blob: d0822811527ac9654a7246eb6bd849ba220e151d [file] [log] [blame]
Changbin Du00b27da2018-02-17 13:39:40 +08001=========================================
2Uprobe-tracer: Uprobe-based Event Tracing
3=========================================
Anton Arapovdecc6bf2013-04-03 18:00:39 +02004
Changbin Du00b27da2018-02-17 13:39:40 +08005:Author: Srikar Dronamraju
Anton Arapovdecc6bf2013-04-03 18:00:39 +02006
Srikar Dronamrajuf3f096c2012-04-11 16:00:43 +05307
8Overview
9--------
10Uprobe based trace events are similar to kprobe based trace events.
Anton Blanchard6b0b7552017-02-16 17:00:50 +110011To enable this feature, build your kernel with CONFIG_UPROBE_EVENTS=y.
Srikar Dronamrajuf3f096c2012-04-11 16:00:43 +053012
13Similar to the kprobe-event tracer, this doesn't need to be activated via
14current_tracer. Instead of that, add probe points via
15/sys/kernel/debug/tracing/uprobe_events, and enable it via
Andreas Zieglere50891d2018-07-16 13:05:57 +020016/sys/kernel/debug/tracing/events/uprobes/<EVENT>/enable.
Srikar Dronamrajuf3f096c2012-04-11 16:00:43 +053017
18However unlike kprobe-event tracer, the uprobe event interface expects the
Anton Arapovdecc6bf2013-04-03 18:00:39 +020019user to calculate the offset of the probepoint in the object.
Srikar Dronamrajuf3f096c2012-04-11 16:00:43 +053020
21Synopsis of uprobe_tracer
22-------------------------
Changbin Du00b27da2018-02-17 13:39:40 +080023::
24
Namhyung Kim306cfe22013-07-03 16:44:46 +090025 p[:[GRP/]EVENT] PATH:OFFSET [FETCHARGS] : Set a uprobe
26 r[:[GRP/]EVENT] PATH:OFFSET [FETCHARGS] : Set a return uprobe (uretprobe)
27 -:[GRP/]EVENT : Clear uprobe or uretprobe event
Srikar Dronamrajuf3f096c2012-04-11 16:00:43 +053028
Anton Arapovdecc6bf2013-04-03 18:00:39 +020029 GRP : Group name. If omitted, "uprobes" is the default value.
30 EVENT : Event name. If omitted, the event name is generated based
Namhyung Kim306cfe22013-07-03 16:44:46 +090031 on PATH+OFFSET.
Anton Arapovdecc6bf2013-04-03 18:00:39 +020032 PATH : Path to an executable or a library.
Namhyung Kim306cfe22013-07-03 16:44:46 +090033 OFFSET : Offset where the probe is inserted.
Srikar Dronamrajuf3f096c2012-04-11 16:00:43 +053034
Anton Arapovdecc6bf2013-04-03 18:00:39 +020035 FETCHARGS : Arguments. Each probe can have up to 128 args.
36 %REG : Fetch register REG
Namhyung Kimb079d372013-07-03 18:34:23 +090037 @ADDR : Fetch memory at ADDR (ADDR should be in userspace)
Namhyung Kimb7e0bf32013-11-25 13:42:47 +090038 @+OFFSET : Fetch memory at OFFSET (OFFSET from same file as PATH)
Namhyung Kimb079d372013-07-03 18:34:23 +090039 $stackN : Fetch Nth entry of stack (N >= 0)
40 $stack : Fetch stack address.
41 $retval : Fetch return value.(*)
Omar Sandoval35abb672016-06-08 18:38:02 -070042 $comm : Fetch current task comm.
Namhyung Kimb079d372013-07-03 18:34:23 +090043 +|-offs(FETCHARG) : Fetch memory at FETCHARG +|- offs address.(**)
44 NAME=FETCHARG : Set NAME as the argument name of FETCHARG.
45 FETCHARG:TYPE : Set TYPE as the type of FETCHARG. Currently, basic types
Masami Hiramatsu17ce3dc2016-08-18 17:57:50 +090046 (u8/u16/u32/u64/s8/s16/s32/s64), hexadecimal types
47 (x8/x16/x32/x64), "string" and bitfield are supported.
Namhyung Kimb079d372013-07-03 18:34:23 +090048
49 (*) only for return probe.
50 (**) this is useful for fetching a field of data structures.
51
52Types
53-----
54Several types are supported for fetch-args. Uprobe tracer will access memory
55by given type. Prefix 's' and 'u' means those types are signed and unsigned
Masami Hiramatsubdca79c22016-08-18 17:59:21 +090056respectively. 'x' prefix implies it is unsigned. Traced arguments are shown
57in decimal ('s' and 'u') or hexadecimal ('x'). Without type casting, 'x32'
58or 'x64' is used depends on the architecture (e.g. x86-32 uses x32, and
59x86-64 uses x64).
Namhyung Kimb079d372013-07-03 18:34:23 +090060String type is a special type, which fetches a "null-terminated" string from
61user space.
62Bitfield is another special type, which takes 3 parameters, bit-width, bit-
Changbin Du00b27da2018-02-17 13:39:40 +080063offset, and container-size (usually 32). The syntax is::
Namhyung Kimb079d372013-07-03 18:34:23 +090064
65 b<bit-width>@<bit-offset>/<container-size>
66
Omar Sandoval35abb672016-06-08 18:38:02 -070067For $comm, the default type is "string"; any other type is invalid.
68
Srikar Dronamrajuf3f096c2012-04-11 16:00:43 +053069
70Event Profiling
71---------------
Anton Arapovdecc6bf2013-04-03 18:00:39 +020072You can check the total number of probe hits and probe miss-hits via
Srikar Dronamrajuf3f096c2012-04-11 16:00:43 +053073/sys/kernel/debug/tracing/uprobe_profile.
Anton Arapovdecc6bf2013-04-03 18:00:39 +020074The first column is event name, the second is the number of probe hits,
Srikar Dronamrajuf3f096c2012-04-11 16:00:43 +053075the third is the number of probe miss-hits.
76
77Usage examples
78--------------
Anton Arapovdecc6bf2013-04-03 18:00:39 +020079 * Add a probe as a new uprobe event, write a new definition to uprobe_events
Changbin Du00b27da2018-02-17 13:39:40 +080080 as below (sets a uprobe at an offset of 0x4245c0 in the executable /bin/bash)::
Srikar Dronamrajuf3f096c2012-04-11 16:00:43 +053081
Marcin Nowakowski70587632016-10-06 09:52:12 +020082 echo 'p /bin/bash:0x4245c0' > /sys/kernel/debug/tracing/uprobe_events
Srikar Dronamrajuf3f096c2012-04-11 16:00:43 +053083
Changbin Du00b27da2018-02-17 13:39:40 +080084 * Add a probe as a new uretprobe event::
Srikar Dronamrajuf3f096c2012-04-11 16:00:43 +053085
Marcin Nowakowski70587632016-10-06 09:52:12 +020086 echo 'r /bin/bash:0x4245c0' > /sys/kernel/debug/tracing/uprobe_events
Srikar Dronamrajuf3f096c2012-04-11 16:00:43 +053087
Changbin Du00b27da2018-02-17 13:39:40 +080088 * Unset registered event::
Srikar Dronamrajuf3f096c2012-04-11 16:00:43 +053089
Marcin Nowakowski70587632016-10-06 09:52:12 +020090 echo '-:p_bash_0x4245c0' >> /sys/kernel/debug/tracing/uprobe_events
Anton Arapovdecc6bf2013-04-03 18:00:39 +020091
Changbin Du00b27da2018-02-17 13:39:40 +080092 * Print out the events that are registered::
Anton Arapovdecc6bf2013-04-03 18:00:39 +020093
94 cat /sys/kernel/debug/tracing/uprobe_events
95
Changbin Du00b27da2018-02-17 13:39:40 +080096 * Clear all events::
Anton Arapovdecc6bf2013-04-03 18:00:39 +020097
98 echo > /sys/kernel/debug/tracing/uprobe_events
99
100Following example shows how to dump the instruction pointer and %ax register
Changbin Du00b27da2018-02-17 13:39:40 +0800101at the probed text address. Probe zfree function in /bin/zsh::
Srikar Dronamrajuf3f096c2012-04-11 16:00:43 +0530102
103 # cd /sys/kernel/debug/tracing/
Anton Arapovdecc6bf2013-04-03 18:00:39 +0200104 # cat /proc/`pgrep zsh`/maps | grep /bin/zsh | grep r-xp
Srikar Dronamrajuf3f096c2012-04-11 16:00:43 +0530105 00400000-0048a000 r-xp 00000000 08:03 130904 /bin/zsh
106 # objdump -T /bin/zsh | grep -w zfree
107 0000000000446420 g DF .text 0000000000000012 Base zfree
108
Changbin Du00b27da2018-02-17 13:39:40 +08001090x46420 is the offset of zfree in object /bin/zsh that is loaded at
1100x00400000. Hence the command to uprobe would be::
Srikar Dronamrajuf3f096c2012-04-11 16:00:43 +0530111
Anton Arapovdecc6bf2013-04-03 18:00:39 +0200112 # echo 'p:zfree_entry /bin/zsh:0x46420 %ip %ax' > uprobe_events
Srikar Dronamrajuf3f096c2012-04-11 16:00:43 +0530113
Changbin Du00b27da2018-02-17 13:39:40 +0800114And the same for the uretprobe would be::
Anton Arapovdecc6bf2013-04-03 18:00:39 +0200115
116 # echo 'r:zfree_exit /bin/zsh:0x46420 %ip %ax' >> uprobe_events
117
Changbin Du00b27da2018-02-17 13:39:40 +0800118.. note:: User has to explicitly calculate the offset of the probe-point
119 in the object.
120
121We can see the events that are registered by looking at the uprobe_events file.
122::
Srikar Dronamrajuf3f096c2012-04-11 16:00:43 +0530123
124 # cat uprobe_events
Anton Arapovdecc6bf2013-04-03 18:00:39 +0200125 p:uprobes/zfree_entry /bin/zsh:0x00046420 arg1=%ip arg2=%ax
126 r:uprobes/zfree_exit /bin/zsh:0x00046420 arg1=%ip arg2=%ax
Srikar Dronamrajuec83db02012-05-08 16:41:26 +0530127
Changbin Du00b27da2018-02-17 13:39:40 +0800128Format of events can be seen by viewing the file events/uprobes/zfree_entry/format.
129::
Srikar Dronamrajuec83db02012-05-08 16:41:26 +0530130
Anton Arapovdecc6bf2013-04-03 18:00:39 +0200131 # cat events/uprobes/zfree_entry/format
132 name: zfree_entry
Srikar Dronamrajuec83db02012-05-08 16:41:26 +0530133 ID: 922
134 format:
Anton Arapovdecc6bf2013-04-03 18:00:39 +0200135 field:unsigned short common_type; offset:0; size:2; signed:0;
136 field:unsigned char common_flags; offset:2; size:1; signed:0;
137 field:unsigned char common_preempt_count; offset:3; size:1; signed:0;
138 field:int common_pid; offset:4; size:4; signed:1;
139 field:int common_padding; offset:8; size:4; signed:1;
Srikar Dronamrajuec83db02012-05-08 16:41:26 +0530140
Anton Arapovdecc6bf2013-04-03 18:00:39 +0200141 field:unsigned long __probe_ip; offset:12; size:4; signed:0;
142 field:u32 arg1; offset:16; size:4; signed:0;
143 field:u32 arg2; offset:20; size:4; signed:0;
Srikar Dronamrajuec83db02012-05-08 16:41:26 +0530144
145 print fmt: "(%lx) arg1=%lx arg2=%lx", REC->__probe_ip, REC->arg1, REC->arg2
Srikar Dronamrajuf3f096c2012-04-11 16:00:43 +0530146
147Right after definition, each event is disabled by default. For tracing these
Changbin Du00b27da2018-02-17 13:39:40 +0800148events, you need to enable it by::
Srikar Dronamrajuf3f096c2012-04-11 16:00:43 +0530149
150 # echo 1 > events/uprobes/enable
151
152Lets disable the event after sleeping for some time.
Changbin Du00b27da2018-02-17 13:39:40 +0800153::
Anton Arapovdecc6bf2013-04-03 18:00:39 +0200154
Srikar Dronamrajuf3f096c2012-04-11 16:00:43 +0530155 # sleep 20
156 # echo 0 > events/uprobes/enable
157
158And you can see the traced information via /sys/kernel/debug/tracing/trace.
Changbin Du00b27da2018-02-17 13:39:40 +0800159::
Srikar Dronamrajuf3f096c2012-04-11 16:00:43 +0530160
161 # cat trace
162 # tracer: nop
163 #
164 # TASK-PID CPU# TIMESTAMP FUNCTION
165 # | | | | |
Anton Arapovdecc6bf2013-04-03 18:00:39 +0200166 zsh-24842 [006] 258544.995456: zfree_entry: (0x446420) arg1=446420 arg2=79
167 zsh-24842 [007] 258545.000270: zfree_exit: (0x446540 <- 0x446420) arg1=446540 arg2=0
168 zsh-24842 [002] 258545.043929: zfree_entry: (0x446420) arg1=446420 arg2=79
169 zsh-24842 [004] 258547.046129: zfree_exit: (0x446540 <- 0x446420) arg1=446540 arg2=0
Srikar Dronamrajuf3f096c2012-04-11 16:00:43 +0530170
Anton Arapovdecc6bf2013-04-03 18:00:39 +0200171Output shows us uprobe was triggered for a pid 24842 with ip being 0x446420
172and contents of ax register being 79. And uretprobe was triggered with ip at
1730x446540 with counterpart function entry at 0x446420.