Re: [Qemu-devel] [PATCH] include/fpu/softfloat: Fix compilation with Clang on s390x

["Alex Bennée" <alex.bennee@linaro.org>]

Thomas Huth <thuth@redhat.com> writes:

> On 2019-01-14 17:37, Alex Bennée wrote:
>>
>> Philippe Mathieu-Daudé <philmd@redhat.com> writes:
>>
>>> On 1/14/19 1:12 PM, Thomas Huth wrote:
>>>> Clang v7.0.1 does not like the __int128 variable type for inline
>>>> assembly on s390x:
>>>>
>>>> In file included from fpu/softfloat.c:97:
>>>> include/fpu/softfloat-macros.h:647:9: error: inline asm error:
>>>>  This value type register class is not natively supported!
>>>>     asm("dlgr %0, %1" : "+r"(n) : "r"(d));
>>>>         ^
>>>>
>>>> Disable this code part there now when compiling with Clang, so that
>>>> the generic code gets used instead.
>>>>
>>>> Signed-off-by: Thomas Huth <thuth@redhat.com>
>>>> ---
>>>>  include/fpu/softfloat-macros.h | 2 +-
>>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> diff --git a/include/fpu/softfloat-macros.h b/include/fpu/softfloat-macros.h
>>>> index b1d772e..bd5b641 100644
>>>> --- a/include/fpu/softfloat-macros.h
>>>> +++ b/include/fpu/softfloat-macros.h
>>>> @@ -641,7 +641,7 @@ static inline uint64_t udiv_qrnnd(uint64_t *r, uint64_t n1,
>>>>      uint64_t q;
>>>>      asm("divq %4" : "=a"(q), "=d"(*r) : "0"(n0), "1"(n1), "rm"(d));
>>>>      return q;
>>>> -#elif defined(__s390x__)
>>>> +#elif defined(__s390x__) && !defined(__clang__)
>>>
>>> Can we rather check if __int128 is natively supported? So this part get
>>> compiled once Clang do support it, else we'll never use it...
>>
>> We already define CONFIG_INT128 so you could just use that.
>>
>> Thomas does the s390 clang leave CONFIG_INT128=y in config-host.mak?
>
> Yes, CONFIG_INT128=y is also set with Clang on s390x. It's really just
> that it does not like __int128  to be passed as parameters for inline
> assembly...

What about something like this:

modified   include/fpu/softfloat-macros.h
@@ -641,12 +641,6 @@ static inline uint64_t udiv_qrnnd(uint64_t *r, uint64_t n1,
     uint64_t q;
     asm("divq %4" : "=a"(q), "=d"(*r) : "0"(n0), "1"(n1), "rm"(d));
     return q;
-#elif defined(__s390x__)
-    /* Need to use a TImode type to get an even register pair for DLGR.  */
-    unsigned __int128 n = (unsigned __int128)n1 << 64 | n0;
-    asm("dlgr %0, %1" : "+r"(n) : "r"(d));
-    *r = n >> 64;
-    return n;
 #elif defined(_ARCH_PPC64) && defined(_ARCH_PWR7)
     /* From Power ISA 2.06, programming note for divdeu.  */
     uint64_t q1, q2, Q, r1, r2, R;
@@ -663,6 +657,11 @@ static inline uint64_t udiv_qrnnd(uint64_t *r, uint64_t n1,
     }
     *r = R;
     return Q;
+#elif defined(CONFIG_INT128)
+    unsigned __int128 n = (unsigned __int128)n1 << 64 | n0;
+    unsigned __int128 q = n / d;
+    *r = q >> 64;
+    return q;
 #else
     uint64_t d0, d1, q0, q1, r1, r0, m;

--
Alex Bennée