Fix ro segments with regions (dotnet#58811)

There were a couple places in the mark and relocation phases where the regions logic couldn't cope with objects outside of the memory range reserved for the GC heap. These objects may occur in read-only segments (but only if FEATURE_BASICFREEZE is enabled).

The check for objects within the address range reserved for the GC is centralized in helper is_in_heap_range. If FEATURE_BASICFREEZE is enabled, this helper checks that the object is actually in the address range for the heap, otherwise a simple check for non-null is sufficient. There are asserts to make sure that objects are either null, in range, or in a read-only segment if FEATURE_BASICFREEZE is enabled.

src/coreclr/gc/gc.cpp

@@ -22286,13 +22286,31 @@ BOOL gc_heap::gc_mark1 (uint8_t* o)
     return marked;
 }
 
+#ifdef USE_REGIONS
+inline bool is_in_heap_range (uint8_t* o)
+{
+#ifdef FEATURE_BASICFREEZE
+    // we may have frozen objects in read only segments
+    // outside of the reserved address range of the gc heap
+    assert (((g_gc_lowest_address <= o) && (o < g_gc_highest_address)) ||
+        (o == nullptr) || (ro_segment_lookup (o) != nullptr));
+    return ((g_gc_lowest_address <= o) && (o < g_gc_highest_address));
+#else //FEATURE_BASICFREEZE
+    // without frozen objects, every non-null pointer must be
+    // within the heap
+    assert ((o == nullptr) || (g_gc_lowest_address <= o) && (o < g_gc_highest_address));
+    return (o != nullptr);
+#endif //FEATURE_BASICFREEZE
+}
+#endif //USE_REGIONS
+
 inline
 BOOL gc_heap::gc_mark (uint8_t* o, uint8_t* low, uint8_t* high, int condemned_gen)
 {
 #ifdef USE_REGIONS
     assert (low == 0);
     assert (high == 0);
-    if (o)
+    if (is_in_heap_range (o))
     {
         BOOL already_marked = marked (o);
         if (already_marked)
@@ -23318,7 +23336,7 @@ inline
 void gc_heap::mark_object (uint8_t* o THREAD_NUMBER_DCL)
 {
 #ifdef USE_REGIONS
-    if ((o != nullptr) && is_in_condemned_gc (o))
+    if (is_in_heap_range (o) && is_in_condemned_gc (o))
     {
         mark_object_simple (&o THREAD_NUMBER_ARG);
     }
@@ -30499,7 +30517,7 @@ void gc_heap::relocate_address (uint8_t** pold_address THREAD_NUMBER_DCL)
 {
     uint8_t* old_address = *pold_address;
 #ifdef USE_REGIONS
-    if (!old_address || !should_check_brick_for_reloc (old_address))
+    if (!is_in_heap_range (old_address) || !should_check_brick_for_reloc (old_address))
     {
         return;
     }
@@ -30639,7 +30657,8 @@ gc_heap::check_demotion_helper (uint8_t** pval, uint8_t* parent_obj)
 {
 #ifdef USE_REGIONS
     uint8_t* child_object = *pval;
-    if (!child_object) return;
+    if (!is_in_heap_range (child_object))
+        return;
     int child_object_plan_gen = get_region_plan_gen_num (child_object);
     bool child_obj_demoted_p = is_region_demoted (child_object);
 
@@ -35875,7 +35894,8 @@ gc_heap::mark_through_cards_helper (uint8_t** poo, size_t& n_gen,
     assert (nhigh == 0);
     assert (next_boundary == 0);
     uint8_t* child_object = *poo;
-    if (!child_object) return;
+    if (!is_in_heap_range (child_object))
+        return;
     int child_object_gen = get_region_gen_num (child_object);
     int saved_child_object_gen = child_object_gen;
     uint8_t* saved_child_object = child_object;
@@ -43182,7 +43202,7 @@ bool GCHeap::IsPromoted(Object* object)
     else
     {
 #ifdef USE_REGIONS
-        return (o ? (gc_heap::is_in_condemned_gc (o) ? gc_heap::is_mark_set (o) : true) : true);
+        return (is_in_heap_range (o) ? (gc_heap::is_in_condemned_gc (o) ? gc_heap::is_mark_set (o) : true) : true);
 #else
         gc_heap* hp = gc_heap::heap_of (o);
         return (!((o < hp->gc_high) && (o >= hp->gc_low))