On Fri, 28 Aug 2026 03:47:02 GMT, Ioi Lam <[email protected]> wrote:
> `FieldClosure` is used for iterating fields in an object. For Valhalla, it
> has been enhanced to handle fields that are inside inlined fields. However,
> the current implementation has two problems:
>
> [1] It type casts the address of an inlined field into an `oop` pointer. This
> is unsafe as many operations, such as getting the header of an `oop`, will
> not work with such an `oop` pointer:
>
> https://github.com/openjdk/jdk/blob/b1f975efa481bd5e20c1b7d58a87d0866df205e6/src/hotspot/share/runtime/fieldDescriptor.cpp#L216
>
> [2] The parameter `base_offset` is used in many functions. Its meaning is
> unclear and inconsistent.
>
> https://github.com/openjdk/jdk/blob/b1f975efa481bd5e20c1b7d58a87d0866df205e6/src/hotspot/share/runtime/fieldDescriptor.cpp#L159
>
> https://github.com/openjdk/jdk/blob/b1f975efa481bd5e20c1b7d58a87d0866df205e6/src/hotspot/share/oops/instanceKlass.hpp#L99-L101
>
> This RFE refactors `FieldClosure` to avoid the above problems. `FieldClosure`
> now carries information about inlined fields. This information can be used by
> various field iteration code to simplify their operations. See
> `FieldClosure::inline_klass()` and `FieldClosure::inline_offset()`.
>
> As a result, users of `FieldClosure` and `FieldDescriptor()` no longer need
> to perform obscure arithmetics with `InlineKlass::payload_offset()`.
>
> This RFE also moves a few common operations into utility functions to avoid
> code duplication.
>
> Also:
> - Fixed a bug in `FlatArrayKlass::oop_print_elements_on()` in the handling of
> nullable elements.
>
> ---------
> - [x] I confirm that I make this contribution in accordance with the [OpenJDK
> Interim AI Policy](https://openjdk.org/legal/ai).
src/hotspot/share/oops/flatArrayKlass.cpp line 438:
> 436: if (base_offset >= max_jint - 0x1000) {
> 437: // TODO: the oopDesc::xxx_at() APIs are limited to int offsets,
> but it's
> 438: // possible for a value object be inlined at an offset higher
> than 0x7ffffffff.
`FlatArrayKlass::max_elements()` is supposed to prevent this from happening.
Did you find a bug in it?
-------------
PR Review Comment: https://git.openjdk.org/jdk/pull/32565#discussion_r3924942281
