teach libretrobridge stuff how to check for changed serialize size

BizHawk.Emulation.Cores/Libretro/LibretroApi.cs

@@ -150,6 +150,7 @@ namespace BizHawk.Emulation.Cores.Libretro
 		{
 			public retro_system_info retro_system_info;
 			public retro_system_av_info retro_system_av_info;
+			public uint retro_serialize_size_initial; //size_t :(
 			public uint retro_serialize_size; //size_t :(
 			public uint retro_region;
 			public uint retro_api_version;

BizHawk.Emulation.Cores/Libretro/LibretroApi_CMD.cs

@@ -58,6 +58,13 @@ namespace BizHawk.Emulation.Cores.Libretro
 			return true;
 		}
 
+		public uint CMD_UpdateSerializeSize()
+		{
+			Message(eMessage.CMD_UpdateSerializeSize);
+			WaitForCMD();
+			return comm->env.retro_serialize_size;
+		}
+
 		public bool CMD_Serialize(byte[] data)
 		{
 			bool ret = false;

BizHawk.Emulation.Cores/Libretro/LibretroApi_Enums.cs

@@ -24,6 +24,7 @@ namespace BizHawk.Emulation.Cores.Libretro
 			CMD_Deinit,
 			CMD_Reset,
 			CMD_Run,
+			CMD_UpdateSerializeSize,
 			CMD_Serialize,
 			CMD_Unserialize,
 			CMD_LAST,

BizHawk.Emulation.Cores/Libretro/LibretroCore.cs

@@ -374,6 +374,7 @@ namespace BizHawk.Emulation.Cores.Libretro
 
 		public void SaveStateBinary(System.IO.BinaryWriter writer)
 		{
+			api.CMD_UpdateSerializeSize();
 			if (savebuff == null || savebuff.Length != api.comm->env.retro_serialize_size)
 			{
 				savebuff = new byte[api.comm->env.retro_serialize_size];
@@ -404,6 +405,7 @@ namespace BizHawk.Emulation.Cores.Libretro
 
 		public byte[] SaveStateBinary()
 		{
+			api.CMD_UpdateSerializeSize();
 			if (savebuff == null || savebuff.Length != api.comm->env.retro_serialize_size)
 			{
 				savebuff = new byte[api.comm->env.retro_serialize_size];

LibretroBridge/vs2015/LibretroBridge.cpp

@@ -89,6 +89,7 @@ enum eMessage : s32
 	CMD_Deinit,
 	CMD_Reset,
 	CMD_Run,
+	CMD_UpdateSerializeSize,
 	CMD_Serialize,
 	CMD_Unserialize,
 	CMD_LAST,
@@ -140,6 +141,7 @@ struct CommStruct
 		//set by the core
 		retro_system_info retro_system_info;
 		retro_system_av_info retro_system_av_info;
+		size_t retro_serialize_size_initial;
 		size_t retro_serialize_size;
 		u32 retro_region;
 		u32 retro_api_version;
@@ -694,7 +696,7 @@ static void LoadHandler(eMessage msg)
 
 	//Between calls to retro_load_game() and retro_unload_game(), the returned size is never allowed to be larger than a previous returned
 	//value, to ensure that the frontend can allocate a save state buffer once.
-	comm.env.retro_serialize_size = comm.funs.retro_serialize_size();
+	comm.env.retro_serialize_size_initial = comm.env.retro_serialize_size = comm.funs.retro_serialize_size();
 
 	//not sure when this can be called, but it's surely safe here
 	comm.env.retro_region = comm.funs.retro_get_region();
@@ -722,6 +724,11 @@ void cmd_Run()
 	comm.funs.retro_run();
 }
 
+void cmd_UpdateSerializeSize()
+{
+	comm.env.retro_serialize_size = comm.funs.retro_serialize_size();
+}
+
 void cmd_Serialize()
 {
 	comm.value = !!comm.funs.retro_serialize(comm.buf[BufId::Param0], comm.buf_size[BufId::Param0]);
@@ -765,6 +772,7 @@ const Action kHandlers_CMD[] = {
 	cmd_Deinit,
 	cmd_Reset,
 	cmd_Run,
+	cmd_UpdateSerializeSize,
 	cmd_Serialize,
 	cmd_Unserialize,
 };