linux-kernel - [PATCH] kbuild: remove GCC's default -Wpacked-bitfield-compat flag

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Date: Wed,  6 Mar 2024 21:47:09 +0900
From: Masahiro Yamada <masahiroy@...nel.org>
To: linux-kbuild@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
	Masahiro Yamada <masahiroy@...nel.org>,
	Bill Wendling <morbo@...gle.com>,
	Justin Stitt <justinstitt@...gle.com>,
	Nathan Chancellor <nathan@...nel.org>,
	Nick Desaulniers <ndesaulniers@...gle.com>,
	Nicolas Schier <nicolas@...sle.eu>,
	llvm@...ts.linux.dev
Subject: [PATCH] kbuild: remove GCC's default -Wpacked-bitfield-compat flag

Commit 4a5838ad9d2d ("kbuild: Add extra gcc checks") added the
-Wpacked-bitfield-compat flag.

GCC manual says:
  "This warning is enabled by default. Use -Wno-packed-bitfield-compat
   to disable this warning."

The test code in the manual:

  struct foo
  {
    char a:4;
    char b:8;
  } __attribute__ ((packed));

.. emits "note: offset of packed bit-field ‘b’ has changed in GCC 4.4"
without W=3.

Let's remove it, as it is a default with GCC.

Clang does not support this flag, so its removal will not affect Clang
builds.

Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
---

 scripts/Makefile.extrawarn | 1 -
 1 file changed, 1 deletion(-)

diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn
index a9e552a1e910..8192b497aae8 100644
--- a/scripts/Makefile.extrawarn
+++ b/scripts/Makefile.extrawarn
@@ -185,7 +185,6 @@ KBUILD_CFLAGS += -Wpointer-arith
 KBUILD_CFLAGS += -Wredundant-decls
 KBUILD_CFLAGS += -Wsign-compare
 KBUILD_CFLAGS += -Wswitch-default
-KBUILD_CFLAGS += $(call cc-option, -Wpacked-bitfield-compat)
 
 KBUILD_CPPFLAGS += -DKBUILD_EXTRA_WARN3
 
-- 
2.40.1