diff --git a/gcc/testsuite/gcc.dg/builtin-object-size-common.h b/gcc/testsuite/gcc.dg/builtin-object-size-common.h
index 66ff7cdd953a..b677067c6e6b 100644
--- a/gcc/testsuite/gcc.dg/builtin-object-size-common.h
+++ b/gcc/testsuite/gcc.dg/builtin-object-size-common.h
@@ -30,3 +30,14 @@ unsigned nfails = 0;
       __builtin_abort ();						      \
     return 0;								      \
   } while (0)
+
+#define EXPECT(p, _v) do {						      \
+  size_t v = _v;							      \
+  if (p == v)								      \
+    __builtin_printf ("ok:  %s == %zd\n", #p, p);			      \
+  else									      \
+    {									      \
+      __builtin_printf ("WAT: %s == %zd (expected %zd)\n", #p, p, v);	      \
+      FAIL ();								      \
+    }									      \
+} while (0);
diff --git a/gcc/testsuite/gcc.dg/flex-array-counted-by-3.c b/gcc/testsuite/gcc.dg/flex-array-counted-by-3.c
new file mode 100644
index 000000000000..0066c32ca808
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/flex-array-counted-by-3.c
@@ -0,0 +1,63 @@
+/* test the attribute counted_by and its usage in
+ * __builtin_dynamic_object_size.  */ 
+/* { dg-do run } */
+/* { dg-options "-O2" } */
+
+#include "builtin-object-size-common.h"
+
+struct flex {
+  int b;
+  int c[];
+} *array_flex;
+
+struct annotated {
+  int b;
+  int c[] __attribute__ ((counted_by (b)));
+} *array_annotated;
+
+struct nested_annotated {
+  struct {
+    union {
+      int b;
+      float f;	
+    };
+    int n;
+  };
+  int c[] __attribute__ ((counted_by (b)));
+} *array_nested_annotated;
+
+void __attribute__((__noinline__)) setup (int normal_count, int attr_count)
+{
+  array_flex
+    = (struct flex *)malloc (sizeof (struct flex)
+			     + normal_count *  sizeof (int));
+  array_flex->b = normal_count;
+
+  array_annotated
+    = (struct annotated *)malloc (sizeof (struct annotated)
+				  + attr_count *  sizeof (int));
+  array_annotated->b = attr_count;
+
+  array_nested_annotated
+    = (struct nested_annotated *)malloc (sizeof (struct nested_annotated)
+					 + attr_count *  sizeof (int));
+  array_nested_annotated->b = attr_count;
+
+  return;
+}
+
+void __attribute__((__noinline__)) test ()
+{
+    EXPECT(__builtin_dynamic_object_size(array_flex->c, 1), -1);
+    EXPECT(__builtin_dynamic_object_size(array_annotated->c, 1),
+	   array_annotated->b * sizeof (int));
+    EXPECT(__builtin_dynamic_object_size(array_nested_annotated->c, 1),
+	   array_nested_annotated->b * sizeof (int));
+}
+
+int main(int argc, char *argv[])
+{
+  setup (10,10);   
+  test ();
+  DONE ();
+}
diff --git a/gcc/testsuite/gcc.dg/flex-array-counted-by-4.c b/gcc/testsuite/gcc.dg/flex-array-counted-by-4.c
new file mode 100644
index 000000000000..3ce7f3545549
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/flex-array-counted-by-4.c
@@ -0,0 +1,178 @@
+/* test the attribute counted_by and its usage in
+__builtin_dynamic_object_size: what's the correct behavior when the
+allocation size mismatched with the value of counted_by attribute?
+we should always use the latest value that is hold by the counted_by
+field.  */
+/* { dg-do run } */
+/* { dg-options "-O -fstrict-flex-arrays=3" } */
+
+#include "builtin-object-size-common.h"
+
+struct annotated {
+  size_t foo;
+  char others;
+  char array[] __attribute__((counted_by (foo)));
+};
+
+#define noinline __attribute__((__noinline__))
+#define SIZE_BUMP 10 
+#define MAX(a, b) ((a) > (b) ? (a) : (b))
+
+/* In general, Due to type casting, the type for the pointee of a pointer
+   does not say anything about the object it points to,
+   So, __builtin_object_size can not directly use the type of the pointee
+   to decide the size of the object the pointer points to.
+
+   there are only two reliable ways:
+   A. observed allocations  (call to the allocation functions in the routine)
+   B. observed accesses     (read or write access to the location of the
+                             pointer points to)
+
+   that provide information about the type/existence of an object at
+   the corresponding address.
+
+   for A, we use the "alloc_size" attribute for the corresponding allocation
+   functions to determine the object size;
+   (We treat counted_by attribute the same as the "alloc_size" attribute)
+
+   For B, we use the SIZE info of the TYPE attached to the corresponding access.
+
+   The only other way in C which ensures that a pointer actually points
+   to an object of the correct type is 'static':
+
+   void foo(struct P *p[static 1]);
+
+   See https://gcc.gnu.org/pipermail/gcc-patches/2023-July/624814.html
+   for more details.  */
+
+/* in the following function, malloc allocated more space than the value
+   of counted_by attribute.  Then what's the correct behavior we expect 
+   the __builtin_dynamic_object_size should have for each of the cases?  */
+
+static struct annotated * noinline alloc_buf_more (size_t index)
+{
+  struct annotated *p;
+  size_t allocated_size
+    = MAX (sizeof (struct annotated),
+	   (__builtin_offsetof (struct annotated, array[0])
+	    + (index + SIZE_BUMP) * sizeof (char)));
+  p = (struct annotated *) malloc (allocated_size);
+
+  p->foo = index;
+
+  /*when checking the observed access p->array, we have info on both
+    observered allocation and observed access,
+    A.1 from observed allocation: 
+    	allocated_size - offsetof (struct annotated, array[0])
+
+    A.2 from the counted-by attribute:
+    	p->foo * sizeof (char)
+
+    we always use the latest value that is hold by the counted-by field.
+   */
+
+  EXPECT(__builtin_dynamic_object_size(p->array, 0),
+	 (p->foo) * sizeof(char));
+
+  EXPECT(__builtin_dynamic_object_size(p->array, 1),
+	 (p->foo) * sizeof(char));
+
+  EXPECT(__builtin_dynamic_object_size(p->array, 2),
+	 (p->foo) * sizeof(char));
+
+  EXPECT(__builtin_dynamic_object_size(p->array, 3),
+	 (p->foo) * sizeof(char));
+
+  /*when checking the pointer p, we only have info on the observed allocation.
+    So, the object size info can only been obtained from the call to malloc.
+    for both MAXIMUM and MINIMUM: A = (index + SIZE_BUMP) * sizeof (char)  */
+  EXPECT(__builtin_dynamic_object_size(p, 0), allocated_size);
+  EXPECT(__builtin_dynamic_object_size(p, 1), allocated_size);
+  EXPECT(__builtin_dynamic_object_size(p, 2), allocated_size);
+  EXPECT(__builtin_dynamic_object_size(p, 3), allocated_size);
+  return p;
+}
+
+/* in the following function, malloc allocated less space than the value
+   of counted_by attribute.  Then what's the correct behavior we expect 
+   the __builtin_dynamic_object_size should have for each of the cases?
+   NOTE: this is an user error, GCC should issue warnings for such case.
+   this is a seperate issue we should address later.  */
+
+static struct annotated * noinline alloc_buf_less (size_t index)
+{
+  struct annotated *p;
+  size_t allocated_size
+    = MAX (sizeof (struct annotated),
+	   (__builtin_offsetof (struct annotated, array[0])
+	    + (index) * sizeof (char)));
+  p = (struct annotated *) malloc (allocated_size);
+
+  p->foo = index + SIZE_BUMP;
+
+  /*when checking the observed access p->array, we have info on both
+    observered allocation and observed access,
+    A.1 from observed allocation:
+    	allocated_size - offsetof (struct annotated, array[0])
+    A.2 from the counted-by attribute:
+    	p->foo * sizeof (char)
+
+    we always use the latest value that is hold by the counted-by field.
+   */
+
+  EXPECT(__builtin_dynamic_object_size(p->array, 0),
+	 (p->foo) * sizeof(char));
+
+  EXPECT(__builtin_dynamic_object_size(p->array, 1),
+	 (p->foo) * sizeof(char));
+
+  EXPECT(__builtin_dynamic_object_size(p->array, 2),
+	 (p->foo) * sizeof(char));
+
+  EXPECT(__builtin_dynamic_object_size(p->array, 3),
+	 (p->foo) * sizeof(char));
+
+  /*when checking the pointer p, we only have info on the observed
+    allocation. So, the object size info can only been obtained from
+    the call to malloc.  */
+  EXPECT(__builtin_dynamic_object_size(p, 0), allocated_size);
+  EXPECT(__builtin_dynamic_object_size(p, 1), allocated_size);
+  EXPECT(__builtin_dynamic_object_size(p, 2), allocated_size);
+  EXPECT(__builtin_dynamic_object_size(p, 3), allocated_size);
+  return p;
+}
+
+int main ()
+{
+  struct annotated *p, *q;
+  p = alloc_buf_more (10);
+  q = alloc_buf_less (10);
+
+  /*when checking the access p->array, we only have info on the counted-by
+    value.  */ 
+  EXPECT(__builtin_dynamic_object_size(p->array, 0), p->foo * sizeof(char));
+  EXPECT(__builtin_dynamic_object_size(p->array, 1), p->foo * sizeof(char));
+  EXPECT(__builtin_dynamic_object_size(p->array, 2), p->foo * sizeof(char));
+  EXPECT(__builtin_dynamic_object_size(p->array, 3), p->foo * sizeof(char));
+  /*when checking the pointer p, we have no observed allocation nor observed
+    access, therefore, we cannot determine the size info here.  */
+  EXPECT(__builtin_dynamic_object_size(p, 0), -1);
+  EXPECT(__builtin_dynamic_object_size(p, 1), -1);
+  EXPECT(__builtin_dynamic_object_size(p, 2), 0);
+  EXPECT(__builtin_dynamic_object_size(p, 3), 0);
+
+  /*when checking the access p->array, we only have info on the counted-by
+    value.  */ 
+  EXPECT(__builtin_dynamic_object_size(q->array, 0), q->foo * sizeof(char));
+  EXPECT(__builtin_dynamic_object_size(q->array, 1), q->foo * sizeof(char));
+  EXPECT(__builtin_dynamic_object_size(q->array, 2), q->foo * sizeof(char));
+  EXPECT(__builtin_dynamic_object_size(q->array, 3), q->foo * sizeof(char));
+  /*when checking the pointer p, we have no observed allocation nor observed
+    access, therefore, we cannot determine the size info here.  */
+  EXPECT(__builtin_dynamic_object_size(q, 0), -1);
+  EXPECT(__builtin_dynamic_object_size(q, 1), -1);
+  EXPECT(__builtin_dynamic_object_size(q, 2), 0);
+  EXPECT(__builtin_dynamic_object_size(q, 3), 0);
+
+  DONE ();
+}
diff --git a/gcc/tree-object-size.cc b/gcc/tree-object-size.cc
index 018fbc30cbb6..74d778f71eed 100644
--- a/gcc/tree-object-size.cc
+++ b/gcc/tree-object-size.cc
@@ -60,6 +60,7 @@ static tree compute_object_offset (tree, const_tree);
 static bool addr_object_size (struct object_size_info *,
 			      const_tree, int, tree *, tree *t = NULL);
 static tree alloc_object_size (const gcall *, int);
+static tree access_with_size_object_size (const gcall *, int);
 static tree pass_through_call (const gcall *);
 static void collect_object_sizes_for (struct object_size_info *, tree);
 static void expr_object_size (struct object_size_info *, tree, tree);
@@ -749,6 +750,48 @@ addr_object_size (struct object_size_info *osi, const_tree ptr,
   return false;
 }
 
+/* Compute __builtin_object_size for a CALL to .ACCESS_WITH_SIZE,
+   OBJECT_SIZE_TYPE is the second argument from __builtin_object_size.
+   the 2nd, 3rd, and the 4th parameters of the call determine the size of
+   the CALL:
+
+   2nd argument REF_TO_SIZE: The reference to the size of the object,
+   3rd argument TYPE_OF_SIZE: The size referenced by the REF_TO_SIZE represents
+     0: unknown;
+     1: the number of the elements of the object type;
+     2: the number of bytes;
+   4th argument PREC_OF_SIZE: The precision of the object refed by REF_TO_SIZE
+
+   the size of the element can be retrived from the result type of the call,
+   which is the pointer to the type of element.  */
+static tree
+access_with_size_object_size (const gcall *call, int object_size_type)
+{
+  gcc_assert (gimple_call_internal_p (call, IFN_ACCESS_WITH_SIZE));
+  tree result_type = gimple_call_return_type (call);
+  gcc_assert (POINTER_TYPE_P (result_type));
+  tree element_size = TYPE_SIZE_UNIT (TREE_TYPE (result_type));
+  tree ref_to_size = gimple_call_arg (call, 1);
+  unsigned int type_of_size = TREE_INT_CST_LOW (gimple_call_arg (call, 2));
+  unsigned int prec_of_size = TREE_INT_CST_LOW (gimple_call_arg (call, 3));
+  tree type = build_nonstandard_integer_type (prec_of_size, 1);
+  tree size = fold_build2 (MEM_REF, type, ref_to_size,
+			   build_int_cst (ptr_type_node, 0));
+
+  if (type_of_size == 0)
+    return size_unknown (object_size_type);
+  else if (type_of_size == 1)
+    size = size_binop (MULT_EXPR,
+		       fold_convert (sizetype, size),
+		       fold_convert (sizetype, element_size));
+  else
+    size = fold_convert (sizetype, size);
+
+  if (!todo)
+    todo = TODO_update_ssa_only_virtuals;
+
+  return size;
+}
 
 /* Compute __builtin_object_size for CALL, which is a GIMPLE_CALL.
    Handles calls to functions declared with attribute alloc_size.
@@ -1350,8 +1393,12 @@ call_object_size (struct object_size_info *osi, tree ptr, gcall *call)
 
   bool is_strdup = gimple_call_builtin_p (call, BUILT_IN_STRDUP);
   bool is_strndup = gimple_call_builtin_p (call, BUILT_IN_STRNDUP);
+  bool is_access_with_size
+	 = gimple_call_internal_p (call, IFN_ACCESS_WITH_SIZE);
   if (is_strdup || is_strndup)
     bytes = strdup_object_size (call, object_size_type, is_strndup);
+  else if (is_access_with_size)
+    bytes = access_with_size_object_size (call, object_size_type);
   else
     bytes = alloc_object_size (call, object_size_type);
 
