From bc78bacca3f3f9f7367afc6dbf56a4733f47e3f6 Mon Sep 17 00:00:00 2001 From: Nathan Chancellor Date: Mon, 7 Apr 2025 16:22:12 -0700 Subject: [PATCH 5.15] kbuild: Add '-fno-builtin-wcslen' commit 84ffc79bfbf70c779e60218563f2f3ad45288671 upstream. 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) Disable this optimization with '-fno-builtin-wcslen', which prevents the compiler from assuming that wcslen() is available in the kernel's C library. [ More to the point - it's not that we couldn't implement wcslen(), it's that this isn't an optimization at all in the context of the kernel. Replacing a simple inlined loop with a function call to the same loop is just stupid and pointless if you don't have long strings and fancy libraries with vectorization support etc. For the regular 'strlen()' cases, we want the compiler to do this in order to handle the trivial case of constant strings. And we do have optimized versions of 'strlen()' on some architectures. But for wcslen? Just no. - Linus ] Cc: stable@vger.kernel.org Link: https://github.com/llvm/llvm-project/commit/9694844d7e36fd5e01011ab56b64f27b867aa72d [1] Signed-off-by: Nathan Chancellor Signed-off-by: Linus Torvalds [nathan: Resolve small conflict in older trees] Signed-off-by: Nathan Chancellor --- Makefile | 3 +++ 1 file changed, 3 insertions(+) diff --git a/Makefile b/Makefile index 619f4ec0f613..035578b9fafc 100644 --- a/Makefile +++ b/Makefile @@ -1066,6 +1066,9 @@ KBUILD_CFLAGS += $(call cc-option,-Werror=incompatible-pointer-types) # Require designated initializers for all marked structures KBUILD_CFLAGS += $(call cc-option,-Werror=designated-init) +# Ensure compilers do not transform certain loops into calls to wcslen() +KBUILD_CFLAGS += -fno-builtin-wcslen + # change __FILE__ to the relative path from the srctree KBUILD_CPPFLAGS += $(call cc-option,-fmacro-prefix-map=$(srctree)/=) base-commit: f7347f4005727f3155551c0550f4deb9c40b56c2 -- 2.49.0