On Fri, 23 Feb 2024, Richard Sandiford wrote:
Are there two distinct ABIs for aarch64-*-mingw*? Or are these distinctions ignored on aarch64 and just retained for compatibility?
On Windows on AArch64, the calling convention normally matches regular AAPCS64 - so the ms_abi attribute normally has no effect. However, for variadic functions, the calling convention differs, so the ms_abi attribute could be used to implement functions with the Windows vararg calling convention on Linux.
(As far as I know, the correct Windows vararg calling convention is not yet implemented in this patch series, but would be a later addition.)
Clang/LLVM does implement the Windows AArch64 vararg calling convention, and it used to be necessary for Wine on AArch64 before, but as Jacek mentioned, it's no longer needed by Wine.
ARM64EC is an entirely different thing though, both out of scope for this patchset, and also a much bigger thing than an MS_ABI attribute.
// Martin
