leandrof/linux
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

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

Browse Source 
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: Changbin Du <changbin.du@intel.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
This commit is contained in:
Changbin Du 2018-02-17 13:39:40 +08:00 committed by Jonathan Corbet
parent 263ee77574
commit 00b27da349
2 changed files with 27 additions and 18 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
Documentation/trace/index.rst
View File

@ -10,3 +10,4 @@ Linux Tracing Technologies
ftrace
ftrace-uses
kprobetrace
uprobetracer

44
Documentation/trace/uprobetracer.txt → Documentation/trace/uprobetracer.rst
View File

@ -1,7 +1,8 @@
Uprobe-tracer: Uprobe-based Event Tracing
=========================================
=========================================
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
@ -103,24 +106,27 @@ at the probed text address. Probe zfree function in /bin/zsh:
# objdump -T /bin/zsh | grep -w zfree
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:
0x46420 is the offset of zfree in object /bin/zsh that is loaded at
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