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

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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)

Disable this optimization with '-fno-builtin-wcslen', which prevents the compiler from assuming that wcslen() is available in the kernel's C library

Cc: stable@vger.kernel.org Link: https://github.com/llvm/llvm-project/commit/9694844d7e36fd5e01011ab56b64f27b... [1] Signed-off-by: Nathan Chancellor nathan@kernel.org --- Makefile | 3 +++ 1 file changed, 3 insertions(+)

diff --git a/Makefile b/Makefile index 38689a0c3605..f42418556507 100644 --- a/Makefile +++ b/Makefile @@ -1068,6 +1068,9 @@ ifdef CONFIG_CC_IS_GCC KBUILD_CFLAGS += -fconserve-stack endif

+# Ensure compilers do not transform certain loops into calls to wcslen() +KBUILD_CFLAGS += -fno-builtin-wcslen + # change __FILE__ to the relative path to the source directory ifdef building_out_of_srctree KBUILD_CPPFLAGS += $(call cc-option,-ffile-prefix-map=$(srcroot)/=)

--- base-commit: 0af2f6be1b4281385b618cb86ad946eded089ac8 change-id: 20250407-fno-builtin-wcslen-90a858ae7d54

Best regards,