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

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Date:   Thu, 8 Feb 2018 14:29:14 +1100
From:   Kees Cook <keescook@...omium.org>
To:     Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
        Oleg Nesterov <oleg@...hat.com>,
        wangnan0 <wangnan0@...wei.com>,
        Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
        Namhyung Kim <namhyung@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] trace_uprobe: Simplify probes_seq_show()

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);

-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
>



-- 
Kees Cook
Pixel Security