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--libs is inconsistent for python-config --libs and pkgconfig python --libs #59795
Description
| BPO | 15590 |
|---|---|
| Nosy | @doko42, @vstinner, @ned-deily, @haubi, @tdsmith |
| PRs | |
| Files |
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 = None
created_at = <Date 2012-08-08.10:43:17.763>
labels = ['type-bug', 'build']
title = '--libs is inconsistent for python-config --libs and pkgconfig python --libs'
updated_at = <Date 2019-05-31.17:06:59.316>
user = 'https://github.com/doko42'bugs.python.org fields:
activity = <Date 2019-05-31.17:06:59.316>
actor = 'ned.deily'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Build']
creation = <Date 2012-08-08.10:43:17.763>
creator = 'doko'
dependencies = []
files = ['35485']
hgrepos = ['250']
issue_num = 15590
keywords = ['patch', 'needs review']
message_count = 11.0
messages = ['167683', '167686', '219665', '219679', '219680', '219764', '219774', '219821', '219823', '219825', '235875']
nosy_count = 6.0
nosy_names = ['doko', 'vstinner', 'ned.deily', 'Arfrever', 'haubi', 'tdsmith']
pr_nums = ['737']
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue15590'
versions = ['Python 2.7', 'Python 3.4', 'Python 3.5']
Activity
doko42 commentedon Aug 8, 2012
seen with at least 2.7, 3.2 and 3.3:
python-config uses the SYSLIBS macro, while pkg-config uses the LIBS macro.
depending on what you want to do, both can be wrong or right:
to build an extension, LIBS should be used.
to link an embedded interpreter, SYSLIBS should be used,
which might not be complete.
Howver in this case MODLIBS is missing.
a patch should be easy once we can define the intended behaviour.
Arfrever commentedon Aug 8, 2012
Behavior of 'pkg-config python' is more useful since without --static option only the set of directly needed libraries is returned.
In Python 3.3 or 3.4 --static option could be introduced in python-config and behavior without this option could be changed to match 'pkg-config python'.
haubi commentedon Jun 3, 2014
Well, they should not be identical, as they are for different use cases.
"pkg-config python" is to build an application containing a python interpreter (like python$EXE):
+ Link against libpython.so. Additionally,
+ re-export symbols from libpython.so for the python-modules (platform-specific).
= This is similar to build against any other library, thus using 'pkg-config python'.
"python-config" is to build a python-module (like build/lib.<platform>-<pyver>/*.so):
+ No need to link against libpython.so, instead
+ expect symbols from libpython.so to be available at runtime, platform specific either
+ as a list of symbols to import from "the main executable" (AIX), or
+ as undefined symbols at build-time (Linux, others), or
= This is specific to python-modules, thus using 'python-config'.
Arfrever commentedon Jun 3, 2014
They are not for different cases. Difference between is a result of the fact that they were implemented independently at different times.
Linking of extension modules against libpythonX.Y.so is a good idea anyway. It avoids build failure with LDFLAGS="-Wl,--no-undefined".
doko42 commentedon Jun 3, 2014
they are. assume you build the zlib and elementtree extensions as builtins, then libs for an interpreter includes libz and libexpat, while they are not needed for extensions.
haubi commentedon Jun 4, 2014
So this diff - depending on issue#21660 - now drops showing any $LIBS from python-config, as python-modules usually do not link against any python-known libraries.
Instead, now there is a new configure variable LINKFORMODULE, which is shown by python-config --ldflags.
And $LINKFORSHARED is added to python.pc (for pkg-config).
Eventually, this allows to drop those Darwin hackery wrt. python-framework, as the python library isn't linked against the modules any more - but to PYTHONFRAMEWORK via LINKFORMODULE instead.
However, I don't have any Darwin around here: anyone?
For AIX, this looks good so far.
Thanks!
Arfrever commentedon Jun 4, 2014
Michael Haubenwallner: Could you show output of 'python-config-3.5 --ldflags' and 'python-config-3.5 --libs' without and with this patch (on GNU/Linux and AIX)?
haubi commentedon Jun 5, 2014
For AIX, with both these configure variants:
$ configure --prefix=/prefix --enable-shared CC=gcc CXX=g++ OPT=
$ configure --prefix=/prefix --enable-shared --without-computed-gotos CC=xlc_r CXX=xlC_r OPT=
the output changes like this:
For Linux, with this configure variant:
$ configure --prefix=/prefix --enable-shared CC=gcc CXX=g++
the output changes like this:
$ PKG_CONFIG_PATH=/prefix/lib/pkgconfig pkg-config --libs python-3.4 old: -L/prefix/lib -lpython3.4m new: -L/prefix/lib -lpython3.4m -Xlinker -export-dynamic $ /prefix/bin/python3.4-config --ldflags old: -L/prefix/lib -lpthread -ldl -lutil -lm -lpython3.4m -Xlinker -export-dynamic new: # Yes, nothing. Not sure if python modules should have undefined python symbols, or link against libpython.soJust found out that distutils.command.build_ext.get_libraries() does add libpython.so for Linux and similar (not Darwin and AIX).
Actually, distutils.command.build_ext.get_libraries() should add $LINKFORMODULE instead now, so LDSHARED does not need to carry.
More thoughts? (will post results with --disable-shared as separate comment)
haubi commentedon Jun 5, 2014
Now for --disable-shared:
For AIX, with both these configure variants:
$ configure --prefix=/prefix --disable-shared CC=gcc CXX=g++ OPT=
$ configure --prefix=/prefix --disable-shared --without-computed-gotos CC=xlc_r CXX=xlC_r OPT=
the output changes like this:
For Linux, with this configure variant:
$ configure --prefix=/prefix --enable-shared CC=gcc CXX=g++
the output changes like this:
$ PKG_CONFIG_PATH=/prefix/lib/pkgconfig pkg-config --libs python-3.4 old: -L/prefix/lib -lpython3.4m new: -L/prefix/lib -lpython3.4m -Xlinker -export-dynamic $ /prefix/bin/python3.4-config --ldflags old: -L/prefix/lib/python3.4/config-3.4m -L/prefix/lib -lpthread -ldl -lutil -lm -lpython3.4m -Xlinker -export-dynamic new: # Yes, nothing.And with --disable-shared, even distutils.command.build_ext.get_libraries() does *not* add libpython.so for Linux and similar, so python-shipped modules are linked with python symbols undefined now - but still as shared libraries.
haubi commentedon Jun 5, 2014
Erm, the latter should read:
For Linux, with this configure variant:
$ configure --prefix=/prefix --disable-shared CC=gcc CXX=g++
Now reading GNU ld manpage for Linux:
ld(1), at '--export-dynamic', tells about '--dynamic-list=file' to export specific symbols only - which actually looks similar to '-bE:file' for AIX...
tdsmith commentedon Feb 13, 2015
On Darwin, it would be nice if LINKFORMODULE used "-undefined dynamic_lookup" instead of explicitly linking to a framework binary. Modules with explicit links to a framework cause segfaults when they are imported from a different, but compatible, framework interpreter -- i.e., building against the system Python 2.7 but importing from a user-installed Python 2.7 causes an immediate crash.
I'm a maintainer of Homebrew, a package manager for OS X, and I spend a lot of time tracking down and eliminating errant explicit framework links because they make packaging binaries much harder for us and cause crashes for users.