[FFmpeg-devel] Why 'You can only build one library type at once on MinGW'?

[Diego Biurrun]

On Wed, May 09, 2007 at 05:21:48PM +0800, Zuxy Meng wrote:
> Hi,
> 
> 2007/5/9, Michel Bardiaux <mbardiaux at mediaxim.be>:
> > Zuxy Meng wrote:
> > > Hi,
> > >
> > > 2007/5/9, Michel Bardiaux <mbardiaux at mediaxim.be>:
> > >> M?ns Rullg?rd wrote:
> > >>> "Zuxy Meng" <zuxy.meng at gmail.com> writes:
> > >>>
> > >>>> Hi,
> > >>>>
> > >>>> I don't understand. IIRC shared and nonshared objects are the same
> > >>>> under Windows,
> > >> No they're not.
> > >
> > > Any details?
> > >
> > >>>> while under Linux they're different (shared objects
> > >>>> needs to be compiled with -fPIC and access global data through %ebx?),
> > >> No, PIC is usually not required. PIC just guarantees the dso can be
> > >> relocated to any address. Without that its not possible to run when
> > >> there are conflicts of address ranges.
> > >>
> > >>>> so building the two simultaneously on Windows should be easier! I
> > >>>> removed that warning from configure and succeeded in building static
> > >>>> .a and dynamic .dll at the same time, and full test passed.
> > >>> Look a bit closer at those libraries.  IIRC the linker did some rather
> > >>> crazy things, but the details escape me.
> > >>>
> > >> When using the libraries in Visual-Studio, you need the dll *and* a
> > >> static lib that contains just the exported symbols.
> > >>
> > >> If the .a obtained is bigger than the dll, then its a 'normal' static
> > >> lib and the dll is useless. If it's small, it can be used to link to the
> > >> dll, but not on its own.
> > >
> > > Sure. Under each directory I got a .a, a .dll.a (import lib) and a
> > > dll. I don't see there're any problems.
> >
> > It would indeed be nifty to be able to build both shared and static
> > together on mingw. But there is more to test: does make install work
> > correctly? Does linking to the .a work correctly in VisualStudio? Ditto
> > shared?
> 
> For shared libraries, make install on mingw never works, regardless
> whether we build static and shared libraries together or not: dlls
> gets installed under $PREFIX/lib, while it should go to $PREFIX/bin;

I thought this only applied to Cygwin..   Are you sure?  Anyway, the fix
should be as simple as adding

    shlibdir="$bindir"

to the MinGW section around line 1153.

> dll.a doesn't get installed altogether.

Hmmm, this could be a problem.

> I don't have a VS for checking right now, but IIRC the VS linker can't
> recognize .a (while mingw binutils can work well with .lib), not to
> mention .dll.a. You have to generate an import library manually by
> using the 'lib' program. Again this has nothing to do with
> simultaneous building of both static and shared libraries.

Note that VS is unsupported, but plain MinGW is supposed to work.

Diego