Re: [PATCH] c: Extend the -Wpadded message with actual padding size

[Andrew Pinski <pinskia@gmail.com>]

On Wed, Jun 22, 2022 at 1:34 AM Vit Kabele <vit.kabele@sysgo.com> wrote:
>
> Hello,
>
> On Mon, Jun 20, 2022 at 04:05:17PM -0700, Andrew Pinski wrote:
> > > new file mode 100644
> > > index 00000000000..e8f1044a36b
> > > --- /dev/null
> > > +++ b/gcc/testsuite/c-c++-common/Wpadded.c
> > > @@ -0,0 +1,10 @@
> > > +/* { dg-do compile } */
> > > +/* { dg-options "-Wpadded" } */
> > > +
> > > +/*
> > > + * The struct is on single line, because C++ compiler emits the -Wpadded
> > > + * warning at the first line of the struct, while the C compiler at the last
> > > + * line of the struct definition. This way the test passes on both
> > > + */
> > > +struct S { __UINT32_TYPE__ i; char c; }; /* { dg-warning "padding struct size to alignment boundary with 3 bytes" } */
> > > +
> > Note the testcase will fail on some targets where alignment is 1 for everything.
> > You most likely want the dg-warning to be like it is in gcc.dg/Wpadded.c:
> > /* { dg-warning "padding struct size to alignment boundary with 3
> > bytes" ""  { target { ! default_packed } } } */
> >
> > You might want the following from the same file too:
> > /* -fpack-struct is necessary because the warning expected requires the initial
> >    packing to be larger than 1, which cannot be guaranteed for all targets.
> >    We won't get a warning anyway if the target has "packed" structure
> >    layout.  */
> > /* { dg-options "-Wpadded -fpack-struct=8" } */
> > /* { dg-additional-options "-mno-ms-bitfields" { target *-*-mingw* } } */
> I added the ! default_packed directive, but I am not sure whether the
> -fpack-struct is needed. Could you please provide a name of the particular target
> with such alignment constraints so I can test it?

cris is one example. See
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=23304 (which is why
default_packed was added).

Thanks,
Andrew


>
> --
> Thank you,
> Vit Kabele