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

[Jean-Baptiste Kempf]

OK for me.

On Mon, Apr 6, 2020, at 14:01, Steve Lhomme wrote:
> OK for me.
> 
> On 2020-04-06 13:51, Martin Storsjö wrote:
> > On Fri, 3 Apr 2020, Martin Storsjö wrote:
> > 
> >> On Fri, 3 Apr 2020, Steve Lhomme wrote:
> >>
> >>> 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;
> >>> }
> >>
> >> Yeah, except we can't count on executing test apps - so it'd have to 
> >> be something like "$CC -E | tail -1" on something like this:
> >>
> >> #include <windows.h>
> >> _WIN32_WINNT
> >>
> >>
> >>>>> 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.
> >>
> >> Yes, it's possible - mingw-w64 normally default to 0x502, but it's 
> >> settable when installing mingw-w64-headers 
> >> (--with-default-win32-winnt=whatever) - llvm-mingw defaults to 0x0601.
> >>
> >> So therefore I think one gets a more consistent experience if config.h 
> >> doesn't force it to a lower version. On 4.0/master it's not an issue 
> >> as it sets the same version as the toolchain, but the generic 
> >> mechanism would be good for 3.0 I think, to avoid forcing 0x502 on 
> >> llvm-mingw there.
> > 
> > So if there's no objections to this one, I'd push this one for master, 
> > and then send new suggested backports for 3.0.
> > 
> > // Martin
> > 
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Jean-Baptiste Kempf -  President
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