Date:	Fri, 14 Feb 2014 14:43:12 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Cc:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	David Ahern <dsahern@...il.com>, linux-kernel@...r.kernel.org,
	"Steven Rostedt (Red Hat)" <rostedt@...dmis.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Ingo Molnar <mingo@...hat.com>,
	"David A. Long" <dave.long@...aro.org>,
	yrl.pp-manager.tt@...achi.com, Namhyung Kim <namhyung@...nel.org>
Subject: Re: [PATCH -tip v3 00/11] perf-probe: Updates for handling local
 functions correctly and distro debuginfo

Ping? :)

(2014/02/06 14:32), Masami Hiramatsu wrote:
> Hi,
> 
> Here is the 3rd version of the series for handling local
> functions correctly with perf-probe. This version also
> includes distro debuginfo-file support (a small
> enhancement, based on existing feature).
> 
> In this version, I used ref_reloc_sym based probe point
> instead of absolute address/"_stext", because kASLR
> changes the address offset randomly and the debuginfo
> doesn't know that offset. Recently perftools supports
> kASLR by introducing ref_reloc_sym (which is usually
> "_text" or "_stext"). Since we already ensured that
> the kmap->ref_reloc_sym symbol exists in the kernel,
> it is safe to reuse it for the reference point of
> probe points.
> 
> Note that this series requires a bugfix patch:
>   perf-probe: Do not add offset to uprobe address
>   https://lkml.org/lkml/2014/2/5/7
> 
> 
> Issue 1)
>  Current perf-probe can't handle probe-points for kprobes,
>  since it uses symbol-based probe definition. The symbol
>  based definition is easy to read and robust for differnt
>  kernel and modules. However, when user gives a local
>  function name which has several different instances,
>  it may put probes on wrong (or unexpected) address.
>  On the other hand, since uprobe events are based on the
>  actual address, it can avoid this issue.
> 
>  E.g.
> In the case to probe t_show local functions (which has
> 4 different instances.
>   ----
>   # grep " t_show\$" /proc/kallsyms
>   ffffffff810d9720 t t_show
>   ffffffff810e2e40 t t_show
>   ffffffff810ece30 t t_show
>   ffffffff810f4ad0 t t_show
>   # ./perf probe -fa "t_show \$vars"
>   Added new events:
>     probe:t_show         (on t_show with $vars)
>     probe:t_show_1       (on t_show with $vars)
>     probe:t_show_2       (on t_show with $vars)
>     probe:t_show_3       (on t_show with $vars)
> 
>   You can now use it in all perf tools, such as:
> 
>           perf record -e probe:t_show_3 -aR sleep 1
>   ----
> OK, we have 4 different t_show()s. All functions have
> different arguments as below;
>   ----
>   # cat /sys/kernel/debug/tracing/kprobe_events
>   p:probe/t_show t_show m=%di:u64 v=%si:u64
>   p:probe/t_show_1 t_show m=%di:u64 v=%si:u64 t=%si:u64
>   p:probe/t_show_2 t_show m=%di:u64 v=%si:u64 fmt=%si:u64
>   p:probe/t_show_3 t_show m=%di:u64 v=%si:u64 file=%si:u64
>   ----
> However, all of them have been put on the *same* address.
>   ----
>   # cat /sys/kernel/debug/kprobes/list
>   ffffffff810d9720  k  t_show+0x0    [DISABLED]
>   ffffffff810d9720  k  t_show+0x0    [DISABLED]
>   ffffffff810d9720  k  t_show+0x0    [DISABLED]
>   ffffffff810d9720  k  t_show+0x0    [DISABLED]
>   ----
>  oops...
> 
> Issue 2)
>  With the debuginfo, issue 1 can be solved by using
>  _stext-based probe definition instead of local symbol-based.
>  However, without debuginfo, perf-probe can only use
>  symbol-map in the binary (or kallsyms). The map provides
>  symbol find methods, but it returns only the first matched
>  symbol. To put probes on all functions which have given
>  symbol, we need a symbol-list iterator for the map.
> 
>  E.g. (built perf with NO_DWARF=1)
> In the case to probe t_show and identity__map_ip in perf.
>   ----
>   # ./perf probe -a t_show
>   Added new event:
>     probe:t_show         (on t_show)
> 
>   You can now use it in all perf tools, such as:
> 
>           perf record -e probe:t_show -aR sleep 1
> 
>   # ./perf probe -x perf -a identity__map_ip
>   no symbols found in /kbuild/ksrc/linux-3/tools/perf/perf, maybe install a debug package?
>   Failed to load map.
>     Error: Failed to add events. (-22)
>   ----
>  oops.....
> 
> 
> Solutions)
> To solve the issue 1, this series changes perf probe to
> use _stext-based probe definition. This means that we
> also need to fix the --list options to analyze actual
> probe address from _stext address. (and that has been
> done in this series).
> 
> E.g. with this series;
>   ----
>   # ./perf probe -a "t_show \$vars"
>   Added new events:
>     probe:t_show         (on t_show with $vars)
>     probe:t_show_1       (on t_show with $vars)
>     probe:t_show_2       (on t_show with $vars)
>     probe:t_show_3       (on t_show with $vars)
> 
>   You can now use it in all perf tools, such as:
> 
>           perf record -e probe:t_show_3 -aR sleep 1
> 
>   # cat /sys/kernel/debug/tracing/kprobe_events
>   p:probe/t_show _stext+889880 m=%di:u64 v=%si:u64
>   p:probe/t_show_1 _stext+928568 m=%di:u64 v=%si:u64 t=%si:u64
>   p:probe/t_show_2 _stext+969512 m=%di:u64 v=%si:u64 fmt=%si:u64
>   p:probe/t_show_3 _stext+1001416 m=%di:u64 v=%si:u64 file=%si:u64
> 
>   # cat /sys/kernel/debug/kprobes/list
>   ffffffffb50d95e0  k  t_show+0x0    [DISABLED]
>   ffffffffb50e2d00  k  t_show+0x0    [DISABLED]
>   ffffffffb50f4990  k  t_show+0x0    [DISABLED]
>   ffffffffb50eccf0  k  t_show+0x0    [DISABLED]
>   ----
> This time we can see the events are set in different
> addresses.
> 
> And for the issue 2, the last patch introduces symbol
> iterators for map, dso and symbols (since the symbol
> list is the symbols and it is included in dso, and perf
> probe accesses dso via map).
> 
> E.g. with this series (built perf with NO_DWARF=1);
>   ----
>   # ./perf probe -a t_show
>   Added new events:
>     probe:t_show         (on t_show)
>     probe:t_show_1       (on t_show)
>     probe:t_show_2       (on t_show)
>     probe:t_show_3       (on t_show)
> 
>   You can now use it in all perf tools, such as:
> 
>           perf record -e probe:t_show_3 -aR sleep 1
> 
>   # ./perf probe -x perf -a identity__map_ip
>   Added new events:
>     probe_perf:identity__map_ip (on identity__map_ip in /kbuild/ksrc/linux-3/tools/perf/perf)
>     probe_perf:identity__map_ip_1 (on identity__map_ip in /kbuild/ksrc/linux-3/tools/perf/perf)
>     probe_perf:identity__map_ip_2 (on identity__map_ip in /kbuild/ksrc/linux-3/tools/perf/perf)
>     probe_perf:identity__map_ip_3 (on identity__map_ip in /kbuild/ksrc/linux-3/tools/perf/perf)
> 
>   You can now use it in all perf tools, such as:
> 
>           perf record -e probe_perf:identity__map_ip_3 -aR sleep 1
>   ----
> Now, even without the debuginfo, both the kprobe and
> uprobe are set 4 different places correctly.
> 
> BTW, while testing above, I've found some bugs and
> another minor issue; perf-probe doesn't show the
> modules and binaries in which probes are set.
> I've also fixed it in this series as below.
> 
> Without the fix;
> 
>   # ./perf probe -m drm drm_av_sync_delay
>   # ./perf probe -x perf dso__load_vmlinux
> 
>   # ./perf probe -l
>     probe:drm_av_sync_delay (on drm_av_sync_delay)
>     probe_perf:dso__load_vmlinux (on 0x000000000006d110)
> 
> With this fix;
> 
>   # ./perf probe -l
>     probe:drm_av_sync_delay (on drm_av_sync_delay in drm)
>     probe_perf:dso__load_vmlinux (on 0x000000000006d110 in /kbuild/ksrc/linux-3/tools/perf/perf)
> 
> Changes from v2:
>  - Use ref_reloc_sym instead of "_stext" for reference point.
>    (Thanks for Namhyung Kim!)
>  - Add 2 cleanup patches for reducing the redundant features.
>  - Add distro-style debuginfo support.
> 
> TODO:
>  - Support local functions in modules. This requires kernel
>  side enhancement to allow setting probes by the relative
>  addresses in modules too.
>  - Uprobe-event MUST traces the change of given binary even
>  when the event is disabled. I've found that user can replace
>  the target binary after setting events and the events can be
>  enabled on the different instructions...
> 
> ---
> 
> Masami Hiramatsu (11):
>       [BUGFIX] perf-probe: Fix to do exit call for symbol maps
>       [CLEANUP] perf-probe: Remove incorrect symbol check for --list
>       [CLEANUP] perf-probe: Replace line_list with intlist
>       [CLEANUP] perf-probe: Unify show_available_functions for uprobes/kprobes
>       perf-probe: Show in what binaries/modules probes are set
>       perf-probe: Use ref_reloc_sym based address instead of the symbol name
>       perf-probe: Find given address from offline dwarf
>       perf-probe: Show appropriate symbol for ref_reloc_sym based kprobes
>       perf-probe: Show source-level or symbol-level info for uprobes
>       perf-probe: Allow to add events on the local functions
>       perf probe: Support distro-style debuginfo for uprobe
> 
> 
>  tools/perf/builtin-probe.c     |   12 -
>  tools/perf/util/dso.h          |   10 
>  tools/perf/util/map.h          |   10 
>  tools/perf/util/probe-event.c  |  863 ++++++++++++++++++++++------------------
>  tools/perf/util/probe-event.h  |   12 -
>  tools/perf/util/probe-finder.c |  198 ++-------
>  tools/perf/util/probe-finder.h |    5 
>  tools/perf/util/symbol.h       |   11 +
>  8 files changed, 566 insertions(+), 555 deletions(-)
> 


-- 
Masami HIRAMATSU
IT Management Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@...achi.com


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