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[mono][sgen] Add separate card mark function to be used with debug #109698

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Nov 28, 2024
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[mono][sgen] Add separate card mark function to be used with debug #109698

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32 changes: 30 additions & 2 deletions src/mono/mono/sgen/sgen-cardtable.c
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Original file line number Diff line number Diff line change
Expand Up @@ -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
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so is this only enabled in debug builds ?

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Sort of, only if certain debug flags are passed at runtime via env vars this is used to mark cards when copying objects. It is a conservative approach. It might be useful to backport since there are active crashes there that are not actionable and this PR should at least fix the use of some GC debugging features that might help investigate.

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
Expand Down Expand Up @@ -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);

Expand Down Expand Up @@ -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;
}
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2 changes: 1 addition & 1 deletion src/mono/mono/sgen/sgen-cardtable.h
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Expand Up @@ -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
Expand Down
2 changes: 1 addition & 1 deletion src/mono/mono/sgen/sgen-gc.c
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Expand Up @@ -3909,7 +3909,7 @@ 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)");

Expand Down