From f3f096cfedf8113380c56fc855275cc75cd8cf55 Mon Sep 17 00:00:00 2001 From: Srikar Dronamraju Date: Wed, 11 Apr 2012 16:00:43 +0530 Subject: tracing: Provide trace events interface for uprobes 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 Acked-by: Steven Rostedt Acked-by: Masami Hiramatsu Cc: Linus Torvalds Cc: Ananth N Mavinakayanahalli Cc: Jim Keniston Cc: Linux-mm Cc: Oleg Nesterov Cc: Andi Kleen Cc: Christoph Hellwig Cc: Arnaldo Carvalho de Melo Cc: Anton Arapov Cc: Peter Zijlstra Link: http://lkml.kernel.org/r/20120411103043.GB29437@linux.vnet.ibm.com Signed-off-by: Ingo Molnar --- Documentation/trace/uprobetracer.txt | 95 ++++++++++++++++++++++++++++++++++++ 1 file changed, 95 insertions(+) create mode 100644 Documentation/trace/uprobetracer.txt (limited to 'Documentation') diff --git a/Documentation/trace/uprobetracer.txt b/Documentation/trace/uprobetracer.txt new file mode 100644 index 000000000000..eae40a003eec --- /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//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 + +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. -- cgit v1.2.3