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

[Samuel Martin]

On Mon, Nov 7, 2016 at 9:19 AM, Thomas Petazzoni
<thomas.petazzoni at free-electrons.com> wrote:
> 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.

Ha! Sorry, I did not get you were talking about png here :s

>
> 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.

As you said, I don't think it's gonna change, plus I may be sometime lazy! ;)

>
>> > 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



-- 
Samuel