LAHF - Load Status Flags Into AH Register

Opcode

Instruction

Op/ En

64-Bit Mode

Compat/ Leg Mode

Description

9F

LAHF

ZO

Invalid1

Valid

Load: AH := EFLAGS(SF:ZF:0:AF:0:PF:1:CF).

NOTES:

1. Valid in specific steppings; see Description section.

Instruction Operand Encoding

Op/En

Operand 1

Operand 2

Operand 3

Operand 4

ZO

N/A

N/A

N/A

N/A

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.