6.6-stable review patch. If anyone has any objections, please let me know.
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From: Nathan Chancellor nathan@kernel.org
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/9694844d7e36fd5e01011ab56b64f27b... [1] Signed-off-by: Nathan Chancellor nathan@kernel.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org [nathan: Resolve small conflict in older trees] Signed-off-by: Nathan Chancellor nathan@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- Makefile | 3 +++ 1 file changed, 3 insertions(+)
--- a/Makefile +++ b/Makefile @@ -1004,6 +1004,9 @@ 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 from the srctree KBUILD_CPPFLAGS += $(call cc-option,-fmacro-prefix-map=$(srctree)/=)