Commit d39a1d74 authored Feb 20, 2026 by Kees Cook

compiler_types: Disable __builtin_counted_by_ref for Clang

Unfortunately, there is a corner case of __builtin_counted_by_ref()
usage that crashes[1] Clang since support was introduced in Clang 19.
Disable it prior to Clang 22. Found while tested kmalloc_obj treewide
refactoring (via kmalloc_flex() usage).

Link: https://github.com/llvm/llvm-project/issues/182575

 [1]
Signed-off-by: Kees Cook <kees@kernel.org>

parent d79526b8

include/linux/compiler_types.h

+2 −1

Original line number	Diff line number	Diff line
		@@ -552,7 +552,8 @@ struct ftrace_likely_data {
		* gcc: https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html#index-_005f_005fbuiltin_005fcounted_005fby_005fref
		* clang: https://clang.llvm.org/docs/LanguageExtensions.html#builtin-counted-by-ref
		*/
		#if __has_builtin(__builtin_counted_by_ref)
		#if __has_builtin(__builtin_counted_by_ref) && \
		!defined(CONFIG_CC_HAS_BROKEN_COUNTED_BY_REF)
		/**
		* __flex_counter() - Get pointer to counter member for the given
		* flexible array, if it was annotated with __counted_by()

init/Kconfig

+5 −0

Original line number	Diff line number	Diff line
		@@ -150,6 +150,11 @@ config CC_HAS_COUNTED_BY_PTR
		# supported since gcc 16.0.0
		default y if CC_IS_GCC && GCC_VERSION >= 160000

		config CC_HAS_BROKEN_COUNTED_BY_REF
		bool
		# https://github.com/llvm/llvm-project/issues/182575
		default y if CC_IS_CLANG && CLANG_VERSION < 220000

		config CC_HAS_MULTIDIMENSIONAL_NONSTRING
		def_bool $(success,echo 'char tag[][4] __attribute__((__nonstring__)) = { };' \| $(CC) $(CLANG_FLAGS) -x c - -c -o /dev/null -Werror)