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

[Zuxy Meng]

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;
dll.a doesn't get installed altogether.

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.

BTW: I still wonder why objects (.o) for shared and static libraries
differ in Windows. Can u explain a little bit to me or point me a URL
explaining this?
-- 
Zuxy
Beauty is truth,
While truth is beauty.
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