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Message-Id: <20170304113551.6a008b969a3ed713729cbd57@kernel.org>
Date: Sat, 4 Mar 2017 11:35:51 +0900
From: Masami Hiramatsu <mhiramat@...nel.org>
To: Masami Hiramatsu <mhiramat@...nel.org>
Cc: "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Steven Rostedt <rostedt@...dmis.org>,
Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
linuxppc-dev@...ts.ozlabs.org,
Ananth N Mavinakayanahalli <ananth@...ux.vnet.ibm.com>,
Michael Ellerman <mpe@...erman.id.au>
Subject: Re: [PATCH v4 2/3] perf: kretprobes: offset from reloc_sym if
kernel supports it
On Sat, 4 Mar 2017 09:49:11 +0900
Masami Hiramatsu <mhiramat@...nel.org> wrote:
> On Thu, 2 Mar 2017 23:25:06 +0530
> "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com> wrote:
>
> > We indicate support for accepting sym+offset with kretprobes through a
> > line in ftrace README. Parse the same to identify support and choose the
> > appropriate format for kprobe_events.
>
> Could you give us an example of this change here? :)
> for example, comment of commit 613f050d68a8 .
>
> I think the code is OK, but we need actual example of result.
Hi Naveen,
I've tried following commands
$ grep "[Tt] user_read$" /proc/kallsyms
0000000000000000 T user_read
0000000000000000 t user_read
$ sudo ./perf probe -D user_read%return
r:probe/user_read _text+3539616
r:probe/user_read_1 _text+3653408
OK, looks good. However, when I set the retprobes, I got an error.
$ sudo ./perf probe -a user_read%return
Failed to write event: Invalid argument
Error: Failed to add events.
And kernel rejected that.
$ dmesg -k | tail -n 1
[ 850.315068] Given offset is not valid for return probe.
Hmm, curious..
I tried normal probes
$ sudo ./perf probe -D user_read
p:probe/user_read _text+3539616
p:probe/user_read_1 _text+3653408
$ sudo ./perf probe -a user_read
Added new events:
probe:user_read (on user_read)
probe:user_read_1 (on user_read)
You can now use it in all perf tools, such as:
perf record -e probe:user_read_1 -aR sleep 1
It works!
$ sudo ./perf probe -l
probe:user_read (on user_read@...urity/keys/user_defined.c)
probe:user_read_1 (on user_read@...inux/ss/policydb.c)
$ sudo cat /sys/kernel/debug/kprobes/list
ffffffff9237bf20 k user_read+0x0 [DISABLED][FTRACE]
ffffffff923602a0 k user_read+0x0 [DISABLED][FTRACE]
So, the both "_text+3539616" and "_text+3653408" are correctly located
on the entry address of user_read functions. It seems kernel-side
symbol+offset check is wrong.
Thank you,
>
> Thanks,
>
> >
> > Signed-off-by: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com>
> > ---
> > tools/perf/util/probe-event.c | 12 +++++-------
> > tools/perf/util/probe-file.c | 7 +++++++
> > tools/perf/util/probe-file.h | 1 +
> > 3 files changed, 13 insertions(+), 7 deletions(-)
> >
> > diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
> > index 35f5b7b7715c..faf5789902f5 100644
> > --- a/tools/perf/util/probe-event.c
> > +++ b/tools/perf/util/probe-event.c
> > @@ -757,7 +757,9 @@ post_process_kernel_probe_trace_events(struct probe_trace_event *tevs,
> > }
> >
> > for (i = 0; i < ntevs; i++) {
> > - if (!tevs[i].point.address || tevs[i].point.retprobe)
> > + if (!tevs[i].point.address)
> > + continue;
> > + if (tevs[i].point.retprobe && !kretprobe_offset_is_supported())
> > continue;
> > /* If we found a wrong one, mark it by NULL symbol */
> > if (kprobe_warn_out_range(tevs[i].point.symbol,
> > @@ -1528,11 +1530,6 @@ static int parse_perf_probe_point(char *arg, struct perf_probe_event *pev)
> > return -EINVAL;
> > }
> >
> > - if (pp->retprobe && !pp->function) {
> > - semantic_error("Return probe requires an entry function.\n");
> > - return -EINVAL;
> > - }
> > -
> > if ((pp->offset || pp->line || pp->lazy_line) && pp->retprobe) {
> > semantic_error("Offset/Line/Lazy pattern can't be used with "
> > "return probe.\n");
> > @@ -2841,7 +2838,8 @@ static int find_probe_trace_events_from_map(struct perf_probe_event *pev,
> > }
> >
> > /* Note that the symbols in the kmodule are not relocated */
> > - if (!pev->uprobes && !pp->retprobe && !pev->target) {
> > + if (!pev->uprobes && !pev->target &&
> > + (!pp->retprobe || kretprobe_offset_is_supported())) {
> > reloc_sym = kernel_get_ref_reloc_sym();
> > if (!reloc_sym) {
> > pr_warning("Relocated base symbol is not found!\n");
> > diff --git a/tools/perf/util/probe-file.c b/tools/perf/util/probe-file.c
> > index 8a219cd831b7..1542cd0d6799 100644
> > --- a/tools/perf/util/probe-file.c
> > +++ b/tools/perf/util/probe-file.c
> > @@ -879,6 +879,7 @@ int probe_cache__show_all_caches(struct strfilter *filter)
> >
> > enum ftrace_readme {
> > FTRACE_README_PROBE_TYPE_X = 0,
> > + FTRACE_README_KRETPROBE_OFFSET,
> > FTRACE_README_END,
> > };
> >
> > @@ -889,6 +890,7 @@ static struct {
> > #define DEFINE_TYPE(idx, pat) \
> > [idx] = {.pattern = pat, .avail = false}
> > DEFINE_TYPE(FTRACE_README_PROBE_TYPE_X, "*type: * x8/16/32/64,*"),
> > + DEFINE_TYPE(FTRACE_README_KRETPROBE_OFFSET, "*place (kretprobe): *"),
> > };
> >
> > static bool scan_ftrace_readme(enum ftrace_readme type)
> > @@ -939,3 +941,8 @@ bool probe_type_is_available(enum probe_type type)
> >
> > return true;
> > }
> > +
> > +bool kretprobe_offset_is_supported(void)
> > +{
> > + return scan_ftrace_readme(FTRACE_README_KRETPROBE_OFFSET);
> > +}
> > diff --git a/tools/perf/util/probe-file.h b/tools/perf/util/probe-file.h
> > index a17a82eff8a0..dbf95a00864a 100644
> > --- a/tools/perf/util/probe-file.h
> > +++ b/tools/perf/util/probe-file.h
> > @@ -65,6 +65,7 @@ struct probe_cache_entry *probe_cache__find_by_name(struct probe_cache *pcache,
> > const char *group, const char *event);
> > int probe_cache__show_all_caches(struct strfilter *filter);
> > bool probe_type_is_available(enum probe_type type);
> > +bool kretprobe_offset_is_supported(void);
> > #else /* ! HAVE_LIBELF_SUPPORT */
> > static inline struct probe_cache *probe_cache__new(const char *tgt __maybe_unused)
> > {
> > --
> > 2.11.1
> >
>
>
> --
> Masami Hiramatsu <mhiramat@...nel.org>
--
Masami Hiramatsu <mhiramat@...nel.org>
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