Re: [PATCH] xfsprogs: don't warn about packed members

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Tue, Dec 17, 2019 at 06:54:01AM -0500, Brian Foster wrote:
> On Tue, Dec 17, 2019 at 08:52:45AM +1100, Dave Chinner wrote:
> > From: Dave Chinner <dchinner@redhat.com>
> > 
> > gcc 9.2.1 throws lots of new warnings during the build like this:
> > 
> > xfs_format.h:790:3: warning: taking address of packed member of ‘struct xfs_agfl’ may result in an unaligned pointer value [-Waddress-of-packed-member]
> >   790 |   &(XFS_BUF_TO_AGFL(bp)->agfl_bno[0]) : \
> >       |   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > xfs_alloc.c:3149:13: note: in expansion of macro ‘XFS_BUF_TO_AGFL_BNO’
> >  3149 |  agfl_bno = XFS_BUF_TO_AGFL_BNO(mp, agflbp);
> >       |             ^~~~~~~~~~~~~~~~~~~
> > 
> > We know this packed structure aligned correctly, so turn off this
> > warning to shut gcc up.
> > 
> > Signed-off-by: Dave Chinner <dchinner@redhat.com>
> > ---
> 
> I'm wondering if we could just use offsetof() in this case so we don't
> have to disable a warning for the entire project, particularly if this
> is triggered by a small number of macros..

...and maybe kill the shouty macro while we're at it. :)

--D

> Brian
> 
> >  include/builddefs.in | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/include/builddefs.in b/include/builddefs.in
> > index 4700b52706a7..6fdc9ebb70c7 100644
> > --- a/include/builddefs.in
> > +++ b/include/builddefs.in
> > @@ -13,7 +13,7 @@ OPTIMIZER = @opt_build@
> >  MALLOCLIB = @malloc_lib@
> >  LOADERFLAGS = @LDFLAGS@
> >  LTLDFLAGS = @LDFLAGS@
> > -CFLAGS = @CFLAGS@ -D_FILE_OFFSET_BITS=64
> > +CFLAGS = @CFLAGS@ -D_FILE_OFFSET_BITS=64 -Wno-address-of-packed-member
> >  BUILD_CFLAGS = @BUILD_CFLAGS@ -D_FILE_OFFSET_BITS=64
> >  
> >  LIBRT = @librt@
> > -- 
> > 2.24.0.rc0
> > 
>