[odb-users] gcc plugin support on RHEL/CentOS 5 and 6?

[Boris Kolpackov]

Hi Dave,

Dave Johansen <davejohansen at gmail.com> writes:

> But like you mentioned previously, RHEL 5 and 6 only come with GCC 4.4,
> so what do you recommend as the best way to do this?

I think the best way to package ODB for RHEL 5 and 6 is to re-package
the binary package that we provide. Again, this will be a "legacy"
solution. For RHEL 7 and for Fedora that come with GCC 4.5 or later
we can implement the nice and clean "from source" approach.

I think using our binary package is better than trying to build and
package both GCC and ODB from source for the following reasons:

1. Building and especially packaging a private copy of GCC won't
   be trivial.

2. We already take great care to build a portable package that
   can work on a wide range of Linux distributions. Might as
   well re-use this hard work.

3. We are planning to keep releasing this binary package for the
   foreseeable future.

If you look inside, say, odb-X.Y.Z-x86_64-linux-gnu, you will see
that it already resembles a Linux filesystem pretty closely. That
is, the ODB compiler is in the bin/ sub-directory, configuration
is in etc/, and so on.

The only thing that doesn't quite fit is the x86_64-linux-gnu/
sub-directory which contains the private copy of GCC. Now, while
you can move doc/ and man/ sub-directories pretty much anywhere
you want, bin/, etc/, and x86_64-linux-gnu/ are expected to be
all at the same level: the ODB compiler uses the executable path
(i.e., .../bin/odb) to construct the paths to the default options
file (in etc/) and to the g++ executable (in x86_64-linux-gnu/).

The good news is that it is possible to override the path to g++
with the -x ODB compiler option. The bad news is that this option
is not recognized in the default options file, which is where we
could have conveniently put it if we were to move/rename
x86_64-linux-gnu to something more suitable.

So I went ahead and fixed this. If you would like to give it a try,
the binary for the 2.2.0.a2 pre-release is here:

http://codesynthesis.com/~boris/tmp/odb/odb-2.2.0.a2-x86_64-linux-gnu.tar.bz2

And the rest of the pre-release is here:

http://codesynthesis.com/download/odb/pre-release/

Specifically, with this binary, we can do the following:

1. Rename x86_64-linux-gnu/ to, say, lib/odb/gcc/, so that it is installed
   in /usr/lib/odb/gcc.

2. Add the following option to etc/odb/default.options:

   -x /usr/lib/odb/gcc/bin/g++

Other than that, the .spec file would just need to copy all the parts
into the right places, and that's it.

Now, that would only apply to packaging the ODB compiler. All the other
packages (libodb, libodb-<db>, etc) would be built and packaged from
source using the stock GCC that comes with RHEL.

Boris