On Sat, 4 Mar 2017 11:35:51 +0900 Masami Hiramatsu <mhira...@kernel.org> wrote:
> On Sat, 4 Mar 2017 09:49:11 +0900
> Masami Hiramatsu <mhira...@kernel.org> wrote:
>
> > On Thu, 2 Mar 2017 23:25:06 +0530
> > "Naveen N. Rao" <naveen.n....@linux.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..
Ah, I see.
static int create_trace_kprobe(int argc, char **argv)
...
} else {
/* a symbol specified */
symbol = argv[1];
/* TODO: support .init module functions */
ret = traceprobe_split_symbol_offset(symbol, &offset);
if (ret) {
pr_info("Failed to parse symbol.\n");
return ret;
}
if (offset && is_return &&
!arch_function_offset_within_entry(offset)) {
pr_info("Given offset is not valid for return
probe.\n");
return -EINVAL;
}
}
So, actually, traceprobe_split_symbol_offset() just split out symbol
and offset from symbol string (e.g. "_text+3539616").
So, you should use kallsyms_lookup_size_offset() here again to check
offset.
Please try attached patch (I've already tested on x86-64).
$ sudo ./perf probe -a user_read%return
Added new events:
probe:user_read (on user_read%return)
probe:user_read_1 (on user_read%return)
You can now use it in all perf tools, such as:
perf record -e probe:user_read_1 -aR sleep 1
$ sudo ./perf probe -l
probe:user_read (on user_read%return@security/keys/user_defined.c)
probe:user_read_1 (on user_read%return@selinux/ss/policydb.c)
$ sudo cat /sys/kernel/debug/kprobes/list
ffffffff9637bf70 r user_read+0x0 [DISABLED][FTRACE]
ffffffff963602f0 r user_read+0x0 [DISABLED][FTRACE]
Thank you,
--
Masami Hiramatsu <mhira...@kernel.org>
tracing-kprobe-check-kretprobe
Description: Binary data
