Check Upper Bound

Encoding

Description

The BNDCU/BNDCN instructions compare the address in the second source operand against the upper bound in the first source operand. If the second source is greater (outside the bounds), a #BR exception is raised and BNDSTATUS is set to 1.

By default, the value stored in the upper bound is stored in its inverted (one's complement) form. The BNDCU instruction should be used when that assumption is true, and will invert it before comparison. Otherwise, use the BNDCN instruction.

If the second source operand is a general purpose register, the value contained in it is treated as the address to compare against. If, however, it is a memory location, the effective address is calculated (see LEA - Load Effective Address) and used in the comparison. At no time is memory accessed.

Which instruction form is used depends on the operating mode of the processor. In 16-bit and 32-bit modes, the 32-bit form is used. In 64-bit mode, the 64-bit form is used.

Operation

public void BNDCU(Bound bnd, IntPtr addr)
{
    // uninvert the stored version (that itself is inverted)
    if (addr > ~bnd.Upper)
    {
        BNDSTATUS.Abd = 0;
        BNDSTATUS.EC = 1; // bounds violation
        #BR;
    }
}

public void BNDCN(Bound bnd, IntPtr addr)
{
    if (addr > bnd.Upper)
    {
        BNDSTATUS.Abd = 0;
        BNDSTATUS.EC = 1; // bounds violation
        #BR;
    }
}

Flags Affected

Intrinsics

void _bnd_chk_ptr_ubounds(const void *address)

Exceptions

Real-Address Mode

Virtual-8086 Mode

Protected Mode

Compatibility Mode

Long Mode