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Message-Id: <20110920120420.25326.53974.sendpatchset@srdronam.in.ibm.com> Date: Tue, 20 Sep 2011 17:34:20 +0530 From: Srikar Dronamraju <srikar@...ux.vnet.ibm.com> To: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...e.hu> Cc: Steven Rostedt <rostedt@...dmis.org>, Srikar Dronamraju <srikar@...ux.vnet.ibm.com>, Linux-mm <linux-mm@...ck.org>, Arnaldo Carvalho de Melo <acme@...radead.org>, Linus Torvalds <torvalds@...ux-foundation.org>, Jonathan Corbet <corbet@....net>, Hugh Dickins <hughd@...gle.com>, Christoph Hellwig <hch@...radead.org>, Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>, Thomas Gleixner <tglx@...utronix.de>, Andi Kleen <andi@...stfloor.org>, Oleg Nesterov <oleg@...hat.com>, LKML <linux-kernel@...r.kernel.org>, Jim Keniston <jkenisto@...ux.vnet.ibm.com>, Roland McGrath <roland@...k.frob.com>, Ananth N Mavinakayanahalli <ananth@...ibm.com>, Andrew Morton <akpm@...ux-foundation.org> Subject: [PATCH v5 3.1.0-rc4-tip 21/26] tracing: uprobes Documentation Documents how to trace user space applications using uprobe tracer. Signed-off-by: Srikar Dronamraju <srikar@...ux.vnet.ibm.com> --- Documentation/trace/uprobetracer.txt | 94 ++++++++++++++++++++++++++++++++++ 1 files changed, 94 insertions(+), 0 deletions(-) create mode 100644 Documentation/trace/uprobetracer.txt diff --git a/Documentation/trace/uprobetracer.txt b/Documentation/trace/uprobetracer.txt new file mode 100644 index 0000000..6c18ffe --- /dev/null +++ b/Documentation/trace/uprobetracer.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. + -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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