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Cross-translating PyPy for ARM

Here we describe the setup required and the steps needed to follow to translate an interpreter using PyPy's translation toolchain to target ARM.

To translate an interpreter for an ARM based platform you can either cross translate, what we will describe below, or translate directly on the ARM based system following the normal translation steps, but this is not really feasible on most ARM powered devices.

To cross translate you run the translation toolchain on a more powerful machine and generate a binary for ARM using a cross compiler to compile the generated C code. There are several constraints when doing this. Specially we currently only support Linux as translation host and target platforms (tested with Ubuntu). Also you need a 32-bit PyPy or Python to run the translation toolchain.

Requirements

The tools required to cross translate from Linux to a ARM based Linux are

  • A checkout of PyPy's arm-backend-2 branch.
  • The GCC arm cross compiler (on Ubuntu it is the gcc-arm-linux-gnueabi package) but other toolchains should also work.
  • Scratchbox 2, a cross-compilation engine (scratchbox2 Ubuntu package).
  • rootstock (rootstock Ubuntu package).
  • A 32-bit PyPy or Python.

Setup

First we will need to create a rootfs image or tarball for the target distribution (Ubuntu natty in our case) containing the required packages to translate PyPy.

sudo rootstock --fqdn pypysb2 --login pypy --password pypy \
               --seed build-essential,libgc-dev,libffi-dev \
               --dist natty

When the rootfs command finishes you should have an archive containing the created rootfs, create a directory and unpack the archive there. This directory is going to serve as the scratchbox2 environment.

If you are using the gcc-arm-linux-gnueabi toolchain read the section Scracthbox 2 issues before continuing.

Go into the directory containing the rootfs and create a Scratchbox 2 environment:

sb2-init -n -c qemu-arm NAME /usr/bin/arm-linux-gnueabi-gcc or codesourcery compiler

Where NAME is the name we choose for the sb2 environment.

Finally, using the newly created scratchbox run the sb2-built-libtool command.

sb2 -t NAME /usr/bin/sb2-build-libtool

Now you should have a working cross compilation toolchain in place

Translation

Having performed all the preliminary steps you should now be able to cross translate a program for ARM. You can use this minimal target to test your setup before applying it to a larger project.

First you need to set two environment variables so the translator knows how to use the scratchbox environment. You need to set the SB2 environment variable to point to the path of the unpacked rootfs and the SB2OPT should contain the command line options for the sb2 command. If our rootfs is in the folder /home/user/sb2 and the scratchbox environment is called "arm", the variables would be defined as follows.

export SB2=~/sb2
export SB2OPT='-t arm'

Once this is set, you can call the translator

~/path_to_pypy_checkout/pypy/translator/goal/translate.py -O1 --platform=arm target.py
def main(args):
    print "Hello World"
    return 0

def target(*args):
    return main, None

Scracthbox 2 issues

At least on Ubuntu, compiling within the scratchbox will fail if you are using the arm-linux-gnueabi-gcc compiler. There is a problem with Ubuntu's current version of scratchbox2, it is fixed in the upcoming release, but that does not help much right now. This issue detects some configurations options wrong and adds some flags to the gcc calls that make them fail. To fix this there is the option to modify Scratchbox 2 itself. In this case you would need to change the file

/usr/share/scratchbox2/scripts/sb2-config-gcc-toolchain

Find the line

echo "" | $GCC_FULLPATH -E - -Wno-poison-system-directories > /dev/null 2>&1

and replace it with

echo "" | $GCC_FULLPATH -x c - -Wno-poison-system-directories > /dev/null 2>&1

Alternatively after the call to sb2-build-libtool, mentioned above, fails you can edit the files

~/.scratchbox2/NAME/sb2.config.d/gcc.config.(sh|lua)

removing every occurence of -Wno-poison-system-directories and then calling the command again

sb2 -t NAME /usr/bin/sb2-build-libtool

Following one of the two approaches should yield a working setup.