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

[David Laight]

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@xxxxxxxxxx>
> 
> Reviewed-by: Nathan Chancellor <nathan@xxxxxxxxxx>

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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