Re: [PATCH -tip 0/8] perf-probe: Updates for handling local functionscorrectly

[Masami Hiramatsu]

Hi Arnaldo,

Could you wait for pulling this series?
I've found that this series has an obvious bug on
kaslr enabled kernel. I'll fix that by using
the relative address from _stext for kprobes.

Thank you,

(2014/01/23 11:29), Masami Hiramatsu wrote:
> Hi,
> 
> Here is a series of patches for handling local functions
> correctly in perf-probe.
> 
> 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 -f 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
>  address-based probe definition instead of 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 address-based probe definition. This means that we
> also need to fix the --list options to analyze probe
> addresses instead of symbols (and that has been done
> in this series).
> 
> E.g. with this series;
> ----
> # ./perf probe -f 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 0xffffffff810d9720 m=%di:u64 v=%si:u64
> p:probe/t_show_1 0xffffffff810e2e40 m=%di:u64 v=%si:u64 t=%si:u64
> p:probe/t_show_2 0xffffffff810ece30 m=%di:u64 v=%si:u64 fmt=%si:u64
> p:probe/t_show_3 0xffffffff810f4ad0 m=%di:u64 v=%si:u64 file=%si:u64
> 
> # cat /sys/kernel/debug/kprobes/list
> ffffffff810e2e40  k  t_show+0x0    [DISABLED]
> ffffffff810ece30  k  t_show+0x0    [DISABLED]
> ffffffff810f4ad0  k  t_show+0x0    [DISABLED]
> ffffffff810d9720  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 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)
> 
> 
> 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 (8):
>       [BUGFIX] perf-probe: Fix to do exit call for symbol maps
>       [BUGFIX] perf-tools: Load map before using map->map_ip
>       perf-probe: Show in what binaries/modules probes are set
>       perf-probe: Use the actual address instead of the symbol name
>       perf-probe: Show source level information for address only kprobes
>       perf-probe: Show symbol+offset for address only kprobes
>       perf-probe: Show source-level or symbol-level info for uprobes
>       perf-probe: Allow to add events on the local functions
> 
> 
>  tools/perf/util/dso.h         |   10 +
>  tools/perf/util/map.c         |    3 
>  tools/perf/util/map.h         |   10 +
>  tools/perf/util/probe-event.c |  661 ++++++++++++++++++++++-------------------
>  tools/perf/util/symbol.h      |   11 +
>  5 files changed, 387 insertions(+), 308 deletions(-)
> 


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


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