This documentation tries to help people who intend to use Python on

AIX.

There used to be many issues with Python on AIX, but the major ones

have been corrected for version 3.2, so that Python should now work

rather well on this platform. The remaining known issues are listed in

this document.

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Compiling Python

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You can compile Python with gcc or the native AIX compiler. The native

compiler used to give better performances on this system with older

versions of Python. With Python 3.2 it may not be the case anymore,

as this compiler does not allow compiling Python with computed gotos.

Some benchmarks need to be done.

Compiling with gcc:

cd Python-3.2

CC=gcc OPT="-O2" ./configure --enable-shared

make

There are various aliases for the native compiler. The recommended

alias for compiling Python is 'xlc_r', which provides a better level of

compatibility and handles thread initialization properly.

It is a good idea to add the '-qmaxmem=70000' option, otherwise the

compiler considers various files too complex to optimize.

Compiling with xlc:

cd Python-3.2

CC=xlc_r OPT="-O2 -qmaxmem=70000" ./configure --without-computed-gotos --enable-shared

make

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Memory Limitations

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Note: this section may not apply when compiling Python as a 64 bit

application.

By default on AIX each program gets one segment register for its data

segment. As each segment register covers 256 MiB, a Python program that

would use more than 256 MiB will raise a MemoryError. The standard

Python test suite is one such application.

To allocate more segment registers to Python, you must use the linker

option -bmaxdata or the ldedit tool to specify the number of bytes you

need in the data segment.

For example, if you want to allow 512 MiB of memory for Python (this is

enough for the test suite to run without MemoryErrors), you should run

the following command at the end of compilation:

ldedit -b maxdata:0x20000000 ./python

You can allow up to 2 GiB of memory for Python by using the value

0x80000000 for maxdata.

It is also possible to go beyond 2 GiB of memory by activating Large

Page Use. You should consult the IBM documentation if you need to use

this option. You can also follow the discussion of this problem

in issue 11212 at bugs.python.org.

http://publib.boulder.ibm.com/infocenter/aix/v6r1/index.jsp?topic=/com.ibm.aix.cmds/doc/aixcmds3/ldedit.htm

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Known issues

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Those issues are currently affecting Python on AIX:

* Python has not been fully tested on AIX when compiled as a 64 bit

application.

* issue 3526: the memory used by a Python process will never be

released to the system. If you have a Python application on AIX that

uses a lot of memory, you should read this issue and you may

consider using the provided patch that implements a custom malloc

implementation

* issue 11192: test_socket fails

* issue 11190: test_locale fails

* issue 11193: test_subprocess fails

* issue 9920: minor arithmetic issues in cmath

* issue 11215: test_fileio fails

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Implementation details for developers

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Python and python modules can now be built as shared libraries on AIX

as usual.

AIX shared libraries require that an "export" and "import" file be

provided at compile time to list all extern symbols which may be

shared between modules. The "export" file (named python.exp) for the

modules and the libraries that belong to the Python core is created by

the "makexp_aix" script before performing the link of the python

binary. It lists all global symbols (exported during the link) of the

modules and the libraries that make up the python executable.

When shared library modules (.so files) are made, a second shell

script is invoked. This script is named "ld_so_aix" and is also

provided with the distribution in the Modules subdirectory. This

script acts as an "ld" wrapper which hides the explicit management of

"export" and "import" files; it adds the appropriate arguments (in the

appropriate order) to the link command that creates the shared module.

Among other things, it specifies that the "python.exp" file is an

"import" file for the shared module.

This mechanism should be transparent.