Re: MIPS: bug: gettimeofday syscall broken on CI20 board

From: H. Nikolaus Schaller
Date: Wed Nov 27 2019 - 08:53:31 EST


Hi Vincenzo,

> Am 26.11.2019 um 11:52 schrieb Vincenzo Frascino <vincenzo.frascino@xxxxxxx>:
>
> Hi Nikolaus,
>
> 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.

>
> On 17/11/2019 13:14, H. Nikolaus Schaller wrote:
>> Hi Vincenzo,
>>
>
> [...]
>
>>
>> If I look at the definition of vdso_data it *is* significantly differen
>> from mips_vdso_data.
>>
>> 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.
>>
>
> vdso_data and mips_vdso_data before are not part of the ABI hence they are not
> bind by a contract with the userspace.
>
> 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.

>
>> Please advise what I should try or check to narrow down further.
>>
>
> I had a look at [1] line 200 and seems that the error you are seeing is
> generated by:
> if (gettimeofday(&tv, NULL) == -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.
>
> [1] http://users.isc.org/~each/doxygen/bind9/isc_2unix_2time_8c-source.html
>
>> BR and thanks,
>> Nikolaus Schaller
>>
>
> 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
#include <stdio.h>
#include <time.h>
#include <sys/time.h>

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

printf("r = %d\n", r);
printf("tv.sec = %ld\n", tv.tv_sec);
printf("tv.usec = %d\n", tv.tv_usec);
printf("rt = %d\n", rt);
printf("t = %ld\n", t);
}
root@letux:~# make gettime
cc gettime.c -o gettime
root@letux:~# ./gettime
r = -1
tv.sec = 1431857456
tv.usec = 2012065500
rt = 1478206565
t = 1478206565
root@letux:~# ./gettime
r = -1
tv.sec = 1431873840
tv.usec = 2012065500
rt = 1478206573
t = 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
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
9.11
root@letux:~#

b) same system booted with 4.19 kernel:

root@letux:~# ./gettime
r = 0
tv.sec = 1574862135
tv.usec = 27974
rt = 1574862135
t = 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
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
9.11
root@letux:~#