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

[Stefan Hajnoczi]

On Fri, Aug 22, 2014 at 9:20 AM, Daniel P. Berrange <address@hidden> wrote:
> 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.

Nice, and Paolo sent me an automated way of doing that:

On Fri, Aug 22, 2014 at 12:14:28AM +0200, Paolo Bonzini wrote:
> You need to set PKG_CONFIG_LIBDIR to
>
> /usr/lib/$MULTILIBDIR/pkgconfig
>
> where MULTILIBDIR is
>
>     if $CC -print-multiarch >/dev/null 2>&1; then
>       MULTILIBDIR=`$CC -print-multiarch $CFLAGS $CPPFLAGS`
>     fi
>     if test -z "$MULTILIBDIR"; then
>       MULTILIBDIR=`$CC --print-multi-os-directory $CFLAGS $CPPFLAGS`
>     fi
>
> This will point at /usr/lib/pkgconfig/glib-2.0.pc instead of
> /usr/lib64/pkgconfig/glib-2.0.pc

I tested that it works.

Stefan