LAHF (Load Status Flags into AH Register)

Opcodes

Opcode Instruction Op/En 64-Bit Mode Compat/Leg Mode Description
9F LAHF NP Invalid* Valid Load: AH ← EFLAGS(SF:ZF:0:AF:0:PF:1:CF).

NOTES: *Valid in specific steppings. See Description section.

Instruction Operand Encoding

Op/En Operand 1 Operand 2 Operand 3 Operand 4
NP 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.