[PATCH] D89490: Introduce __attribute__((darwin_abi))

[Adrien Guinet via Phabricator via cfe-commits]

aguinet added a comment.

> I may be over-reacting to the way the patch seemed to be touching on the C++ ABI in multiple places.  My understanding is that `ms_abi` is just a calling-convention attribute; it's basically "use the (default) calling convention that MSVC would use for this function".  If that's all you want, then this is reasonable, although I am worried about creating a new attribute for every system that Wine chooses to target.

I literally based this patch on how ms_abi was implemented. It's unfortunately more than just teaching clang to change the calling convention on LLVM IR functions. The fact that ABI implementations are spread all over the place between various places in LLVM is, as far as I remember, a known problem discussed many times on llvm-dev, and looks like a hard one to fix.

> About "darwin": technically, every Apple platform has a different ABI.  Our current ARM64 platforms do all agree about things like the calling convention, at least if you count newer watches (which use a 32-on-64 ABI in userspace) as not ARM64.  That is not true of other architectures, most notably on ARM32, where the 32-bit iOS ABI is very different from the armv7k Apple Watch ABI; and it is certainly conceivable that Apple might release a new ARM64 platform in the future with a different calling convention.  The more technically correct and future-proof thing would be to use the OS name (or maybe even the triple!) in the attribute, probably as an argument to the attribute, like `__attribute__((target_abi("arm64-apple-ios")))`.

I'm a bit afraid that `__attribute__((target_abi(XX)))` would conflict with the existing `__attribute__((ms_abi))`. Maybe, not to conflict with the MS ABI implementation, we could introduce `__attribute__((darwin_abi("arm64-ios")))` (and arm64-tvos, arm64-osx, ...)?

About Apple that would create as much ABIs as products, I guess we have a living example: is the ABI for OSX/ARM64 different than the ABI for iOS/ARM64? I can't seem find any official documentation about this :/ (only talking about arm64 here, but I get your points about armv7 targets).

Thanks!


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https://reviews.llvm.org/D89490