x86_64 General Purpose Registers Reference

The x86_64 instruction set architechture includes 16 general purpose regisers, each of which can be addressed in full, or by the lower 32, 16 and 8 bits.

General Purpose 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`

Addressing

General purpose registers in x86_64 are addressed as follows, using rax as an example:

┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━rax━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
┃                               ┏━━━━━━━━━━━━━━eax━━━━━━━━━━━━━┫
┃                               ┃               ┏━━━━━━ax━━━━━━┫
┃                               ┃               ┃       ┏━━al━━┫
0000000000000000000000000000000000000000000000000000000000000000