[lworld] Integrated: 8378099: [lworld] Wrong adapter choice when is_interp_only_mode is set

[Marc Chevalier]

On Wed, 18 Feb 2026 10:32:52 GMT, Marc Chevalier <mchevalier at openjdk.org> wrote:

> In `SharedRuntime::get_resolved_entry` when `current->is_interp_only_mode()` we need to go to the interpreter, and thus we must always return a c2i adapter (and not the entry point of another compiled method).
> 
> https://github.com/openjdk/valhalla/blob/d5e3620d5a0b13cce9c19bafd5b2dd881b8bf9e9/src/hotspot/share/runtime/sharedRuntime.cpp#L1635-L1641
> 
> Yet, here, we disregard the kind of call, or the caller. Yet, under, we make the correct distinction:
> 
> https://github.com/openjdk/valhalla/blob/d5e3620d5a0b13cce9c19bafd5b2dd881b8bf9e9/src/hotspot/share/runtime/sharedRuntime.cpp#L1643-L1652
> 
> Indeed, if the caller is C1, the call won't be scalarized, so we don't need the packing logic that would be required for a scalarized call from C2, for instance... Overall, we must distinguish the 3 same cases as when `is_interp_only_mode` is not set. The only difference is that instead of picking the compiled entry point if available, and only an adapter as a fallback, we must take the adapter. Right now, the code is correct only if `!caller_does_not_scalarize && (is_static_call || is_optimized)` (so, especially not calls from C1).
> 
> I've slightly changed the shape of the code to make that more clear, and also to be less likely to forget a case if we add new variations in the calling convention!
> 
> If this error doesn't show up so often, that's because `is_interp_only_mode()` is only set by JVMTI:
> 
> https://github.com/openjdk/valhalla/blob/d5e3620d5a0b13cce9c19bafd5b2dd881b8bf9e9/src/hotspot/share/prims/jvmtiThreadState.cpp#L322-L328
> and
> https://github.com/openjdk/valhalla/blob/d5e3620d5a0b13cce9c19bafd5b2dd881b8bf9e9/src/hotspot/share/prims/jvmtiThreadState.inline.hpp#L151-L153
> 
> So, without JVMTI, it is impossible to observe this bug, which is unfortunate. So, how to test that, not to do the same error again? A test involving JVMTI would be brittle, and we can do better than adding yet another test: making better usage of existing tests. Now, `StressCallingConvention` will sometimes make `get_resolved_entry` behaves as if `is_interp_only_mode` is set. Doing so causes SO MANY crashes in `TestCallingConventionC1`, which is expected. With the fix, it works again as expected.
> 
> The frequency of `is_interp_only_mode` being randomly true when stressing is currently set at a very arbitrary 1/2^10 which is around 0.1%. I've also tested with a probability of 1/2, and I get basically the same behavior: plenty of crashes with the improved stress without the fix, and no crashes with the fix...

This pull request has now been integrated.

Changeset: c27e815e
Author:    Marc Chevalier <mchevalier at openjdk.org>
URL:       https://git.openjdk.org/valhalla/commit/c27e815e6f3dcca4bcbe30eb0cabc3018cc3141e
Stats:     23 lines in 4 files changed: 16 ins; 1 del; 6 mod

8378099: [lworld] Wrong adapter choice when is_interp_only_mode is set

Reviewed-by: thartmann

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PR: https://git.openjdk.org/valhalla/pull/2124