]>
Commit | Line | Data |
---|---|---|
decc6bfb AA |
1 | Uprobe-tracer: Uprobe-based Event Tracing |
2 | ========================================= | |
3 | ||
4 | Documentation written by Srikar Dronamraju | |
5 | ||
f3f096cf SD |
6 | |
7 | Overview | |
8 | -------- | |
9 | Uprobe based trace events are similar to kprobe based trace events. | |
ec83db0f | 10 | To enable this feature, build your kernel with CONFIG_UPROBE_EVENT=y. |
f3f096cf SD |
11 | |
12 | Similar to the kprobe-event tracer, this doesn't need to be activated via | |
13 | current_tracer. Instead of that, add probe points via | |
14 | /sys/kernel/debug/tracing/uprobe_events, and enable it via | |
15 | /sys/kernel/debug/tracing/events/uprobes/<EVENT>/enabled. | |
16 | ||
17 | However unlike kprobe-event tracer, the uprobe event interface expects the | |
decc6bfb | 18 | user to calculate the offset of the probepoint in the object. |
f3f096cf SD |
19 | |
20 | Synopsis of uprobe_tracer | |
21 | ------------------------- | |
decc6bfb AA |
22 | p[:[GRP/]EVENT] PATH:SYMBOL[+offs] [FETCHARGS] : Set a uprobe |
23 | r[:[GRP/]EVENT] PATH:SYMBOL[+offs] [FETCHARGS] : Set a return uprobe (uretprobe) | |
24 | -:[GRP/]EVENT : Clear uprobe or uretprobe event | |
f3f096cf | 25 | |
decc6bfb AA |
26 | GRP : Group name. If omitted, "uprobes" is the default value. |
27 | EVENT : Event name. If omitted, the event name is generated based | |
28 | on SYMBOL+offs. | |
29 | PATH : Path to an executable or a library. | |
30 | SYMBOL[+offs] : Symbol+offset where the probe is inserted. | |
f3f096cf | 31 | |
decc6bfb AA |
32 | FETCHARGS : Arguments. Each probe can have up to 128 args. |
33 | %REG : Fetch register REG | |
f3f096cf SD |
34 | |
35 | Event Profiling | |
36 | --------------- | |
decc6bfb | 37 | You can check the total number of probe hits and probe miss-hits via |
f3f096cf | 38 | /sys/kernel/debug/tracing/uprobe_profile. |
decc6bfb | 39 | The first column is event name, the second is the number of probe hits, |
f3f096cf SD |
40 | the third is the number of probe miss-hits. |
41 | ||
42 | Usage examples | |
43 | -------------- | |
decc6bfb AA |
44 | * Add a probe as a new uprobe event, write a new definition to uprobe_events |
45 | as below: (sets a uprobe at an offset of 0x4245c0 in the executable /bin/bash) | |
46 | ||
47 | echo 'p: /bin/bash:0x4245c0' > /sys/kernel/debug/tracing/uprobe_events | |
48 | ||
49 | * Add a probe as a new uretprobe event: | |
50 | ||
51 | echo 'r: /bin/bash:0x4245c0' > /sys/kernel/debug/tracing/uprobe_events | |
52 | ||
53 | * Unset registered event: | |
f3f096cf | 54 | |
decc6bfb | 55 | echo '-:bash_0x4245c0' >> /sys/kernel/debug/tracing/uprobe_events |
f3f096cf | 56 | |
decc6bfb | 57 | * Print out the events that are registered: |
f3f096cf | 58 | |
decc6bfb | 59 | cat /sys/kernel/debug/tracing/uprobe_events |
f3f096cf | 60 | |
decc6bfb | 61 | * Clear all events: |
f3f096cf | 62 | |
decc6bfb AA |
63 | echo > /sys/kernel/debug/tracing/uprobe_events |
64 | ||
65 | Following example shows how to dump the instruction pointer and %ax register | |
66 | at the probed text address. Probe zfree function in /bin/zsh: | |
f3f096cf SD |
67 | |
68 | # cd /sys/kernel/debug/tracing/ | |
decc6bfb | 69 | # cat /proc/`pgrep zsh`/maps | grep /bin/zsh | grep r-xp |
f3f096cf SD |
70 | 00400000-0048a000 r-xp 00000000 08:03 130904 /bin/zsh |
71 | # objdump -T /bin/zsh | grep -w zfree | |
72 | 0000000000446420 g DF .text 0000000000000012 Base zfree | |
73 | ||
decc6bfb AA |
74 | 0x46420 is the offset of zfree in object /bin/zsh that is loaded at |
75 | 0x00400000. Hence the command to uprobe would be: | |
76 | ||
77 | # echo 'p:zfree_entry /bin/zsh:0x46420 %ip %ax' > uprobe_events | |
78 | ||
79 | And the same for the uretprobe would be: | |
f3f096cf | 80 | |
decc6bfb | 81 | # echo 'r:zfree_exit /bin/zsh:0x46420 %ip %ax' >> uprobe_events |
f3f096cf | 82 | |
decc6bfb | 83 | Please note: User has to explicitly calculate the offset of the probe-point |
f3f096cf SD |
84 | in the object. We can see the events that are registered by looking at the |
85 | uprobe_events file. | |
86 | ||
87 | # cat uprobe_events | |
decc6bfb AA |
88 | p:uprobes/zfree_entry /bin/zsh:0x00046420 arg1=%ip arg2=%ax |
89 | r:uprobes/zfree_exit /bin/zsh:0x00046420 arg1=%ip arg2=%ax | |
ec83db0f | 90 | |
decc6bfb | 91 | Format of events can be seen by viewing the file events/uprobes/zfree_entry/format |
ec83db0f | 92 | |
decc6bfb AA |
93 | # cat events/uprobes/zfree_entry/format |
94 | name: zfree_entry | |
ec83db0f SD |
95 | ID: 922 |
96 | format: | |
decc6bfb AA |
97 | field:unsigned short common_type; offset:0; size:2; signed:0; |
98 | field:unsigned char common_flags; offset:2; size:1; signed:0; | |
99 | field:unsigned char common_preempt_count; offset:3; size:1; signed:0; | |
100 | field:int common_pid; offset:4; size:4; signed:1; | |
101 | field:int common_padding; offset:8; size:4; signed:1; | |
ec83db0f | 102 | |
decc6bfb AA |
103 | field:unsigned long __probe_ip; offset:12; size:4; signed:0; |
104 | field:u32 arg1; offset:16; size:4; signed:0; | |
105 | field:u32 arg2; offset:20; size:4; signed:0; | |
ec83db0f SD |
106 | |
107 | print fmt: "(%lx) arg1=%lx arg2=%lx", REC->__probe_ip, REC->arg1, REC->arg2 | |
f3f096cf SD |
108 | |
109 | Right after definition, each event is disabled by default. For tracing these | |
110 | events, you need to enable it by: | |
111 | ||
112 | # echo 1 > events/uprobes/enable | |
113 | ||
114 | Lets disable the event after sleeping for some time. | |
decc6bfb | 115 | |
f3f096cf SD |
116 | # sleep 20 |
117 | # echo 0 > events/uprobes/enable | |
118 | ||
119 | And you can see the traced information via /sys/kernel/debug/tracing/trace. | |
120 | ||
121 | # cat trace | |
122 | # tracer: nop | |
123 | # | |
124 | # TASK-PID CPU# TIMESTAMP FUNCTION | |
125 | # | | | | | | |
decc6bfb AA |
126 | zsh-24842 [006] 258544.995456: zfree_entry: (0x446420) arg1=446420 arg2=79 |
127 | zsh-24842 [007] 258545.000270: zfree_exit: (0x446540 <- 0x446420) arg1=446540 arg2=0 | |
128 | zsh-24842 [002] 258545.043929: zfree_entry: (0x446420) arg1=446420 arg2=79 | |
129 | zsh-24842 [004] 258547.046129: zfree_exit: (0x446540 <- 0x446420) arg1=446540 arg2=0 | |
130 | ||
131 | Output shows us uprobe was triggered for a pid 24842 with ip being 0x446420 | |
132 | and contents of ax register being 79. And uretprobe was triggered with ip at | |
133 | 0x446540 with counterpart function entry at 0x446420. |