[release/10.0] [mono] Fix interface call in case of reabstraction - #131475
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[release/10.0] [mono] Fix interface call in case of reabstraction#131475github-actions[bot] wants to merge 2 commits into
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An interface is assigned an offset in the vtable of a class that implements it, so that a call through a method on that interface will do a call through the vtable slot. There are multiple places where this offset computation happens, for example `mono_class_setup_count_virtual_methods`. Method reabstraction doesn't create a new slot. Interface calls are dispatched through imt slots that are placed before the vtable. A slot is initialized in `build_imt_slots` so that it calls through the corresponding vtable slot. For slots where we have collision of multiple interface methods, we emit some thunk that does repeated checks to dispatch to the right method. The `build_imt_slots` method didn't handle reabstraction so the vtable slot to be called for an interface method was incorrectly computed. This would appear to suggest that all cases of interface method reabstraction are broken. However, it wasn't the case because even though we incorrectly initialize the imt_slot with the wrong implementing method, `mini_resolve_imt_method` will end up patching the imt_slot if we don't have collisions, over-writting with the correct target. Added a testcase with multiple reabstracted methods on a type.
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July 28, 2026 15:33
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Backport of #131219 to release/10.0
/cc @BrzVlad
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IMPORTANT: If this backport is for a servicing release, please verify that:
release/X.0-staging, notrelease/X.0.release/X.0(no-stagingsuffix).Package authoring no longer needed in .NET 9
IMPORTANT: Starting with .NET 9, you no longer need to edit a NuGet package's csproj to enable building and bump the version.
Keep in mind that we still need package authoring in .NET 8 and older versions.