build: add way to keep unused symbols when linking NetworkManager

NetworkManager (and NetworkManager-all-sym) must not only contain symbols
that are used by itself. Also the device and settings plugin are dlopen'd
by NetworkManager and use symobls form the binary.

That means, if a symbols is only used by a plugin, then we must make sure
that the linker keeps it in the binary. Add a mechanism for that.

Makefile.am

@@ -2656,6 +2656,12 @@ $(src_core_libNetworkManagerTest_la_OBJECTS): $(src_libnm_core_public_mkenums_h)
 
 ###############################################################################
 
+# NetworkManager binary also must contain symbols that are not used by the binary
+# itself, but by the plugins (that are dlopened). We need to explicitly include
+# them during linking.
+networkmanager_undefined_symbols = \
+	$(NULL)
+
 noinst_PROGRAMS += src/core/NetworkManager-all-sym
 
 src_core_NetworkManager_all_sym_CPPFLAGS = $(src_core_cppflags)
@@ -2670,6 +2676,7 @@ src_core_NetworkManager_all_sym_LDADD = \
 
 src_core_NetworkManager_all_sym_LDFLAGS = \
 	-rdynamic \
+	$(networkmanager_undefined_symbols:%=-u %) \
 	$(SANITIZER_EXEC_LDFLAGS) \
 	$(NULL)
 
@@ -2696,6 +2703,7 @@ src_core_NetworkManager_LDADD = \
 src_core_NetworkManager_LDFLAGS = \
 	-rdynamic \
 	-Wl,--version-script="src/core/NetworkManager.ver" \
+	$(networkmanager_undefined_symbols:%=-u %) \
 	$(SANITIZER_EXEC_LDFLAGS) \
 	$(NULL)
 

src/core/meson.build

@@ -270,6 +270,14 @@ endif
 subdir('devices')
 subdir('settings/plugins')
 
+# NetworkManager binary also must contain symbols that are not used by the binary
+# itself, but by the plugins (that are dlopened). We need to explicitly include
+# them during linking.
+networkmanager_undefined_symbols_args = []
+foreach s: []
+  networkmanager_undefined_symbols_args += ['-u', s]
+endforeach
+
 # NetworkManager binary
 
 # libNetworkManager.a, as built by meson doesn't contain all symbols
@@ -284,7 +292,9 @@ NetworkManager_all_sym = executable(
     nm_deps,
     libudev_dep,
   ],
-  link_args: '-Wl,--no-gc-sections',
+  link_args: [
+    '-Wl,--no-gc-sections',
+  ] + networkmanager_undefined_symbols_args,
   link_whole: [
     libNetworkManager,
     libNetworkManagerBase,
@@ -345,7 +355,7 @@ NetworkManager = executable(
   link_args: [
     '-rdynamic',
     '-Wl,--version-script,@0@'.format(ver_script.full_path()),
-  ],
+  ] + networkmanager_undefined_symbols_args,
   link_depends: ver_script,
   install: true,
   install_dir: nm_sbindir,