[vlc-devel] [PATCH] configure: Check the toolchain default _WIN32_WINNT in addition to a command line override

[Steve Lhomme]

On 2020-04-03 13:57, Martin Storsjö wrote:
> On Fri, 3 Apr 2020, Steve Lhomme wrote:
> 
>> On 2020-04-03 13:27, Martin Storsjö wrote:
>>> Since 255e2ce27, we try not to override _WIN32_WINNT in case it already
>>> is defined on the command line to a higher value. However, if it isn't
>>> specified on the command line, but the toolchain headers default to
>>> a newer version, we should also honor it and keep that version instead
>>> of forcing a lower version here. (If the toolchain defaults to a newer
>>> version, runtime libs of the toolchain may rely on such a new version
>>> anyway, so forcing a lower target within VLC might be useless.)
>>
>> This seems OK although it may create issues with code like this:
>> #ifdef HAVE_CONFIG_H
>> # include "config.h"
>> #endif
>>
>> #if !defined(_WIN32_WINNT) || _WIN32_WINNT < 0x0601 // _WIN32_WINNT_WIN7
>> # undef _WIN32_WINNT
>> # define _WIN32_WINNT 0x0601 // _WIN32_WINNT_WIN7
>> #endif
> 
>>
>> In this case the user may not set value in the command-line and the 
>> default one from the toolchain is used. But it may be higher than Win7 
>> but then we force it down.
> 
> Hmm, you're right...
> 
> To handle that case gracefully, we would either need to include _mingw.h 
> (which sets such defaults, if __MINGW32__ is defined) between config.h 
> and the _WIN32_WINNT adjustment, or try to parse out the toolchain 
> default value in configure and set that in config.h, instead of the VLC 
> default.

That would be nice but it sounds tricky.
Or maybe using the output of such a program in the configure script:

#include <windows.h>
#include <stdio.h>
int main(void) {
   printf("0x%04X", _WIN32_WINNT);
   return 0;
}

>> On the other hand it's not a regression. In that case we use to set 
>> the value in config.h to Win7 and it would never pick the default 
>> toolchain one. But we need to keep this in mind. Especially when 
>> backporting to 3.0 (because win7 is a bad example since that's the 
>> minimum in 4.0 anyway).
> 
> Well this is only an issue for the specific source files where we 
> override the common version, right?
> 
>> I'm OK with the change if we decide we don't want people to compile 
>> 4.0 for anything lower than Win7.
> 
> I don't see how this patch is an issue for that particular case though. 
> If you intentionally want to compile for a lower version, pass 
> -D_WIN32_WINNT=0x0600 in CFLAGS/CXXFLAGS, then it will always be defined

Ah yes, so it's only for toolchain that would have a default (but not 
force via the command-line) version higher than Win7 where we might 
benefit of new API. I don't know if that's possible in mingw64, like 
when WINSTORECOMPAT is set. I don't think that's the case with MSVC.


> and used, except for the few source files where we force a custom value 
> - but those files where we force a custom value is where we normally use 
> GetProcAddress() and similar things anyway, right?
> 
> // Martin
> 
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