plugins: do not limit exported symbols if modules are active

On Mac --enable-modules and --enable-plugins are currently incompatible, because the
Apple -Wl,-exported_symbols_list command line options prevents the export of any
symbols needed by the modules.  On x86 -Wl,--dynamic-list does not have this effect,
but only because the -Wl,--export-dynamic option provided by gmodule-2.0.pc overrides
it.  On Apple there is no -Wl,--export-dynamic, because it is the default, and thus
no override.

Either way, when modules are active there is no reason to include the plugin_ldflags.
While at it, avoid the useless -Wl,--export-dynamic when --enable-plugins is
specified but --enable-modules is not; this way, the GNU and Apple configurations
are more similar.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/516


Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
[AJB: fix noexport to no-export]
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20210811100550.54714-1-pbonzini@redhat.com>
Cc: qemu-stable@nongnu.org

configure

@@ -3187,9 +3187,8 @@ glib_req_ver=2.56
 glib_modules=gthread-2.0
 if test "$modules" = yes; then
     glib_modules="$glib_modules gmodule-export-2.0"
-fi
-if test "$plugins" = "yes"; then
-    glib_modules="$glib_modules gmodule-2.0"
+elif test "$plugins" = "yes"; then
+    glib_modules="$glib_modules gmodule-no-export-2.0"
 fi
 
 for i in $glib_modules; do

plugins/meson.build

-if 'CONFIG_HAS_LD_DYNAMIC_LIST' in config_host
-  plugin_ldflags = ['-Wl,--dynamic-list=' + (meson.build_root() / 'qemu-plugins-ld.symbols')]
-elif 'CONFIG_HAS_LD_EXPORTED_SYMBOLS_LIST' in config_host
-  plugin_ldflags = ['-Wl,-exported_symbols_list,' + (meson.build_root() / 'qemu-plugins-ld64.symbols')]
-else
-  plugin_ldflags = []
+plugin_ldflags = []
+# Modules need more symbols than just those in plugins/qemu-plugins.symbols
+if not enable_modules
+  if 'CONFIG_HAS_LD_DYNAMIC_LIST' in config_host
+    plugin_ldflags = ['-Wl,--dynamic-list=' + (meson.build_root() / 'qemu-plugins-ld.symbols')]
+  elif 'CONFIG_HAS_LD_EXPORTED_SYMBOLS_LIST' in config_host
+    plugin_ldflags = ['-Wl,-exported_symbols_list,' + (meson.build_root() / 'qemu-plugins-ld64.symbols')]
+  endif
 endif
 
 specific_ss.add(when: 'CONFIG_PLUGIN', if_true: [files(