[Clang] Update 'counted_by' documentation
Describe a limitation of the 'counted_by' attribute when used in unions.
Also fix a errant typo.
diff --git a/clang/include/clang/Basic/AttrDocs.td b/clang/include/clang/Basic/AttrDocs.td
index 2e8d775..c025acd 100644
--- a/clang/include/clang/Basic/AttrDocs.td
+++ b/clang/include/clang/Basic/AttrDocs.td
@@ -7825,5 +7825,33 @@
--p->count;
p->array[index] = val;
}
+
+Flexible array members, with the ``counted_by`` attribute, in unions are
+supported with one limitation. If multiple flexible array members have the
+``counted_by`` attribute, ``__builtin_dynamic_object_size`` won't be able to
+calculate the object's size. For instance, in this example:
+
+.. code-block:: c
+
+ struct union_of_fams {
+ int flags;
+ union {
+ unsigned long normal_field;
+ struct {
+ int count1;
+ int arr1[] __counted_by(count1);
+ };
+ struct {
+ signed char count2;
+ int arr2[] __counted_by(count2);
+ };
+ };
+ };
+
+ size_t get_size(struct union_of_fams *p) {
+ return __builtin_dynamic_object_size(p, 1);
+ }
+
+a call to ``get_size`` will return ``-1``.
}];
}
diff --git a/clang/lib/CodeGen/CGBuiltin.cpp b/clang/lib/CodeGen/CGBuiltin.cpp
index 998fcc3..b5aee3e 100644
--- a/clang/lib/CodeGen/CGBuiltin.cpp
+++ b/clang/lib/CodeGen/CGBuiltin.cpp
@@ -955,7 +955,7 @@
// };
// };
//
- // We don't konw which 'count' to use in this scenario:
+ // We don't know which 'count' to use in this scenario:
//
// size_t get_size(struct union_of_fams *p) {
// return __builtin_dynamic_object_size(p, 1);
