linux-kernel - Re: [PATCH] trace_uprobe: Display correct offset in uprobe

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Date:   Mon, 8 Jan 2018 05:58:19 -0800
From:   Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:     "Tobin C. Harding" <me@...in.cc>
Cc:     Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>,
        rostedt@...dmis.org, mingo@...hat.com, oleg@...hat.com,
        linux-kernel@...r.kernel.org, namhyung@...nel.org
Subject: Re: [PATCH] trace_uprobe: Display correct offset in uprobe_events

* Tobin C. Harding <me@...in.cc> [2018-01-08 17:35:59]:

> On Mon, Jan 08, 2018 at 12:01:04PM +0530, Ravi Bangoria wrote:
> > 
> > 
> > On 01/08/2018 10:49 AM, Srikar Dronamraju wrote:
> > > * Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com> [2018-01-06 11:12:46]:
> > >
> > >> Recently, how the pointers being printed with %p has been changed
> > >> by commit ad67b74d2469 ("printk: hash addresses printed with %p").
> > >> This is causing a regression while showing offset in the
> > >> uprobe_events file. Instead of %p, use %px to display offset.
> > >>
> > >> Signed-off-by: Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>
> > >> ---
> > >>  kernel/trace/trace_uprobe.c | 2 +-
> > >>  1 file changed, 1 insertion(+), 1 deletion(-)
> > >>
> > >> diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
> > >> index 40592e7b3568..268029ae1be6 100644
> > >> --- a/kernel/trace/trace_uprobe.c
> > >> +++ b/kernel/trace/trace_uprobe.c
> > >> @@ -608,7 +608,7 @@ static int probes_seq_show(struct seq_file *m, void *v)
> > >>
> > >>  	/* Don't print "0x  (null)" when offset is 0 */
> > >>  	if (tu->offset) {
> > >> -		seq_printf(m, "0x%p", (void *)tu->offset);
> > >> +		seq_printf(m, "0x%px", (void *)tu->offset);
> > >>  	} else {
> > >>  		switch (sizeof(void *)) {
> > >>  		case 4:
> > > Looks good to me.  Did you consider %pK instead of %px?
> > 
> > Thanks Srikar,
> > 
> > Checked %pK. But I see same issue with that:
> > 
> > perf probe:
> >   Opening /sys/kernel/debug/tracing//uprobe_events write=1
> >   Writing event: p:probe_a/main /tmp/a.out:0x58c
> > 
> > cat /sys/kernel/debug/tracing/uprobe_events:
> >   p:probe_a/main /tmp/a.out:0x0000000014fd571e
> 
> %pK behaves the same as %p (hashes address) when kpt_restrict==0
> 
> Hope this helps,

Thanks Tobin for the clarification. So %px is the right choice.

-- 
thanks and regards
Srikar