Mono: Fix weird crash when loading corlib

2 files changed, 44 insertions, 14 deletions

diff --git a/modules/mono/mono_gd/gd_mono_assembly.cpp b/modules/mono/mono_gd/gd_mono_assembly.cpp
index 57797598e1..27ce39b6d7 100644
--- a/modules/mono/mono_gd/gd_mono_assembly.cpp
+++ b/modules/mono/mono_gd/gd_mono_assembly.cpp
@@ -42,9 +42,15 @@
 #include "gd_mono_class.h"
 
 bool GDMonoAssembly::no_search = false;
+bool GDMonoAssembly::in_preload = false;
+
 Vector<String> GDMonoAssembly::search_dirs;
 
 void GDMonoAssembly::assembly_load_hook(MonoAssembly *assembly, void *user_data) {
+
+	if (no_search)
+		return;
+
 	// If our search and preload hooks fail to load the assembly themselves, the mono runtime still might.
 	// Just do Assembly.LoadFrom("/Full/Path/On/Disk.dll");
 	// In this case, we wouldn't have the assembly known in GDMono, which causes crashes
@@ -122,6 +128,8 @@ MonoAssembly *GDMonoAssembly::_search_hook(MonoAssemblyName *aname, void *user_d
 	return res ? res->get_assembly() : NULL;
 }
 
+static _THREAD_LOCAL_(MonoImage *) image_corlib_loading = NULL;
+
 MonoAssembly *GDMonoAssembly::_preload_hook(MonoAssemblyName *aname, char **assemblies_path, void *user_data, bool refonly) {
 
 	(void)user_data; // UNUSED
@@ -149,10 +157,27 @@ MonoAssembly *GDMonoAssembly::_preload_hook(MonoAssemblyName *aname, char **asse
 		}
 	}
 
+	{
+		// If we find the assembly here, we load it with `mono_assembly_load_from_full`,
+		// which in turn invokes load hooks before returning the MonoAssembly to us.
+		// One of the load hooks is `load_aot_module`. This hook can end up calling preload hooks
+		// again for the same assembly in certain in certain circumstances (the `do_load_image` part).
+		// If this is the case and we return NULL due to the no_search condition below,
+		// it will result in an internal crash later on. Therefore we need to return the assembly we didn't
+		// get yet from `mono_assembly_load_from_full`. Luckily we have the image, which already got it.
+		// This must be done here. If done in search hooks, it would cause `mono_assembly_load_from_full`
+		// to think another MonoAssembly for this assembly was already loaded, making it delete its own,
+		// when in fact both pointers were the same... This hooks thing is confusing.
+		if (image_corlib_loading) {
+			return mono_image_get_assembly(image_corlib_loading);
+		}
+	}
+
 	if (no_search)
 		return NULL;
 
 	no_search = true;
+	in_preload = true;
 
 	String name = mono_assembly_name_get_name(aname);
 	bool has_extension = name.ends_with(".dll");
@@ -187,6 +212,7 @@ MonoAssembly *GDMonoAssembly::_preload_hook(MonoAssemblyName *aname, char **asse
 	}
 
 	no_search = false;
+	in_preload = false;
 
 	return res ? res->get_assembly() : NULL;
 }
@@ -209,23 +235,18 @@ GDMonoAssembly *GDMonoAssembly::_load_assembly_from(const String &p_name, const
 }
 
 void GDMonoAssembly::_wrap_mono_assembly(MonoAssembly *assembly) {
-	String p_name = mono_assembly_name_get_name(mono_assembly_get_name(assembly));
-	GDMonoAssembly **existingassembly = GDMono::get_singleton()->get_loaded_assembly(p_name);
-
-	if (no_search || existingassembly != NULL) {
-		// Not sure whether the existingassembly check matters
-		// since no_search handles it in most cases?
-		// Can't hurt.
-		return;
-	}
+	String name = mono_assembly_name_get_name(mono_assembly_get_name(assembly));
 
 	MonoImage *image = mono_assembly_get_image(assembly);
-	mono_image_addref(image);
 
-	GDMonoAssembly *gdassembly = memnew(GDMonoAssembly(p_name, mono_image_get_filename(image)));
-	gdassembly->assembly = assembly;
-	gdassembly->loaded = true;
-	gdassembly->image = image;
+	GDMonoAssembly *gdassembly = memnew(GDMonoAssembly(name, mono_image_get_filename(image)));
+	Error err = gdassembly->wrapper_for_image(image);
+
+	if (err != OK) {
+		memdelete(gdassembly);
+		ERR_FAIL();
+	}
+
 	MonoDomain *domain = mono_domain_get();
 	GDMono::get_singleton()->add_assembly(domain ? mono_domain_get_id(domain) : 0, gdassembly);
 }
@@ -280,8 +301,16 @@ no_pdb:
 
 #endif
 
+	bool is_corlib_preload = in_preload && name == "mscorlib";
+
+	if (is_corlib_preload)
+		image_corlib_loading = image;
+
 	assembly = mono_assembly_load_from_full(image, image_filename.utf8().get_data(), &status, refonly);
 
+	if (is_corlib_preload)
+		image_corlib_loading = NULL;
+
 	ERR_FAIL_COND_V(status != MONO_IMAGE_OK || assembly == NULL, ERR_FILE_CANT_OPEN);
 
 	loaded = true;
diff --git a/modules/mono/mono_gd/gd_mono_assembly.h b/modules/mono/mono_gd/gd_mono_assembly.h
index e8f2be62f8..2c6d367fc6 100644
--- a/modules/mono/mono_gd/gd_mono_assembly.h
+++ b/modules/mono/mono_gd/gd_mono_assembly.h
@@ -89,6 +89,7 @@ class GDMonoAssembly {
 #endif
 
 	static bool no_search;
+	static bool in_preload;
 	static Vector<String> search_dirs;
 
 	static void assembly_load_hook(MonoAssembly *assembly, void *user_data);