ggc: do not wipe out unrelated data via gt_ggc_rtab [PR111505]

There are 3 GC root tables:

   gt_ggc_rtab
   gt_ggc_deletable_rtab
   gt_pch_scalar_rtab

`deletable` and `scalar` tables are both simple: each element always
contains a pointer to the beginning of the object and it's size is the
full object.

`rtab` is different: it's `base` is a pointer in the middle of the
struct and `stride` points to the next GC pointer in the array.

Before the change there were 2 problems:

1. We memset()ed not just pointers but data around them.
2. We wen out of bounds of the last object described by gt_ggc_rtab
   and triggered bootstrap failures in profile and asan bootstraps.

After the change we handle only pointers themselves like the rest of
ggc-common.cc code.

gcc/
	PR middle-end/111505
	* ggc-common.cc (ggc_zero_out_root_pointers, ggc_common_finalize):
	Add new helper. Use helper instead of memset() to wipe out pointers.

diff --git a/gcc/ggc-common.cc b/gcc/ggc-common.cc
index 95803fa95a17c2202d432411719355fae37619c1..39e2581affde8bb497c95aadddbaeb2648cbe7a8 100644 (file)
--- a/gcc/ggc-common.cc
+++ b/gcc/ggc-common.cc
@@ -75,6 +75,18 @@ ggc_mark_root_tab (const_ggc_root_tab_t rt)
       (*rt->cb) (*(void **) ((char *)rt->base + rt->stride * i));
 }
 
+/* Zero out all the roots in the table RT.  */
+
+static void
+ggc_zero_rtab_roots (const_ggc_root_tab_t rt)
+{
+  size_t i;
+
+  for ( ; rt->base != NULL; rt++)
+    for (i = 0; i < rt->nelt; i++)
+      (*(void **) ((char *)rt->base + rt->stride * i)) = (void*)0;
+}
+
 /* Iterate through all registered roots and mark each element.  */
 
 void
@@ -1307,8 +1319,7 @@ ggc_common_finalize ()
       memset (rti->base, 0, rti->stride * rti->nelt);
 
   for (rt = gt_ggc_rtab; *rt; rt++)
-    for (rti = *rt; rti->base != NULL; rti++)
-      memset (rti->base, 0, rti->stride * rti->nelt);
+    ggc_zero_rtab_roots (*rt);
 
   for (rt = gt_pch_scalar_rtab; *rt; rt++)
     for (rti = *rt; rti->base != NULL; rti++)