New submission from STINNER Victor <vstin...@redhat.com>:
Python can be compiled in "shared" mode: "./configure --enable-shared",
Py_ENABLE_SHARED is defined in pyconfig.h. Most Linux distributions use this
configuration.
By default, Python builds most C extensions using setup.py which is based on
distutils. The get_libraries() method of Lib/distutils/command/build_ext.py
explicity add a dependency to libpythonX.Y if Py_ENABLE_SHARED is defined.
But it is possible to use Modules/Setup to build some C extensions using
Makefile rather than setup.py. If "*shared*" is in Modules/Setup, following
modules will be compiled as libraries (".so" files on Linux). For example, RHEL
and Fedora use this configuration for many C extensions. Problem: C extensions
compiled like are not linked to libpython.
Example of the issue on Fedora 28 with Python 2.7:
$ ldd $(python2 -c 'import _struct; print(_struct.__file__)')
linux-vdso.so.1 (0x00007ffeedf38000)
libpthread.so.0 => /lib64/libpthread.so.0 (0x00007fb4da876000)
libc.so.6 => /lib64/libc.so.6 (0x00007fb4da4b7000)
/lib64/ld-linux-x86-64.so.2 (0x00007fb4daca1000)
=> notice the lack of libpython
Python 3.6 is fine:
$ ldd $(python3 -c 'import _struct; print(_struct.__file__)')
linux-vdso.so.1 (0x00007ffd493dd000)
libpython3.6m.so.1.0 => /lib64/libpython3.6m.so.1.0 (0x00007f47b9160000)
...
Patch used by Fedora to build _struct (and other modules) using Makefile:
https://src.fedoraproject.org/rpms/python2/blob/f27/f/python-2.7.1-config.patch
Another example of patch, to build _contextvars as a shared library:
diff --git a/Modules/Setup b/Modules/Setup
index a0622cc8c6..975aeff70d 100644
--- a/Modules/Setup
+++ b/Modules/Setup
@@ -148,7 +148,7 @@ _symtable symtablemodule.c
# modules are to be built as shared libraries (see above for more
# detail; also note that *static* or *disabled* cancels this effect):
-#*shared*
+*shared*
# GNU readline. Unlike previous Python incarnations, GNU readline is
# now incorporated in an optional module, configured in the Setup file
@@ -166,7 +166,7 @@ _symtable symtablemodule.c
#array arraymodule.c # array objects
#cmath cmathmodule.c _math.c # -lm # complex math library functions
#math mathmodule.c _math.c # -lm # math library functions, e.g. sin()
-#_contextvars _contextvarsmodule.c # Context Variables
+_contextvars _contextvarsmodule.c # Context Variables
#_struct _struct.c # binary structure packing/unpacking
#_weakref _weakref.c # basic weak reference support
#_testcapi _testcapimodule.c # Python C API test module
Attached PR fixes Modules/makesetup to:
* (1) Add a dependency on the Makefile target to libpython: to make sure that
the parallel compilation works as expected
* (2) Add a dependency to libpythonX.Y on the compiled shared library (".so"
file on Linux)
----------
components: Build
messages: 326486
nosy: vstinner
priority: normal
severity: normal
status: open
title: makesetup: must link C extensions to libpython when compiled in shared
mode
versions: Python 3.8
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Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue34814>
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