bpo-36508: python-config don't export LINKFORSHARED

[vstinner]

python-config --ldflags no longer includes flags of the LINKFORSHARED
variable. The LINKFORSHARED variable must only be used to build
executables.

https://bugs.python.org/issue36508

[vstinner]

According to Azure Pipelines PR, macOS build failed with:

/bin/sh: -c: line 1: syntax error: unexpected end of file

Maybe my Makefile.pre.in change is wrong?

 	@ # Substitution happens here, as the completely-expanded BINDIR
 	@ # is not available in configure
 	sed -e "s,@EXENAME@,$(BINDIR)/python$(LDVERSION)$(EXE)," < $(srcdir)/Misc/python-config.in >python-config.py
-	@ # Replace makefile compat. variable references with shell script compat. ones; $(VAR) -> ${VAR}
-	LC_ALL=C sed -e 's,\$$(\([A-Za-z0-9_]*\)),\$$\{\1\},g' < Misc/python-config.sh >python-config
 	@ # On Darwin, always use the python version of the script, the shell
 	@ # version doesn't use the compiler customizations that are provided
 	@ # in python (_osx_support.py).
 	@if test `uname -s` = Darwin; then \
 		cp python-config.py python-config; \
+	else \
+		# Replace makefile compat. variable references with shell script compat. ones; $(VAR) -> ${VAR} \
+		LC_ALL=C sed -e 's,\$$(\([A-Za-z0-9_]*\)),\$$\{\1\},g' < Misc/python-config.sh >python-config; \
 	fi

[vstinner]

Maybe my Makefile.pre.in change is wrong?

It was just an unrelated refactoring change, I reverted it.

[vstinner]

I tested manually, the change works as expected.

Without the change (master branch), --ldflags contains -Xlinker -export-dynamic:

$ git clean -fdx; ./configure --with-pydebug -C && make

$ ./python python-config.py --ldflags
-L/usr/local/lib/python3.8/config-3.8dm-x86_64-linux-gnu -lpython3.8dm -lcrypt -lpthread -ldl -lutil -lm -lm -Xlinker -export-dynamic

$ bash python-config --ldflags
-L/home/vstinner/prog/python/lib/python3.8/config-3.8dm-x86_64-linux-gnu -L/home/vstinner/prog/python/lib -lpython3.8dm -lcrypt -lpthread -ldl  -lutil -lm -lm  -Xlinker -export-dynamic

With the change, --ldflags doesn't contain -Xlinker -export-dynamic:

$ git clean -fdx; ./configure --with-pydebug -C && make

$ ./python python-config.py --ldflags
-L/usr/local/lib/python3.8/config-3.8dm-x86_64-linux-gnu -lpython3.8dm -lcrypt -lpthread -ldl -lutil -lm -lm

$ bash python-config --ldflags
-L/home/vstinner/prog/python/lib/python3.8/config-3.8dm-x86_64-linux-gnu -L/home/vstinner/prog/python/lib -lpython3.8dm -lcrypt -lpthread -ldl  -lutil -lm -lm 

I'm not sure why python-config (shell) and python-config.py (Python) return different output for --ldflags (this behavior can be seen without my change, my change isn't related to that).

---

Note: (with or without the change) configure and Python don't add any LDFLAGS on my Fedora 29:

$ ./python -m sysconfig|grep LDFLAGS
	CONFIGURE_LDFLAGS = ""
	CONFIGURE_LDFLAGS_NODIST = ""
	LDFLAGS = ""
	LDFLAGS_NODIST = ""
	OPENSSL_LDFLAGS = ""
	PY_CORE_LDFLAGS = ""
	PY_LDFLAGS = ""
	PY_LDFLAGS_NODIST = ""

python3 from Fedora 29 contains way more LDFLAGS:

$ python3 -m sysconfig|grep LDFLAGS
	CONFIGURE_LDFLAGS = "-Wl,-z,relro   -Wl,-z,now -specs=/usr/lib/rpm/redhat/redhat-hardened-ld -g"
	CONFIGURE_LDFLAGS_NODIST = "-flto -fuse-linker-plugin -ffat-lto-objects -flto-partition=none -g"
	CONFIG_ARGS = "'--build=x86_64-redhat-linux-gnu' '--host=x86_64-redhat-linux-gnu' '--program-prefix=' '--disable-dependency-tracking' '--prefix=/usr' '--exec-prefix=/usr' '--bindir=/usr/bin' '--sbindir=/usr/sbin' '--sysconfdir=/etc' '--datadir=/usr/share' '--includedir=/usr/include' '--libdir=/usr/lib64' '--libexecdir=/usr/libexec' '--localstatedir=/var' '--sharedstatedir=/var/lib' '--mandir=/usr/share/man' '--infodir=/usr/share/info' '--enable-ipv6' '--enable-shared' '--with-computed-gotos=yes' '--with-dbmliborder=gdbm:ndbm:bdb' '--with-system-expat' '--with-system-ffi' '--enable-loadable-sqlite-extensions' '--with-dtrace' '--with-lto' '--with-ssl-default-suites=openssl' '--with-valgrind' '--without-ensurepip' '--enable-optimizations' 'build_alias=x86_64-redhat-linux-gnu' 'host_alias=x86_64-redhat-linux-gnu' 'CFLAGS=-O2 -g -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -Wp,-D_GLIBCXX_ASSERTIONS -fexceptions -fstack-protector-strong -grecord-gcc-switches -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1 -specs=/usr/lib/rpm/redhat/redhat-annobin-cc1 -m64 -mtune=generic -fasynchronous-unwind-tables -fstack-clash-protection -fcf-protection -D_GNU_SOURCE -fPIC -fwrapv ' 'LDFLAGS=-Wl,-z,relro   -Wl,-z,now -specs=/usr/lib/rpm/redhat/redhat-hardened-ld -g ' 'CPPFLAGS=' 'PKG_CONFIG_PATH=:/usr/lib64/pkgconfig:/usr/share/pkgconfig'"
	LDFLAGS = "-Wl,-z,relro   -Wl,-z,now -specs=/usr/lib/rpm/redhat/redhat-hardened-ld -g"
	OPENSSL_LDFLAGS = ""
	PY_CORE_LDFLAGS = "-Wl,-z,relro   -Wl,-z,now -specs=/usr/lib/rpm/redhat/redhat-hardened-ld -g -flto -fuse-linker-plugin -ffat-lto-objects -flto-partition=none -g"
	PY_LDFLAGS = "-Wl,-z,relro   -Wl,-z,now -specs=/usr/lib/rpm/redhat/redhat-hardened-ld -g"
	PY_LDFLAGS_NODIST = "-flto -fuse-linker-plugin -ffat-lto-objects -flto-partition=none -g"

[miss-islington]

Thanks @vstinner for the PR 🌮🎉.. I'm working now to backport this PR to: 2.7, 3.7.
🐍🍒⛏🤖

[bedevere-bot]

GH-12748 is a backport of this pull request to the 3.7 branch.

[miss-islington]

Sorry, @vstinner, I could not cleanly backport this to 2.7 due to a conflict.
Please backport using cherry_picker on command line.
cherry_picker e65f01f78d7bda3013fc5be485afa87ff56511d9 2.7