| Message ID | 20240306124709.324448-1-masahiroy@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | kbuild: remove GCC's default -Wpacked-bitfield-compat flag | expand |
On Wed, Mar 06, 2024 at 09:47:09PM +0900, Masahiro Yamada wrote: > 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@kernel.org> Reviewed-by: Nathan Chancellor <nathan@kernel.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 > >
From: Nathan Chancellor > Sent: 06 March 2024 16:50 > > On Wed, Mar 06, 2024 at 09:47:09PM +0900, Masahiro Yamada wrote: > > 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@kernel.org> > > Reviewed-by: Nathan Chancellor <nathan@kernel.org> gcc generates pretty crap code for the above. clang is ok unless you extend the structure to 3 bytes. See: https://godbolt.org/z/9c1csonY9 David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
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
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@kernel.org> --- scripts/Makefile.extrawarn | 1 - 1 file changed, 1 deletion(-)