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

[Thomas Huth]

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.

 Thomas