Issue with dllexport/dllimport inline function

[xclaesse@gmail.com]

Le mercredi 12 octobre 2022 à 01:42 +0800, LIU Hao a écrit :
> 在 2022-10-11 22:26, xclaesse@gmail.com 写道:
> > #ifdef GLIB_COMPILATION
> > #  define _GLIB_API _GLIB_EXPORT
> > #  define GLIB_INLINE __attribute__((__dllexport__))
> > __attribute__((__gnu_inline__)) extern inline
> 
> This is not correct. Typically, `dllexport` indicates that 'I want an
> external definition' but 
> `gnu_inline` indicates that 'I do not want an external definition',
> so it's a contradiction: you get 
> either multiple definitions, or none (which causes undefined
> references).

Sorry, that was a wrong copy/paste when writing the email (leftover of
things I tried previously). I can confirm the multiple definition error
I have is when that line is `#  define GLIB_INLINE _GLIB_EXPORT extern
inline`, which expands to `__declspec(dllexport) extern inline`.

> To user code which imports such a function, it should be seen as
> 
>     ```
>     __attribute__((__gnu_inline__))
>     extern inline
>     int g_strcmp0(const char*, const char*)
>     ```
> 
> This has the desired effect: The function can be inlined where
> appropriate. And if not, a call to 
> the external thunk is emitted; no weak definition is emitted in
> either case.
> 
> 
> To the library itself which exports it, it should be seen as
> 
>     ```
>     __attribute__((__dllexport__))
>     extern inline
>     int g_strcmp0(const char*, const char*)
>     ```
> 
> There is no `gnu_inline` in this case. GCC always generates a
> COMDAT/weak/linkonce definition, which 
> will not cause multiple definition errors.

Right, that's what I do and it fails. I made a simplified example:
https://gitlab.gnome.org/xclaesse/inline-example

Build it with:
  meson setup builddir --cross-file cross_file_mingw64.txt
  ninja -C builddir/

And it fails with:
```
x86_64-w64-mingw32-gcc  -o libfoo.dll libfoo.dll.p/foo.c.obj
libfoo.dll.p/bar.c.obj -Wl,--allow-shlib-undefined -shared -Wl,--start-
group -Wl,--out-implib=libfoo.dll.a -fstack-protector -lkernel32 -
luser32 -lgdi32 -lwinspool -lshell32 -lole32 -loleaut32 -luuid -
lcomdlg32 -ladvapi32 -Wl,--end-group
/usr/bin/x86_64-w64-mingw32-ld: libfoo.dll.p/bar.c.obj: in function
`g_strcmp0':
/home/xclaesse/programmation/inline-example/builddir/../foo.h:5:
multiple definition of `g_strcmp0';
libfoo.dll.p/foo.c.obj:/home/xclaesse/programmation/inline-
example/builddir/../foo.h:5: first defined here
```

Thanks for your help!