On Wed, Jan 14, 2015 at 08:18:08PM +0900, Namhyung Kim wrote:
> The commit dfef99cd0b2c ("perf probe: Use ref_reloc_sym based address
> instead of the symbol name") converts kprobes to use ref_reloc_sym
> (i.e. _stext) and offset instead of using symbol's name directly. So
> on my system, adding do_fork ends up with like below:
>
> $ sudo perf probe -v --add do_fork%return
> probe-definition(0): do_fork%return
> symbol:do_fork file:(null) line:0 offset:0 return:1 lazy:(null)
> 0 arguments
> Looking at the vmlinux_path (7 entries long)
> Using /lib/modules/3.17.6-1-ARCH/build/vmlinux for symbols
> Could not open debuginfo. Try to use symbols.
> Opening /sys/kernel/debug/tracing/kprobe_events write=1
> Added new event:
> Writing event: r:probe/do_fork _stext+456136
> Failed to write event: Invalid argument
> Error: Failed to add events. Reason: Operation not permitted (Code: -1)
>
> As you can see, the do_fork was translated to _stext+456136. This was
> because to support (local) symbols that have same name. But the
> problem is that kretprobe requires to be inserted at function start
> point so it simply checks whether it's called with offset 0. And if
> not, it'll return with -EINVAL. You can see it with dmesg.
>
> $ dmesg | tail -1
> [125621.764103] Return probe must be used without offset.
>
> So we need to use the symbol name instead of ref_reloc_sym in case of
> return probes.
>
> Reported-by: Jiri Olsa <jo...@redhat.com>
'perf probe --add do_fork%return' inserts the probe correctly now
Tested-by: Jiri Olsa <jo...@redhat.com>
thanks,
jirka
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