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

[Thomas Huth <thuth@redhat.com>]

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