The commit dfef99cd0b ("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 <jolsa@redhat.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Tested-by: Jiri Olsa <jolsa@redhat.com>
Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: David Ahern <dsahern@gmail.com>
Link: http://lkml.kernel.org/r/1421234288-22758-4-git-send-email-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
25dd9171f5