rts: Zero block flags with -DZ

Block flags are very useful for determining the state of a block.
However, some block allocator users don't touch them, leading to
misleading values. Ensure that we zero then when zero-on-gc is set. This
is safe and makes the flags more useful during debugging.

1 files changed, 12 insertions, 0 deletions

diff --git a/rts/sm/BlockAlloc.c b/rts/sm/BlockAlloc.c
index b3e1e2ce75..2bf497197e 100644
--- a/rts/sm/BlockAlloc.c
+++ b/rts/sm/BlockAlloc.c
@@ -233,6 +233,12 @@ initGroup(bdescr *head)
       last->blocks = 0;
       last->link = head;
   }
+
+#if defined(DEBUG)
+  for (uint32_t i=0; i < head->blocks; i++) {
+      head[i].flags = 0;
+  }
+#endif
 }
 
 #if SIZEOF_VOID_P == SIZEOF_LONG
@@ -792,6 +798,12 @@ freeGroup(bdescr *p)
 
   ASSERT(p->free != (P_)-1);
 
+#if defined(DEBUG)
+  for (uint32_t i=0; i < p->blocks; i++) {
+      p[i].flags = 0;
+  }
+#endif
+
   node = p->node;
 
   p->free = (void *)-1;  /* indicates that this block is free */