fix(mgb/serialization): fix multiple graph load error

GitOrigin-RevId: 89414b014b4ef2a465bca858bc6bcea24f4c951e

src/serialization/impl/serializer_oss.cpp

@@ -846,7 +846,7 @@ GraphLoader::LoadResult GraphLoaderOSS::load(const LoadConfig& config,
     OprLoadContextImpl ctx{this, m_graph->mgb_version()};
     auto result = ctx.load_oprs();
 
-    auto fbs_end = tensor_begin + offset_to_fbs + size;
+    auto fbs_end = tensor_begin + offset_to_fbs + sizeof(size) + size;
     auto cur = m_file->tell();
     mgb_assert(fbs_end > cur);
     // Skip to Graph end
@@ -872,4 +872,4 @@ bool is_fbs_file(InputFile& file) {
 }  // namespace serialization
 }  // namespace mgb
 
-#endif
\ No newline at end of file
+#endif

src/serialization/test/serializer_oss.cpp

@@ -64,6 +64,34 @@ TEST(TestSerializer2, GraphDumpLoad) {
     load();
 }
 
+TEST(TestSerializer2, MultiGraphDumpLoad) {
+    auto fname = GET_OUTPUT_FILE();
+
+    auto dump = [&]() {
+        auto cn = CompNode::load("cpu0");
+        auto graph = ComputingGraph::make();
+        auto x = opr::ImmutableTensor::make(*graph, 1926.0817f, {cn});
+        x.rename("varz");
+        auto dumper = GraphDumper::make(OutputFile::make_fs(fname.c_str()),
+                                        GraphDumpFormat::FLATBUFFERS);
+        // dump twice
+        dumper->dump({x});
+        dumper->dump({x});
+    };
+    auto load = [&]() {
+        GraphLoader::LoadConfig load_config = {};
+        auto loader = GraphLoader::make(InputFile::make_fs(fname.c_str()),
+                                        GraphDumpFormat::FLATBUFFERS);
+        // load twice
+        loader->load(load_config, false);
+        loader = GraphLoader::make(loader->reset_file(), loader->format());
+        loader->load(load_config, false);
+    };
+
+    dump();
+    load();
+}
+
 TEST(TestSerializer2, APlusB) {
     auto fname = GET_OUTPUT_FILE();
     TensorShape shape{2, 3};
@@ -733,4 +761,4 @@ TEST(TestSerializer2, HasOutputDtype) {
     load();
 }
 
-#endif
\ No newline at end of file
+#endif