linux-kernel - Re: [PATCH 2/2] trace_uprobe: Simplify probes_seq

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Date:   Tue, 6 Mar 2018 13:42:43 +0530
From:   Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>
To:     Kees Cook <keescook@...omium.org>, wangnan0 <wangnan0@...wei.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
        Namhyung Kim <namhyung@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>
Subject: Re: [PATCH 2/2] trace_uprobe: Simplify probes_seq_show()



On 02/08/2018 09:13 AM, Ravi Bangoria wrote:
>
> On 02/08/2018 08:59 AM, Kees Cook wrote:
>> On Tue, Feb 6, 2018 at 8:34 PM, Ravi Bangoria
>> <ravi.bangoria@...ux.vnet.ibm.com> wrote:
>>> Simplify probes_seq_show() function. We are using %lx to display
>>> the offset and we don't prepend unnecessary 0s in the offset.
>>>
>>> Signed-off-by: Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>
>>> ---
>>>  kernel/trace/trace_uprobe.c | 21 +++------------------
>>>  1 file changed, 3 insertions(+), 18 deletions(-)
>>>
>>> diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
>>> index c2c965398893..c12a3957e1ee 100644
>>> --- a/kernel/trace/trace_uprobe.c
>>> +++ b/kernel/trace/trace_uprobe.c
>>> @@ -602,24 +602,9 @@ static int probes_seq_show(struct seq_file *m, void *v)
>>>         char c = is_ret_probe(tu) ? 'r' : 'p';
>>>         int i;
>>>
>>> -       seq_printf(m, "%c:%s/%s", c, tu->tp.call.class->system,
>>> -                       trace_event_name(&tu->tp.call));
>>> -       seq_printf(m, " %s:", tu->filename);
>>> -
>>> -       /* Don't print "0x  (null)" when offset is 0 */
>>> -       if (tu->offset) {
>>> -               seq_printf(m, "0x%lx", tu->offset);
>>> -       } else {
>>> -               switch (sizeof(void *)) {
>>> -               case 4:
>>> -                       seq_printf(m, "0x00000000");
>>> -                       break;
>>> -               case 8:
>>> -               default:
>>> -                       seq_printf(m, "0x0000000000000000");
>>> -                       break;
>>> -               }
>>> -       }
>>> +       seq_printf(m, "%c:%s/%s %s:0x%lx", c, tu->tp.call.class->system,
>>> +                       trace_event_name(&tu->tp.call), tu->filename,
>>> +                       tu->offset);
>> To keep the prepended zeros (and avoid the redundant 0x prefix):
>>
>> "...%#0*lx...", ... sizeof(void *) * 2, tu->offset);
>>
>> As in:
>>
>> +       seq_printf(m, "%c:%s/%s %s:%#0*lx", c, tu->tp.call.class->system,
>> +                       trace_event_name(&tu->tp.call), tu->filename,
>> +                       sizeof(void *) * 2, tu->offset);
> This is useful, thanks Kees.
>
> @Wang, Do we really need those 0s? Won't just 0x0 should
> suffice? Here is the sample output...
>
>   # echo "p:probe_a/main /tmp/a.out:0x0" > uprobe_events
>
> Before patch:
>   # cat uprobe_events
>     p:probe_a/main /tmp/a.out:0x0000000000000000
>
> After patch:
>   # cat uprobe_events
>     p:probe_a/main /tmp/a.out:0x0

Wang, ping :)

Kees, I don't hear back from Wang and no one has reported any issues with
the patches yet. Can I have your Acked-by?

Thanks,
Ravi