[Buildroot] [PATCH] package/openjpeg: fix static build

[Thomas Petazzoni <thomas.petazzoni@free-electrons.com>]

Hello,

On Mon, 7 Nov 2016 06:17:36 +0100, Samuel Martin wrote:

> >> + # Try to find lib Z
> >> + IF(BUILD_THIRDPARTY)
> >> +@@ -35,6 +39,9 @@ IF(BUILD_THIRDPARTY)
> >> +   SET(PNG_INCLUDE_DIRNAME ${OPENJPEG_SOURCE_DIR}/thirdparty/libpng PARENT_SCOPE)
> >> + ELSE (BUILD_THIRDPARTY)
> >> +   IF (ZLIB_FOUND)
> >> ++    # Static only build:
> >> ++    #   it is not necessary to invoke pkg_check_module on libpng, because libpng
> >> ++    #   only depends on zlib, which is already checked.  
> >
> > This is correct today, but in the future? The whole point of pkg-config
> > is to not make this sort of assumption.  
> 
> Some cmake modules are so poorly written, they only set the flags
> relative to the package itself (i.e. setting LDFLAGS="-L/usr/lib
> -lfoo" for package foo), and completly ignore/miss/forget the indirect
> dependencies that are required in the case of static build.
> However, cmake can leverage pkgconfig to set all these flags, so the
> proper fix is indeed using it in the module. But that's another story
> for another patch... ;-)
> 
> A future-proof fix is fixing the FindTIFF.cmake module from the cmake
> package itself, making it using pkgconfig to get all the libs in the
> LDFLAGS instead of only -ltiff. This is not easily possible since we
> conditionally build the host-cmake package (patching host-cmake would
> mean no-op-ing commit c2d80a8c5d8b97cdc84c297a3d2d6896fff6560b).

This I understand. What I don't understand is your reasoning of "for
libpng, we don't need to use pkg-config, because the only indirect
dependency is zlib, which is already checked". This is not good, as you
make an assumption on which indirect libraries libpng might use.

Even though I agree libpng is unlikely to change and grow additional
dependencies, you should also use pkg-config on libpng just like you're
doing on libtiff.

> > I fail to understand why one needs to call both FIND_PACKAGE(TIFF) and
> > then check again with PKG_CHECK_MODULES(). Isn't the latter sufficient?  
> 
> Indeed FIND_PACKAGE(TIFF) is redundant with what PKG_CHECK_MODULES()
> does. But to give a chance to this patch to get upstream I have to
> take care platform missing pkgconfig (yeah! it exists :( ...), so
> FIND_PACKAGE() is always called, and PKG_CHECK_MODULES() is called
> only when available (mea culpa, the commit log does not reflect this).

OK, makes sense.

Thanks for the explanation,

Thomas
-- 
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com