lkml.org 
[lkml]   [2011]   [Apr]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    From
    Date
    Subject[PATCH v3 2.6.39-rc1-tip 21/26] 21: Signed-off-by: Srikar Dronamraju <>
    ---
    Documentation/trace/uprobetrace.txt | 94 +++++++++++++++++++++++++++++++++++
    1 files changed, 94 insertions(+), 0 deletions(-)
    create mode 100644 Documentation/trace/uprobetrace.txt

    diff --git a/Documentation/trace/uprobetrace.txt b/Documentation/trace/uprobetrace.txt
    new file mode 100644
    index 0000000..6c18ffe
    --- /dev/null
    +++ b/Documentation/trace/uprobetrace.txt
    @@ -0,0 +1,94 @@
    + Uprobe-tracer: Uprobe-based Event Tracing
    + =========================================
    + Documentation is written by Srikar Dronamraju
    +
    +Overview
    +--------
    +These events are similar to kprobe based events.
    +To enable this feature, build your kernel with CONFIG_UPROBE_EVENTS=y.
    +
    +Similar to the kprobe-event tracer, this doesn't need to be activated via
    +current_tracer. Instead of that, add probe points via
    +/sys/kernel/debug/tracing/uprobe_events, and enable it via
    +/sys/kernel/debug/tracing/events/uprobes/<EVENT>/enabled.
    +
    +
    +Synopsis of uprobe_tracer
    +-------------------------
    + p[:[GRP/]EVENT] PATH:SYMBOL[+offs] [FETCHARGS] : Set a probe
    +
    + GRP : Group name. If omitted, use "uprobes" for it.
    + EVENT : Event name. If omitted, the event name is generated
    + based on SYMBOL+offs.
    + PATH : path to an executable or a library.
    + SYMBOL[+offs] : Symbol+offset where the probe is inserted.
    +
    + FETCHARGS : Arguments. Each probe can have up to 128 args.
    + %REG : Fetch register REG
    +
    +Event Profiling
    +---------------
    + You can check the total number of probe hits and probe miss-hits via
    +/sys/kernel/debug/tracing/uprobe_profile.
    + The first column is event name, the second is the number of probe hits,
    +the third is the number of probe miss-hits.
    +
    +Usage examples
    +--------------
    +To add a probe as a new event, write a new definition to uprobe_events
    +as below.
    +
    + echo 'p: /bin/bash:0x4245c0' > /sys/kernel/debug/tracing/uprobe_events
    +
    + This sets a uprobe at an offset of 0x4245c0 in the executable /bin/bash
    +
    +
    + echo > /sys/kernel/debug/tracing/uprobe_events
    +
    + This clears all probe points.
    +
    +The following example shows how to dump the instruction pointer and %ax
    +a register at the probed text address. Here we are trying to probe
    +function zfree in /bin/zsh
    +
    + # cd /sys/kernel/debug/tracing/
    + # cat /proc/`pgrep zsh`/maps | grep /bin/zsh | grep r-xp
    + 00400000-0048a000 r-xp 00000000 08:03 130904 /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 probe would be :
    +
    + # echo 'p /bin/zsh:0x46420 %ip %ax' > uprobe_events
    +
    +We can see the events that are registered by looking at the uprobe_events
    +file.
    +
    + # cat uprobe_events
    + p:uprobes/p_zsh_0x46420 /bin/zsh:0x0000000000046420
    +
    +Right after definition, each event is disabled by default. For tracing these
    +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
    + #
    + # TASK-PID CPU# TIMESTAMP FUNCTION
    + # | | | | |
    + zsh-24842 [006] 258544.995456: p_zsh_0x46420: (0x446420) arg1=446421 arg2=79
    + zsh-24842 [007] 258545.000270: p_zsh_0x46420: (0x446420) arg1=446421 arg2=79
    + zsh-24842 [002] 258545.043929: p_zsh_0x46420: (0x446420) arg1=446421 arg2=79
    + zsh-24842 [004] 258547.046129: p_zsh_0x46420: (0x446420) arg1=446421 arg2=79
    +
    +Each line shows us probes were triggered for a pid 24842 with ip being
    +0x446421 and contents of ax register being 79.
    +

    \
     
     \ /
      Last update: 2011-04-01 16:49    [W:0.025 / U:185.164 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site