On Wed, Mar 26, 2025 at 7:19 PM Nathan Chancellor nathan@kernel.org wrote:
A recent optimization change in LLVM [1] aims to transform certain loop idioms into calls to strlen() or wcslen(). This change transforms the first while loop in UniStrcat() into a call to wcslen(), breaking the build when UniStrcat() gets inlined into alloc_path_with_tree_prefix():
ld.lld: error: undefined symbol: wcslen
referenced by nls_ucs2_utils.h:54 (fs/smb/client/../../nls/nls_ucs2_utils.h:54) vmlinux.o:(alloc_path_with_tree_prefix) referenced by nls_ucs2_utils.h:54 (fs/smb/client/../../nls/nls_ucs2_utils.h:54) vmlinux.o:(alloc_path_with_tree_prefix)
The kernel does not build with '-ffreestanding' (which would avoid this transformation) because it does want libcall optimizations in general and turning on '-ffreestanding' disables the majority of them. While '-fno-builtin-wcslen' would be more targeted at the problem, it does not work with LTO.
Add a basic wcslen() to avoid this linkage failure. While no architecture or FORTIFY_SOURCE overrides this, add it to string.c instead of string_helpers.c so that it is built with '-ffreestanding', otherwise the compiler might transform it into a call to itself.
...
--- a/include/linux/string.h +++ b/include/linux/string.h @@ -7,6 +7,7 @@ #include <linux/cleanup.h> /* for DEFINE_FREE() */ #include <linux/compiler.h> /* for inline */ #include <linux/types.h> /* for size_t */
+#include <linux/nls_types.h> /* for wchar_t */
I know it's not ordered, but can we at least not make it worse, i.e. squeeze this to be after the compiler.h? Or even somewhere after below the err*.h? Whatever gives a better (sparsely) ordered overall result...
#include <linux/stddef.h> /* for NULL */ #include <linux/err.h> /* for ERR_PTR() */
...
#ifndef __HAVE_ARCH_STRNLEN extern __kernel_size_t strnlen(const char *,__kernel_size_t); #endif +extern __kernel_size_t wcslen(const wchar_t *s);
I'm wondering why we still continue putting this 'extern' keyword. Yes, I see that the rest is like this, but for new code do we really need it?
#ifndef __HAVE_ARCH_STRPBRK extern char * strpbrk(const char *,const char *); #endif