PLUGINS: Use the C++ ABI to call dtors when unloading a plugin.

Avoid linking all plugins against libstdc++ to free up some memory
(about ~40kb on Wii per plugin). Enable it on GameCube, Wii, DS and PSP
(PS2 doesn't have __cxa_atexit support in its libc).

svn-id: r52607

backends/plugins/elf/elf-provider.cpp

@@ -25,11 +25,52 @@
 
 #if defined(DYNAMIC_MODULES) && defined(ELF_LOADER_TARGET)
 
+#ifdef ELF_LOADER_CXA_ATEXIT
+#include <cxxabi.h>
+#endif
+
 #include "backends/plugins/elf/elf-provider.h"
 #include "backends/plugins/dynamic-plugin.h"
 
+#include "common/debug.h"
 #include "common/fs.h"
 
+/* Note about ELF_LOADER_CXA_ATEXIT:
+ *
+ * consider the code:
+ *
+ * class Foobar {
+ *   const char *work() {
+ *     static String foo = "bar";
+ *     return s.c_str();
+ *   }
+ * }
+ *
+ * When instantiating Foobar and calling work() for the first time the String
+ * foo will be constructed. GCC automatically registers its destruction via
+ * either atexit() or __cxa_atexit(). Only the latter will add information
+ * about which DSO did the construction (Using &__dso_handle).
+ *
+ * __cxa_atexit allows plugins to reference C++ ABI symbols in the main
+ * executable without code duplication (No need to link the plugin against
+ * libstdc++), since we can distinguish which registered exit functions belong
+ * to a specific DSO. When unloading a plugin, we just use the C++ ABI call
+ * __cxa_finalize(&__dso_handle) to call all destructors of only that DSO.
+ *
+ * Prerequisites:
+ * - The used libc needs to support __cxa_atexit
+ * - -fuse-cxa-atexit in CXXFLAGS
+ * - Every plugin needs its own hidden __dso_handle symbol
+ *   This is automatically done via REGISTER_PLUGIN_DYNAMIC, see base/plugins.h
+ *
+ * When __cxa_atexit can not be used, each plugin needs to link against
+ * libstdc++ to embed its own set of C++ ABI symbols. When not doing so,
+ * registered destructors of already unloaded plugins will crash the
+ * application upon returning from main().
+ *
+ * See "3.3.5 DSO Object Destruction API" of the C++ ABI
+ */
+
 DynamicPlugin::VoidFunc ELFPlugin::findSymbol(const char *symbol) {
 	void *func = 0;
 
@@ -71,6 +112,14 @@ bool ELFPlugin::loadPlugin() {
 
 	bool ret = DynamicPlugin::loadPlugin();
 
+#ifdef ELF_LOADER_CXA_ATEXIT
+	// FIXME HACK: Reverse HACK of findSymbol() :P
+	VoidFunc tmp;
+	tmp = findSymbol("__dso_handle");
+	memcpy(&_dso_handle, &tmp, sizeof(VoidFunc));
+	debug(2, "elfloader: __dso_handle is %p", _dso_handle);
+#endif
+
 	_dlHandle->discard_symtab();
 
 	return ret;
@@ -80,6 +129,14 @@ void ELFPlugin::unloadPlugin() {
 	DynamicPlugin::unloadPlugin();
 
 	if (_dlHandle) {
+#ifdef ELF_LOADER_CXA_ATEXIT
+		if (_dso_handle) {
+			debug(2, "elfloader: calling __cxa_finalize");
+			__cxxabiv1::__cxa_finalize(_dso_handle);
+			_dso_handle = 0;
+		}
+#endif
+
 		if (!_dlHandle->close())
 			warning("elfloader: Failed unloading plugin '%s'", _filename.c_str());
 

backends/plugins/elf/elf-provider.h

@@ -45,13 +45,15 @@ class ELFPlugin : public DynamicPlugin {
 protected:
 	DLObject *_dlHandle;
 	Common::String _filename;
+	void *_dso_handle;
 
 	virtual VoidFunc findSymbol(const char *symbol);
 
 public:
 	ELFPlugin(const Common::String &filename) :
 		_dlHandle(0),
-		_filename(filename) {
+		_filename(filename),
+		_dso_handle(0) {
 	}
 
 	virtual ~ELFPlugin() {

base/plugins.h

@@ -90,6 +90,13 @@ extern int pluginTypeVersions[PLUGIN_TYPE_MAX];
 #define PLUGIN_ENABLED_DYNAMIC(ID) \
 	(ENABLE_##ID && (ENABLE_##ID == DYNAMIC_PLUGIN) && DYNAMIC_MODULES)
 
+// see comments in backends/plugins/elf/elf-provider.cpp
+#if defined(ELF_LOADER_TARGET) && defined(ELF_LOADER_CXA_ATEXIT)
+#define PLUGIN_DYNAMIC_EXTRA_DECL uint32 __dso_handle __attribute__((visibility ("hidden"))) = 0
+#else
+#define PLUGIN_DYNAMIC_EXTRA_DECL
+#endif
+
 /**
  * REGISTER_PLUGIN_STATIC is a convenience macro which is used to declare
  * the plugin interface for static plugins. Code (such as game engines)
@@ -119,6 +126,7 @@ extern int pluginTypeVersions[PLUGIN_TYPE_MAX];
  */
 #define REGISTER_PLUGIN_DYNAMIC(ID,TYPE,PLUGINCLASS) \
 	extern "C" { \
+		PLUGIN_DYNAMIC_EXTRA_DECL; \
 		PLUGIN_EXPORT int32 PLUGIN_getVersion() { return PLUGIN_VERSION; } \
 		PLUGIN_EXPORT int32 PLUGIN_getType() { return TYPE; } \
 		PLUGIN_EXPORT int32 PLUGIN_getTypeVersion() { return TYPE##_VERSION; } \

configure

@@ -1424,6 +1424,7 @@ case $_host_os in
 		CXXFLAGS="$CXXFLAGS -isystem $DEVKITPRO/libnds/include -isystem $DEVKITPRO/devkitARM/arm-eabi/include"
 		CXXFLAGS="$CXXFLAGS -mcpu=arm9tdmi -mtune=arm9tdmi -fomit-frame-pointer -mthumb-interwork"
 		CXXFLAGS="$CXXFLAGS -ffunction-sections -fdata-sections -fno-strict-aliasing"
+		CXXFLAGS="$CXXFLAGS -fuse-cxa-atexit"
 		LDFLAGS="$LDFLAGS -specs=ds_arm9.specs -mthumb-interwork -mno-fpu -Wl,-Map,map.txt"
 		if test "$_dynamic_modules" = no ; then
   			LDFLAGS="$LDFLAGS -Wl,--gc-sections"
@@ -1495,6 +1496,7 @@ case $_host_os in
 		;;
 	psp)
 		CXXFLAGS="$CXXFLAGS -O3 -I$PSPSDK/include -D_PSP_FW_VERSION=150"
+		CXXFLAGS="$CXXFLAGS -fuse-cxa-atexit"
 		;;
 	solaris*)
 		DEFINES="$DEFINES -DSOLARIS -DSYSTEM_NOT_SUPPORTING_D_TYPE"
@@ -1505,6 +1507,7 @@ case $_host_os in
 	wii)
 		CXXFLAGS="$CXXFLAGS -Os -mrvl -mcpu=750 -meabi -mhard-float"
 		CXXFLAGS="$CXXFLAGS -ffunction-sections -fdata-sections -fmodulo-sched"
+		CXXFLAGS="$CXXFLAGS -fuse-cxa-atexit"
 		CXXFLAGS="$CXXFLAGS -I$DEVKITPRO/libogc/include"
 		# libogc is required to link the cc tests (includes _start())
 		LDFLAGS="$LDFLAGS -mrvl -mcpu=750 -L$DEVKITPRO/libogc/lib/wii -logc"
@@ -2004,7 +2007,7 @@ POST_OBJS_FLAGS		:= -Wl,--no-whole-archive
 '
 		;;
 	ds)
-DEFINES="$DEFINES -DELF_LOADER_TARGET -DONE_PLUGIN_AT_A_TIME"
+DEFINES="$DEFINES -DELF_LOADER_TARGET -DELF_LOADER_CXA_ATEXIT -DONE_PLUGIN_AT_A_TIME"
 _def_plugin='
 #define PLUGIN_PREFIX	""
 #define PLUGIN_SUFFIX	".plg"
@@ -2015,7 +2018,7 @@ PLUGIN_PREFIX		:=
 PLUGIN_SUFFIX		:= .plg
 PLUGIN_EXTRA_DEPS	= $(EXECUTABLE)
 CXXFLAGS		+= -DDYNAMIC_MODULES
-PLUGIN_LDFLAGS		= -nostartfiles -Wl,-q,--just-symbols,$(EXECUTABLE),-T$(srcdir)/backends/plugins/ds/plugin.ld -lstdc++ -lc -mthumb-interwork -mno-fpu -Wl,--retain-symbols-file,$(srcdir)/backends/plugins/elf/plugin.syms
+PLUGIN_LDFLAGS		= -nostartfiles -Wl,-q,--just-symbols,$(EXECUTABLE),-T$(srcdir)/backends/plugins/ds/plugin.ld -mthumb-interwork -mno-fpu -Wl,--retain-symbols-file,$(srcdir)/backends/plugins/elf/plugin.syms
 PRE_OBJS_FLAGS		:= -Wl,--whole-archive
 POST_OBJS_FLAGS		:= -Wl,--no-whole-archive
 '
@@ -2038,7 +2041,7 @@ POST_OBJS_FLAGS := -Wl,-no-whole-archive
 '
 		;;
 	gamecube | wii)
-DEFINES="$DEFINES -DELF_LOADER_TARGET -DPPC_TARGET -DONE_PLUGIN_AT_A_TIME"
+DEFINES="$DEFINES -DELF_LOADER_TARGET -DPPC_TARGET -DELF_LOADER_CXA_ATEXIT -DONE_PLUGIN_AT_A_TIME"
 _def_plugin='
 #define PLUGIN_PREFIX	""
 #define PLUGIN_SUFFIX	".plg"
@@ -2108,7 +2111,7 @@ POST_OBJS_FLAGS		:= -Wl,--no-whole-archive
 '
 		;;
 	psp)
-DEFINES="$DEFINES -DELF_LOADER_TARGET -DMIPS_TARGET"
+DEFINES="$DEFINES -DELF_LOADER_TARGET -DMIPS_TARGET -DELF_LOADER_CXA_ATEXIT"
 _def_plugin='
 #define PLUGIN_PREFIX	""
 #define PLUGIN_SUFFIX	".plg"
@@ -2120,7 +2123,7 @@ PLUGIN_SUFFIX		:= .plg
 PLUGIN_EXTRA_DEPS	= $(EXECUTABLE)
 CXXFLAGS		+= -DDYNAMIC_MODULES
 LDFLAGS			+= -Wl,-T$(srcdir)/backends/platform/psp/main_prog.ld
-PLUGIN_LDFLAGS		= -nostartfiles -Wl,-q,--just-symbols,$(EXECUTABLE),--retain-symbols-file,$(srcdir)/backends/plugins/elf/plugin.syms,-T$(srcdir)/backends/plugins/psp/plugin.ld -lstdc++ -lc -lm -Wl,--wrap,memcpy
+PLUGIN_LDFLAGS		= -nostartfiles -Wl,-q,--just-symbols,$(EXECUTABLE),--retain-symbols-file,$(srcdir)/backends/plugins/elf/plugin.syms,-T$(srcdir)/backends/plugins/psp/plugin.ld -lc -Wl,--wrap,memcpy
 PRE_OBJS_FLAGS		:= -Wl,--whole-archive
 POST_OBJS_FLAGS		:= -Wl,--no-whole-archive
 '