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: Changbin Du <changbin.du@intel.com> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
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@ -10,3 +10,4 @@ Linux Tracing Technologies
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ftrace
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ftrace-uses
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kprobetrace
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uprobetracer
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@ -1,7 +1,8 @@
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Uprobe-tracer: Uprobe-based Event Tracing
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=========================================
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=========================================
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Uprobe-tracer: Uprobe-based Event Tracing
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=========================================
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Documentation written by Srikar Dronamraju
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:Author: Srikar Dronamraju
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Overview
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@ -19,6 +20,8 @@ user to calculate the offset of the probepoint in the object.
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Synopsis of uprobe_tracer
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-------------------------
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::
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p[:[GRP/]EVENT] PATH:OFFSET [FETCHARGS] : Set a uprobe
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r[:[GRP/]EVENT] PATH:OFFSET [FETCHARGS] : Set a return uprobe (uretprobe)
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-:[GRP/]EVENT : Clear uprobe or uretprobe event
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@ -57,7 +60,7 @@ x86-64 uses x64).
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String type is a special type, which fetches a "null-terminated" string from
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user space.
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Bitfield is another special type, which takes 3 parameters, bit-width, bit-
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offset, and container-size (usually 32). The syntax is;
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offset, and container-size (usually 32). The syntax is::
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b<bit-width>@<bit-offset>/<container-size>
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@ -74,28 +77,28 @@ the third is the number of probe miss-hits.
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Usage examples
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--------------
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* Add a probe as a new uprobe event, write a new definition to uprobe_events
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as below: (sets a uprobe at an offset of 0x4245c0 in the executable /bin/bash)
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as below (sets a uprobe at an offset of 0x4245c0 in the executable /bin/bash)::
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echo 'p /bin/bash:0x4245c0' > /sys/kernel/debug/tracing/uprobe_events
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* Add a probe as a new uretprobe event:
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* Add a probe as a new uretprobe event::
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echo 'r /bin/bash:0x4245c0' > /sys/kernel/debug/tracing/uprobe_events
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* Unset registered event:
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* Unset registered event::
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echo '-:p_bash_0x4245c0' >> /sys/kernel/debug/tracing/uprobe_events
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* Print out the events that are registered:
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* Print out the events that are registered::
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cat /sys/kernel/debug/tracing/uprobe_events
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* Clear all events:
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* Clear all events::
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echo > /sys/kernel/debug/tracing/uprobe_events
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Following example shows how to dump the instruction pointer and %ax register
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at the probed text address. Probe zfree function in /bin/zsh:
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at the probed text address. Probe zfree function in /bin/zsh::
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# cd /sys/kernel/debug/tracing/
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# cat /proc/`pgrep zsh`/maps | grep /bin/zsh | grep r-xp
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@ -103,24 +106,27 @@ at the probed text address. Probe zfree function in /bin/zsh:
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# objdump -T /bin/zsh | grep -w zfree
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0000000000446420 g DF .text 0000000000000012 Base zfree
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0x46420 is the offset of zfree in object /bin/zsh that is loaded at
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0x00400000. Hence the command to uprobe would be:
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0x46420 is the offset of zfree in object /bin/zsh that is loaded at
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0x00400000. Hence the command to uprobe would be::
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# echo 'p:zfree_entry /bin/zsh:0x46420 %ip %ax' > uprobe_events
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And the same for the uretprobe would be:
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And the same for the uretprobe would be::
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# echo 'r:zfree_exit /bin/zsh:0x46420 %ip %ax' >> uprobe_events
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Please note: User has to explicitly calculate the offset of the probe-point
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in the object. We can see the events that are registered by looking at the
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uprobe_events file.
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.. note:: User has to explicitly calculate the offset of the probe-point
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in the object.
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We can see the events that are registered by looking at the uprobe_events file.
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::
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# cat uprobe_events
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p:uprobes/zfree_entry /bin/zsh:0x00046420 arg1=%ip arg2=%ax
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r:uprobes/zfree_exit /bin/zsh:0x00046420 arg1=%ip arg2=%ax
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Format of events can be seen by viewing the file events/uprobes/zfree_entry/format
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Format of events can be seen by viewing the file events/uprobes/zfree_entry/format.
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::
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# cat events/uprobes/zfree_entry/format
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name: zfree_entry
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@ -139,16 +145,18 @@ Format of events can be seen by viewing the file events/uprobes/zfree_entry/form
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print fmt: "(%lx) arg1=%lx arg2=%lx", REC->__probe_ip, REC->arg1, REC->arg2
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Right after definition, each event is disabled by default. For tracing these
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events, you need to enable it by:
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events, you need to enable it by::
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# echo 1 > events/uprobes/enable
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Lets disable the event after sleeping for some time.
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::
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# sleep 20
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# echo 0 > events/uprobes/enable
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And you can see the traced information via /sys/kernel/debug/tracing/trace.
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::
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# cat trace
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# tracer: nop
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