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@xxxxxxxxx>
Closes: https://lore.kernel.org/oe-kbuild-all/202501291646.VtwF98qd-lkp@xxxxxxxxx/
Signed-off-by: Nathan Chancellor <nathan@xxxxxxxxxx>
---
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@xxxxxxxxxx>
