[lworld] RFR: 8373787: [lworld] InstanceKlass::size mixes bytes and words

[Frederic Parain]

On Tue, 16 Dec 2025 14:26:05 GMT, Stefan Karlsson <stefank at openjdk.org> wrote:

>> Maybe it could even make sense to tighten the `<=` into a `=`, going by the error message. Thoughts?
>
> I think the reason why the check is there is so that vtables start at the same offset in all Klasses. So, it really just wants to make sure that the array klasses are not so big that they start putting fields where the vtable is supposed to start. I think the comment can be tweaked a little bit here.

It is even weirder when you consider that the RefArrayKlass/FlatArrayKlass::header_size() value is only used for assertion. All paths I've found using this method end up calling `ArrayKlass::static_size()`, where the header size value is asserted, then immediately erased:


int ArrayKlass::static_size(int header_size) {
  // size of an array klass object
  assert(header_size <= InstanceKlass::header_size(), "bad header size");
  // If this assert fails, see comments in base_create_array_klass.
  header_size = InstanceKlass::header_size();
  int vtable_len = Universe::base_vtable_size();
  int size = header_size + vtable_len;
  return align_metadata_size(size);
}


Could we have a more static way to check this header size constraint?

This could be the topic of another CR.

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PR Review Comment: https://git.openjdk.org/valhalla/pull/1804#discussion_r2623531226