Re: [Qemu-devel] issue: linking 64bit glib when building for cpu=i386

["Daniel P. Berrange" <berrange@redhat.com>]

On Thu, Aug 21, 2014 at 08:10:54PM -0400, John Snow wrote:
> I was running a series of tests on 32 and 64 bit hosts to test for
> endianness and variable width issues when I noticed that I couldn't properly
> perform a build of "make check" against a 32bit target from a 64bit host:
> 
> ../../configure --cpu=i386 && make -j4 && make check
> 
> This produces some warnings in tests-cutils about overflowing variables that
> are of type guint64. It's been mentioned on the mailing lists before,
> actually: http://lists.gnu.org/archive/html/qemu-devel/2014-05/msg00452.html
> 
> The problem is that guint64 is being aliased against "unsigned long", which
> is only 4 bytes instead of the implied 8. This occurs because we link
> against the 64bit headers for glib instead of the 32bit ones when we're
> building for i386 from an x86_64 host.
> 
> Our include flags wind up looking like: -I/usr/include/glib-2.0 but
> -I/usr/lib64/glib-2.0/include
> 
> I was discussing the problem with Stefan:
> 
> On 08/21/2014 05:03 AM, Stefan Hajnoczi wrote:
> >The problem is that pkg-config uses libdir=/usr/lib64 by default on
> >amd64 hosts.  It doesn't know that gcc -m32 is being used.
> >
> >This results in glib's 64-bit headers being used where guint64 is just
> >unsigned long.  On 32-bit hosts this is incorrect.
> >
> >Two workarounds:
> >
> >1. yum install pkgconfig.i686 and run it instead of pkgconfig.x86_64
> >
> >2. Use the pkg-config --define-variable libdir=/usr/lib option
> >
> >You can set PKG_CONFIG=path/to/pkg-config.i686 on QEMU's ./configure
> >command-line.
> >
> >This is all distro-specific :(.  Any other solutions?
> >
> >Stefan
> >
> 
> I am not extremely well versed in configure or pkg-config ninjutsu, but I
> must imagine that the ARCH/cpu variables we are setting in configure could
> help us know to call the 32bit pkg-config instead of the native 64bit
> version and fix this issue.
> 
> Does anyone have any good ideas? Surely other projects must have run into
> this elsewhere.

Distros will install pkg-config .pc files for non-native architectures
in a different location normally. The supported / recommended way to
tell pkg-config to look in these alternative dirs is to set the env
variable  PKG_CONFIG_LIBDIR. This replaces the built-in default search
directory that looks for native.

So on a Fedora / RHELL system, to make pkg-config use 32-bit libs you
want to set

   PKG_CONFIG_LIBDIR=/usr/lib/pkgconfig

which replaces the default location of /usr/lib64/pkgconfig. This is
the same thing you'd need to do to build QEMU for say, mingw32 where
you must set something like

   PKG_CONFIG_LIBDIR=/usr/i686-w64-mingw32/sys-root/mingw/lib/pkgconfig/

Note, i say PKG_CONFIG_LIBDIR here, *not* PKG_CONFIG_PATH. The latter
variable adds the default search path - you want to stop it looking in
the default search path completely because it is the wrong arch, so
must use PKG_CONFIG_LIBDIR


Regards,
Daniel
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