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

Instruction	Description	signed-ness	Flags	short jump opcodes	near jump opcodes
JO	Jump if overflow		OF = 1	70	0F 80
JNO	Jump if not overflow		OF = 0	71	0F 81
JS	Jump if sign		SF = 1	78	0F 88
JNS	Jump if not sign		SF = 0	79	0F 89
JE JZ	Jump if equal Jump if zero		ZF = 1	74	0F 84
JNE JNZ	Jump if not equal Jump if not zero		ZF = 0	75	0F 85
JB JNAE JC	Jump if below Jump if not above or equal Jump if carry	unsigned	CF = 1	72	0F 82
JNB JAE JNC	Jump if not below Jump if above or equal Jump if not carry	unsigned	CF = 0	73	0F 83
JBE JNA	Jump if below or equal Jump if not above	unsigned	CF = 1 or ZF = 1	76	0F 86
JA JNBE	Jump if above Jump if not below or equal	unsigned	CF = 0 and ZF = 0	77	0F 87
JL JNGE	Jump if less Jump if not greater or equal	signed	SF <> OF	7C	0F 8C
JGE JNL	Jump if greater or equal Jump if not less	signed	SF = OF	7D	0F 8D
JLE JNG	Jump if less or equal Jump if not greater	signed	ZF = 1 or SF <> OF	7E	0F 8E
JG JNLE	Jump if greater Jump if not less or equal	signed	ZF = 0 and SF = OF	7F	0F 8F
JP JPE	Jump if parity Jump if parity even		PF = 1	7A	0F 8A
JNP JPO	Jump if not parity Jump if parity odd		PF = 0	7B	0F 8B
JCXZ JECXZ	Jump if %CX register is 0 Jump if %ECX register is 0		%CX = 0 %ECX = 0	E3