samsung_sm8750/android_kernel_samsung_sm8750
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

kbuild: Add '-fno-builtin-wcslen'

Browse Source 
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: 9694844d7e [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>
This commit is contained in:
Nathan Chancellor
2025-04-07 16:22:12 -07:00
committed by Greg Kroah-Hartman
parent 8c8d0e8000
commit 9b1f50da60
1 changed files with 3 additions and 0 deletions
Download Patch File Download Diff File Expand all files Collapse all files

3
Makefile
View File

@@ -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)/=)