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

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On 5/25/21 5:13 PM, 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.

See Eric's explanation:
https://www.mail-archive.com/qemu-block@nongnu.org/msg84461.html

> 
> 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?
>