build-sys: create "compatibility libraries" section

Compat stuff is moved to src/compat-libs/.
Warnings are issued when programs are linked with the deprecated library.

Makefile.am

@@ -4364,7 +4364,7 @@ polkitpolicy_in_files += \
 
 EXTRA_DIST += \
 	src/login/logind-gperf.gperf \
-	src/login/libsystemd-login.pc.in \
+	src/compat-libs/libsystemd-login.pc.in \
 	src/login/71-seat.rules.in \
 	src/login/73-seat-late.rules.in \
 	units/systemd-logind.service.in \
@@ -4527,24 +4527,27 @@ clean-python:
 	-rm -f _daemon.la id128.la _journal.la login.la _reader.la
 
 # ------------------------------------------------------------------------------
+if ENABLE_COMPAT_LIBS
+
 define generate-fake-lib
 	$(AM_V_at)$(MKDIR_P) $(dir $@)
-	$(AM_V_GEN)sed -r -n 's/^ +(sd_.*);/void new_\1(void);\n__asm__(".symver new_\1,\1@LIBSYSTEMD_209");\nstatic void (*resolve_\1(void)) (void) {\n\treturn new_\1;\n}\nvoid \1(void) __attribute__((ifunc("resolve_\1")));\n/p' <$< >$@
+	$(AM_V_GEN)sed -r -n 's/^ +(sd_.*);/void new_\1(void);\n__asm__(".symver new_\1,\1@LIBSYSTEMD_209");\nstatic void (*resolve_\1(void)) (void) {\n\treturn new_\1;\n}\nvoid \1(void) __attribute__((ifunc("resolve_\1")));\nobsolete_lib(\1,$(notdir $(basename $<)));\n/p' <$< >$@
 endef
 
 libsystemd_login_la_SOURCES = \
 	libsystemd-login.c \
-	src/login/libsystemd-login.sym
+	src/compat-libs/libsystemd-login.sym
 
 libsystemd_login_la_CFLAGS = \
 	$(AM_CFLAGS) \
 	-fvisibility=default \
+	-imacros $(top_srcdir)/src/compat-libs/linkwarning.h \
 	-fno-lto
 
 libsystemd_login_la_LDFLAGS = \
 	$(AM_LDFLAGS) \
 	-version-info $(LIBSYSTEMD_LOGIN_CURRENT):$(LIBSYSTEMD_LOGIN_REVISION):$(LIBSYSTEMD_LOGIN_AGE) \
-	-Wl,--version-script=$(top_srcdir)/src/login/libsystemd-login.sym
+	-Wl,--version-script=$(top_srcdir)/src/compat-libs/libsystemd-login.sym
 
 libsystemd_login_la_LIBADD = \
 	libsystemd.la
@@ -4552,14 +4555,14 @@ libsystemd_login_la_LIBADD = \
 BUILT_SOURCES += \
 	libsystemd-login.c
 
-libsystemd-login.c: src/login/libsystemd-login.sym
+libsystemd-login.c: src/compat-libs/libsystemd-login.sym
 	$(generate-fake-lib)
 
 lib_LTLIBRARIES += \
 	libsystemd-login.la
 
 pkgconfiglib_DATA += \
-	src/login/libsystemd-login.pc
+	src/compat-libs/libsystemd-login.pc
 
 # move lib from $(libdir) to $(rootlibdir) and update devel link, if needed
 libsystemd-login-install-hook:
@@ -4571,6 +4574,8 @@ libsystemd-login-uninstall-hook:
 INSTALL_EXEC_HOOKS += libsystemd-login-install-hook
 UNINSTALL_EXEC_HOOKS += libsystemd-login-uninstall-hook
 
+endif
+
 # ------------------------------------------------------------------------------
 substitutions = \
        '|rootlibexecdir=$(rootlibexecdir)|' \
@@ -5007,7 +5012,7 @@ test-libsystemd-journal-sym.c: \
 	$(generate-sym-test)
 
 test-libsystemd-login-sym.c: \
-	src/login/libsystemd-login.sym \
+	src/compat-libs/libsystemd-login.sym \
 	src/systemd/sd-login.h
 	$(generate-sym-test)
 
@@ -5059,9 +5064,13 @@ tests += \
 	test-libsystemd-daemon-sym \
 	test-libsystemd-id128-sym \
 	test-libsystemd-journal-sym \
-	test-libsystemd-login-sym \
 	test-libudev-sym
 
+if ENABLE_COMPAT_LIBS
+tests += \
+	test-libsystemd-login-sym
+endif
+
 cppcheck:
 	cppcheck --enable=all -q $(top_srcdir)
 

configure.ac

@@ -258,6 +258,17 @@ AS_IF([test "x$enable_dbus" != "xno"], [
                 [AC_MSG_ERROR([*** dbus-1 support requested but libraries not found])])])
 AM_CONDITIONAL(HAVE_DBUS, [test "$have_dbus" = "yes"])
 
+# ------------------------------------------------------------------------------
+have_compat_libs=no
+AC_ARG_ENABLE([compat_libs], AS_HELP_STRING([--enable-compat-libs],[Enable creation of compatibility libraries]),
+                [case "${enableval}" in
+                        yes) have_compat_libs=yes ;;
+                        no) have_compat_libs=no ;;
+                        *) AC_MSG_ERROR(bad value ${enableval} for --enable-compat-libs) ;;
+                esac],
+                [have_compat_libs=no])
+AM_CONDITIONAL([ENABLE_COMPAT_LIBS], [test "$have_compat_libs" = "yes"])
+
 # ------------------------------------------------------------------------------
 have_coverage=no
 AC_ARG_ENABLE(coverage, AS_HELP_STRING([--enable-coverage], [enable test coverage]))
@@ -1117,6 +1128,7 @@ AC_MSG_RESULT([
         test coverage:           ${have_coverage}
         Split /usr:              ${enable_split_usr}
         SysV compatibility:      ${SYSTEM_SYSV_COMPAT}
+        compatibility libraries: ${have_compat_libs}
 
         prefix:                  ${prefix}
         rootprefix:              ${with_rootprefix}

src/compat-libs/.gitignore

@@ -0,0 +1 @@
+/libsystemd-login.pc

src/compat-libs/libsystemd-login.pc.in

@@ -11,8 +11,8 @@ libdir=@libdir@
 includedir=@includedir@
 
 Name: systemd
-Description: systemd Login Utility Library
+Description: systemd Login Utility Library deprecated compatibility library
 URL: @PACKAGE_URL@
 Version: @PACKAGE_VERSION@
-Libs: -L${libdir} -lsystemd-login
+Libs: -L${libdir} -lsystemd
 Cflags: -I${includedir}

src/compat-libs/linkwarning.h

@@ -0,0 +1,34 @@
+/***
+  This file is part of systemd, but is heavily based on
+  glibc's libc-symbols.h.
+
+  Copyright (C) 1995-1998,2000-2006,2008,2009 Free Software Foundation, Inc
+
+  systemd is free software; you can redistribute it and/or modify it
+  under the terms of the GNU Lesser General Public License as published by
+  the Free Software Foundation; either version 2.1 of the License, or
+  (at your option) any later version.
+
+  systemd is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with systemd; If not, see <http://www.gnu.org/licenses/>.
+***/
+
+
+#define __make_section_unallocated(section_string)      \
+  asm (".section " section_string "\n\t.previous");
+
+#define __sec_comment "\n#APP\n\t#"
+
+#define link_warning(symbol, msg) \
+  __make_section_unallocated (".gnu.warning." #symbol)  \
+  static const char __evoke_link_warning_##symbol[]     \
+    __attribute__ ((used, section (".gnu.warning." #symbol __sec_comment))) \
+    = msg
+
+#define obsolete_lib(name, lib)                         \
+  link_warning(name, #name " was moved to libsystemd. Do not use " #lib ".")

src/login/.gitignore

@@ -1,4 +1,3 @@
-/libsystemd-login.pc
 /logind-gperf.c
 /org.freedesktop.login1.policy
 /71-seat.rules