16 GPRs are 64 bits wide, and the low bytes of all
registers are accessible. Figure 3-3 on page 31 shows the GPRs,
flags register, and instruction-pointer register available in 64-
bit mode. The GPRs include:
- Sixteen 8-bit low-byte registers (AL, BL, CL, DL, SIL, DIL, BPL, SPL, R8B, R9B, R10B, R11B, R12B, R13B, R14B, R15B).
- Four 8-bit high-byte registers (AH, BH, CH, DH), addressable only when no REX prefix is used.
- Sixteen 16-bit registers (AX, BX, CX, DX, DI, SI, BP, SP, R8W, R9W, R10W, R11W, R12W, R13W, R14W, R15W).
- Sixteen 32-bit registers (EAX, EBX, ECX, EDX, EDI, ESI, EBP, ESP, R8D, R9D, R10D, R11D, R12D, R13D, R14D, R15D).
- Sixteen 64-bit registers (RAX, RBX, RCX, RDX, RDI, RSI, RBP, RSP, R8, R9, R10, R11, R12, R13, R14, R15).