Cross compiling to ARM soft-float on i386

Debian has toochain-source and the related packages. These make building cross toochains really easy if you are not trying to do anything fancy. Apparently soft float is a bit too fancy. Another problem with toolchain-source supposedly is that it gets patches slowly. The debian gcc package recommends using the gcc package directly instead of toolchain-source.

Binutils

Gcc, libc

Which one is chicken and which one is egg? Well - starting with gcc is probably most sensible. I did this in several passes.

• Get prebuild arm libc and friends with the tpkg-* scripts. I made my own script cause I wanted to take a look at the deb before installing it. Just wget the needed debs and dpkg-cross them.
• Build gcc against the prebuilt libc with hard-fp (default). This results in hard-fp libc and stuff.
• Start building glibc with the hard-fp gcc with -msoft-float - this fails when linking against the hard-fp libgcc.
• Start rebuilding soft-fp gcc. For some reason I needed to apply a patch I found googling. Could be just that I missed the right config option. Anyway - this fails at the point of linking agaist the hard-fp libc.
• Copy libgcc and friends from the gcc build dir over the ones in the installed hard-fp gcc.
• Continue building libc, dpkg-cross, install.
• Build libfloat with soft-float (easiest in scratchbox), install.
• Continue building gcc. Install.

GNU libc

One problem is that the debian/rules is not prepared for cross compiling. The debhelper stuff expects the sunrpc lib to be installable but it is not cross compilable.

Using scratchbox

With furious tweaking I managed also to add a softfloat toolchain for ARM into scratchbox.

All the debian ARM distros I could find were hard FP. So I'm slowly recompiling stuff for softfloat. Mostly things go quite fine - apt-get source, debian/rules build, fakeroot debian/rules binary. Occasionally linking fails as the preinstalled dev libs are hard FP. Might be wisest to start with the already installed -dev packages and rebuilt and install them. Another trouble is autotools versions. Seems that e.g. the current gcc-3.3 source in debian expects mixed versions of autotools. Scratchbox also sometimes manages to slip native (instead of arm) stuff into the debs.

I have not yet managed to build perl. Perl is handled specially in scratchbox.

Using crosstool

In the end it is probably easiest to just use crosstool. As scratchbox seems to be getting better at supporting foreign toolchains, crosstool built toolchains can also probably be used with scratchbox. With crostool-0.40 I only had to specify a more recent linux kernel version to get a softfloat toolchain built.