Merge llvm-project main llvmorg-18-init-16864-g3b3ee1f53424

This updates llvm, clang, compiler-rt, libc++, libunwind, lld, lldb and
openmp to llvm-project main llvmorg-18-init-16864-g3b3ee1f53424.

PR:		276104
MFC after:	1 month

(cherry picked from commit 297eecfb02bb25902531dbb5c3b9a88caf8adf29)

1 files changed, 78 insertions, 0 deletions

diff --git a/contrib/llvm-project/clang/include/clang/Basic/AttrDocs.td b/contrib/llvm-project/clang/include/clang/Basic/AttrDocs.td
index 5416a0cbdd07..2e8d7752c975 100644
--- a/contrib/llvm-project/clang/include/clang/Basic/AttrDocs.td
+++ b/contrib/llvm-project/clang/include/clang/Basic/AttrDocs.td
@@ -7749,3 +7749,81 @@ but do not pass them to the underlying coroutine or pass them by value.
 .. _`CRT`: https://clang.llvm.org/docs/AttributeReference.html#coro-return-type
 }];
 }
+
+def CountedByDocs : Documentation {
+  let Category = DocCatField;
+  let Content = [{
+Clang supports the ``counted_by`` attribute on the flexible array member of a
+structure in C. The argument for the attribute is the name of a field member
+holding the count of elements in the flexible array. This information can be
+used to improve the results of the array bound sanitizer and the
+``__builtin_dynamic_object_size`` builtin. The ``count`` field member must be
+within the same non-anonymous, enclosing struct as the flexible array member.
+
+This example specifies that the flexible array member ``array`` has the number
+of elements allocated for it in ``count``:
+
+.. code-block:: c
+
+  struct bar;
+
+  struct foo {
+    size_t count;
+    char other;
+    struct bar *array[] __attribute__((counted_by(count)));
+  };
+
+This establishes a relationship between ``array`` and ``count``. Specifically,
+``array`` must have at least ``count`` number of elements available. It's the
+user's responsibility to ensure that this relationship is maintained through
+changes to the structure.
+
+In the following example, the allocated array erroneously has fewer elements
+than what's specified by ``p->count``. This would result in an out-of-bounds
+access not being detected.
+
+.. code-block:: c
+
+  #define SIZE_INCR 42
+
+  struct foo *p;
+
+  void foo_alloc(size_t count) {
+    p = malloc(MAX(sizeof(struct foo),
+                   offsetof(struct foo, array[0]) + count * sizeof(struct bar *)));
+    p->count = count + SIZE_INCR;
+  }
+
+The next example updates ``p->count``, but breaks the relationship requirement
+that ``p->array`` must have at least ``p->count`` number of elements available:
+
+.. code-block:: c
+
+  #define SIZE_INCR 42
+
+  struct foo *p;
+
+  void foo_alloc(size_t count) {
+    p = malloc(MAX(sizeof(struct foo),
+                   offsetof(struct foo, array[0]) + count * sizeof(struct bar *)));
+    p->count = count;
+  }
+
+  void use_foo(int index, int val) {
+    p->count += SIZE_INCR + 1; /* 'count' is now larger than the number of elements of 'array'. */
+    p->array[index] = val;     /* The sanitizer can't properly check this access. */
+  }
+
+In this example, an update to ``p->count`` maintains the relationship
+requirement:
+
+.. code-block:: c
+
+  void use_foo(int index, int val) {
+    if (p->count == 0)
+      return;
+    --p->count;
+    p->array[index] = val;
+  }
+  }];
+}