Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761966Ab3DCQJR (ORCPT ); Wed, 3 Apr 2013 12:09:17 -0400 Received: from mx1.redhat.com ([209.132.183.28]:32492 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759071Ab3DCQJO (ORCPT ); Wed, 3 Apr 2013 12:09:14 -0400 From: Anton Arapov To: Anton Arapov , Oleg Nesterov , Srikar Dronamraju Cc: LKML , Josh Stone , Frank Eigler , Peter Zijlstra , Ingo Molnar , Ananth N Mavinakayanahalli , adrian.m.negreanu@intel.com, Torsten.Polle@gmx.de Subject: [PATCH v1 9/9] uretprobes: Documentation update Date: Wed, 3 Apr 2013 18:00:39 +0200 Message-Id: <1365004839-21982-10-git-send-email-anton@redhat.com> In-Reply-To: <1365004839-21982-1-git-send-email-anton@redhat.com> References: <1365004839-21982-1-git-send-email-anton@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 8627 Lines: 190 add the uretprobe syntax and update an example Signed-off-by: Anton Arapov --- Documentation/trace/uprobetracer.txt | 114 ++++++++++++++++++++--------------- 1 file changed, 67 insertions(+), 47 deletions(-) diff --git a/Documentation/trace/uprobetracer.txt b/Documentation/trace/uprobetracer.txt index 24ce682..d9c3e68 100644 --- a/Documentation/trace/uprobetracer.txt +++ b/Documentation/trace/uprobetracer.txt @@ -1,6 +1,8 @@ - Uprobe-tracer: Uprobe-based Event Tracing - ========================================= - Documentation written by Srikar Dronamraju + Uprobe-tracer: Uprobe-based Event Tracing + ========================================= + + Documentation written by Srikar Dronamraju + Overview -------- @@ -13,78 +15,94 @@ current_tracer. Instead of that, add probe points 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 +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 + p[:[GRP/]EVENT] PATH:SYMBOL[+offs] [FETCHARGS] : Set a uprobe + r[:[GRP/]EVENT] PATH:SYMBOL[+offs] [FETCHARGS] : Set a return uprobe (uretprobe) + -:[GRP/]EVENT : Clear uprobe or uretprobe event - 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. + GRP : Group name. If omitted, "uprobes" is the default value. + 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 + 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 +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 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. + * Add a probe as a new uprobe event, write a new definition to uprobe_events +as below: (sets a uprobe at an offset of 0x4245c0 in the executable /bin/bash) + + echo 'p: /bin/bash:0x4245c0' > /sys/kernel/debug/tracing/uprobe_events + + * Add a probe as a new uretprobe event: + + echo 'r: /bin/bash:0x4245c0' > /sys/kernel/debug/tracing/uprobe_events + + * Unset registered event: - echo 'p: /bin/bash:0x4245c0' > /sys/kernel/debug/tracing/uprobe_events + echo '-:bash_0x4245c0' >> /sys/kernel/debug/tracing/uprobe_events - This sets a uprobe at an offset of 0x4245c0 in the executable /bin/bash + * Print out the events that are registered: - echo > /sys/kernel/debug/tracing/uprobe_events + cat /sys/kernel/debug/tracing/uprobe_events - This clears all probe points. + * Clear all events: -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 + echo > /sys/kernel/debug/tracing/uprobe_events + +Following example shows how to dump the instruction pointer and %ax register +at the probed text address. Probe zfree function in /bin/zsh: # cd /sys/kernel/debug/tracing/ - # cat /proc/`pgrep zsh`/maps | grep /bin/zsh | grep r-xp + # 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 : + 0x46420 is the offset of zfree in object /bin/zsh that is loaded at + 0x00400000. Hence the command to uprobe would be: + + # echo 'p:zfree_entry /bin/zsh:0x46420 %ip %ax' > uprobe_events + + And the same for the uretprobe would be: - # echo 'p /bin/zsh:0x46420 %ip %ax' > uprobe_events + # echo 'r:zfree_exit /bin/zsh:0x46420 %ip %ax' >> uprobe_events -Please note: User has to explicitly calculate the offset of the probepoint +Please note: User has to explicitly calculate the offset of the probe-point 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:0x00046420 arg1=%ip arg2=%ax + p:uprobes/zfree_entry /bin/zsh:0x00046420 arg1=%ip arg2=%ax + r:uprobes/zfree_exit /bin/zsh:0x00046420 arg1=%ip arg2=%ax -The format of events can be seen by viewing the file events/uprobes/p_zsh_0x46420/format +Format of events can be seen by viewing the file events/uprobes/zfree_entry/format - # cat events/uprobes/p_zsh_0x46420/format - name: p_zsh_0x46420 + # cat events/uprobes/zfree_entry/format + name: zfree_entry ID: 922 format: - field:unsigned short common_type; offset:0; size:2; signed:0; - field:unsigned char common_flags; offset:2; size:1; signed:0; - field:unsigned char common_preempt_count; offset:3; size:1; signed:0; - field:int common_pid; offset:4; size:4; signed:1; - field:int common_padding; offset:8; size:4; signed:1; + field:unsigned short common_type; offset:0; size:2; signed:0; + field:unsigned char common_flags; offset:2; size:1; signed:0; + field:unsigned char common_preempt_count; offset:3; size:1; signed:0; + field:int common_pid; offset:4; size:4; signed:1; + field:int common_padding; offset:8; size:4; signed:1; - field:unsigned long __probe_ip; offset:12; size:4; signed:0; - field:u32 arg1; offset:16; size:4; signed:0; - field:u32 arg2; offset:20; size:4; signed:0; + field:unsigned long __probe_ip; offset:12; size:4; signed:0; + field:u32 arg1; offset:16; size:4; signed:0; + field:u32 arg2; offset:20; size:4; signed:0; print fmt: "(%lx) arg1=%lx arg2=%lx", REC->__probe_ip, REC->arg1, REC->arg2 @@ -94,6 +112,7 @@ Right after definition, each event is disabled by default. For tracing these # echo 1 > events/uprobes/enable Lets disable the event after sleeping for some time. + # sleep 20 # echo 0 > events/uprobes/enable @@ -104,10 +123,11 @@ And you can see the traced information via /sys/kernel/debug/tracing/trace. # # 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. + zsh-24842 [006] 258544.995456: zfree_entry: (0x446420) arg1=446420 arg2=79 + zsh-24842 [007] 258545.000270: zfree_exit: (0x446540 <- 0x446420) arg1=446540 arg2=0 + zsh-24842 [002] 258545.043929: zfree_entry: (0x446420) arg1=446420 arg2=79 + zsh-24842 [004] 258547.046129: zfree_exit: (0x446540 <- 0x446420) arg1=446540 arg2=0 + +Output shows us uprobe was triggered for a pid 24842 with ip being 0x446420 +and contents of ax register being 79. And uretprobe was triggered with ip at +0x446540 with counterpart function entry at 0x446420. -- 1.8.1.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/