Re: [PATCH 2/2] trace_uprobe: Simplify probes_seq_show()

[Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com>]

On 02/08/2018 08:59 AM, Kees Cook wrote:
> On Tue, Feb 6, 2018 at 8:34 PM, Ravi Bangoria
> <ravi.bangoria@linux.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@linux.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

Thanks,
Ravi

> -Kees
>
>>         for (i = 0; i < tu->tp.nr_args; i++)
>>                 seq_printf(m, " %s=%s", tu->tp.args[i].name, tu->tp.args[i].comm);
>> --
>> 2.13.6
>>
>
>