What are the names of the new X86_64 processors registers?

assembly x86 x86-64 cpu-registers
Recursion picture Recursion · Nov 18, 2009 · Viewed 76.9k times · Source

Where can I find the names of the new registers for assembly on this architecture?

I am referring to registers in X86 like EAX, ESP, EBX, etc. But I'd like them in 64bit.

I don't think they are the same as when I disassemble my C code, I get r's instead of e's.

Answer

RRUZ picture RRUZ · Nov 18, 2009

The MSDN documentation includes information about the x64 registers.

x64 extends x64's 8 general-purpose registers to be 64-bit, and adds 8 new 64-bit registers. The 64-bit registers have names beginning with "r", so for example the 64-bit extension of eax is called rax. The new registers are named r8 through r15.

The lower 32 bits, 16 bits, and 8 bits of each register are directly addressable in operands. This includes registers, like esi, whose lower 8 bits were not previously addressable. The following table specifies the assembly-language names for the lower portions of 64-bit registers.

64-bit register | Lower 32 bits | Lower 16 bits | Lower 8 bits
==============================================================
rax             | eax           | ax            | al
rbx             | ebx           | bx            | bl
rcx             | ecx           | cx            | cl
rdx             | edx           | dx            | dl
rsi             | esi           | si            | sil
rdi             | edi           | di            | dil
rbp             | ebp           | bp            | bpl
rsp             | esp           | sp            | spl
r8              | r8d           | r8w           | r8b
r9              | r9d           | r9w           | r9b
r10             | r10d          | r10w          | r10b
r11             | r11d          | r11w          | r11b
r12             | r12d          | r12w          | r12b
r13             | r13d          | r13w          | r13b
r14             | r14d          | r14w          | r14b
r15             | r15d          | r15w          | r15b

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