vstinner
commented
5 years ago 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:
$ python3-config --ldflags
-L/usr/lib64 -lpython3.7m -lpthread -ldl -lutil -lm -Xlinker -export-dynamicThe "-export-dynamic" flag causes non-obvious dynamic linking bug like the following bug in Samba which embeds Python:
- https://bugzilla.redhat.com/show_bug.cgi?id=1198161 (python bug)
- https://bugzilla.redhat.com/show_bug.cgi?id=1198158 (bug reported on samba)
- https://bugzilla.redhat.com/show_bug.cgi?id=1197914 (bug originally reported on gdb)
--
History of the LINKFORSHARED variable.
(*) Python build system uses a LINKFORSHARED variable since this commit:
commit 7cc5abd4548629cc41d3951576f41ff2ddd7b5f7 Author: Guido van Rossum \guido@python.org\ Date: Mon Sep 12 10:42:20 1994 +0000
Support shared library creation.The value of the variable changed on Linux with:
commit b65a48e2b631f9a171e6eab699974bd2074f40d7 (HEAD) Author: Guido van Rossum \guido@python.org\ Date: Wed Jun 14 18:21:23 1995 +0000
linux elf shlib; sys/wait.h; don't add -posix for NeXTExtract 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 7cc5abd4548629cc41d3951576f41ff2ddd7b5f7):
../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 c90b17ec8233009e4745dd8f77401f52c5d4a8d5 Author: Martin v. Löwis \martin@v.loewis.de\ Date: Sat Apr 15 08:13:05 2006 +0000
Patch bpo-1161914: Add python-config.The following commit modified Misc/python-config.in to add LINKFORSHARED to python-config --ldflags:
commit a70f3496203cd68d88208a21d90f0ca3503aa2f6 Author: Collin Winter \collinw@gmail.com\ Date: Fri Mar 19 00:08:44 2010 +0000
Make python-config support multiple option flags on the same command line, rather than requiring one invocation per flag.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 ecd4e9de5afab6a5d75a6fa7ebfb62804ba69264 Author: Ned Deily \nad@acm.org\ Date: Tue Jul 24 03:31:48 2012 -0700
Issue bpo-14197: For OS X framework builds, ensure links to the shared
library are created with the proper ABI suffix.diff --git a/Misc/python-config.in b/Misc/python-config.in
index 1d4a81d850..79f0bb14c1 100644
--- a/Misc/python-config.in
+++ b/Misc/python-config.in
@@ -52,7 +52,8 @@ for opt in opt_flags:
if opt == '--ldflags':
if not getvar('Py_ENABLE_SHARED'):
libs.insert(0, '-L' + getvar('LIBPL'))
- libs.extend(getvar('LINKFORSHARED').split())
+ if not getvar('PYTHONFRAMEWORK'):
+ libs.extend(getvar('LINKFORSHARED').split())
print(' '.join(libs))
(*) A shell version of python-config has been added by:
commit 874211978c8097b8e747c90fa3ff41aacabe340f Author: doko@python.org \doko@python.org\ Date: Sat Jan 26 11:39:31 2013 +0100
- Issue bpo-16235: Implement python-config as a shell script.Extract of Misc/python-config.sh.in at this commit:
--ldflags)
LINKFORSHAREDUSED=
if [ -z "$PYTHONFRAMEWORK" ] ; then
LINKFORSHAREDUSED=$LINKFORSHARED
fi
LIBPLUSED=
if [ "$PY_ENABLE_SHARED" = "0" ] ; then
LIBPLUSED="-L$LIBPL"
fi
echo "$LIBPLUSED -L$libdir $LIBS $LINKFORSHAREDUSED"
;;
Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.
Show more details
GitHub fields: ```python assignee = None closed_at =
created_at =
labels = ['3.8', 'build', '3.7']
title = 'python-config --ldflags must not contain LINKFORSHARED ("-Xlinker -export-dynamic" on Linux)'
updated_at =
user = 'https://github.com/vstinner'
```
bugs.python.org fields:
```python
activity =
actor = 'vstinner'
assignee = 'none'
closed = True
closed_date =
closer = 'vstinner'
components = ['Build']
creation =
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']
```