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Re: [Qemu-devel] [RFC] alpha qemu arithmetic exceptions
From: |
Al Viro |
Subject: |
Re: [Qemu-devel] [RFC] alpha qemu arithmetic exceptions |
Date: |
Wed, 2 Jul 2014 06:50:27 +0100 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Wed, Jul 02, 2014 at 05:05:08AM +0100, Al Viro wrote:
> OK, DS10 resurrected and so far seems to be stable (I'll know by tomorrow;
> there's a possibility that chipset heatsink is dodgy, but so far it seems
> to be doing OK). That gives us a EV6 box.
>
> Which glibc version it is? I don't see such failures with your
> axp/axp-next (head at 6b38f4e7f); could you post the details on your
> reproducer? I've tried to guess the likely version by glibc.git, but
> I don't see nearbyint tests with such argument in any version there,
> so I couldn't find it that way...
FWIW,
; cat >a.c <<'EOF'
#include <stdio.h>
#include <fenv.h>
volatile long x;
void __attribute__((noinline)) f(double v)
{
x = v;
}
main()
{
unsigned long tmp, ret;
static char *names[] = {"IOV", "INE", "UNF", "OVF", "DZE", "INV"};
int i;
feclearexcept(FE_ALL_EXCEPT);
f(4.5);
__asm__ __volatile__ (
"stt $f0,%0\n\t"
"trapb\n\t"
"mf_fpcr $f0\n\t"
"trapb\n\t"
"stt $f0,%1\n\t"
"ldt $f0,%0"
: "=m"(tmp), "=m"(ret));
for (i = 0; i < 6; i++)
printf(" %s", (ret >> (57-i)) & 1 ? names[i] : " ");
printf(" %x ", fetestexcept(FE_ALL_EXCEPT));
printf("FE_INEXACT = %x\n", FE_INEXACT);
}
EOF
; gcc -lm a.c
; ./a.out
INE 200000 FE_INEXACT = 200000
; uname -a
Linux wynton 2.6.22-rc7 #1 Thu Aug 30 02:03:17 EDT 2007 alpha GNU/Linux
That's on freshly resurrected DS10, just brought to the last debian/alpha
(i.e. lenny). Kernel had been locally built back before the box has died.
On miles (3.3.6+, AS200) result is different:
INE 0 FE_INEXACT = 200000
On qemu (with debian kernel from lenny - 2.6.26) it's the same as on DS10:
INE 200000 FE_INEXACT = 200000
It _might_ be the difference between 3.3 and 2.6.20-somethine, but I doubt
that. It's definitely not a matter of difference in libc versions - AS200
box has 2.13-38, but static binary built on DS10 (with its 2.7-18) copied on
AS200 behaves there as locally built one (i.e. 0 from fetestexcept(), as
opposed to FE_INEXACT the same static binary produces on DS10 and under
qemu).
AFAICS, it leaves two possibilities - EV45 (AS200) vs. EV6 (DS10) and EV67
(qemu) _or_ some change in the kernel. I'll build 3.x kernel for DS10 and
post the results; shouldn't take long...
- Re: [Qemu-devel] [RFC] alpha qemu arithmetic exceptions, Al Viro, 2014/07/01
- Re: [Qemu-devel] [RFC] alpha qemu arithmetic exceptions, Richard Henderson, 2014/07/01
- Re: [Qemu-devel] [RFC] alpha qemu arithmetic exceptions, Al Viro, 2014/07/01
- Re: [Qemu-devel] [RFC] alpha qemu arithmetic exceptions, Peter Maydell, 2014/07/01
- Re: [Qemu-devel] [RFC] alpha qemu arithmetic exceptions, Richard Henderson, 2014/07/01
- Re: [Qemu-devel] [RFC] alpha qemu arithmetic exceptions, Peter Maydell, 2014/07/01
- Re: [Qemu-devel] [RFC] alpha qemu arithmetic exceptions, Al Viro, 2014/07/02
- Re: [Qemu-devel] [RFC] alpha qemu arithmetic exceptions,
Al Viro <=
- Re: [Qemu-devel] [RFC] alpha qemu arithmetic exceptions, Al Viro, 2014/07/02
- Re: [Qemu-devel] [RFC] alpha qemu arithmetic exceptions, Richard Henderson, 2014/07/02
- Re: [Qemu-devel] [RFC] alpha qemu arithmetic exceptions, Al Viro, 2014/07/02
- Re: [Qemu-devel] [RFC] alpha qemu arithmetic exceptions, Richard Henderson, 2014/07/02
- Re: [Qemu-devel] [RFC] alpha qemu arithmetic exceptions, Al Viro, 2014/07/02
- Re: [Qemu-devel] [RFC] alpha qemu arithmetic exceptions, Al Viro, 2014/07/03
- Re: [Qemu-devel] [RFC] alpha qemu arithmetic exceptions, Al Viro, 2014/07/03
- Re: [Qemu-devel] [RFC] alpha qemu arithmetic exceptions, Richard Henderson, 2014/07/03
- Re: [Qemu-devel] [RFC] alpha qemu arithmetic exceptions, Al Viro, 2014/07/03
- Re: [Qemu-devel] [RFC] alpha qemu arithmetic exceptions, Peter Maydell, 2014/07/03