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I want to backport gcc-4.7 from raring to precise. So I ran backportpackage and uploaded gcc-4.7 to my PPA. However, when Launchpad tries to build it it complains about a missing dependency:

Dependency wait on rhenium (virtual64)

Missing build dependencies: libx32gcc1
Started on 2013-10-24
Finished on 2013-10-24 (took 2 minutes, 46.6 seconds)

From looking at the package info for gcc-4.7 it seems that this should also be contained in the gcc-4.7 package that has been backported.

What do I need to do to make Launchpad find this and build my package?

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Note that "contained in" the package means that it's "built from" the package. I highly advise against this, read the answer by Dima below, it explains why you shouldn't try this at all. (Also, these build deps will fail pretty much all the time because of the package's circular dependency upon itself) – Thomas Ward Oct 30 '13 at 22:05
Could you please explain why you are downvoting? – Chris Nov 7 '13 at 16:03
up vote 3 down vote accepted

I'd advise you against trying to backport gcc-4.7 from raring to precise. It is introducing x32 architecture and expects intrusive changes to glibc which are not safe to run on precise.

Instead if you want to use the raring compiler on the precise box, you can do that trivially with a chroot:

$ apt-get install ubuntu-dev-tools
$ mk-sbuild raring
$ schroot -u root raring-amd64
$ gcc-4.7 -v

Which will get you a raring environment with raring's complier et. al.

ps. if you are really interested in how bootstrapping was done: well one needs to upload staged (incomplete builds) of binutils, glibc, gcc in the correct order a few times until all intermediate packages are available to start doing full builds.

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