[FFmpeg-devel] [PATCH] compat: LoadLibrary isn't available on UWP/WinRT

[Aaron Levinson]

On 6/2/2017 7:11 AM, wm4 wrote:
> On Fri,  2 Jun 2017 15:29:07 +0200
> Hugo Beauzée-Luyssen <hugo at beauzee.fr> wrote:
> 
>> ---
>>   compat/w32dlfcn.h | 4 ++++
>>   1 file changed, 4 insertions(+)
>>
>> diff --git a/compat/w32dlfcn.h b/compat/w32dlfcn.h
>> index bc9bb8c9f5..308763be53 100644
>> --- a/compat/w32dlfcn.h
>> +++ b/compat/w32dlfcn.h
>> @@ -71,7 +71,11 @@ exit:
>>   #ifndef LOAD_LIBRARY_SEARCH_SYSTEM32
>>   #   define LOAD_LIBRARY_SEARCH_SYSTEM32        0x00000800
>>   #endif
>> +#if WINAPI_FAMILY_PARTITION (WINAPI_PARTITION_DESKTOP)
>>       return LoadLibraryExA(name, NULL, LOAD_LIBRARY_SEARCH_APPLICATION_DIR | LOAD_LIBRARY_SEARCH_SYSTEM32);
>> +#else
>> +    return NULL;
>> +#endif
>>   }
>>   #define dlopen(name, flags) win32_dlopen(name)
>>   #define dlclose FreeLibrary
> 
> Isn't it that LoadLibraryW is available, just not the A version?

According to 
https://msdn.microsoft.com/en-us/library/windows/apps/mt654039.aspx#_api-ms-win-core-libraryloader-l1-2-0.dll 
, both the A and W versions of LoadLibrary and LoadLibraryEx would seem 
to be available on UWP.  However, at the same time, I don't see any of 
the LoadLibrary APIs listed at either 
https://msdn.microsoft.com/en-us/library/windows/apps/dn424765.aspx , 
https://docs.microsoft.com/en-us/uwp/win32-and-com/win32-apis , or 
https://docs.microsoft.com/en-us/uwp/win32-and-com/win32-extension-apis 
, so perhaps LoadLibrary and LoadLibraryEx aren't supported.  So, there 
appears to be some conflicting information on MSDN.  According to 
https://msdn.microsoft.com/en-us/library/mt186162.aspx , it is necessary 
to use LoadPackagedLibrary in UWP apps instead of LoadLibrary or 
LoadLibraryEx.

According to the article, "These macros are only available in Windows 
SDK 8.1 and later, so if your code needs to compile with earlier 
versions of the Windows SDK or for other platforms besides Windows, then 
you should also consider the case that none of them are defined."  I'm 
not aware of ffmpeg necessarily having a requirement that it be built 
with the Windows 8.1 SDK or later, and this lack of requirement would 
tend to indicate that the proposed patch isn't sufficient.  Plus, there 
is no reason to #define LOAD_LIBRARY_SEARCH_SYSTEM32 if the code won't 
be built anyway.

Aaron Levinson