linux-kernel - Re: MIPS: bug: gettimeofday syscall broken on CI20 board

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Date:   Wed, 27 Nov 2019 15:29:12 +0100
From:   "H. Nikolaus Schaller" <hns@...delico.com>
To:     Vincenzo Frascino <vincenzo.frascino@....com>
Cc:     linux-mips@...r.kernel.org, Ralf Baechle <ralf@...ux-mips.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Paul Burton <paul.burton@...s.com>,
        MIPS Creator CI20 Development 
        <mips-creator-ci20-dev@...glegroups.com>,
        Discussions about the Letux Kernel 
        <letux-kernel@...nphoenux.org>
Subject: Re: MIPS: bug: gettimeofday syscall broken on CI20 board

Hi Vincenco,

> Am 27.11.2019 um 14:53 schrieb H. Nikolaus Schaller <hns@...delico.com>:
> 
> Hi Vincenzo,
> 
>> Am 26.11.2019 um 11:52 schrieb Vincenzo Frascino <vincenzo.frascino@....com>:
>> 
>> 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
>> 
>> 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@...ux:~# 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);
> }

I realized that this does not allow to distinguish between
uninitialized struct timeval tv and return values. And it
would be nice to print errno. So I have used a new version:

#include <stdio.h>
#include <time.h>
#include <sys/time.h>
#include <errno.h>

int main(void)
{
	struct timeval tv = { 1, 1 };
	int r;
	time_t t;
	int rt;

	r = gettimeofday(&tv, NULL);
	printf("r = %d errno=%d\n", r, errno);
	printf("tv.sec = %ld\n", tv.tv_sec);
	printf("tv.usec = %d\n", tv.tv_usec);

	rt = time(&t);
	printf("rt = %d errno=%d\n", rt, errno);
	printf("t = %ld\n", t);
}

> root@...ux:~# make gettime
> cc     gettime.c   -o gettime
> root@...ux:~# ./gettime 
> r = -1
> tv.sec = 1431857456
> tv.usec = 2012065500
> rt = 1478206565
> t = 1478206565

root@...ux:~# ./gettime 
r = -1 errno=1
tv.sec = 1
tv.usec = 1
rt = 1478193516 errno=1
t = 1478193516
root@...ux:~# 

which means that there is an -EPERM and &tv is not touched.
Well, I did run this as root.

So it may be a completely different reason than changing the
VDSO structure.

> b) same system booted with 4.19 kernel:
> 
> root@...ux:~# ./gettime 
> r = 0
> tv.sec = 1574862135
> tv.usec = 27974
> rt = 1574862135
> t = 1574862135

root@...ux:~# ./gettime 
r = 0 errno=0
tv.sec = 1574863040
tv.usec = 874858
rt = 1574863040 errno=0
t = 1574863040
root@...ux:~#


> root@...ux:~# uname -a
> Linux letux 4.19.86-letux-l400+ #1450 PREEMPT Sun Nov 24 17:17:19 CET 2019 mips GNU/Linux

Please let me know what I should try next.

BR and thanks,
Nikolaus