RPM HOWTO:
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8. Multi-architectural RPM Building

RPM can now be used to build packages for the Intel i386, the Digital Alpha running Linux, and the Sparc (and others). There are several features that make building packages on all platforms easy. The first of these is the "optflags" directive in the /etc/rpmrc. It can be used to set flags used when building software to architecture specific values. Another feature is the "arch" macros in the spec file. They can be used to do different things depending on the architecture you are building on. Another feature is the "Exclude" directive in the header.

8.1. Sample spec File

The following is part of the spec file for the "fileutils" package. It is setup to build on both the Alpha and the Intel.

Summary: GNU File Utilities
Name: fileutils
Version: 3.16
Release: 1
Copyright: GPL
Group: Utilities/File
Source0: prep.ai.mit.edu:/pub/gnu/fileutils-3.16.tar.gz
Source1: DIR_COLORS
Patch: fileutils-3.16-mktime.patch

%description
These are the GNU file management utilities.  It includes programs
to copy, move, list, etc, files.

The ls program in this package now incorporates color ls!

%prep
%setup

%ifarch alpha
%patch -p1
autoconf
%endif
%build
configure --prefix=/usr --exec-prefix=/
make CFLAGS="$RPM_OPT_FLAGS" LDFLAGS=-s

%install
rm -f /usr/info/fileutils*
make install
gzip -9nf /usr/info/fileutils*

.
.
.

8.2. Optflags

In this example, you see how the "optflags" directive is used from the /etc/rpmrc. Depending on which architecture you are building on, the proper value is given to RPM_OPT_FLAGS. You must patch the Makefile for your package to use this variable in place of the normal directives you might use (like -m486 and -O2). You can get a better feel for what needs to be done by installing this source package and then unpacking the source and examine the Makefile. Then look at the patch for the Makefile and see what changes must be made.

8.3. Macros

The %ifarch macro is very important to all of this. Most times you will need to make a patch or two that is specific to one architecture only. In this case, RPM will allow you to apply that patch to just one architecture only.

In the above example, fileutils has a patch for 64 bit machines. Obviously, this should only be applied on the Alpha at the moment. So, we add an %ifarch macro around the 64 bit patch like so:

%ifarch axp
%patch1 -p1
%endif

This will insure that the patch is not applied on any architecture except the alpha.

8.4. Excluding Architectures from Packages

So that you can maintain source RPMs in one directory for all platforms, we have implemented the ability to "exclude" packages from being built on certain architectures. This is so you can still do things like

rpm --rebuild /usr/src/SRPMS/*.rpm

and have the right packages build. If you haven't yet ported an application to a certain platform, all you have to do is add a line like:

ExcludeArch: alpha

to the header of the spec file of the source package. Then rebuild the package on the platform that it does build on. You'll then have a source package that builds on an Intel and can easily be skipped on an Alpha.

8.5. Finishing Up

Using RPM to make multi-architectural packages is usually easier to do than getting the package itself to build both places. As more of the hard packages get built this is getting much easier, however. As always, the best help when you get stuck building an RPM is to look a similar source package.