From aff64d43d4ad9621532f33fdd70e0eccd1c2d2b2 Mon Sep 17 00:00:00 2001
From: Flyinghead <raphael.jean@gmail.com>
Date: Fri, 11 Apr 2025 12:02:53 +0200
Subject: [PATCH] libretro: don't restart the emu in retro_serialize_size

Stop the emu in retro_serialize_size and don't restart it until after
the state is saved in retro_serialize. This avoids issues when the
actual state size is greater than what retro_serialize_size returned.
Issue #1885
---
 shell/libretro/libretro.cpp | 33 ++++++++++++++++-----------------
 1 file changed, 16 insertions(+), 17 deletions(-)

diff --git a/shell/libretro/libretro.cpp b/shell/libretro/libretro.cpp
index 70a301e2a..a4bf1b0ab 100644
--- a/shell/libretro/libretro.cpp
+++ b/shell/libretro/libretro.cpp
@@ -1176,8 +1176,9 @@ void retro_run()
 		glsm_ctl(GLSM_CTL_STATE_BIND, nullptr);
 #endif
 
-	// On the first call, we start the emulator
-	if (first_run)
+	if (!emu.running())
+		// It could be the first time retro_run() is called,
+		// or it was paused in retro_serialize_size() and retro_serialize() was never called
 		emu.start();
 
 	poll_cb();
@@ -2318,17 +2319,16 @@ size_t retro_serialize_size()
 	DEBUG_LOG(SAVESTATE, "retro_serialize_size");
 	std::lock_guard<std::mutex> lock(mtx_serialization);
 
-	if (!first_run)
-		try {
-			emu.stop();
-		} catch (const FlycastException& e) {
-			ERROR_LOG(COMMON, "%s", e.what());
-			return 0;
-		}
+	try {
+		emu.stop();
+	} catch (const FlycastException& e) {
+		ERROR_LOG(COMMON, "%s", e.what());
+		return 0;
+	}
 
 	Serializer ser;
 	dc_serialize(ser);
-	if (!first_run)
+	if (!first_run && ser.size() == 0)
 		emu.start();
 
 	return ser.size();
@@ -2339,13 +2339,12 @@ bool retro_serialize(void *data, size_t size)
 	DEBUG_LOG(SAVESTATE, "retro_serialize %d bytes", (int)size);
 	std::lock_guard<std::mutex> lock(mtx_serialization);
 
-	if (!first_run)
-		try {
-			emu.stop();
-		} catch (const FlycastException& e) {
-			ERROR_LOG(COMMON, "%s", e.what());
-			return false;
-		}
+	try {
+		emu.stop();
+	} catch (const FlycastException& e) {
+		ERROR_LOG(COMMON, "%s", e.what());
+		return false;
+	}
 
 	Serializer ser(data, size);
 	dc_serialize(ser);