AMD64 NASM Cheatsheet

Sizes

Size (bits)	Size (bytes)	Name	NASM Mnemonics / Directives
8	1	byte	DB, RESB
16	2	word	DW, RESW
32	4	dword	DD, RESD
64	8	qword	DQ, RESQ
80	10	tword	DT, REST
128	16	oword	DO, RESO, DDQ, RESDQ
256	32	yword	DY, RESY
512	64	zword	DZ, RESZ

Register	Usage	Preserved Across Function Calls
%rax	Temporary register; with variable arguments passes information about the number of vector registers used; 1st return register	No
%rbx	Callee-saved register; optionally used as base pointer	Yes
%rcx	Used to pass 4th integer argument to functions	No
%rdx	Used to pass 3rd argument to functions; 2nd return register	No
%rsp	Stack pointer	Yes
%rbp	Callee-saved register; optionally used as frame pointer	Yes
%rsi	Used to pass 2nd argument to functions	No
%rdi	Used to pass 1st argument to functions	No
%r8	Used to pass 5th argument to functions	No
%r9	Used to pass 6th argument to functions	No
%r10	Temporary register, used for passing a function’s static chain pointer	No
%r11	Temporary register	No
%r12–%r15	Callee-saved registers	Yes
%xmm0–%xmm1	Used to pass and return floating point arguments	No
%xmm2–%xmm7	Used to pass floating point arguments	No
%xmm8–%xmm15	Temporary registers	No
%mmx0–%mmx7	Temporary registers	No
%st0, %st1	Temporary registers; used to return long double arguments	No
%st2–%st7	Temporary registers	No
%fs	Reserved for system (as thread specific data register)	No
mxcsr	SSE2 control and status word	Partial
x87 SW	x87 status word	No
x87 CW	x87 control word	Yes