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 <[email protected]>
---
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
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 <[email protected]>
Reviewed-by: Nathan Chancellor <[email protected]>
> ---
>
> 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 <[email protected]>
>
> Reviewed-by: Nathan Chancellor <[email protected]>
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
-
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