On Mon, 14 Jul 2025 23:23:21 GMT, Chris Plummer <[email protected]> wrote:
>> Thank you for the concern. But I'm kind of puzzled with your observation.
>> The JVMTI implementation should return `JVMTI_ERROR_OPAQUE_FRAME` for
>> platform threads.
>> Though I wonder if it also was the case before virtual thread support was
>> added.
>>
>> The `VM_BaseGetOrSetLocal::doit()` have the following checks in place:
>>
>>
>> void VM_BaseGetOrSetLocal::doit() {
>> . . .
>> frame fr = _jvf->fr();
>> if (_set && _depth != 0 &&
>> Continuation::is_frame_in_continuation(_jvf->thread(), fr)) {
>> _result = JVMTI_ERROR_OPAQUE_FRAME; // deferred locals are not fully
>> supported in continuations
>> return;
>> }
>> Method* method = _jvf->method();
>> if (getting_receiver()) {
>> if (method->is_static()) {
>> _result = JVMTI_ERROR_INVALID_SLOT; ### This check is for
>> GetLocalInstance
>> return;
>> }
>> } else {
>> if (method->is_native()) {
>> _result = JVMTI_ERROR_OPAQUE_FRAME; ### This check is before calls to
>> ### check_slot_type_no_lvt() and
>> check_slot_type_lvt()
>> return;
>> }
>> if (!check_slot_type_no_lvt(_jvf)) { ### This has checks for
>> JVMTI_ERROR_INVALID_SLOT
>> return;
>> }
>> if (method->has_localvariable_table() &&
>> !check_slot_type_lvt(_jvf)) { ### This has checks for
>> JVMTI_ERROR_INVALID_SLOT
>> return;
>> }
>> }
>> . . .
>
> My concern was that Set/GetLocal could produce JVMTI_ERROR_OPAQUE_FRAME for a
> native frame, and JDI was not handling this, but is appears that JDI is
> prevening Set/GetLocal on a native frame. Read on for more details.
>
> It looks like historically Set/GetLocal has returned JVMTI_ERROR_OPAQUE_FRAME
> for native methods. However, JDI does not check for this, so I had some
> concern about that because JVMTI_ERROR_OPAQUE_FRAME would result in a
> JDIInternalError. However, I think now that JDI would never result in a JVMTI
> Set/GetLocal call when the frame is native because of checks JDI does ahead
> of time. The JDI Set/GetValue APIs take a LocalVariable, the source of which
> would preclude ever getting one for a frame that is for a native method. I
> think what is most common is to call StackFrame.visibleVariables() to get all
> the LocalVariables, and if this is done on a native method, you simply get no
> LocalVariables, thus you have nothing to pass to Set/GetLocal.
>
> So I think the only time JDI will see JVMTI_ERROR_OPAQUE_FRAME is for the
> virtual thread case, which for SetLocal requires that the frame be the
> topmost frame and the virtual thread be mounted. The JDI spec is already
> covering this, so probably no changes are needed.
Okay, thanks. This sounds right. 👍
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PR Review Comment: https://git.openjdk.org/jdk/pull/26111#discussion_r2206180435
