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

[John Snow <jsnow@redhat.com>]

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.

-- 
—js