lkml.org 
[lkml]   [2012]   [Apr]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
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


\
 
 \ /
  Last update: 2012-04-12 15:05    [from the cache]
©2003-2011 Jasper Spaans