linux-kernel - [PATCH] scripts/Makefile.extrawarn: Do not show clang's non-kprintf warnings at W=1

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Message-Id: <20250131-makefile-extrawarn-fix-clang-format-non-kprintf-v1-1-6c6747ada0d4@kernel.org>
Date: Fri, 31 Jan 2025 15:55:28 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: Masahiro Yamada <masahiroy@...nel.org>, 
 Nicolas Schier <nicolas@...sle.eu>, Arnd Bergmann <arnd@...db.de>, 
 Andrew Morton <akpm@...ux-foundation.org>
Cc: Andy Shevchenko <andy.shevchenko@...il.com>, 
 linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org, 
 llvm@...ts.linux.dev, kernel test robot <lkp@...el.com>, 
 Nathan Chancellor <nathan@...nel.org>
Subject: [PATCH] scripts/Makefile.extrawarn: Do not show clang's
 non-kprintf warnings at W=1

Clang's -Wformat-overflow and -Wformat-truncation have chosen to check
'%p' unlike GCC but it does not know about the kernel's pointer
extensions in lib/vsprintf.c, so the developers split that part of the
warning out for the kernel to disable because there will always be false
positives.

Commit 908dd508276d ("kbuild: enable -Wformat-truncation on clang") did
disabled these warnings but only in a block that would be called when
W=1 was not passed, so they would appear with W=1. Move the disabling of
the non-kprintf warnings to a block that always runs so that they are
never seen, regardless of warning level.

Fixes: 908dd508276d ("kbuild: enable -Wformat-truncation on clang")
Reported-by: kernel test robot <lkp@...el.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202501291646.VtwF98qd-lkp@intel.com/
Signed-off-by: Nathan Chancellor <nathan@...nel.org>
---
 scripts/Makefile.extrawarn | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn
index 1d13cecc7cc7..8878f71463fc 100644
--- a/scripts/Makefile.extrawarn
+++ b/scripts/Makefile.extrawarn
@@ -31,6 +31,11 @@ KBUILD_CFLAGS-$(CONFIG_CC_NO_ARRAY_BOUNDS) += -Wno-array-bounds
 ifdef CONFIG_CC_IS_CLANG
 # The kernel builds with '-std=gnu11' so use of GNU extensions is acceptable.
 KBUILD_CFLAGS += -Wno-gnu
+
+# Clang checks for overflow/truncation with '%p', while GCC does not:
+# https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111219
+KBUILD_CFLAGS += $(call cc-disable-warning, format-overflow-non-kprintf)
+KBUILD_CFLAGS += $(call cc-disable-warning, format-truncation-non-kprintf)
 else
 
 # gcc inanely warns about local variables called 'main'
@@ -102,11 +107,6 @@ KBUILD_CFLAGS += $(call cc-disable-warning, packed-not-aligned)
 KBUILD_CFLAGS += $(call cc-disable-warning, format-overflow)
 ifdef CONFIG_CC_IS_GCC
 KBUILD_CFLAGS += $(call cc-disable-warning, format-truncation)
-else
-# Clang checks for overflow/truncation with '%p', while GCC does not:
-# https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111219
-KBUILD_CFLAGS += $(call cc-disable-warning, format-overflow-non-kprintf)
-KBUILD_CFLAGS += $(call cc-disable-warning, format-truncation-non-kprintf)
 endif
 KBUILD_CFLAGS += $(call cc-disable-warning, stringop-truncation)
 

---
base-commit: fd8c09ad0d87783b9b6a27900d66293be45b7bad
change-id: 20250131-makefile-extrawarn-fix-clang-format-non-kprintf-d4ddea38eeb3

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