7d0a463c0d
See https://postmarketos.org/edge/2025/11/11/kernels-llvm/ for the background behind this change and how we're handling these MRs. [ci:skip-kconfigcheck]: bulk toolchain change Part-of: <https://gitlab.postmarketos.org/postmarketOS/pmaports/-/merge_requests/8033>
54 lines
2.3 KiB
Diff
54 lines
2.3 KiB
Diff
From 84ffc79bfbf70c779e60218563f2f3ad45288671 Mon Sep 17 00:00:00 2001
|
|
From: Nathan Chancellor <nathan@kernel.org>
|
|
Date: Mon, 7 Apr 2025 16:22:12 -0700
|
|
Subject: [PATCH] kbuild: Add '-fno-builtin-wcslen'
|
|
|
|
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 <nathan@kernel.org>
|
|
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
|
|
---
|
|
Makefile | 3 +++
|
|
1 file changed, 3 insertions(+)
|
|
|
|
diff --git a/Makefile b/Makefile
|
|
index 38689a0c36052b..f4241855650711 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)/=)
|