LAHF

LAHF — Load Status Flags into AH Register

			64-Bit Mode	Compat/Leg Mode	Description
			Invalid*	Valid	Load: AH ← EFLAGS(SF:ZF:0:AF:0:PF:1:CF).

*Valid in specific steppings. See Description section.

Instruction Operand Encoding ¶

Op/En	Operand 1	Operand 2	Operand 3	Operand 4
ZO	NA	NA	NA	NA

Description ¶

This instruction executes as described above in compatibility mode and legacy mode. It is valid in 64-bit mode only if CPUID.80000001H:ECX.LAHF-SAHF[bit 0] = 1.

Operation ¶

IF 64-Bit Mode
    THEN
        IF CPUID.80000001H:ECX.LAHF-SAHF[bit 0] = 1;
            THEN AH ← RFLAGS(SF:ZF:0:AF:0:PF:1:CF);
            ELSE #UD;
        FI;
    ELSE
        AH ← EFLAGS(SF:ZF:0:AF:0:PF:1:CF);
FI;

Flags Affected ¶

None. The state of the flags in the EFLAGS register is not affected.

Protected Mode Exceptions ¶

#UD	If the LOCK prefix is used.

Real-Address Mode Exceptions ¶

Same exceptions as in protected mode.

Virtual-8086 Mode Exceptions ¶

Same exceptions as in protected mode.

Compatibility Mode Exceptions ¶

Same exceptions as in protected mode.

64-Bit Mode Exceptions ¶

#UD	If CPUID.80000001H:ECX.LAHF-SAHF[bit 0] = 0.
	If the LOCK prefix is used.