Building a x86 cross compiler on a x86_64 Debian based system

Supposedly building a cross compiler on Debian is a rather simple process.

Thus when I started out, wishing to build myself a cross compiler to easily build i386 kernel packages for a semi-embedded x86 system, I thought the most significant problem I’d encounter would be the time it usually takes for building (cross) compilers.

The build system:

$ lsb_release -dc
Description:    Ubuntu 9.10
Codename:       karmic
$ uname -smo
Linux x86_64 GNU/Linux

The target system:

$ lsb_release -dc
Description:    Ubuntu 8.04.4 LTS
Codename:       hardy
$ uname -smo
Linux i686 GNU/Linux

Following these instructions creating a cross compilation package for binutils is easy enough and seems to work without a hitch. After fetching the source package and installing build dependencies these commands got me a nice binutils-i486-linux-gnu package.

$ export TARGET=$(dpkg-architecture -ai386 -qDEB_HOST_GNU_TYPE 2>/dev/null)
$ fakeroot debian/rules binary-cross > ../binutils.log 2>&1 || echo "Build error: $?"

It is then, during the conversion and installation of cross compilation library packages, that the first problems began. The instructions mention having to convert and install these packages (version and architecture of the target system):

• libc6
• libc6-dev
• linux-kernel-headers
• provided by linux-libc-dev

As it turns out, the libc6 package depends on the libgcc1 package. Thus you’ll also have to install that package. Then it turns out that libgcc1 also depends on gcc-4.2-base, and that poses a problem, as dpkg-cross simply refuses to convert that package with this error message:

$ dpkg-cross -a i386 -b gcc-4.2-base_4.2.4-1ubuntu3_i386.deb
dpkg-cross: package gcc-4.2-base doesn't provide any useful files. Skipping.

Going from there I just had to make sure that libgcc1-i386-cross (the cross compilation package produced from libgcc1) doesn’t depend on gcc-4.2-base‘s hypothetical i386 cross compilation package. This was easily enough accomplished by reconverting libgcc1 and telling dpkg-cross to ignore gcc-4.2-base:

$ dpkg-cross -a i386 -b -X gcc-4.2-base libgcc1_4.2.4-1ubuntu4_i386.deb

Then, after installing that new version of libgcc1-i386-cross and our just built version of binutils-i486-linux-gnu, we can continue with building GCC itself. These are the series of commands specified on the Debian wiki (make sure to unset TARGET beforehand):

$ export GCC_TARGET=$ARCH
$ debian/rules control
$ dpkg-buildpackage -us -uc -rfakeroot -b > ../gcc.log 2>&1 || echo "Build error: $?"

After quite some troubleshooting time, however, I discovered that the commands mentioned proved insufficient. Linker errors occurred when the build scripts got the stupendous idea of building an amd64 version of libgcc – first of all, I already have one, I’m running an amd64 system, secondly my target architecture is i386 and not amd64. Setting DEB_CROSS_NO_BIARCH solved this problem by simply disabling of including amd64 in the target architectures:

$ export GCC_TARGET=i386
$ export DEB_CROSS_NO_BIARCH=yes
$ debian/rules control
$ dpkg-buildpackage -us -uc -rfakeroot -b > ../gcc.log 2>&1 || echo "Build error: $?"

When the build process finally finished I thought to just install the packages and start the cross compiler. Unfortunately life rarely is as easy as you hope it is.

Apparently the built versions of libgcc1-i386-cross of libobjc2-i386-cross had a rather curious dependency: libc6-i386-i386-cross.¹

Yes? You get it? We need some kind of double i386 architecture as cross compile target? – Well I didn’t, so I fell back to manually editing the packages, by extracting, editing and repackaging by means of dpkg-deb and altering the libc6-i386-i386-cross dependency and changing it to libc6-i386-cross.

That proved to be enough and now I’m able to easily cross compile a kernel (more easily than by means of -m32).