Re: [PATCH] configure: Check whether we can compile the s390-ccw bios with -msoft-float

[Thomas Huth]

On 25/05/2021 17.13, Philippe Mathieu-Daudé wrote:
> On 5/25/21 4:40 PM, Thomas Huth wrote:
> > On 25/05/2021 16.31, Cornelia Huck wrote:
> > > On Tue, 25 May 2021 16:20:32 +0200
> > > Thomas Huth <thuth@redhat.com> wrote:
> > >
> > > > The -msoft-float switch is not available in older versions of Clang.
> > > > Since we rely on the compiler to not generate floating point
> > > > instructions
> > > > unexpectedly, we block those old compilers now via a test in the
> > > > configure
> > > > script. Note that for some weird reasons, the Clang compiler only
> > > > complains
> > > > about the missing soft-float support if no other flags are passed via
> > > > "-Wl,..." to the linker. So we have to use "compile_object" instead of
> > > > "compile_prog" for this check.
> > >
> > > Ugh.
> >
> > It's maybe better to use compile_object for testing -msoft-float anyway
> > since it could influence the way of linking against libraries (if I get
> > https://reviews.llvm.org/D72189 right).
> >
> > > > Signed-off-by: Thomas Huth <thuth@redhat.com>
> > > > ---
> > > >    configure | 2 +-
> > > >    1 file changed, 1 insertion(+), 1 deletion(-)
> > > >
> > > > diff --git a/configure b/configure
> > > > index 676239c697..673419ff31 100755
> > > > --- a/configure
> > > > +++ b/configure
> > > > @@ -5462,7 +5462,7 @@ if test "$cpu" = "s390x" ; then
> > > >      write_c_skeleton
> > > >      compile_prog "-march=z900" ""
> > > >      has_z900=$?
> > > > -  if [ $has_z900 = 0 ] || compile_prog "-march=z10" ""; then
> > > > +  if [ $has_z900 = 0 ] || compile_object "-march=z10 -msoft-float
> > > > -Werror"; then
> > >
> > > Do you believe that we should have caught the various clang
> > > specialties now?
> >
> > Apart from one compiler warning that just popped up today, yes. I'm
> > seeing this compiler warning with Clang 12.0 now:
> >
> > roms/SLOF/lib/libnet/ipv6.c:447:18: warning: variable length array
> > folded to constant array as an extension [-Wgnu-folding-constant]
> >                  unsigned short raw[ip6size];
> >                                 ^
> >
> > ... not sure what to do with that one yet.
>
> Fix it? =)
>
> Same class as:
> https://gitlab.freedesktop.org/slirp/libslirp/-/commit/6690d55626cc
>
> -- >8 --
> diff --git a/lib/libnet/ipv6.c b/lib/libnet/ipv6.c
> index 6420004..b7daeda 100644
> --- a/lib/libnet/ipv6.c
> +++ b/lib/libnet/ipv6.c
> @@ -441,10 +441,9 @@ static unsigned short ip6_checksum(struct ip6hdr
> *ip6h, unsigned char *packet,
>   {
>          int i;
>          unsigned long checksum;
> -       const int ip6size = sizeof(struct ip6hdr)/sizeof(unsigned short);
>          union {
>                  struct ip6hdr ip6h;
> -               unsigned short raw[ip6size];
> +               unsigned short raw[sizeof(struct ip6hdr) /
> sizeof(unsigned short)];
>          } pseudo;
>
>          memcpy (&pseudo.ip6h, ip6h, sizeof(struct ip6hdr));
> @@ -455,7 +454,7 @@ static unsigned short ip6_checksum(struct ip6hdr
> *ip6h, unsigned char *packet,
>          for (checksum = 0, i = 0; i < bytes; i += 2)
>                  checksum += (packet[i] << 8) | packet[i + 1];
>
> -       for (i = 0; i < ip6size; i++)
> +       for (i = 0; i < sizeof(pseudo.raw); i++)
>                  checksum += pseudo.raw[i];
>
>          checksum = (checksum >> 16) + (checksum & 0xffff);
> ---
>
> Do you want me to send the fix since I have it ready?

Yes, please!

 Thanks,
  Thomas