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: seebpo-14197.--Python build system uses a LINKFORSHARED variable, extract of configure.ac:# LINKFORSHARED are the flags passed to the $(CC) command that links# the python executable -- this is only needed for a few systemsThis variable is set to "-Xlinker -export-dynamic" on Linux. Extract of ld manual page for --export-dynamic option:---When creating a dynamically linked executable, using the -Eoption or the --export-dynamic option causes the linker toadd all symbols to the dynamic symbol table.  The dynamicsymbol table is the set of symbols which are visible fromdynamic objects at run time.If you do not use either of these options (or use the--no-export-dynamic option to restore the default behavior),the dynamic symbol table will normally contain only thosesymbols which are referenced by some dynamic objectmentioned in the link.If you use "dlopen" to load a dynamic object which needs torefer back to the symbols defined by the program, ratherthan some other dynamic object, then you will probably needto use this option when linking the program itself.You can also use the dynamic list to control what symbolsshould be added to the dynamic symbol table if the outputformat supports it.  See the description of --dynamic-list.Note that this option is specific to ELF targeted ports.  PEtargets support a similar function to export all symbolsfrom a DLL or EXE; see the description of--export-all-symbols below.---Both configure.ac and ld manual page mention an "executable", whereas LINKFORSHARED is currently exported in python-config --ldflags. Example on Fedora 29:$ 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:commit7cc5abd4548629cc41d3951576f41ff2ddd7b5f7Author: 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:commitb65a48e2b631f9a171e6eab699974bd2074f40d7 (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 fiThe variable was only used to build the "python" executable. Extract ofModules/Makefile.in (at commit7cc5abd4548629cc41d3951576f41ff2ddd7b5f7):../python:config.o $(MYLIBS) Makefile$(CC) $(OPT) config.o $(LINKFORSHARED) \      $(MYLIBS) $(MODLIBS) $(LIBS) $(SYSLIBS) -o pythonmv python ../python(*) The python-config script was created as a Python script by:commitc90b17ec8233009e4745dd8f77401f52c5d4a8d5Author: Martin v. Löwis <martin@v.loewis.de>Date:   Sat Apr 15 08:13:05 2006 +0000    Patch#1161914: Add python-config.The following commit modifiedMisc/python-config.in to add LINKFORSHARED to python-config --ldflags:commita70f3496203cd68d88208a21d90f0ca3503aa2f6Author: 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 modifiedMisc/python-config.in to not add LINKFORSHARED into "libs" when built on macOS (if PYTHONFRAMEWORK is defined):commitecd4e9de5afab6a5d75a6fa7ebfb62804ba69264Author: Ned Deily <nad@acm.org>Date:   Tue Jul 24 03:31:48 2012 -0700    Issue#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.inindex1d4a81d850..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:commit874211978c8097b8e747c90fa3ff41aacabe340fAuthor:doko@python.org <doko@python.org>Date:   Sat Jan 26 11:39:31 2013 +0100    - Issue#16235: Implement python-config as a shell script.Extract ofMisc/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"        ;;

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:AC_MSG_RESULT($CCSHARED)# LINKFORSHARED are the flags passed to the $(CC) command that links# the python executable -- this is only needed for a few systemsAC_MSG_CHECKING(LINKFORSHARED)if test -z "$LINKFORSHARED"thencase $ac_sys_system/$ac_sys_release inAIX*)LINKFORSHARED='-Wl,-bE:Modules/python.exp -lld';;hp*|HP*)    LINKFORSHARED="-Wl,-E -Wl,+s";;#    LINKFORSHARED="-Wl,-E -Wl,+s -Wl,+b\$(BINLIBDEST)/lib-dynload";;Linux-android*) LINKFORSHARED="-pie -Xlinker -export-dynamic";;Linux*|GNU*) LINKFORSHARED="-Xlinker -export-dynamic";;# -u libsys_s pulls in all symbols in libsysDarwin/*)LINKFORSHARED="$extra_undefs -framework CoreFoundation"# Issue#18075: the default maximum stack size (8MBytes) is too# small for the default recursion limit. Increase the stack size# to ensure that tests don't crashLINKFORSHARED="-Wl,-stack_size,1000000 $LINKFORSHARED"if test "$enable_framework"thenLINKFORSHARED="$LINKFORSHARED "'$(PYTHONFRAMEWORKDIR)/Versions/$(VERSION)/$(PYTHONFRAMEWORK)'fiLINKFORSHARED="$LINKFORSHARED";;OpenUNIX*|UnixWare*) LINKFORSHARED="-Wl,-Bexport";;SCO_SV*) LINKFORSHARED="-Wl,-Bexport";;ReliantUNIX*) LINKFORSHARED="-W1 -Blargedynsym";;FreeBSD*|NetBSD*|OpenBSD*|DragonFly*)if [[ "`$CC -dM -E - </dev/null | grep __ELF__`" != "" ]]thenLINKFORSHARED="-Wl,--export-dynamic"fi;;SunOS/5*) case $CC in  *gcc*)    if $CC -Xlinker --help 2>&1 | grep export-dynamic >/dev/null    thenLINKFORSHARED="-Xlinker --export-dynamic"    fi;;  esac;;CYGWIN*)if test $enable_shared = "no"thenLINKFORSHARED='-Wl,--out-implib=$(LDLIBRARY)'fi;;QNX*)# -Wl,-E causes the symbols to be added to the dynamic# symbol table so that they can be found when a module# is loaded.  -N 2048K causes the stack size to be set# to 2048 kilobytes so that the stack doesn't overflow# when running test_compile.py.LINKFORSHARED='-Wl,-E -N 2048K';;VxWorks*)LINKFORSHARED='--export-dynamic';;esacfiAC_MSG_RESULT($LINKFORSHARED)

See alsobpo-10112: "Use -Wl,--dynamic-list=x.list, not -Xlinker -export-dynamic".

New changesete65f01f78d7bda3013fc5be485afa87ff56511d9 by Victor Stinner in branch 'master':bpo-36508: python-config don't export LINKFORSHARED (GH-12661)https://github.com/python/cpython/commit/e65f01f78d7bda3013fc5be485afa87ff56511d9

New changesetcd46b09b0863c787dd54c433fae52bd8bdfaecd0 by Victor Stinner (Miss Islington (bot)) in branch '3.7':bpo-36508: python-config don't export LINKFORSHARED (GH-12661) (GH-12748)https://github.com/python/cpython/commit/cd46b09b0863c787dd54c433fae52bd8bdfaecd0

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.