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Commit f3f096cf authored by Srikar Dronamraju's avatar Srikar Dronamraju Committed by Ingo Molnar
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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: default avatarSrikar Dronamraju <srikar@linux.vnet.ibm.com>
Acked-by: default avatarSteven Rostedt <rostedt@goodmis.org>
Acked-by: default avatarMasami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Jim Keniston <jkenisto@linux.vnet.ibm.com>
Cc: Linux-mm <linux-mm@kvack.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@infradead.org>
Cc: Anton Arapov <anton@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20120411103043.GB29437@linux.vnet.ibm.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 8ab83f56

Documentation/trace/uprobetracer.txt

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+95 −0
Original line number Original line Diff line number Diff line 
		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



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.

arch/Kconfig

+1 −1
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@@ -78,7 +78,7 @@ config OPTPROBES 




config UPROBES

config UPROBES

	bool "Transparent user-space probes (EXPERIMENTAL)"

	bool "Transparent user-space probes (EXPERIMENTAL)"

	depends on ARCH_SUPPORTS_UPROBES && PERF_EVENTS

	depends on UPROBE_EVENTS && PERF_EVENTS

	default n

	default n

	help

	help

	  Uprobes is the user-space counterpart to kprobes: they

	  Uprobes is the user-space counterpart to kprobes: they

kernel/trace/Kconfig

+16 −0
Original line number Original line Diff line number Diff line
@@ -386,6 +386,22 @@ config KPROBE_EVENT 
	  This option is also required by perf-probe subcommand of perf tools.

	  This option is also required by perf-probe subcommand of perf tools.

	  If you want to use perf tools, this option is strongly recommended.

	  If you want to use perf tools, this option is strongly recommended.





config UPROBE_EVENT

	bool "Enable uprobes-based dynamic events"

	depends on ARCH_SUPPORTS_UPROBES

	depends on MMU

	select UPROBES

	select PROBE_EVENTS

	select TRACING

	default n

	help

	  This allows the user to add tracing events on top of userspace

	  dynamic events (similar to tracepoints) on the fly via the trace

	  events interface. Those events can be inserted wherever uprobes

	  can probe, and record various registers.

	  This option is required if you plan to use perf-probe subcommand

	  of perf tools on user space applications.



config PROBE_EVENTS

config PROBE_EVENTS

	def_bool n

	def_bool n

kernel/trace/Makefile

+1 −0
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@@ -62,5 +62,6 @@ ifeq ($(CONFIG_TRACING),y) 
obj-$(CONFIG_KGDB_KDB) += trace_kdb.o

obj-$(CONFIG_KGDB_KDB) += trace_kdb.o

endif

endif

obj-$(CONFIG_PROBE_EVENTS) += trace_probe.o

obj-$(CONFIG_PROBE_EVENTS) += trace_probe.o

obj-$(CONFIG_UPROBE_EVENT) += trace_uprobe.o





libftrace-y := ftrace.o
 
libftrace-y := ftrace.o

kernel/trace/trace.h

+5 −0
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@@ -103,6 +103,11 @@ struct kretprobe_trace_entry_head { 
	unsigned long		ret_ip;

	unsigned long		ret_ip;

};

};





struct uprobe_trace_entry_head {

	struct trace_entry	ent;

	unsigned long		ip;

};



/*

/*

 * trace_flag_type is an enumeration that holds different

 * trace_flag_type is an enumeration that holds different

 * states when a trace occurs. These are:

 * states when a trace occurs. These are: