This page is to capture ARM64EC status and progress on LLVM support for windows on arm. The documentation can be found here Understanding Arm64EC ABI and assembly code | Microsoft Docs 23.
Status
...
For now we will create exit thunk for every indirect call. Microsoft create exit based on function types. So the same type function will share one exit thunk.
...
Variadic function exit thunk under review: ⚙ D129727 [ARM64EC 11/?] Add support for lowering variadic indirect calls. (llvm.org)
...
Entry thunk totally has not been implemented yet because of undocumented hybmp$x section.
...
Adjustor thunk has not been implemented yet.
...
ARM64EC ABI support is under development by Qualcomm.
Up-to-date information can be found here https://discourse.llvm.org/t/initial-patches-for-arm64ec-windows-11-now-posted/62449