[Buildroot] [PATCH 1/1] package/pkgconf: add host link to pkg-config

[Thomas Petazzoni <thomas.petazzoni@bootlin.com>]

Hello Stuart,

On Thu, 4 Apr 2019 21:30:40 +0000
"Summers, Stuart" <stuart.summers@intel.com> wrote:

> > However, the wrapper assumes by default we are building for the
> > target,
> > and therefore returns results valid for cross-compilation. To return
> > results valid for native build, the following environment variables
> > need to be passed:
> > 
> >         PKG_CONFIG="$(PKG_CONFIG_HOST_BINARY)" \
> >         PKG_CONFIG_SYSROOT_DIR="/" \
> >         PKG_CONFIG_ALLOW_SYSTEM_CFLAGS=1 \
> >         PKG_CONFIG_ALLOW_SYSTEM_LIBS=1 \
> >         PKG_CONFIG_LIBDIR="$(HOST_DIR)/lib/pkgconfig:$(HOST_DIR)/shar
> > e/pkgconfig"  
> 
> I apologize if I'm missing something obvious, but adding this to
> packages/pkgconf/pkgconf.mk did not seem to make any difference. I also
> tried adding this to linux/linux.mk. The latter I didn't do a full
> "make clean", but did on the former.

Adding those lines to pkgconf.mk will indeed make no difference: they
should be added to the package calling pkg-config, in cases where
pkg-config should return results valid for building native code (i.e
not cross-compiled). Did you try to put this in LINUX_MAKE_ENV for
example ?

> > detect
> > libelf, what about just adding host-pkgconf to LINUX_DEPENDENCIES 
> > when
> > BR2_LINUX_KERNEL_NEEDS_HOST_LIBELF is enabled ?  
> 
> At least without including the changes I had, I was seeing host-pkgconf 
> show up in output/build even without adding this to LINUX_DEPENDENCIES,
> although that seems like the right thing to add anyway.

linux depends on host-kmod, and host-kmod depends on host-pkgconf, so
indeed, host-pkgconf will always be pulled in. However, since Linux is
using it directly, I think it makes sense to add the host-pkgconf
dependency to LINUX_DEPENDENCIES.

> > This is definitely wrong and will break the wrapper we install.  
> 
> Thanks for the feedback and makes sense. Just looking at the right way
> to work around this.

The completely correct way would be:

 - To have pkg-config return results for native build

 - To have <tuple>-pkg-config return results for cross-compilation

But then, when cross-building, we need to convince the packages that
they need to call <tuple>-pkg-config. The autotools PKG_CHECK_MODULES()
macro does this by default, so a majority of packages would be OK. But
there are also lots of packages that call "pkg-config" directly, and
those would have to be fixed.

Best regards,

Thomas
-- 
Thomas Petazzoni, CTO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com