CLAC
Clear AC Flag in EFLAGS Register
stableVMJITAOTinstruction
Encodings
| Opcode | Instruction | Op/En | 64-bit | Compat/Legacy | Description |
|---|---|---|---|---|---|
NP 0F 01 CA | CLAC | ZO | Valid | Valid | Clear the AC flag in the EFLAGS register. |
Measured cost
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Flags named
ACAlignment check
Description
Clears the AC flag bit in EFLAGS register. This disables any alignment checking of user-mode data accesses. If the SMAP bit is set in the CR4 register, this disallows explicit supervisor-mode data accesses to user-mode pages.
This instruction's operation is the same in non-64-bit modes and 64-bit mode. Attempts to execute CLAC when CPL > 0 cause #UD.
Operation
EFLAGS.AC := 0;Flags affected
AC cleared. Other flags are unaffected.
Exceptions
Protected mode
#UD | If the LOCK prefix is used. If the CPL > 0. If CPUID.07H.00H:EBX.SMAP[20] = 0. |
Real address mode
#UD | If the LOCK prefix is used. If CPUID.07H.00H:EBX.SMAP[20] = 0. |
Virtual-8086 mode
#UD | The CLAC instruction is not recognized in virtual-8086 mode. |
Compatibility mode
#UD | If the LOCK prefix is used. If the CPL > 0. If CPUID.07H.00H:EBX.SMAP[20] = 0. |
64-bit mode
#UD | If the LOCK prefix is used. If the CPL > 0. If CPUID.07H.00H:EBX.SMAP[20] = 0. |