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108 lines
3.2 KiB
ReStructuredText
108 lines
3.2 KiB
ReStructuredText
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:mod:`dl` --- Call C functions in shared objects
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================================================
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.. module:: dl
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:platform: Unix
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:synopsis: Call C functions in shared objects.
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.. sectionauthor:: Moshe Zadka <moshez@zadka.site.co.il>
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The :mod:`dl` module defines an interface to the :cfunc:`dlopen` function, which
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is the most common interface on Unix platforms for handling dynamically linked
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libraries. It allows the program to call arbitrary functions in such a library.
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.. warning::
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The :mod:`dl` module bypasses the Python type system and error handling. If
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used incorrectly it may cause segmentation faults, crashes or other incorrect
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behaviour.
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.. note::
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This module will not work unless ``sizeof(int) == sizeof(long) == sizeof(char
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*)`` If this is not the case, :exc:`SystemError` will be raised on import.
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The :mod:`dl` module defines the following function:
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.. function:: open(name[, mode=RTLD_LAZY])
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Open a shared object file, and return a handle. Mode signifies late binding
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(:const:`RTLD_LAZY`) or immediate binding (:const:`RTLD_NOW`). Default is
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:const:`RTLD_LAZY`. Note that some systems do not support :const:`RTLD_NOW`.
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Return value is a :class:`dlobject`.
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The :mod:`dl` module defines the following constants:
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.. data:: RTLD_LAZY
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Useful as an argument to :func:`open`.
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.. data:: RTLD_NOW
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Useful as an argument to :func:`open`. Note that on systems which do not
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support immediate binding, this constant will not appear in the module. For
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maximum portability, use :func:`hasattr` to determine if the system supports
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immediate binding.
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The :mod:`dl` module defines the following exception:
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.. exception:: error
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Exception raised when an error has occurred inside the dynamic loading and
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linking routines.
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Example::
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>>> import dl, time
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>>> a=dl.open('/lib/libc.so.6')
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>>> a.call('time'), time.time()
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(929723914, 929723914.498)
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This example was tried on a Debian GNU/Linux system, and is a good example of
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the fact that using this module is usually a bad alternative.
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.. _dl-objects:
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Dl Objects
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----------
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Dl objects, as returned by :func:`open` above, have the following methods:
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.. method:: dl.close()
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Free all resources, except the memory.
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.. method:: dl.sym(name)
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Return the pointer for the function named *name*, as a number, if it exists in
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the referenced shared object, otherwise ``None``. This is useful in code like::
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>>> if a.sym('time'):
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... a.call('time')
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... else:
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... time.time()
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(Note that this function will return a non-zero number, as zero is the *NULL*
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pointer)
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.. method:: dl.call(name[, arg1[, arg2...]])
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Call the function named *name* in the referenced shared object. The arguments
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must be either Python integers, which will be passed as is, Python strings, to
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which a pointer will be passed, or ``None``, which will be passed as *NULL*.
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Note that strings should only be passed to functions as :ctype:`const char\*`,
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as Python will not like its string mutated.
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There must be at most 10 arguments, and arguments not given will be treated as
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``None``. The function's return value must be a C :ctype:`long`, which is a
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Python integer.
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