[PATCH] D85802: [clang] Add -fc++-abi= flag for specifying which C++ ABI to use

Mon Oct 24 10:53:46 PDT 2022

mcgrathr added a comment.

In D85802#3879950 <https://reviews.llvm.org/D85802#3879950>, @dblaikie wrote:

> In D85802#3879888 <https://reviews.llvm.org/D85802#3879888>, @mcgrathr wrote:
>
>> In D85802#3876106 <https://reviews.llvm.org/D85802#3876106>, @dblaikie wrote:
>>
>>>> The C++ ABI is not part of the Fuchsia system ABI, nor what we call the "Fuchsia compiler ABI". Different users of C++ are free to use whatever C++ ABI they like. Only the backend ABI independent of language-specific issues is necessary to interoperate with other code on Fuchsia.
>>>
>>> Sure enough - but I'm still sort of confused by why the Fuschia Clang target/compiler needs more than one C++ ABI. What is it interoperating with? (GCC doesn't have a Fuschia target implemented, does it? So what's it mean to target the GCC C++ ABI? what is compiling the code that Fuschia is trying to interoperate with when Clang targets Fuschia with a non-default C++ ABI?)
>>
>> When we use GCC we're using the generic ELF targets. I think it's sufficient for us to tell you that indeed we do want the option of multiple C++ ABIs to select from without justifying everything about our work to a Clang reviewer before we can proceed with meeting the requirements of our system.
>
> Would the generic ELF target support in Clang be adequate to meet that requirement, then? (so Fuschia target could be the custom C++ ABI (& custom C ABI if you likee) and a generic ELF target could be used for GCC ELF compatibility) - then we wouldn't need any C++ ABI customizability?

No. All the aspects of the Fuchsia target not specific to C++ we still want done the same way when interoperating with this code.  We're quite confident that what we want is a Fuchsia target with multiple options for the C++ ABI.  If you don't want that flexibility to be available to other targets, then fine (though I think that's a poor choice, personally).  Second-guessing everything about how we're organized our system and build is not a very helpful tactic in compiler reviews.  It would be much appreciated if this review were constrained to how the compiler should work rather than what we should want to do.

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https://reviews.llvm.org/D85802