This will crash rakudo.

use v6.c;

use nqp;
use NativeCall;

class A is repr('CStruct') {
        has int32   $.one;
        has int32   $.two;
        has int32   $.three;
        has Pointer $.four;
}

class B is A is repr('CStruct') {
        method getA {
                nativecast(A, self);
        }
}

sub setObjAttr($obj, $attr, $val) is export {
    nqp::bindattr(
        nqp::decont($obj), $obj.WHAT, $attr, nqp::decont($val)
    );
}

sub MAIN {
        my $a = A.new(:one(1), :two(22), :three(333));
        my $b = B.new(:one(2), :two(66), :three(888));

        my $p = nativecast(Pointer, $a);

        # cw: This works.
        setObjAttr($a, '$!four', $p);
        # cw: This causes segfault.
        #setObjAttr($b, '$!four', $p);
        # cw: Should not cause a segfault.
        setObjAttr($b.getA, '$!four', $p);
        # cw: This still causes segfault.
        setObjAttr($b, '$!four', $p, :what(A));
}