linux-kernel - [PATCH] kbuild: Properly disable -Wunterminated-string-initialization for clang

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [thread-next>] [day] [month] [year] [list]
Message-Id: <20250430-unterminated-string-init-clang-v1-1-10eab729bf3d@kernel.org>
Date: Wed, 30 Apr 2025 15:56:34 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>, 
 Masahiro Yamada <masahiroy@...nel.org>, 
 Nicolas Schier <nicolas.schier@...ux.dev>
Cc: linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org, 
 llvm@...ts.linux.dev, Nathan Chancellor <nathan@...nel.org>
Subject: [PATCH] kbuild: Properly disable
 -Wunterminated-string-initialization for clang

Clang and GCC have different behaviors around disabling warnings
included in -Wall and -Wextra and the order in which flags are
specified, which is exposed by clang's new support for
-Wunterminated-string-initialization.

  $ cat test.c
  const char foo[3] = "FOO";
  const char bar[3] __attribute__((__nonstring__)) = "BAR";

  $ clang -fsyntax-only -Wextra test.c
  test.c:1:21: warning: initializer-string for character array is too long, array size is 3 but initializer has size 4 (including the null terminating character); did you mean to use the 'nonstring' attribute? [-Wunterminated-string-initialization]
      1 | const char foo[3] = "FOO";
        |                     ^~~~~
  $ clang -fsyntax-only -Wextra -Wno-unterminated-string-initialization test.c
  $ clang -fsyntax-only -Wno-unterminated-string-initialization -Wextra test.c
  test.c:1:21: warning: initializer-string for character array is too long, array size is 3 but initializer has size 4 (including the null terminating character); did you mean to use the 'nonstring' attribute? [-Wunterminated-string-initialization]
      1 | const char foo[3] = "FOO";
        |                     ^~~~~

  $ gcc -fsyntax-only -Wextra test.c
  test.c:1:21: warning: initializer-string for array of ‘char’ truncates NUL terminator but destination lacks ‘nonstring’ attribute (4 chars into 3 available) [-Wunterminated-string-initialization]
      1 | const char foo[3] = "FOO";
        |                     ^~~~~
  $ gcc -fsyntax-only -Wextra -Wno-unterminated-string-initialization test.c
  $ gcc -fsyntax-only -Wno-unterminated-string-initialization -Wextra test.c

Move -Wextra up right below -Wall in Makefile.extrawarn to ensure these
flags are at the beginning of the warning options list. Move the couple
of warning options that have been added to the main Makefile since
commit e88ca24319e4 ("kbuild: consolidate warning flags in
scripts/Makefile.extrawarn") to scripts/Makefile.extrawarn after -Wall /
-Wextra to ensure they get properly disabled for all compilers.

Fixes: 9d7a0577c9db ("gcc-15: disable '-Wunterminated-string-initialization' entirely for now")
Link: https://github.com/llvm/llvm-project/issues/10359
Signed-off-by: Nathan Chancellor <nathan@...nel.org>
---
I am sending this to Linus since he added
-Wno-unterminated-string-initialization so it seems reasonable to take a
fix for it but if it should just go via Masahiro's kbuild tree, that's
fine as well.
---
 Makefile                   | 7 -------
 scripts/Makefile.extrawarn | 9 ++++++++-
 2 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/Makefile b/Makefile
index 5aa9ee52a765..94be5dfb81fb 100644
--- a/Makefile
+++ b/Makefile
@@ -1052,13 +1052,6 @@ NOSTDINC_FLAGS += -nostdinc
 # perform bounds checking.
 KBUILD_CFLAGS += $(call cc-option, -fstrict-flex-arrays=3)
 
-#Currently, disable -Wstringop-overflow for GCC 11, globally.
-KBUILD_CFLAGS-$(CONFIG_CC_NO_STRINGOP_OVERFLOW) += $(call cc-disable-warning, stringop-overflow)
-KBUILD_CFLAGS-$(CONFIG_CC_STRINGOP_OVERFLOW) += $(call cc-option, -Wstringop-overflow)
-
-#Currently, disable -Wunterminated-string-initialization as broken
-KBUILD_CFLAGS += $(call cc-disable-warning, unterminated-string-initialization)
-
 # disable invalid "can't wrap" optimizations for signed / pointers
 KBUILD_CFLAGS	+= -fno-strict-overflow
 
diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn
index 2d6e59561c9d..d88acdf40855 100644
--- a/scripts/Makefile.extrawarn
+++ b/scripts/Makefile.extrawarn
@@ -8,6 +8,7 @@
 
 # Default set of warnings, always enabled
 KBUILD_CFLAGS += -Wall
+KBUILD_CFLAGS += -Wextra
 KBUILD_CFLAGS += -Wundef
 KBUILD_CFLAGS += -Werror=implicit-function-declaration
 KBUILD_CFLAGS += -Werror=implicit-int
@@ -56,6 +57,13 @@ KBUILD_CFLAGS += -Wno-pointer-sign
 # globally built with -Wcast-function-type.
 KBUILD_CFLAGS += $(call cc-option, -Wcast-function-type)
 
+# Currently, disable -Wstringop-overflow for GCC 11, globally.
+KBUILD_CFLAGS-$(CONFIG_CC_NO_STRINGOP_OVERFLOW) += $(call cc-disable-warning, stringop-overflow)
+KBUILD_CFLAGS-$(CONFIG_CC_STRINGOP_OVERFLOW) += $(call cc-option, -Wstringop-overflow)
+
+# Currently, disable -Wunterminated-string-initialization as broken
+KBUILD_CFLAGS += $(call cc-disable-warning, unterminated-string-initialization)
+
 # The allocators already balk at large sizes, so silence the compiler
 # warnings for bounds checks involving those possible values. While
 # -Wno-alloc-size-larger-than would normally be used here, earlier versions
@@ -82,7 +90,6 @@ KBUILD_CFLAGS += $(call cc-option,-Werror=designated-init)
 # Warn if there is an enum types mismatch
 KBUILD_CFLAGS += $(call cc-option,-Wenum-conversion)
 
-KBUILD_CFLAGS += -Wextra
 KBUILD_CFLAGS += -Wunused
 
 #

---
base-commit: b4432656b36e5cc1d50a1f2dc15357543add530e
change-id: 20250430-unterminated-string-init-clang-89f5ee3e969e

Best regards,
-- 
Nathan Chancellor <nathan@...nel.org>