README
1Python Misc subdirectory
2========================
3
4This directory contains files that wouldn't fit in elsewhere. Some
5documents are only of historic importance.
6
7Files found here
8----------------
9
10ACKS Acknowledgements
11gdbinit Handy stuff to put in your .gdbinit file, if you use gdb
12HISTORY News from previous releases -- oldest last
13indent.pro GNU indent profile approximating my C style
14NEWS News for this release (for some meaning of "this")
15Porting Mini-FAQ on porting to new platforms
16python-config.in Python script template for python-config
17python.man UNIX man page for the python interpreter
18python.pc.in Package configuration info template for pkg-config
19python-wing*.wpr Wing IDE project file
20README The file you're reading now
21README.AIX Information about using Python on AIX
22README.coverity Information about running Coverity's Prevent on Python
23README.valgrind Information for Valgrind users, see valgrind-python.supp
24SpecialBuilds.txt Describes extra symbols you can set for debug builds
25svnmap.txt Map of old SVN revs and branches to hg changeset ids,
26 help history-digging
27valgrind-python.supp Valgrind suppression file, see README.valgrind
28vgrindefs Python configuration for vgrind (a generic pretty printer)
29
README.AIX
1
2This documentation tries to help people who intend to use Python on
3AIX.
4
5There used to be many issues with Python on AIX, but the major ones
6have been corrected for version 3.2, so that Python should now work
7rather well on this platform. The remaining known issues are listed in
8this document.
9
10
11======================================================================
12 Compiling Python
13----------------------------------------------------------------------
14
15You can compile Python with gcc or the native AIX compiler. The native
16compiler used to give better performances on this system with older
17versions of Python. With Python 3.2 it may not be the case anymore,
18as this compiler does not allow compiling Python with computed gotos.
19Some benchmarks need to be done.
20
21Compiling with gcc:
22
23cd Python-3.2
24CC=gcc OPT="-O2" ./configure --enable-shared
25make
26
27There are various aliases for the native compiler. The recommended
28alias for compiling Python is 'xlc_r', which provides a better level of
29compatibility and handles thread initialization properly.
30
31It is a good idea to add the '-qmaxmem=70000' option, otherwise the
32compiler considers various files too complex to optimize.
33
34Compiling with xlc:
35
36cd Python-3.2
37CC=xlc_r OPT="-O2 -qmaxmem=70000" ./configure --without-computed-gotos --enable-shared
38make
39
40Note:
41On AIX 5.3 and earlier, you will also need to specify the
42"--disable-ipv6" flag to configure. This has been corrected in AIX
436.1.
44
45
46======================================================================
47 Memory Limitations
48----------------------------------------------------------------------
49
50Note: this section may not apply when compiling Python as a 64 bit
51application.
52
53By default on AIX each program gets one segment register for its data
54segment. As each segment register covers 256 MiB, a Python program that
55would use more than 256 MiB will raise a MemoryError. The standard
56Python test suite is one such application.
57
58To allocate more segment registers to Python, you must use the linker
59option -bmaxdata or the ldedit tool to specify the number of bytes you
60need in the data segment.
61
62For example, if you want to allow 512 MiB of memory for Python (this is
63enough for the test suite to run without MemoryErrors), you should run
64the following command at the end of compilation:
65
66ldedit -b maxdata:0x20000000 ./python
67
68You can allow up to 2 GiB of memory for Python by using the value
690x80000000 for maxdata.
70
71It is also possible to go beyond 2 GiB of memory by activating Large
72Page Use. You should consult the IBM documentation if you need to use
73this option. You can also follow the discussion of this problem
74in issue 11212 at bugs.python.org.
75
76http://publib.boulder.ibm.com/infocenter/aix/v6r1/index.jsp?topic=/com.ibm.aix.cmds/doc/aixcmds3/ldedit.htm
77
78
79======================================================================
80 Known issues
81----------------------------------------------------------------------
82
83Those issues are currently affecting Python on AIX:
84
85* Python has not been fully tested on AIX when compiled as a 64 bit
86 application.
87
88* issue 3526: the memory used by a Python process will never be
89 released to the system. If you have a Python application on AIX that
90 uses a lot of memory, you should read this issue and you may
91 consider using the provided patch that implements a custom malloc
92 implementation
93
94* issue 11192: test_socket fails
95
96* issue 11190: test_locale fails
97
98* issue 11193: test_subprocess fails
99
100* issue 9920: minor arithmetic issues in cmath
101
102* issue 11215: test_fileio fails
103
104
105
106======================================================================
107 Implementation details for developers
108----------------------------------------------------------------------
109
110Python and python modules can now be built as shared libraries on AIX
111as usual.
112
113AIX shared libraries require that an "export" and "import" file be
114provided at compile time to list all extern symbols which may be
115shared between modules. The "export" file (named python.exp) for the
116modules and the libraries that belong to the Python core is created by
117the "makexp_aix" script before performing the link of the python
118binary. It lists all global symbols (exported during the link) of the
119modules and the libraries that make up the python executable.
120
121When shared library modules (.so files) are made, a second shell
122script is invoked. This script is named "ld_so_aix" and is also
123provided with the distribution in the Modules subdirectory. This
124script acts as an "ld" wrapper which hides the explicit management of
125"export" and "import" files; it adds the appropriate arguments (in the
126appropriate order) to the link command that creates the shared module.
127Among other things, it specifies that the "python.exp" file is an
128"import" file for the shared module.
129
130This mechanism should be transparent.
131
README.coverity
1
2Coverity has a static analysis tool (Prevent) which is similar to Klocwork.
3They run their tool on the Python source code (SVN head) on a daily basis.
4The results are available at:
5
6 http://scan.coverity.com/
7
8About 20 people have access to the analysis reports. Other
9people can be added by request.
10
11Prevent was first run on the Python 2.5 source code in March 2006.
12There were originally about 100 defects reported. Some of these
13were false positives. Over 70 issues were uncovered.
14
15Each warning has a unique id and comments that can be made on it.
16When checking in changes due to a warning, the unique id
17as reported by the tool was added to the SVN commit message.
18
19False positives were annotated so that the comments can
20be reviewed and reversed if the analysis was incorrect.
21
22Contact python-dev@python.org for more information.
23
README.valgrind
1This document describes some caveats about the use of Valgrind with
2Python. Valgrind is used periodically by Python developers to try
3to ensure there are no memory leaks or invalid memory reads/writes.
4
5If you want to enable valgrind support in Python, you will need to
6configure Python --with-valgrind option or an older option
7--without-pymalloc.
8
9UPDATE: Python 3.6 now supports PYTHONMALLOC=malloc environment variable which
10can be used to force the usage of the malloc() allocator of the C library.
11
12If you don't want to read about the details of using Valgrind, there
13are still two things you must do to suppress the warnings. First,
14you must use a suppressions file. One is supplied in
15Misc/valgrind-python.supp. Second, you must do one of the following:
16
17 * Uncomment Py_USING_MEMORY_DEBUGGER in Objects/obmalloc.c,
18 then rebuild Python
19 * Uncomment the lines in Misc/valgrind-python.supp that
20 suppress the warnings for PyObject_Free and PyObject_Realloc
21
22If you want to use Valgrind more effectively and catch even more
23memory leaks, you will need to configure python --without-pymalloc.
24PyMalloc allocates a few blocks in big chunks and most object
25allocations don't call malloc, they use chunks doled about by PyMalloc
26from the big blocks. This means Valgrind can't detect
27many allocations (and frees), except for those that are forwarded
28to the system malloc. Note: configuring python --without-pymalloc
29makes Python run much slower, especially when running under Valgrind.
30You may need to run the tests in batches under Valgrind to keep
31the memory usage down to allow the tests to complete. It seems to take
32about 5 times longer to run --without-pymalloc.
33
34Apr 15, 2006:
35 test_ctypes causes Valgrind 3.1.1 to fail (crash).
36 test_socket_ssl should be skipped when running valgrind.
37 The reason is that it purposely uses uninitialized memory.
38 This causes many spurious warnings, so it's easier to just skip it.
39
40
41Details:
42--------
43Python uses its own small-object allocation scheme on top of malloc,
44called PyMalloc.
45
46Valgrind may show some unexpected results when PyMalloc is used.
47Starting with Python 2.3, PyMalloc is used by default. You can disable
48PyMalloc when configuring python by adding the --without-pymalloc option.
49If you disable PyMalloc, most of the information in this document and
50the supplied suppressions file will not be useful. As discussed above,
51disabling PyMalloc can catch more problems.
52
53PyMalloc uses 256KB chunks of memory, so it can't detect anything
54wrong within these blocks. For that reason, compiling Python
55--without-pymalloc usually increases the usefulness of other tools.
56
57If you use valgrind on a default build of Python, you will see
58many errors like:
59
60 ==6399== Use of uninitialised value of size 4
61 ==6399== at 0x4A9BDE7E: PyObject_Free (obmalloc.c:711)
62 ==6399== by 0x4A9B8198: dictresize (dictobject.c:477)
63
64These are expected and not a problem. Tim Peters explains
65the situation:
66
67 PyMalloc needs to know whether an arbitrary address is one
68 that's managed by it, or is managed by the system malloc.
69 The current scheme allows this to be determined in constant
70 time, regardless of how many memory areas are under pymalloc's
71 control.
72
73 The memory pymalloc manages itself is in one or more "arenas",
74 each a large contiguous memory area obtained from malloc.
75 The base address of each arena is saved by pymalloc
76 in a vector. Each arena is carved into "pools", and a field at
77 the start of each pool contains the index of that pool's arena's
78 base address in that vector.
79
80 Given an arbitrary address, pymalloc computes the pool base
81 address corresponding to it, then looks at "the index" stored
82 near there. If the index read up is out of bounds for the
83 vector of arena base addresses pymalloc maintains, then
84 pymalloc knows for certain that this address is not under
85 pymalloc's control. Otherwise the index is in bounds, and
86 pymalloc compares
87
88 the arena base address stored at that index in the vector
89
90 to
91
92 the arbitrary address pymalloc is investigating
93
94 pymalloc controls this arbitrary address if and only if it lies
95 in the arena the address's pool's index claims it lies in.
96
97 It doesn't matter whether the memory pymalloc reads up ("the
98 index") is initialized. If it's not initialized, then
99 whatever trash gets read up will lead pymalloc to conclude
100 (correctly) that the address isn't controlled by it, either
101 because the index is out of bounds, or the index is in bounds
102 but the arena it represents doesn't contain the address.
103
104 This determination has to be made on every call to one of
105 pymalloc's free/realloc entry points, so its speed is critical
106 (Python allocates and frees dynamic memory at a ferocious rate
107 -- everything in Python, from integers to "stack frames",
108 lives in the heap).
109