Documentation / trace / uprobetracer.txt
Custom Search
Based on kernel version 3.9. Page generated on 2013-05-02 23:15 EST.
1 Uprobe-tracer: Uprobe-based Event Tracing 2 ========================================= 3 Documentation written by Srikar Dronamraju 4 5 Overview 6 -------- 7 Uprobe based trace events are similar to kprobe based trace events. 8 To enable this feature, build your kernel with CONFIG_UPROBE_EVENT=y. 9 10 Similar to the kprobe-event tracer, this doesn't need to be activated via 11 current_tracer. Instead of that, add probe points via 12 /sys/kernel/debug/tracing/uprobe_events, and enable it via 13 /sys/kernel/debug/tracing/events/uprobes/<EVENT>/enabled. 14 15 However unlike kprobe-event tracer, the uprobe event interface expects the 16 user to calculate the offset of the probepoint in the object 17 18 Synopsis of uprobe_tracer 19 ------------------------- 20 p[:[GRP/]EVENT] PATH:SYMBOL[+offs] [FETCHARGS] : Set a probe 21 22 GRP : Group name. If omitted, use "uprobes" for it. 23 EVENT : Event name. If omitted, the event name is generated 24 based on SYMBOL+offs. 25 PATH : path to an executable or a library. 26 SYMBOL[+offs] : Symbol+offset where the probe is inserted. 27 28 FETCHARGS : Arguments. Each probe can have up to 128 args. 29 %REG : Fetch register REG 30 31 Event Profiling 32 --------------- 33 You can check the total number of probe hits and probe miss-hits via 34 /sys/kernel/debug/tracing/uprobe_profile. 35 The first column is event name, the second is the number of probe hits, 36 the third is the number of probe miss-hits. 37 38 Usage examples 39 -------------- 40 To add a probe as a new event, write a new definition to uprobe_events 41 as below. 42 43 echo 'p: /bin/bash:0x4245c0' > /sys/kernel/debug/tracing/uprobe_events 44 45 This sets a uprobe at an offset of 0x4245c0 in the executable /bin/bash 46 47 echo > /sys/kernel/debug/tracing/uprobe_events 48 49 This clears all probe points. 50 51 The following example shows how to dump the instruction pointer and %ax 52 a register at the probed text address. Here we are trying to probe 53 function zfree in /bin/zsh 54 55 # cd /sys/kernel/debug/tracing/ 56 # cat /proc/`pgrep zsh`/maps | grep /bin/zsh | grep r-xp 57 00400000-0048a000 r-xp 00000000 08:03 130904 /bin/zsh 58 # objdump -T /bin/zsh | grep -w zfree 59 0000000000446420 g DF .text 0000000000000012 Base zfree 60 61 0x46420 is the offset of zfree in object /bin/zsh that is loaded at 62 0x00400000. Hence the command to probe would be : 63 64 # echo 'p /bin/zsh:0x46420 %ip %ax' > uprobe_events 65 66 Please note: User has to explicitly calculate the offset of the probepoint 67 in the object. We can see the events that are registered by looking at the 68 uprobe_events file. 69 70 # cat uprobe_events 71 p:uprobes/p_zsh_0x46420 /bin/zsh:0x00046420 arg1=%ip arg2=%ax 72 73 The format of events can be seen by viewing the file events/uprobes/p_zsh_0x46420/format 74 75 # cat events/uprobes/p_zsh_0x46420/format 76 name: p_zsh_0x46420 77 ID: 922 78 format: 79 field:unsigned short common_type; offset:0; size:2; signed:0; 80 field:unsigned char common_flags; offset:2; size:1; signed:0; 81 field:unsigned char common_preempt_count; offset:3; size:1; signed:0; 82 field:int common_pid; offset:4; size:4; signed:1; 83 field:int common_padding; offset:8; size:4; signed:1; 84 85 field:unsigned long __probe_ip; offset:12; size:4; signed:0; 86 field:u32 arg1; offset:16; size:4; signed:0; 87 field:u32 arg2; offset:20; size:4; signed:0; 88 89 print fmt: "(%lx) arg1=%lx arg2=%lx", REC->__probe_ip, REC->arg1, REC->arg2 90 91 Right after definition, each event is disabled by default. For tracing these 92 events, you need to enable it by: 93 94 # echo 1 > events/uprobes/enable 95 96 Lets disable the event after sleeping for some time. 97 # sleep 20 98 # echo 0 > events/uprobes/enable 99 100 And you can see the traced information via /sys/kernel/debug/tracing/trace. 101 102 # cat trace 103 # tracer: nop 104 # 105 # TASK-PID CPU# TIMESTAMP FUNCTION 106 # | | | | | 107 zsh-24842 [006] 258544.995456: p_zsh_0x46420: (0x446420) arg1=446421 arg2=79 108 zsh-24842 [007] 258545.000270: p_zsh_0x46420: (0x446420) arg1=446421 arg2=79 109 zsh-24842 [002] 258545.043929: p_zsh_0x46420: (0x446420) arg1=446421 arg2=79 110 zsh-24842 [004] 258547.046129: p_zsh_0x46420: (0x446420) arg1=446421 arg2=79 111 112 Each line shows us probes were triggered for a pid 24842 with ip being 113 0x446421 and contents of ax register being 79.
- [ trace ]
- events-kmem.txt
- events-power.txt
- events.txt
- ftrace-design.txt
- ftrace.txt
- function-graph-fold.vim
- kprobetrace.txt
- mmiotrace.txt
- [ postprocess ]
- ring-buffer-design.txt
- tracepoint-analysis.txt
- tracepoints.txt
- uprobetracer.txt
Information is copyright its respective author. All material is available from the Linux Kernel Source distributed under a GPL License. This page is provided as a free service by mjmwired.net.