Subject: [PATCH 6.12 4/4] kbuild: Properly disable -Wunterminated-string-initialization for clang

From: Nathan Chancellor <[email-masked]>
Date: Wed, 30 Apr 2025 15:56:34 -0700

commit 4f79eaa2ceac86a0e0f304b0bab556cca5bf4f30 upstream.

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 <[email-masked]>
Signed-off-by: Linus Torvalds <[email-masked]>
Signed-off-by: Nathan Chancellor <[email-masked]>
---
 Makefile                   | 7 -------
 scripts/Makefile.extrawarn | 9 ++++++++-
 2 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/Makefile b/Makefile
index 7f4436415bf4..551d7556e88a 100644
--- a/Makefile
+++ b/Makefile
@@ -997,13 +997,6 @@ 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 32dcf9eb4fa8..5652d9035232 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
@@ -68,6 +69,13 @@ 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
@@ -97,7 +105,6 @@ KBUILD_CFLAGS += $(call cc-option,-Wenum-conversion)
 # Explicitly clear padding bits during variable initialization
 KBUILD_CFLAGS += $(call cc-option,-fzero-init-padding-bits=all)
 
-KBUILD_CFLAGS += -Wextra
 KBUILD_CFLAGS += -Wunused
 
 #
-- 
2.49.0