[mono][sgen] Add separate card mark function to be used with debug (#110269)

When marking cards for a non-array object or a an element vt in an object, it is enough to mark a card for any address within that object/vt because they are always fully scanned. Cardtable consistency checks are not accounting for this detail and it is difficult to have it implemented. Instead, when having such debug flags enabled, we use an explicit approach where every single card is being marked.

Co-authored-by: Vlad Brezae <[email protected]>

Author: github-actions[bot]

src/mono/mono/sgen/sgen-cardtable.c

@@ -165,6 +165,31 @@ sgen_card_table_wbarrier_range_copy (gpointer _dest, gconstpointer _src, int siz
 	}
 }
 
+// Marks more cards so that it works with remset consistency debug checks
+static void
+sgen_card_table_wbarrier_range_copy_debug (gpointer _dest, gconstpointer _src, int size)
+{
+	GCObject **dest = (GCObject **)_dest;
+	GCObject **src = (GCObject **)_src;
+
+	size_t nursery_bits = sgen_nursery_bits;
+	char *start = sgen_nursery_start;
+	G_GNUC_UNUSED char *end = sgen_nursery_end;
+
+	while (size) {
+		GCObject *value = *src;
+		*dest = value;
+		if (SGEN_PTR_IN_NURSERY (value, nursery_bits, start, end) || sgen_concurrent_collection_in_progress) {
+			volatile guint8 *card_address = (volatile guint8 *)sgen_card_table_get_card_address ((mword)dest);
+			*card_address = 1;
+			sgen_dummy_use (value);
+		}
+		++src;
+		++dest;
+		size -= SIZEOF_VOID_P;
+	}
+}
+
 MONO_RESTORE_WARNING
 
 #ifdef SGEN_HAVE_OVERLAPPING_CARDS
@@ -606,7 +631,7 @@ sgen_cardtable_scan_object (GCObject *obj, mword block_obj_size, guint8 *cards,
 }
 
 void
-sgen_card_table_init (SgenRememberedSet *remset)
+sgen_card_table_init (SgenRememberedSet *remset, gboolean consistency_checks)
 {
 	sgen_cardtable = (guint8 *)sgen_alloc_os_memory (CARD_COUNT_IN_BYTES, (SgenAllocFlags)(SGEN_ALLOC_INTERNAL | SGEN_ALLOC_ACTIVATE), "card table", MONO_MEM_ACCOUNT_SGEN_CARD_TABLE);
 
@@ -637,7 +662,10 @@ sgen_card_table_init (SgenRememberedSet *remset)
 
 	remset->find_address = sgen_card_table_find_address;
 	remset->find_address_with_cards = sgen_card_table_find_address_with_cards;
-	remset->wbarrier_range_copy = sgen_card_table_wbarrier_range_copy;
+	if (consistency_checks)
+		remset->wbarrier_range_copy = sgen_card_table_wbarrier_range_copy_debug;
+	else
+		remset->wbarrier_range_copy = sgen_card_table_wbarrier_range_copy;
 
 	need_mod_union = sgen_get_major_collector ()->is_concurrent;
 }

src/mono/mono/sgen/sgen-cardtable.h

@@ -30,7 +30,7 @@ void sgen_card_table_preclean_mod_union (guint8 *cards, guint8 *cards_preclean,
 guint8* sgen_get_card_table_configuration (int *shift_bits, gpointer *mask);
 guint8* sgen_get_target_card_table_configuration (int *shift_bits, target_mgreg_t *mask);
 
-void sgen_card_table_init (SgenRememberedSet *remset);
+void sgen_card_table_init (SgenRememberedSet *remset, gboolean consistency_checks);
 
 /*How many bytes a single card covers*/
 #define CARD_BITS 9

src/mono/mono/sgen/sgen-gc.c

@@ -3895,7 +3895,7 @@ sgen_gc_init (void)
 
 	memset (&remset, 0, sizeof (remset));
 
-	sgen_card_table_init (&remset);
+	sgen_card_table_init (&remset, remset_consistency_checks);
 
 	sgen_register_root (NULL, 0, sgen_make_user_root_descriptor (sgen_mark_normal_gc_handles), ROOT_TYPE_NORMAL, MONO_ROOT_SOURCE_GC_HANDLE, GINT_TO_POINTER (ROOT_TYPE_NORMAL), "GC Handles (SGen, Normal)");