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    SubjectRe: [PATCH UPDATED 3/3] tracing: Provide trace events interface for uprobes
    (2012/04/11 19:30), Srikar Dronamraju wrote:
    > From: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
    >
    > Implements trace_event support for uprobes. In its current form it can
    > be used to put probes at a specified offset in a file and dump the
    > required registers when the code flow reaches the probed address.
    >
    > 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
    > 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
    > # echo 'p /bin/zsh:0x46420 %ip %ax' > uprobe_events
    > # cat uprobe_events
    > p:uprobes/p_zsh_0x46420 /bin/zsh:0x0000000000046420
    > # echo 1 > events/uprobes/enable
    > # sleep 20
    > # echo 0 > events/uprobes/enable
    > # 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
    >
    > Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
    > ---
    >
    > Changelog (since v9)
    > - Handle comments from Steven Rostedt about uprobe tracer documentation.
    > - Disable preemption while in perf handler as suggested by Jiri Olsa.
    >
    > Changelog (since v5)
    > - Added uprobe tracer documentation to this patch.
    >
    > Documentation/trace/uprobetracer.txt | 95 ++++
    > arch/Kconfig | 2
    > kernel/trace/Kconfig | 16 +
    > kernel/trace/Makefile | 1
    > kernel/trace/trace.h | 5
    > kernel/trace/trace_kprobe.c | 2
    > kernel/trace/trace_probe.c | 14 -
    > kernel/trace/trace_probe.h | 3
    > kernel/trace/trace_uprobe.c | 788 ++++++++++++++++++++++++++++++++++
    > 9 files changed, 919 insertions(+), 7 deletions(-)
    > create mode 100644 Documentation/trace/uprobetracer.txt
    > create mode 100644 kernel/trace/trace_uprobe.c
    >
    > diff --git a/Documentation/trace/uprobetracer.txt b/Documentation/trace/uprobetracer.txt
    > new file mode 100644
    > index 0000000..eae40a0
    > --- /dev/null
    > +++ b/Documentation/trace/uprobetracer.txt
    > @@ -0,0 +1,95 @@
    > + Uprobe-tracer: Uprobe-based Event Tracing
    > + =========================================
    > + Documentation written by Srikar Dronamraju
    > +
    > +Overview
    > +--------
    > +Uprobe based trace events are similar to kprobe based trace 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.
    > +
    > +However unlike kprobe-event tracer, the uprobe event interface expects the
    > +user to calculate the offset of the probepoint in the object
    > +
    > +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
    > +
    > +Please note: User has to explicitly calculate the offset of the probepoint
    > +in the object. 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

    Doesn't uprobe_events show the arguments of existing events?
    And also, could you add an event format of above event here?

    Thank you,

    --
    Masami HIRAMATSU
    Software Platform Research Dept. Linux Technology Center
    Hitachi, Ltd., Yokohama Research Laboratory
    E-mail: masami.hiramatsu.pt@hitachi.com


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