[PATCH v2] Makefile.extrawarn: Move -Wunaligned-access to W=1

[Nathan Chancellor]

-Wunaligned-access is a new warning in clang that is default enabled for
arm and arm64 under certain circumstances within the clang frontend (see
LLVM commit below). On v5.17-rc2, an ARCH=arm allmodconfig build shows
1284 total/70 unique instances of this warning (most of the instances
are in header files), which is quite noisy.

To keep a normal build green through CONFIG_WERROR, only show this
warning with W=1, which will allow automated build systems to catch new
instances of the warning so that the total number can be driven down to
zero eventually since catching unaligned accesses at compile time would
be generally useful.

Cc: stable@xxxxxxxxxxxxxxx
Link: https://github.com/llvm/llvm-project/commit/35737df4dcd28534bd3090157c224c19b501278a
Link: https://github.com/ClangBuiltLinux/linux/issues/1569
Link: https://github.com/ClangBuiltLinux/linux/issues/1576
Signed-off-by: Nathan Chancellor <nathan@xxxxxxxxxx>
---

v1 -> v2: https://lore.kernel.org/r/20220201232229.2992968-1-nathan@xxxxxxxxxx/

* Move to W=1 instead of W=2 so that new instances are caught (Arnd).
* Add links to the ClangBuiltLinux issue tracker.

 scripts/Makefile.extrawarn | 1 +
 1 file changed, 1 insertion(+)

diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn
index d53825503874..8be892887d71 100644
--- a/scripts/Makefile.extrawarn
+++ b/scripts/Makefile.extrawarn
@@ -51,6 +51,7 @@ KBUILD_CFLAGS += -Wno-sign-compare
 KBUILD_CFLAGS += -Wno-format-zero-length
 KBUILD_CFLAGS += $(call cc-disable-warning, pointer-to-enum-cast)
 KBUILD_CFLAGS += -Wno-tautological-constant-out-of-range-compare
+KBUILD_CFLAGS += $(call cc-disable-warning, unaligned-access)
 endif
 
 endif

base-commit: 26291c54e111ff6ba87a164d85d4a4e134b7315c
-- 
2.35.1