[clang] 4a3fb9c - [Clang] Update 'counted_by' documentation
Bill Wendling via cfe-commits
cfe-commits at lists.llvm.org
Wed Jan 10 15:40:46 PST 2024
Author: Bill Wendling
Date: 2024-01-10T15:36:33-08:00
New Revision: 4a3fb9ce27dda17e97341f28005a28836c909cfc
URL: https://github.com/llvm/llvm-project/commit/4a3fb9ce27dda17e97341f28005a28836c909cfc
DIFF: https://github.com/llvm/llvm-project/commit/4a3fb9ce27dda17e97341f28005a28836c909cfc.diff
LOG: [Clang] Update 'counted_by' documentation
Describe a limitation of the 'counted_by' attribute when used in unions.
Also fix a errant typo.
Added:
Modified:
clang/include/clang/Basic/AttrDocs.td
clang/lib/CodeGen/CGBuiltin.cpp
Removed:
################################################################################
diff --git a/clang/include/clang/Basic/AttrDocs.td b/clang/include/clang/Basic/AttrDocs.td
index 2e8d7752c9751e..c025acd3b106a3 100644
--- a/clang/include/clang/Basic/AttrDocs.td
+++ b/clang/include/clang/Basic/AttrDocs.td
@@ -7825,5 +7825,33 @@ requirement:
--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 998fcc3af58175..b5aee3eaa53c5d 100644
--- a/clang/lib/CodeGen/CGBuiltin.cpp
+++ b/clang/lib/CodeGen/CGBuiltin.cpp
@@ -955,7 +955,7 @@ CodeGenFunction::emitFlexibleArrayMemberSize(const Expr *E, unsigned Type,
// };
// };
//
- // 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);
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