Re: [PATCH v1 0/5] perf/sdt: SDT events listing/probing

[Masami Hiramatsu]

Hi,

(2014/10/01 0:29), Hemant Kumar wrote:
> This patchset helps in listing dtrace style markers(SDT) present in user space
> applications through perf.
> Notes/markers are placed at important places by the
> developers. They have a negligible overhead when not enabled.
> We can enable them and probe at these places and find some important information
> like the arguments' values, etc.
> 
> We have lots of applications which use SDT markers today, like:
> Postgresql, MySql, Mozilla, Perl, Python, Java, Ruby, libvirt, QEMU, glib
> 
> To add SDT markers into user applications:
> We need to have this header sys/sdt.h present.
> sys/sdt.h used is version 3.
> If not present, install systemtap-sdt-devel package (for fedora-20).
> 
> With this patchset,
> - Use perf sdt-cache --add to add SDT events to a cache.
>  # perf sdt-cache --add ./user_app
> 
>   4 SDT events added for /home/user/user_app!
> 
> - Use perf sdt-cache --del to remove SDT events from the cache>
>  # perf sdt-cache --del ./user_app
> 
>  4 events removed for /home/user/user_app!
> 
> - Dump the cache onto stdout using perf sdt-cache --dump:
>  # perf sdt-cache --dump
>   /home/user/user_app :
>   %user_app:foo_start
>   %user_app:fun_start
> 
> - To probe and trace an SDT event :
>   # perf record -e %user_app:foo_start -aR sleep 10

Looks great! :)

However, when I've tried to build, I got below errors..

  CC       util/sdt.o
util/sdt.c: In function âsdt_errâ:
util/sdt.c:72:3: error: implicit declaration of function âpr_errâ [-Werror=implicit-function-declaration]
   pr_err("%s: No SDT events found\n", target);
   ^
util/sdt.c:72:3: error: nested extern declaration of âpr_errâ [-Werror=nested-externs]
util/sdt.c: In function âfile_hash_list__initâ:
util/sdt.c:489:3: error: implicit declaration of function âpr_debugâ [-Werror=implicit-function-declaration]
   pr_debug("Error in madvise\n");
   ^
util/sdt.c:489:3: error: nested extern declaration of âpr_debugâ [-Werror=nested-externs]
cc1: all warnings being treated as errors

Perhaps, you might working on the old tree. Could you update it?

Thank you,

> 
> The support for perf to sdt events has undergone a lot of changes since it was
> introduced. After a lot of discussions (https://lkml.org/lkml/2014/7/20/284), the
> patchset is subdivided for ease of review.
> Previously, a patchset supporting "perf list sdt" was posted, but it didn't make
> much sense since, only listing SDT events for an ELF won't help.
> This patchset aims at adding a sub-command "sdt-cache" to perf to manage a cache
> for management of the SDT events.
> 
>  This link shows an example of marker probing with Systemtap:
>  https://sourceware.org/systemtap/wiki/AddingUserSpaceProbingToApps
> 
>  This link provides important info regarding SDT notes:
>  http://sourceware.org/systemtap/wiki/UserSpaceProbeImplementation
> 
>  - Markers in binaries :
>  These SDT markers are present in the ELF in the section named
>  ".note.stapsdt".
>  Here, the name of the marker, its provider, type, location, base
>  address, semaphore address.
>  We can retrieve these values using the members name_off and desc_off in
>  Nhdr structure. If these are not enabled, they are present in the ELF as nop.
> 
> Changes since last series :
> - Changed the entire (linked) list structure to hash lists to manage the SDT events.
> - Added a sub command "sdt-cache" to perf to manage SDT events in the system.
> - Added support to add and remove SDT events onto a cache.
> - Added support to "perf record" to probe and record the SDT events.
> 
> TODO:
> - Add support to add most of the SDT events on a system to the cache.
> - Recognizing arguments and support to probe on them.
> 
> ---
> 
> Hemant Kumar (5):
>       perf/sdt: ELF support for SDT
>       perf/sdt: Add SDT events into a cache
>       perf/sdt: Show SDT cache contents
>       perf/sdt: Delete SDT events from cache
>       perf/sdt: Add support to perf record to trace SDT events
> 
> 
>  tools/perf/Makefile.perf       |    3 
>  tools/perf/builtin-record.c    |   21 +
>  tools/perf/builtin-sdt-cache.c |  108 +++++
>  tools/perf/builtin.h           |    1 
>  tools/perf/perf.c              |    1 
>  tools/perf/util/parse-events.c |    7 
>  tools/perf/util/parse-events.h |    7 
>  tools/perf/util/probe-event.c  |  120 ++++-
>  tools/perf/util/probe-event.h  |    8 
>  tools/perf/util/probe-finder.c |    3 
>  tools/perf/util/sdt.c          |  925 ++++++++++++++++++++++++++++++++++++++++
>  tools/perf/util/sdt.h          |   30 +
>  tools/perf/util/symbol-elf.c   |  207 +++++++++
>  tools/perf/util/symbol.h       |   21 +
>  14 files changed, 1440 insertions(+), 22 deletions(-)
>  create mode 100644 tools/perf/builtin-sdt-cache.c
>  create mode 100644 tools/perf/util/sdt.c
>  create mode 100644 tools/perf/util/sdt.h
> 


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


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