[mbr] Fix encmap boundary and method RVA lookup. (#50248)

Two separate issues:

1. When we process the EnC map, any tables after the last one that has an
update gets an "enc_recs" pointer that's one past the last row of the
table.  (the enc_recs pointer is used to speed up relative address lookup).  So
at lookup time if enc_recs says to look past the end of the EnC map table, we
know there won't be any updates - return -1.

2. When looking for the updated RVA of a method, we need to go through every
delta and find the latest one that has an update for the given method.  The
problem is that if a later generation doesn't have an update, we would take the
NULL return value at face value and it would look like the method had no
updates to its body - we would go back to using the original version from
before any updates were applied.  Instead now ignore lookup table misses and
remember the last successful lookup.  Fixes
dotnet/runtime#50190

src/mono/mono/metadata/loader.c

@@ -2001,16 +2001,26 @@ get_method_update_rva (MonoImage *image_base, uint32_t idx)
 {
 	gpointer loc = NULL;
 	uint32_t cur = mono_metadata_update_get_thread_generation ();
+	int generation = -1;
 	GList *ptr = image_base->delta_image;
 	/* Go through all the updates that the current thread can see and see
 	 * if they updated the method.  Keep the latest visible update */
 	for (; ptr != NULL; ptr = ptr->next) {
 		MonoImage *image_delta = (MonoImage*) ptr->data;
 		if (image_delta->generation > cur)
 			break;
-		if (image_delta->method_table_update)
-			loc = g_hash_table_lookup (image_delta->method_table_update, GUINT_TO_POINTER (idx));
+		if (image_delta->method_table_update) {
+			gpointer result = g_hash_table_lookup (image_delta->method_table_update, GUINT_TO_POINTER (idx));
+			/* if it's not in the table of a later generation, the
+			 * later generation didn't modify the method
+			 */
+			if (result != NULL) {
+				loc = result;
+				generation = image_delta->generation;
+			}
+		}
 	}
+	mono_trace (G_LOG_LEVEL_DEBUG, MONO_TRACE_METADATA_UPDATE, "method lookup idx=0x%08x returned gen=%d il=%p", idx, generation, loc);
 	return loc;
 }
 #endif

src/mono/mono/metadata/metadata-update.c

@@ -635,11 +635,17 @@ mono_image_relative_delta_index (MonoImage *image_dmeta, int token)
 	g_assert (delta_info);
 
 	int index_map = delta_info->enc_recs [table];
+	int encmap_rows = table_info_get_rows (encmap);
+
+	/* if the table didn't have any updates in this generation and the
+	 * table index is bigger than the last table that got updates,
+	 * enc_recs will point past the last row */
+	if (index_map - 1 == encmap_rows)
+		return -1;
 	guint32 cols[MONO_ENCMAP_SIZE];
 	mono_metadata_decode_row (encmap, index_map - 1, cols, MONO_ENCMAP_SIZE);
 	int map_entry = cols [MONO_ENCMAP_TOKEN];
 
-	int encmap_rows = table_info_get_rows (encmap);
 	while (mono_metadata_token_table (map_entry) == table && mono_metadata_token_index (map_entry) < index && index_map < encmap_rows) {
 		mono_metadata_decode_row (encmap, ++index_map - 1, cols, MONO_ENCMAP_SIZE);
 		map_entry = cols [MONO_ENCMAP_TOKEN];
@@ -849,6 +855,7 @@ apply_enclog_pass1 (MonoImage *image_base, MonoImage *image_dmeta, gconstpointer
 static void
 set_update_method (MonoImage *image_base, uint32_t generation, MonoImage *image_dmeta, uint32_t token_index, const char* il_address)
 {
+	mono_trace (G_LOG_LEVEL_INFO, MONO_TRACE_METADATA_UPDATE, "setting method 0x%08x in g=%d IL=%p", token_index, generation, (void*)il_address);
 	/* FIXME: this is a race if other threads are doing a lookup. */
 	g_hash_table_insert (image_base->method_table_update, GUINT_TO_POINTER (token_index), GUINT_TO_POINTER (generation));
 	g_hash_table_insert (image_dmeta->method_table_update, GUINT_TO_POINTER (token_index), (gpointer) il_address);