linux-kernel - Re: [PATCH] trace: Make trace

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Message-ID: <CAK8P3a2Tm0qFiMx7VgK8bprncCCJ_w0ePrqPU3ex4LVm4fceaw@mail.gmail.com>
Date:   Mon, 27 Mar 2017 16:53:09 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     kbuild test robot <lkp@...el.com>,
        Deepa Dinamani <deepa.kernel@...il.com>, kbuild-all@...org,
        Ingo Molnar <mingo@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        y2038 Mailman List <y2038@...ts.linaro.org>
Subject: Re: [PATCH] trace: Make trace_hwlat timestamp y2038 safe

On Mon, Mar 27, 2017 at 4:28 PM, Steven Rostedt <rostedt@...dmis.org> wrote:
> On Mon, 27 Mar 2017 11:55:52 +0200
> Arnd Bergmann <arnd@...db.de> wrote:
>
>> On Mon, Mar 27, 2017 at 11:25 AM, kbuild test robot <lkp@...el.com> wrote:
>> > Hi Deepa,
>> >
>> > [auto build test WARNING on tip/perf/core]
>> > [also build test WARNING on v4.11-rc4 next-20170327]
>> > [if your patch is applied to the wrong git tree, please drop us a note to help improve the system]
>> >
>> > url:    https://github.com/0day-ci/linux/commits/Deepa-Dinamani/trace-Make-trace_hwlat-timestamp-y2038-safe/20170327-150010
>> > config: x86_64-randconfig-n0-03271517 (attached as .config)
>> > compiler: gcc-4.8 (Debian 4.8.4-1) 4.8.4
>> > reproduce:
>> >         # save the attached .config to linux build tree
>> >         make ARCH=x86_64
>> >
>> > All warnings (new ones prefixed by >>):
>> >
>> >    kernel/trace/trace_output.c: In function 'trace_hwlat_print':
>> >>> kernel/trace/trace_output.c:1168:5: warning: format '%lld' expects argument of type 'long long int', but argument 6 has type '__kernel_time_t' [-Wformat=]
>> >         field->timestamp.tv_nsec);
>>
>> This happens on 64-bit architectures because 'struct timespec64' is defined to
>> be equal to 'struct timespec', which has a 'long' tv_sec rather than
>> 'long long'.
>>
>> A cast to 's64' is probably the best workaround.
>>
>> >    kernel/trace/trace_output.c: In function 'trace_hwlat_raw':
>> >    kernel/trace/trace_output.c:1202:5: warning: format '%lld' expects argument of type 'long long int', but argument 5 has type '__kernel_time_t' [-Wformat=]
>> >         field->seqnum);
>>
>> Same here.
>>
>
> Actually, I believe that "%zd" will work. It's made to work with size_t
> which is long long on 32 and long on 64.

size_t is always 'long', not 'long long'. We have %pad for dma_addr_t
which may be 'long' or 'long long', but it is configuration dependent
which one it is on 32-bit.

We could probably introduce a %pts format string for timespec64
and have that pretty-printed.

         Arnd