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python-config --ldflags must not contain LINKFORSHARED ("-Xlinker -export-dynamic" on Linux) #80689
Description
| BPO | 36508 |
|---|---|
| Nosy | @doko42, @pitrou, @vstinner, @ned-deily |
| PRs |
Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.
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GitHub fields:
assignee = None
closed_at = <Date 2019-04-16.13:04:17.579>
created_at = <Date 2019-04-02.15:00:19.982>
labels = ['3.8', 'build', '3.7']
title = 'python-config --ldflags must not contain LINKFORSHARED ("-Xlinker -export-dynamic" on Linux)'
updated_at = <Date 2019-04-16.13:04:17.574>
user = 'https://github.com/vstinner'bugs.python.org fields:
activity = <Date 2019-04-16.13:04:17.574>
actor = 'vstinner'
assignee = 'none'
closed = True
closed_date = <Date 2019-04-16.13:04:17.579>
closer = 'vstinner'
components = ['Build']
creation = <Date 2019-04-02.15:00:19.982>
creator = 'vstinner'
dependencies = []
files = []
hgrepos = []
issue_num = 36508
keywords = ['patch']
message_count = 6.0
messages = ['339341', '339344', '339345', '339771', '340339', '340340']
nosy_count = 4.0
nosy_names = ['doko', 'pitrou', 'vstinner', 'ned.deily']
pr_nums = ['12661', '12748']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue36508'
versions = ['Python 3.7', 'Python 3.8']
Activity
vstinner commentedon Apr 2, 2019
python-config --ldflags must not contain LINKFORSHARED.
Attached PR modifies python-config --ldflags to no longer include LINKFORSHARED.
This similar change was already made on macOS: see bpo-14197.
--
Python build system uses a LINKFORSHARED variable, extract of configure.ac:
# LINKFORSHARED are the flags passed to the $(CC) command that links
# the python executable -- this is only needed for a few systems
This variable is set to "-Xlinker -export-dynamic" on Linux. Extract of ld manual page for --export-dynamic option:
---
When creating a dynamically linked executable, using the -E
option or the --export-dynamic option causes the linker to
add all symbols to the dynamic symbol table. The dynamic
symbol table is the set of symbols which are visible from
dynamic objects at run time.
If you do not use either of these options (or use the
--no-export-dynamic option to restore the default behavior),
the dynamic symbol table will normally contain only those
symbols which are referenced by some dynamic object
mentioned in the link.
If you use "dlopen" to load a dynamic object which needs to
refer back to the symbols defined by the program, rather
than some other dynamic object, then you will probably need
to use this option when linking the program itself.
You can also use the dynamic list to control what symbols
should be added to the dynamic symbol table if the output
format supports it. See the description of --dynamic-list.
Note that this option is specific to ELF targeted ports. PE
targets support a similar function to export all symbols
from a DLL or EXE; see the description of
--export-all-symbols below.
---
Both configure.ac and ld manual page mention an "executable", whereas LINKFORSHARED is currently exported in python-config --ldflags. Example on Fedora 29:
The "-export-dynamic" flag causes non-obvious dynamic linking bug like the following bug in Samba which embeds Python:
--
History of the LINKFORSHARED variable.
(*) Python build system uses a LINKFORSHARED variable since this commit:
commit 7cc5abd
Author: Guido van Rossum <guido@python.org>
Date: Mon Sep 12 10:42:20 1994 +0000
The value of the variable changed on Linux with:
commit b65a48e (HEAD)
Author: Guido van Rossum <guido@python.org>
Date: Wed Jun 14 18:21:23 1995 +0000
Extract of the configure.in change:
if test -z "$LINKFORSHARED"
then
case $ac_sys_system in
hp*|HP*) LINKFORSHARED="-Wl,-E";;
+ Linux*) LINKFORSHARED="-rdynamic";;
esac
fi
The variable was only used to build the "python" executable. Extract of Modules/Makefile.in (at commit 7cc5abd):
../python: config.o $(MYLIBS) Makefile
$(CC) $ (OPT) config.o $(LINKFORSHARED) \
$(MYLIBS) $ (MODLIBS) $(LIBS) $ (SYSLIBS) -o python
mv python ../python
(*) The python-config script was created as a Python script by:
commit c90b17e
Author: Martin v. Löwis <martin@v.loewis.de>
Date: Sat Apr 15 08:13:05 2006 +0000
The following commit modified Misc/python-config.in to add LINKFORSHARED to python-config --ldflags:
commit a70f349
Author: Collin Winter <collinw@gmail.com>
Date: Fri Mar 19 00:08:44 2010 +0000
Extract:
+ elif opt in ('--libs', '--ldflags'):
+ libs = getvar('LIBS').split() + getvar('SYSLIBS').split()
+ libs.append('-lpython'+pyver)
+ # add the prefix/lib/pythonX.Y/config dir, but only if there is no
+ # shared library in prefix/lib/.
+ if opt == '--ldflags':
+ if not getvar('Py_ENABLE_SHARED'):
+ libs.insert(0, '-L' + getvar('LIBPL'))
+ libs.extend(getvar('LINKFORSHARED').split())
+ print ' '.join(libs)
The following commit modified Misc/python-config.in to not add LINKFORSHARED into "libs" when built on macOS (if PYTHONFRAMEWORK is defined):
commit ecd4e9d
Author: Ned Deily <nad@acm.org>
Date: Tue Jul 24 03:31:48 2012 -0700
(*) A shell version of python-config has been added by:
commit 8742119
Author: doko@python.org <doko@python.org>
Date: Sat Jan 26 11:39:31 2013 +0100
Extract of Misc/python-config.sh.in at this commit:
vstinner commentedon Apr 2, 2019
I'm a little bit scared by the idea of backporting such change in Python 2.7 and 3.7 stable branches, even if I think that it's a correct bugfix. I'm scared by the number of platforms, I don't know all these linker flags and I am not able to test all combinations:
fi
AC_MSG_RESULT($LINKFORSHARED)
[-]python-config --ldflags must not contain LINKFORSHARED[/-][+]python-config --ldflags must not contain LINKFORSHARED ("-Xlinker -export-dynamic" on Linux)[/+]vstinner commentedon Apr 2, 2019
See also bpo-10112: "Use -Wl,--dynamic-list=x.list, not -Xlinker -export-dynamic".
vstinner commentedon Apr 9, 2019
New changeset e65f01f by Victor Stinner in branch 'master':
bpo-36508: python-config don't export LINKFORSHARED (GH-12661)
e65f01f
vstinner commentedon Apr 16, 2019
New changeset cd46b09 by Victor Stinner (Miss Islington (bot)) in branch '3.7':
bpo-36508: python-config don't export LINKFORSHARED (GH-12661) (GH-12748)
cd46b09
vstinner commentedon Apr 16, 2019
The bug is fixed in 3.7 and master (future 3.8) branches. I prefer to leave 2.7 unchanged. I close the issue.
Python 2.7 is affected as well, but I'm really scared to touch the build system of Python 2.7 which is very stable. Even for Python 3.7, I wasn't fully comfortable to merge my fix.