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Subject: Re: MIPS: bug: gettimeofday syscall broken on CI20 board
From:   "H. Nikolaus Schaller" <hns@goldelico.com>
In-Reply-To: <3190d1a4-96c4-1843-3ae1-bae3a97af9fb@arm.com>
Date:   Wed, 27 Nov 2019 14:53:20 +0100
Cc:     Ralf Baechle <ralf@linux-mips.org>,
        Paul Burton <paul.burton@mips.com>, linux-mips@vger.kernel.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        MIPS Creator CI20 Development 
        <mips-creator-ci20-dev@googlegroups.com>,
        Discussions about the Letux Kernel 
        <letux-kernel@openphoenux.org>
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Message-Id: <8D151C34-41A1-4DFE-92D6-D1B27AEC8730@goldelico.com>
References: <18788C50-F29B-4BD7-89F6-B056FF490214@goldelico.com> <703DC004-96E8-463D-8870-3CC410FE1C5E@goldelico.com> <3190d1a4-96c4-1843-3ae1-bae3a97af9fb@arm.com>
To:     Vincenzo Frascino <vincenzo.frascino@arm.com>
Sender: linux-kernel-owner@vger.kernel.org
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Hi Vincenzo,

> Am 26.11.2019 um 11:52 schrieb Vincenzo Frascino =
<vincenzo.frascino@arm.com>:
>=20
> Hi Nikolaus,
>=20
> sorry for the delay in answering to your email but due to personal =
reasons I had
> to pull off the linux development for few weeks.

No problem.

>=20
> On 17/11/2019 13:14, H. Nikolaus Schaller wrote:
>> Hi Vincenzo,
>>=20
>=20
> [...]
>=20
>>=20
>> If I look at the definition of vdso_data it *is* significantly =
differen
>> from mips_vdso_data.
>>=20
>> What I would assume is that the struct mips_vdso_data is embossed in =
user
>> space code and therefore using vdso_data instead is breaking API.
>>=20
>=20
> vdso_data and mips_vdso_data before are not part of the ABI hence they =
are not
> bind by a contract with the userspace.
>=20
> This means that they can change at any point and if a userspace =
software relies
> on a specific layout of these data structures is doing something =
wrong.

Maybe the libs are clever enough to find that out dynamically but I have =
no
idea about how gettimeofday() and user-space VDSO is implemented to =
handle such
changes.

>=20
>> Please advise what I should try or check to narrow down further.
>>=20
>=20
> I had a look at [1] line 200 and seems that the error you are seeing =
is
> generated by:
>  if (gettimeofday(&tv, NULL) =3D=3D -1) { ... }

Yes.

> I do not have a CI20 hence I can't do the test myself: could you =
please write a
> small application that invokes gettimeofday() as per above and report =
the
> behavior (I am even interested in the value returned). If we can =
reproduce the
> problem in a smaller environment it is easier to debug and get to the =
solution.
>=20
> [1] =
http://users.isc.org/~each/doxygen/bind9/isc_2unix_2time_8c-source.html
>=20
>> BR and thanks,
>> Nikolaus Schaller
>>=20
>=20
> Let me know.

I have done this and it seems as if tv_usec reports something that is =
beyond 1e6 us
or remains unchanged by the syscall. tv_sec seems to be set correctly. =
And,
gettimeofday() reports -1.

hwclock isn't set on 45.4 kernel because I have no ethernet connection =
due to the bug.

BR,
Nikolaus


Here is the log

a) with 5.4 kernel

root@letux:~# cat gettime.c=20
#include <stdio.h>
#include <time.h>
#include <sys/time.h>

int main(void)
{
struct timeval tv;
int r =3D gettimeofday(&tv, NULL);
time_t t;
int rt =3D time(&t);

printf("r =3D %d\n", r);
printf("tv.sec =3D %ld\n", tv.tv_sec);
printf("tv.usec =3D %d\n", tv.tv_usec);
printf("rt =3D %d\n", rt);
printf("t =3D %ld\n", t);
}
root@letux:~# make gettime
cc     gettime.c   -o gettime
root@letux:~# ./gettime=20
r =3D -1
tv.sec =3D 1431857456
tv.usec =3D 2012065500
rt =3D 1478206565
t =3D 1478206565
root@letux:~# ./gettime=20
r =3D -1
tv.sec =3D 1431873840
tv.usec =3D 2012065500
rt =3D 1478206573
t =3D 1478206573
root@letux:~# uname -a
Linux letux 5.4.0-letux-l400+ #1485 PREEMPT Wed Nov 27 10:23:16 CET 2019 =
mips GNU/Linux
root@letux:~# cat /proc/cpuinfo=20
system type             : JZ4780
machine                 : img,ci20
processor               : 0
cpu model               : Ingenic JZRISC V4.15  FPU V0.0
BogoMIPS                : 1196.85
wait instruction        : yes
microsecond timers      : no
tlb_entries             : 32
extra interrupt vector  : yes
hardware watchpoint     : yes, count: 1, address/irw mask: [0x0fff]
isa                     : mips1 mips2 mips32r1 mips32r2
ASEs implemented        :
shadow register sets    : 1
kscratch registers      : 0
package                 : 0
core                    : 0
VCED exceptions         : not available
VCEI exceptions         : not available

root@letux:~# dpkg -l | grep libc6
ii  libc6:mipsel                   2.24-11+deb9u4                 mipsel =
      GNU C Library: Shared libraries
ii  libc6-dev:mipsel               2.24-11+deb9u4                 mipsel =
      GNU C Library: Development Libraries and Header Files
root@letux:~# cat /etc/debian_version=20
9.11
root@letux:~#=20

b) same system booted with 4.19 kernel:

root@letux:~# ./gettime=20
r =3D 0
tv.sec =3D 1574862135
tv.usec =3D 27974
rt =3D 1574862135
t =3D 1574862135
root@letux:~# uname -a
Linux letux 4.19.86-letux-l400+ #1450 PREEMPT Sun Nov 24 17:17:19 CET =
2019 mips GNU/Linux
root@letux:~# cat /proc/cpuinfo=20
system type             : JZ4780
machine                 : img,ci20
processor               : 0
cpu model               : Ingenic JZRISC V4.15  FPU V0.0
BogoMIPS                : 1196.85
wait instruction        : yes
microsecond timers      : no
tlb_entries             : 32
extra interrupt vector  : yes
hardware watchpoint     : yes, count: 1, address/irw mask: [0x0fff]
isa                     : mips1 mips2 mips32r1 mips32r2
ASEs implemented        :
shadow register sets    : 1
kscratch registers      : 0
package                 : 0
core                    : 0
VCED exceptions         : not available
VCEI exceptions         : not available

root@letux:~# cat /etc/debian_version=20
9.11
root@letux:~#=20