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LAHF
Henk-Jan Lebbink edited this page Jun 4, 2026
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LAHF — Load Status Flags Into AH Register
| Opcode | Instruction | Op/ En | 64-Bit Mode1 | Compat/ Leg Mode | Description |
| 9F LAHF | ZO | Invalid1 | Valid | Load: AH := EFLAGS(SF:ZF:0:AF:0:PF:1:CF). |
NOTES:
- Valid in specific steppings; see Description section.
| Op/En | Operand 1 | Operand 2 | Operand 3 | Operand 4 |
| ZO | N/A | N/A | N/A | N/A |
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_64[0] = 1.
IF 64-Bit ModeTHENIF CPUID.80000001H:ECX.LAHF_SAHF_64[0] = 1;THEN AH ← RFLAGS(SF:ZF:0:AF:0:PF:1:CF);ELSE #UD; FI;ELSEAH
← EFLAGS(SF:ZF:0:AF:0:PF:1:CF);FI;None. The state of the flags in the EFLAGS register is not affected.
#UD If the LOCK prefix is used.
Same exceptions as in protected mode.
Same exceptions as in protected mode.
Same exceptions as in protected mode.
#UD If CPUID.80000001H:ECX.LAHF_SAHF_64[0] = 0. If the LOCK prefix is used.
Source: Intel® 64 and IA-32 Architectures Software Developer's Manual, Combined Volumes (Order Number 325462-091US, March 2026)
Generated: 7-6-2026