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Showing posts from July, 2011

Packing executables

One of the biggest challenges with embedding platforms is the limitation related to file sizes. Here is the hint how to make executables smaller - strip them and pack them:

strip is a tool from GNU binutils, it discards symbols. Usually the platform toolchain has one.upx is an excellent executable packer. Can be downloaded as binary or sources from the UPX sf.net site.
As an example, I'll show you the packing of Python 2.6.7 binary:

$ ls -s --block-size=KB python
6493kB python
$ strip -s python
$ ls -s --block-size=KB python
1696kB python
$ upx --best python
                       Ultimate Packer for eXecutables
                          Copyright (C) 1996 - 2010
UPX 3.05        Markus Oberhumer, Laszlo Molnar & John Reiser   Apr 27th 2010

        File size         Ratio      Format      Name
   --------------------   ------   -----------   -----------
   1692400 ->    608896   35.98%  linux/ElfAMD   python

Packed 1 file.
$ ls -s --block-size=KB python
611kB python

So, we've got 10:1 …

Compiling Python: Modules/Setup

A little hint for Python developers who use it for embedded or unconventional platforms (like Cray supercomputers if you're lucky): it can be compiled and used without any dynamic libraries. I've got the problem with stripped libc.so - some Python shared object (like _socket.so) try to use it, but can't find anything because it's stripped. The only choice I had is using Python without these shared objects.

Fortunately, Python support it out of the box. After configuring it, you can use Modules/Setup file to set up which modules have to be compiled within the Python binary:
The build process works like this:
 1. Build all modules that are declared as static in Modules/Setup,
    combine them into libpythonxy.a, combine that into python.
 2. Build all modules that are listed as shared in Modules/Setup.
 3. Invoke setup.py. That builds all modules that
    a) are not builtin, and
    b) are not listed in Modules/Setup, and
    c) can be build on the target
For example, if you wa…