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Subject[PATCH -tip v3 00/11] perf-probe: Updates for handling local functions correctly and distro debuginfo
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Date
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@hitachi.com



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