Re: [Qemu-devel] [PATCH 04/25] Add hard build dependency on glib

[David Gibson]

On Wed, Jul 27, 2011 at 06:54:09PM +1000, Benjamin Herrenschmidt wrote:
> 
> > You're probably setting up your cross environment incorrectly which, 
> > unfortunately, is very common.
> > 
> > The proper thing to do is to have GCC use a different system include 
> > directory and a different prefix.  That will result in a directory where 
> > there are gcc binaries with normal names installed in ${cross_prefix}/bin
> > 
> > You need to build and install pkg-config to this prefix too, and then 
> > when it comes time to actually doing the QEMU configure, you should do 
> > something like:
> > 
> > export PATH=${cross_prefix}/bin:$PATH
> > export PKG_CONFIG_PATH=${cross_prefix}/lib/pkg-config:$PKG_CONFIG_PATH
> > 
> > Many automated cross compiler environment scripts will install specially 
> > named versions of gcc and binutils in your normal $PATH.  The trouble 
> > is, this is a bit of a hack and unless you know to make this hack work 
> > with other build tools, it all comes tumbling down.

We're not, as a rule, cross building.  We're doing compiles of ppc64
binaries on a ppc32.  Although that can be approached as a
cross-build, it's a common enough special case that it should be able
to handle this without setting a full cross-build environment.  At the
moment this does seem to work for building x86_64 binaries on a 32-bit
x86 system, but I suspect this is only accident.

> Well, that hard requirement is causing us problem on our 32/64-bit cross
> builds as well.
> 
> It looks like glib (at least recent versions in -sid) can't be built
> 64-bit on a 32-bit system :-( At least not without fixing some horrid
> bugs in there related to some generated include path from what David
> says (I'll let him comment further).

Actually, I think it can (provided a 64-bit glib is installed,
including a 64-bit version of glibconfig.h), and it's not *as* painful
to set up as I previously thought, although it's still not nice.

> In general, every time you add a library requirement without some config
> option to disable it for cases such as ours, you add pain :-)
> 
> Now, in the specific case of glib, I understand why you would want to
> get rid of re-invented wheels and use it, so I'm not specifically
> criticizing that specific change, we'll eventually have to fix it
> anyways. Just a heads up to be careful with hard requirements in
> general.
> 
> Cheers,
> Ben.
> 
> 

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson