Re: [PATCH v4 2/3] perf: kretprobes: offset from reloc_sym if kernel supports it

[Masami Hiramatsu <mhiramat@kernel.org>]

On Mon, 6 Mar 2017 20:34:10 +0530
"Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> wrote:

> On 2017/03/04 09:49AM, Masami Hiramatsu wrote:
> > On Thu,  2 Mar 2017 23:25:06 +0530
> > "Naveen N. Rao" <naveen.n.rao@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.
> 
> Sure :)
> As an example, without this perf patch, but with the ftrace changes:
> 
>   naveen@ubuntu:~/linux/tools/perf$ sudo cat /sys/kernel/debug/tracing/README | grep kretprobe
>   place (kretprobe): [<module>:]<symbol>[+<offset>]|<memaddr>
>   naveen@ubuntu:~/linux/tools/perf$ 
>   naveen@ubuntu:~/linux/tools/perf$ sudo ./perf probe -v do_open%return
>   probe-definition(0): do_open%return 
>   symbol:do_open file:(null) line:0 offset:0 return:1 lazy:(null)
>   0 arguments
>   Looking at the vmlinux_path (8 entries long)
>   Using /boot/vmlinux for symbols
>   Open Debuginfo file: /boot/vmlinux
>   Try to find probe point from debuginfo.
>   Matched function: do_open [2d0c7d8]
>   Probe point found: do_open+0
>   Matched function: do_open [35d76b5]
>   found inline addr: 0xc0000000004ba984
>   Failed to find "do_open%return",
>    because do_open is an inlined function and has no return point.
>   An error occurred in debuginfo analysis (-22).
>   Trying to use symbols.
>   Opening /sys/kernel/debug/tracing//kprobe_events write=1
>   Writing event: r:probe/do_open do_open+0
>   Writing event: r:probe/do_open_1 do_open+0
>   Added new events:
>     probe:do_open        (on do_open%return)
>     probe:do_open_1      (on do_open%return)
> 
>   You can now use it in all perf tools, such as:
> 
> 	  perf record -e probe:do_open_1 -aR sleep 1
> 
>   naveen@ubuntu:~/linux/tools/perf$ sudo cat /sys/kernel/debug/kprobes/list
>   c000000000041370  k  kretprobe_trampoline+0x0    [OPTIMIZED]
>   c0000000004433d0  r  do_open+0x0    [DISABLED]
>   c0000000004433d0  r  do_open+0x0    [DISABLED]
> 
> And after this patch (and the subsequent powerpc patch):
> 
>   naveen@ubuntu:~/linux/tools/perf$ sudo ./perf probe -v do_open%return
>   probe-definition(0): do_open%return 
>   symbol:do_open file:(null) line:0 offset:0 return:1 lazy:(null)
>   0 arguments
>   Looking at the vmlinux_path (8 entries long)
>   Using /boot/vmlinux for symbols
>   Open Debuginfo file: /boot/vmlinux
>   Try to find probe point from debuginfo.
>   Matched function: do_open [2d0c7d8]
>   Probe point found: do_open+0
>   Matched function: do_open [35d76b5]
>   found inline addr: 0xc0000000004ba984
>   Failed to find "do_open%return",
>    because do_open is an inlined function and has no return point.
>   An error occurred in debuginfo analysis (-22).
>   Trying to use symbols.
>   Opening /sys/kernel/debug/tracing//README write=0
>   Opening /sys/kernel/debug/tracing//kprobe_events write=1
>   Writing event: r:probe/do_open _text+4469712
>   Writing event: r:probe/do_open_1 _text+4956248
>   Added new events:
>     probe:do_open        (on do_open%return)
>     probe:do_open_1      (on do_open%return)
> 
>   You can now use it in all perf tools, such as:
> 
> 	  perf record -e probe:do_open_1 -aR sleep 1
> 
>   naveen@ubuntu:~/linux/tools/perf$ sudo cat /sys/kernel/debug/kprobes/list
>   c000000000041370  k  kretprobe_trampoline+0x0    [OPTIMIZED]
>   c0000000004433d0  r  do_open+0x0    [DISABLED]
>   c0000000004ba058  r  do_open+0x8    [DISABLED]

Ok, with this usage example.

Acked-by: Masami Hiramatsu <mhiramat@kernel.org>

Thanks,

> 
> 
> Thanks,
> - Naveen
> 


-- 
Masami Hiramatsu <mhiramat@kernel.org>