kbuild: turn on -Wextra by default

Patch series "kbuild: enable more warnings by default", v3.

All the warning fixes I sent for these warnings have been merged into
mainline or linux-next, so let's turn them on by default.


This patch (of 6):

The -Wextra option controls a number of different warnings that differ
slightly by compiler version.  Some are useful in general, others are
better left at W=1 or higher.  Based on earlier work, the ones that should
be disabled by default are left for the higher warning levels already, and
a lot of the useful ones have no remaining output when enabled.

Move the -Wextra option up into the set of default-enabled warnings and
just rely on the individual ones getting disabled as needed.

The -Wunused warning was always grouped with this, so turn it on by
default as well, except for the -Wunused-parameter warning that really has
no value at all for the kernel since many interfaces have intentionally
unused arguments.

Link: https://lkml.kernel.org/r/20240415122037.1983124-1-arnd@kernel.org
Link: https://lkml.kernel.org/r/20240415122037.1983124-2-arnd@kernel.org
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Nathan Chancellor <nathan@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: Nicolas Schier <nicolas@fjasle.eu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

scripts/Makefile.extrawarn

@@ -82,12 +82,14 @@ 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
+
 #
 # W=1 - warnings which may be relevant and do not occur too often
 #
 ifneq ($(findstring 1, $(KBUILD_EXTRA_WARN)),)
 
-KBUILD_CFLAGS += -Wextra -Wunused -Wno-unused-parameter
 KBUILD_CFLAGS += $(call cc-option, -Wrestrict)
 KBUILD_CFLAGS += -Wmissing-format-attribute
 KBUILD_CFLAGS += -Wold-style-definition
@@ -190,6 +192,7 @@ else
 
 # The following turn off the warnings enabled by -Wextra
 KBUILD_CFLAGS += -Wno-sign-compare
+KBUILD_CFLAGS += -Wno-unused-parameter
 
 endif