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Commit 00b27da3 authored by Changbin Du's avatar Changbin Du Committed by Jonathan Corbet
Browse files

trace doc: convert trace/uprobetracer.txt to rst format 



This converts the plain text documentation to reStructuredText format and
add it into Sphinx TOC tree. No essential content change.

Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: default avatarChangbin Du <changbin.du@intel.com>
Signed-off-by: default avatarJonathan Corbet <corbet@lwn.net>
parent 263ee775

Documentation/trace/index.rst

+1 −0
Original line number Diff line number Diff line
@@ -10,3 +10,4 @@ Linux Tracing Technologies 
   ftrace

   ftrace-uses

   kprobetrace

   uprobetracer

Documentation/trace/uprobetracer.txt→Documentation/trace/uprobetracer.rst

+26 −18
Original line number Diff line number Diff line 
=========================================

Uprobe-tracer: Uprobe-based Event Tracing

=========================================



           Documentation written by Srikar Dronamraju

:Author: Srikar Dronamraju





Overview
@@ -19,6 +20,8 @@ user to calculate the offset of the probepoint in the object. 


Synopsis of uprobe_tracer

-------------------------

::



  p[:[GRP/]EVENT] PATH:OFFSET [FETCHARGS] : Set a uprobe

  r[:[GRP/]EVENT] PATH:OFFSET [FETCHARGS] : Set a return uprobe (uretprobe)

  -:[GRP/]EVENT                           : Clear uprobe or uretprobe event
@@ -57,7 +60,7 @@ x86-64 uses x64). 
String type is a special type, which fetches a "null-terminated" string from

user space.

Bitfield is another special type, which takes 3 parameters, bit-width, bit-

offset, and container-size (usually 32). The syntax is;

offset, and container-size (usually 32). The syntax is::



 b<bit-width>@<bit-offset>/<container-size>
@@ -74,28 +77,28 @@ the third is the number of probe miss-hits. 
Usage examples

--------------

 * Add a probe as a new uprobe event, write a new definition to uprobe_events

as below: (sets a uprobe at an offset of 0x4245c0 in the executable /bin/bash)

   as below (sets a uprobe at an offset of 0x4245c0 in the executable /bin/bash)::



    echo 'p /bin/bash:0x4245c0' > /sys/kernel/debug/tracing/uprobe_events



 * Add a probe as a new uretprobe event:

 * Add a probe as a new uretprobe event::



    echo 'r /bin/bash:0x4245c0' > /sys/kernel/debug/tracing/uprobe_events



 * Unset registered event:

 * Unset registered event::



    echo '-:p_bash_0x4245c0' >> /sys/kernel/debug/tracing/uprobe_events



 * Print out the events that are registered:

 * Print out the events that are registered::



    cat /sys/kernel/debug/tracing/uprobe_events



 * Clear all events:

 * Clear all events::



    echo > /sys/kernel/debug/tracing/uprobe_events



Following example shows how to dump the instruction pointer and %ax register

at the probed text address. Probe zfree function in /bin/zsh:

at the probed text address. Probe zfree function in /bin/zsh::



    # cd /sys/kernel/debug/tracing/

    # cat /proc/`pgrep zsh`/maps | grep /bin/zsh | grep r-xp
@@ -104,23 +107,26 @@ at the probed text address. Probe zfree function in /bin/zsh: 
    0000000000446420 g    DF .text  0000000000000012  Base        zfree



0x46420 is the offset of zfree in object /bin/zsh that is loaded at

  0x00400000. Hence the command to uprobe would be:

0x00400000. Hence the command to uprobe would be::



    # echo 'p:zfree_entry /bin/zsh:0x46420 %ip %ax' > uprobe_events



  And the same for the uretprobe would be:

And the same for the uretprobe would be::



    # echo 'r:zfree_exit /bin/zsh:0x46420 %ip %ax' >> uprobe_events



Please note: User has to explicitly calculate the offset of the probe-point

in the object. We can see the events that are registered by looking at the

uprobe_events file.

.. note:: User has to explicitly calculate the offset of the probe-point

	in the object.



We can see the events that are registered by looking at the uprobe_events file.

::



    # cat uprobe_events

    p:uprobes/zfree_entry /bin/zsh:0x00046420 arg1=%ip arg2=%ax

    r:uprobes/zfree_exit /bin/zsh:0x00046420 arg1=%ip arg2=%ax



Format of events can be seen by viewing the file events/uprobes/zfree_entry/format

Format of events can be seen by viewing the file events/uprobes/zfree_entry/format.

::



    # cat events/uprobes/zfree_entry/format

    name: zfree_entry
@@ -139,16 +145,18 @@ Format of events can be seen by viewing the file events/uprobes/zfree_entry/form 
    print fmt: "(%lx) arg1=%lx arg2=%lx", REC->__probe_ip, REC->arg1, REC->arg2



Right after definition, each event is disabled by default. For tracing these

events, you need to enable it by:

events, you need to enable it by::



    # echo 1 > events/uprobes/enable



Lets disable the event after sleeping for some time.

::



    # sleep 20

    # echo 0 > events/uprobes/enable



And you can see the traced information via /sys/kernel/debug/tracing/trace.

::



    # cat trace

    # tracer: nop