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 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?