HOWTO Cross Compile Python 2.5

October 06, 2006 at 04:04 PM | categories: Computers, Programming | View Comments

Recently I needed to compile Python for an embedded target. I used version 2.5 though it looks like that choice may have made it harder for me. I used 2.5 because I didn't want to have to figure out how to cross compile the cElementTree extension. Unfortunately I still ended up having to figure out how to get PyXML to build for my target. Fortunately I did get everything to work with a bit of fiddling. For posterity, here are some notes about what I did and what problems I had.

I started with Klaus Reimer's ARM cross-compiling howto and made made some updates required by changes between Python 2.2 and 2.5.

The changes I made are captured in an updated patch to apply against the 2.5 source tree. The changes made the are to disable rules that cause configure failures when cross compiling because they look for files on the target system or require a test program to be compiled and run. The other changes I added over the patch from Klaus Reimer are for a specific issue I had where md5 and sha hash algorithms were not built because which builds the modules is not cross compile aware and detected the OpenSSL libraries on my build machine rather than the target.

You can apply the patch with the following command:

~/tmp/Python2.5$ patch -p1 < ../Python2.5_xcompile.patch

I next generated a "host" python as in Reimer's instructions:

~/tmp/Python2.5$ ./configure
~/tmp/Python2.5$ make python Parser/pgen
~/tmp/Python2.5$ mv python hostpython
~/tmp/Python2.5$ mv Parser/pgen Parser/hostpgen
~/tmp/Python2.5$ make distclean

I exported necessary variables like CC, CXX, AR, RANLIB, LD, CFLAGS, CXXFLAGS, LDFLAGS for my target. The key is for these to point to the libraries you are going to use.

To build and "install" python for the my target I used the following commands:

~/tmp/Python2.5$ ./configure --host=ppc-linux --build=i686-pc-linux-gnu --prefix=/python
~/tmp/Python2.5$ make EXTRA_CFLAGS="$CFLAGS" HOSTPYTHON=./hostpython HOSTPGEN=./Parser/hostpgen BLDSHARED='ppc-linux-gcc -shared' CROSS_COMPILE=yes
~/tmp/Python2.5$ make install EXTRA_CFLAGS="$CFLAGS" HOSTPYTHON=./hostpython BLDSHARED='ppc-linux-gcc -shared' CROSS_COMPILE=yes prefix=/home/lambacck/tmp/dest/python

Note that I needed to use EXTRA_CFLAGS to add my target specific CFLAGS because for some reason the Python configure process does not honor the ones I provided while doing configure. The LDFLAGS variable, however, did work.

Also notice that I set the prefix in the configure step to be /python and the set another prefix in the make install step. The prefix in the configure step is where we are putting python on the file system on the target. The prefix in the install step is where we are putting all of the bits to be able to package them up to be ready to send to the target.

After all that I have a (mostly) functional python environment on my target, but I still needed to get PyXML built. I downloaded the latest distribution, modified so that expat was forced into little-endian mode and ran the following commands:

~/tmp/PyXML-0.8.4$ LDSHARED='ppc-linux-gcc -shared' CC="${CC}" OPT='-DNDEBUG -g -O3 -Wall -Wstrict-prototypes' ~/tmp/Python-2.5/hostpython -E build
~/tmp/PyXML-0.8.4$ LDSHARED='ppc-linux-gcc -shared' CC="${CC}" OPT='-DNDEBUG -g -O3 -Wall -Wstrict-prototypes' ~/tmp/cross_python/Python-2.5/hostpython -E install --prefix=$HOME/tmp/dest/python/ --install-scripts=/home/lambacck/tmp/dest/python/bin

It looks like Distutils and the Python build process in general could use some cross compile support. I think this is currently far harder than it has to be.

Update Oct 10, 2005: I would like to point out that on the system that I the executable used to compile hostpython was called gcc and I then updated paths so that a gcc targeted at ppc called gcc was first in my path. Therefore in both cases the compiler was gcc and not gcc for the hostpython and ppc-linux-gcc for the target python.

Update Dec 6, 2006: It looks like double dashes have been turned into single dashes by Wordpress. Specifically the host, build, prefix and install-scripts arguments to configure and should have double dashes.

Update Jun 30, 2010: Translation to Portuguese. Commands converted to use arm processor. Thanks Anuma.

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