在 2019/11/24 2:34, Nikolay Sivov 写道:
>
> Thanks, I think mingw headers are broken when in C mode. Like I said, vtbl
> method prototype should be:
>
> D2D1_SIZE_F * (STDMETHODCALLTYPE *GetSize)(
> ID2D1HwndRenderTarget *This,
> D2D1_SIZE_F *__ret);
>
> In Wine we generate it from .idl sources, fixed up inline wrapper is like
> this:
>
> static FORCEINLINE D2D1_SIZE_F
> ID2D1HwndRenderTarget_GetSize(ID2D1HwndRenderTarget* This) {
> D2D1_SIZE_F __ret;
> return *This->lpVtbl->GetSize(This,&__ret);
> }
>
>
>
As Microsoft doesn't provide C interfaces we have to look at their C++
declarations:
```
STDMETHOD_(D2D1_SIZE_F, GetSize)(
) CONST PURE;
```
The above method is of `ID2D1RenderTarget` which is a direct base of
`ID2D1HwndRenderTarget` and where it gets inherited.
This prototype says it is a function taking only an implicit `this`
argument and returning a `D2D1_SIZE_F`.
Note that `D2D1_SIZE_F` is defined as a `struct` of two `FLOAT`s (see
'd2dbasetypes.h' from mingw-w64 or Win8 SDK and earlier, or 'dcommon.h'
from Win10 SDK):
```
struct D2D_SIZE_F {
FLOAT width;
FLOAT height;
};
typedef struct D2D_SIZE_F D2D1_SIZE_F;
```
This struct has 64 bits. According to MSDN it should be returned in RAX [1].
But, MSDN is wrong about member functions [2]. The online compiler shows
that it is returned by reference. The `this` argument goes into RCX, and
the pointer to uninitialized storage for the returned struct goes into RDX.
Our current definition
```
#define ID2D1HwndRenderTarget_GetSize(this) \
(this)->lpVtbl->Base.GetSize((ID2D1RenderTarget*)(this))
```
is an indirect call to a non-member function, so [1] is correct that the
result is returned in RAX [2].
So, yes, you are right, the mingw-w64 definitions are broken. I think
inline wrappers are necessary to work around the calling convention
problem. Patches are welcome.
[1]
https://docs.microsoft.com/en-us/cpp/build/x64-calling-convention?view=vs-2019#return-values
[2] https://gcc.godbolt.org/z/3GyBGG
--
Best regards,
LH_Mouse
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