Clear Alignment Check Flag

Encoding

EncodingOperand
zoNone

Description

The CLAC instruction clears the AC flag (alignment checking) in the EFLAGS register.

This instruction can only be executed when CPL is 0 (i.e. ring 0). Attempts to execute this instruction in less privileged rings will cause a #UD exception to be raised.

Operation

public void CLAC()
{
    EFLAGS.AC = 0;
}

Flags Affected

CF (carry flag)
Unmodified.
PF (parity flag)
Unmodified.
AF (auxiliary flag)
Unmodified.
ZF (zero flag)
Unmodified.
SF (sign flag)
Unmodified.
OF (overflow flag)
Unmodified.
AC (alignment check flag)
Cleared.

Exceptions

Real-Address Mode

#UD
  • If the LOCK prefix is used.

Virtual-8086 Mode

#UD
  • If in Virtual-8086 Mode.

Protected Mode

#UD
  • If CPL is greater than 0.
  • If the LOCK prefix is used.

Compatibility Mode

#UD
  • If CPL is greater than 0.
  • If the LOCK prefix is used.

Long Mode

#UD
  • If CPL is greater than 0.
  • If the LOCK prefix is used.