XPost: linux.debian.ports.68k

Hello,

While debugging OCaml 4.13.1's testsuite on m68k, I've noticed that the following:

-----8<-----
#include <stdio.h>
#include <math.h>
#include <stdint.h>
#include <stdlib.h>

int main(int argc, char** argv) {
int i = atoi(argv[1]);
union { double d; int64_t i; } u[2];
u[0].i = 0x7FF0000000000001L;
u[1].d = -u[0].d;
printf("%Lx, %F\n", u[i].i, u[i].d);
}
-----8<-----

when compiled with "gcc -O0" and run with argument "1", returns:

fff0000000000000, -INF

which seems to be incorrect.

For reference, on amd64 (and seemingly on arm64, armhf, i386, ppc64el,
s390x as well), it returns:

fff0000000000001, -NAN

which seems to be the correct behaviour.


Does anybody here have an explanation?


Cheers,

--
Stéphane

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XPost: linux.debian.ports.68k

Le 22/12/2021 à 13:45, Stéphane Glondu a écrit :

While debugging OCaml 4.13.1's testsuite on m68k, I've noticed that the following:
[...]
which seems to be incorrect.
[...]

Another simpler example, not involving unions:

-----8<-----
#include <stdio.h>
#include <math.h>
#include <stdlib.h>

int main(int argc, char** argv) {
double d[2];
d[0] = NAN;
d[1] = -d[0];
printf("%F\n", d[1]);
}
-----8<-----

returns "-INF" instead of "-NAN".


Cheers,

--
Stéphane

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XPost: linux.debian.ports.68k

Hi Stéphane!

On 12/22/21 14:47, Stéphane Glondu wrote:

Another simpler example, not involving unions:

-----8<-----
#include <stdio.h>
#include <math.h>
#include <stdlib.h>

int main(int argc, char** argv) {
double d[2];
d[0] = NAN;
d[1] = -d[0];
printf("%F\n", d[1]);
}
-----8<-----

returns "-INF" instead of "-NAN".

It might be an emulation issue with QEMU which has some issues with FPU emulation.

I can test it on real hardware but not until after Christmas.

Adrian

--
.''`. John Paul Adrian Glaubitz
: :' : Debian Developer - glaubitz@debian.org
`. `' Freie Universitaet Berlin - glaubitz@physik.fu-berlin.de
`- GPG: 62FF 8A75 84E0 2956 9546 0006 7426 3B37 F5B5 F913

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XPost: linux.debian.ports.68k

Le 22/12/2021 à 15:40, John Paul Adrian Glaubitz a écrit :

Hi Stéphane!

On 12/22/21 14:47, Stéphane Glondu wrote:

Another simpler example, not involving unions:

-----8<-----
#include <stdio.h>
#include <math.h>
#include <stdlib.h>

int main(int argc, char** argv) {
double d[2];
d[0] = NAN;
d[1] = -d[0];
printf("%F\n", d[1]);
}
-----8<-----

returns "-INF" instead of "-NAN".

It might be an emulation issue with QEMU which has some issues with FPU emulation.

I can test it on real hardware but not until after Christmas.

Adrian

With Qemu 6.2.50 (from git repo):

-NAN

With Quadra 800 with 68040 FPU:

NAN

Built with Qemu and debian bookworm/sid, gcc (Debian 10.2.0-15) 10.2.0.

On Quadra 800 it's executed on a debian/etch (not enough memory, 40 MB, to execute sid installer).

So it seems your test works better on Qemu than on real hardware.

First test gives me:

Qemu: fff0000000000001, -NAN
Q800: 7ff8000000000001, NAN

Qemu reuses fonctions common to all emulated archs, so we will have results closer to x86 than to
real 68040.

Thanks,
Laurent

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XPost: linux.debian.ports.68k

Hi Laurent!

On 12/22/21 17:48, Laurent Vivier wrote:

With Qemu 6.2.50 (from git repo):

-NAN

With Quadra 800 with 68040 FPU:

NAN

Built with Qemu and debian bookworm/sid, gcc (Debian 10.2.0-15) 10.2.0.

On Quadra 800 it's executed on a debian/etch (not enough memory, 40 MB, to execute sid installer).

So it seems your test works better on Qemu than on real hardware.

First test gives me:

Qemu: fff0000000000001, -NAN
Q800: 7ff8000000000001, NAN

Qemu reuses fonctions common to all emulated archs, so we will have results closer to x86 than to real 68040.

I will update the QEMU version on the Debian Porterbox then. Has the latest QEMU version
integrated all the changes for the m68k-virt machine or are there any other patches
missing?

I think the kernel part is not yet fully upstreamed, is it?

Adrian

--
.''`. John Paul Adrian Glaubitz
: :' : Debian Developer - glaubitz@debian.org
`. `' Freie Universitaet Berlin - glaubitz@physik.fu-berlin.de
`- GPG: 62FF 8A75 84E0 2956 9546 0006 7426 3B37 F5B5 F913

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XPost: linux.debian.ports.68k

Le 23/12/2021 à 09:56, John Paul Adrian Glaubitz a écrit :

Hi Laurent!

On 12/22/21 17:48, Laurent Vivier wrote:

With Qemu 6.2.50 (from git repo):

-NAN

With Quadra 800 with 68040 FPU:

NAN

Built with Qemu and debian bookworm/sid, gcc (Debian 10.2.0-15) 10.2.0.

On Quadra 800 it's executed on a debian/etch (not enough memory, 40 MB, to execute sid installer).

So it seems your test works better on Qemu than on real hardware.

First test gives me:

Qemu: fff0000000000001, -NAN
Q800: 7ff8000000000001, NAN

Qemu reuses fonctions common to all emulated archs, so we will have results closer to x86 than to real 68040.

I will update the QEMU version on the Debian Porterbox then. Has the latest QEMU version
integrated all the changes for the m68k-virt machine or are there any other patches
missing?

No other patches are missing.

I think the kernel part is not yet fully upstreamed, is it?

Correct. I try to resend a patch this week to have this merged, but spare time is missing.

Thanks,
Laurent

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