Re: [Qemu-devel] [PULL 0/7] check-softfloat, fp-bench and clang compile fixes

[Emilio G. Cota]

On Fri, Jan 18, 2019 at 17:41:15 +0000, Alex Bennée wrote:
> 
> Emilio G. Cota <c...@braap.org> writes:
> 
> > On Thu, Jan 17, 2019 at 18:55:33 +0000, Peter Maydell wrote:
> >> On Thu, 17 Jan 2019 at 18:30, Emilio G. Cota <c...@braap.org> wrote:
> >> > What are the contents of "int-to-float.err"?
> >>
> >> linux1@lxub05:~$ cat qemu/build/all/tests/fp/int-to-float.err
(snip)
> >> >> Testing i32_to_f128
> >> 372 tests total.
> >> 21 tests performed; 20 errors found.
> >
> > I see, so i32_to_f128 is failing on this host. Is there
> > a s390x machine I could access? I don't see one in the
> > gcc compile farm.
> 
> I've managed to reproduce this in a s390x VM, for Debian install runes:
> 
>   
> https://wiki.qemu.org/Documentation/Platforms/S390X#Debian_Install_Example_.28TCG.29

It's an endianness issue -- I've reproduced it on both gcc110
(POWER7) from gcc's compile farm and on the s390 machine provided
by Peter (thanks!). Both machines are big endian.

I have a fix for the 128 conversions (below), but not for the
int-to-f80 conversions (the ones that work on little endian).
I have no more time to look into this, so if someone can take
a look, I'd appreciate it.

I'm a little puzzled because given these definitions:

// our floatx80
typedef struct {
    uint64_t low;
    uint16_t high;
} floatx80;

// softfloat's
#ifdef LITTLEENDIAN
struct extFloat80M { uint64_t signif; uint16_t signExp; };
#else
struct extFloat80M { uint16_t signExp; uint64_t signif; };
#endif

I fail to see why just copying low/high to/from signif/signExp
to convert between them fails to work.

Thanks,

                Emilio

---
diff --git a/tests/fp/wrap.inc.c b/tests/fp/wrap.inc.c
index d3bf600cd0..68f57bc167 100644
--- a/tests/fp/wrap.inc.c
+++ b/tests/fp/wrap.inc.c
@@ -87,8 +87,13 @@ static float128_t qemu_to_soft128(float128 a)
     float128_t ret;
     struct uint128 *to = (struct uint128 *)&ret;

+#ifdef LITTLEENDIAN
     to->v0 = a.low;
     to->v64 = a.high;
+#else
+    to->v0 = a.high;
+    to->v64 = a.low;
+#endif
     return ret;
 }

@@ -97,8 +102,13 @@ static float128 soft_to_qemu128(float128_t a)
     struct uint128 *from = (struct uint128 *)&a;
     float128 ret;

+#ifdef LITTLEENDIAN
     ret.low = from->v0;
     ret.high = from->v64;
+#else
+    ret.low = from->v64;
+    ret.high = from->v0;
+#endif
     return ret;
 }