[Mingw-w64-public] How to fix error with macros in d3d12?

[Zebediah Figura]

(+ wine-devel)

On 6/11/22 13:26, LIU Hao wrote:
> 在 2022-06-12 01:59, Zebediah Figura 写道:
>>> The combination of `extern` with `__gnu_inline__` is necessary to suppress generation of a function
>>> body if the attached function could not be inlined when compiling as C99.
>>
>> Why do we need that?
>>
> 
> Otherwise there would be errors about multiple definitions.
> 
> 
>>> I don't think there is
>>> anything we can do with these headers. Perhaps WIDL should not generate `static` for `FORCEINLINE`
>>> functions; or, if that is not an option, `static __inline__` might be a better alternative.
>>
>> Is it legal to use 'static __forceinline' or 'extern __forceinline' with MSVC? If so I imagine we
>> should find a solution that allows them.
>>
> 
> Yes, unfortunately. I don't think there is a solution. `extern inline` and `inline` are not
> equivalent in C.
> 
> 

Right, so, apparently MSVC treats both "inline" and "__forceinline" as 
magic bullets—they can both appear with or without 'static' and 
'extern'; they'll always generate a function body but can also be 
defined in multiple source files (in fact, if the definition differs and 
the functions aren't static, an arbitrary one is picked and no warning 
is even printed.) And for good measure you can always take the address 
too. [So as far as I can tell there's no difference between "inline" and 
"extern inline" as far as MSVC is concerned.]

I guess we can't do anything about that without modifying the language. 
But of course in lieu of that we should probably fix our headers. I see 
at least three options:

(1) Use "FORCEINLINE" instead of "static FORCEINLINE" for these 
functions. MSVC never uses FORCEINLINE with static or extern, so this 
would be more consistent. The downside is we'd need to provide import 
library definitions for all of these functions, though, which seems less 
than ideal. (Unless combined with option 3 below.)

(2) Use "static inline" for COM wrappers. This of course drops the 
__always_inline__ attribute. I'm inclined to assert that's a non-issue, 
but then again I never really saw the point of __always_inline__ anyway. 
[I guess it can be used to force the compiler to inline even when 
-finline isn't enough, but surely that would never be the case here...]

(2b) Or use "static inline __attribute((__always_inline__))", and define 
a new macro to encapsulate that.

(3) Define __forceinline as "static inline" rather than "extern inline". 
I have to assume there was a reason this wasn't done in the first place, 
but there's no documentation in the file and I couldn't easily find 
discussion about it. As far as I can tell this actually matches MSVC 
almost exactly, except that multiple definitions will be generated if 
something takes the function address. That is arguably a break in 
behaviour which is worse than just failing to link, though.


I think my preferred solution is 2 (or 2b I guess). I'm planning to send 
the attached patch to winehq (since we need to sync widl from there), 
but I'd like to hear some feedback from the mingw-w64 project first.

ἔρρωσθε,
Zeb
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