diff options
author | Masami Hiramatsu <mhiramat@redhat.com> | 2009-08-19 15:13:57 -0400 |
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committer | Frederic Weisbecker <fweisbec@gmail.com> | 2009-08-26 20:32:16 -0400 |
commit | d8ec91850efaf6cee9234c80260fe03881242374 (patch) | |
tree | 70bac1f4c607b06ba57d0dbe3c394c8df0a0f50e | |
parent | 413d37d1eb69c1765b9ace0a612dac9b6c990e66 (diff) |
tracing: Add kprobe-based event tracer documentation
Add the documentation to use the kprobe based event tracer.
[fweisbec@gmail.com: Split tracer and its Documentation in two patchs]
Signed-off-by: Masami Hiramatsu <mhiramat@redhat.com>
Acked-by: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Frank Ch. Eigler <fche@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Jason Baron <jbaron@redhat.com>
Cc: Jim Keniston <jkenisto@us.ibm.com>
Cc: K.Prasad <prasad@linux.vnet.ibm.com>
Cc: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Przemysław Pawełczyk <przemyslaw@pawelczyk.it>
Cc: Roland McGrath <roland@redhat.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Tom Zanussi <tzanussi@gmail.com>
Cc: Vegard Nossum <vegard.nossum@gmail.com>
LKML-Reference: <20090813203510.31965.29123.stgit@localhost.localdomain>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
-rw-r--r-- | Documentation/trace/kprobetrace.txt | 139 |
1 files changed, 139 insertions, 0 deletions
diff --git a/Documentation/trace/kprobetrace.txt b/Documentation/trace/kprobetrace.txt new file mode 100644 index 000000000000..efff6eb1b3db --- /dev/null +++ b/Documentation/trace/kprobetrace.txt | |||
@@ -0,0 +1,139 @@ | |||
1 | Kprobe-based Event Tracer | ||
2 | ========================= | ||
3 | |||
4 | Documentation is written by Masami Hiramatsu | ||
5 | |||
6 | |||
7 | Overview | ||
8 | -------- | ||
9 | This tracer is similar to the events tracer which is based on Tracepoint | ||
10 | infrastructure. Instead of Tracepoint, this tracer is based on kprobes(kprobe | ||
11 | and kretprobe). It probes anywhere where kprobes can probe(this means, all | ||
12 | functions body except for __kprobes functions). | ||
13 | |||
14 | Unlike the function tracer, this tracer can probe instructions inside of | ||
15 | kernel functions. It allows you to check which instruction has been executed. | ||
16 | |||
17 | Unlike the Tracepoint based events tracer, this tracer can add and remove | ||
18 | probe points on the fly. | ||
19 | |||
20 | Similar to the events tracer, this tracer doesn't need to be activated via | ||
21 | current_tracer, instead of that, just set probe points via | ||
22 | /sys/kernel/debug/tracing/kprobe_events. And you can set filters on each | ||
23 | probe events via /sys/kernel/debug/tracing/events/kprobes/<EVENT>/filter. | ||
24 | |||
25 | |||
26 | Synopsis of kprobe_events | ||
27 | ------------------------- | ||
28 | p[:EVENT] SYMBOL[+offs|-offs]|MEMADDR [FETCHARGS] : Set a probe | ||
29 | r[:EVENT] SYMBOL[+0] [FETCHARGS] : Set a return probe | ||
30 | |||
31 | EVENT : Event name. | ||
32 | SYMBOL[+offs|-offs] : Symbol+offset where the probe is inserted. | ||
33 | MEMADDR : Address where the probe is inserted. | ||
34 | |||
35 | FETCHARGS : Arguments. | ||
36 | %REG : Fetch register REG | ||
37 | sN : Fetch Nth entry of stack (N >= 0) | ||
38 | sa : Fetch stack address. | ||
39 | @ADDR : Fetch memory at ADDR (ADDR should be in kernel) | ||
40 | @SYM[+|-offs] : Fetch memory at SYM +|- offs (SYM should be a data symbol) | ||
41 | aN : Fetch function argument. (N >= 0)(*) | ||
42 | rv : Fetch return value.(**) | ||
43 | ra : Fetch return address.(**) | ||
44 | +|-offs(FETCHARG) : fetch memory at FETCHARG +|- offs address.(***) | ||
45 | |||
46 | (*) aN may not correct on asmlinkaged functions and at the middle of | ||
47 | function body. | ||
48 | (**) only for return probe. | ||
49 | (***) this is useful for fetching a field of data structures. | ||
50 | |||
51 | |||
52 | Per-Probe Event Filtering | ||
53 | ------------------------- | ||
54 | Per-probe event filtering feature allows you to set different filter on each | ||
55 | probe and gives you what arguments will be shown in trace buffer. If an event | ||
56 | name is specified right after 'p:' or 'r:' in kprobe_events, the tracer adds | ||
57 | an event under tracing/events/kprobes/<EVENT>, at the directory you can see | ||
58 | 'id', 'enabled', 'format' and 'filter'. | ||
59 | |||
60 | enabled: | ||
61 | You can enable/disable the probe by writing 1 or 0 on it. | ||
62 | |||
63 | format: | ||
64 | It shows the format of this probe event. It also shows aliases of arguments | ||
65 | which you specified to kprobe_events. | ||
66 | |||
67 | filter: | ||
68 | You can write filtering rules of this event. And you can use both of aliase | ||
69 | names and field names for describing filters. | ||
70 | |||
71 | |||
72 | Usage examples | ||
73 | -------------- | ||
74 | To add a probe as a new event, write a new definition to kprobe_events | ||
75 | as below. | ||
76 | |||
77 | echo p:myprobe do_sys_open a0 a1 a2 a3 > /sys/kernel/debug/tracing/kprobe_events | ||
78 | |||
79 | This sets a kprobe on the top of do_sys_open() function with recording | ||
80 | 1st to 4th arguments as "myprobe" event. | ||
81 | |||
82 | echo r:myretprobe do_sys_open rv ra >> /sys/kernel/debug/tracing/kprobe_events | ||
83 | |||
84 | This sets a kretprobe on the return point of do_sys_open() function with | ||
85 | recording return value and return address as "myretprobe" event. | ||
86 | You can see the format of these events via | ||
87 | /sys/kernel/debug/tracing/events/kprobes/<EVENT>/format. | ||
88 | |||
89 | cat /sys/kernel/debug/tracing/events/kprobes/myprobe/format | ||
90 | name: myprobe | ||
91 | ID: 23 | ||
92 | format: | ||
93 | field:unsigned short common_type; offset:0; size:2; | ||
94 | field:unsigned char common_flags; offset:2; size:1; | ||
95 | field:unsigned char common_preempt_count; offset:3; size:1; | ||
96 | field:int common_pid; offset:4; size:4; | ||
97 | field:int common_tgid; offset:8; size:4; | ||
98 | |||
99 | field: unsigned long ip; offset:16;tsize:8; | ||
100 | field: int nargs; offset:24;tsize:4; | ||
101 | field: unsigned long arg0; offset:32;tsize:8; | ||
102 | field: unsigned long arg1; offset:40;tsize:8; | ||
103 | field: unsigned long arg2; offset:48;tsize:8; | ||
104 | field: unsigned long arg3; offset:56;tsize:8; | ||
105 | |||
106 | alias: a0; original: arg0; | ||
107 | alias: a1; original: arg1; | ||
108 | alias: a2; original: arg2; | ||
109 | alias: a3; original: arg3; | ||
110 | |||
111 | print fmt: "%lx: 0x%lx 0x%lx 0x%lx 0x%lx", ip, arg0, arg1, arg2, arg3 | ||
112 | |||
113 | |||
114 | You can see that the event has 4 arguments and alias expressions | ||
115 | corresponding to it. | ||
116 | |||
117 | echo > /sys/kernel/debug/tracing/kprobe_events | ||
118 | |||
119 | This clears all probe points. and you can see the traced information via | ||
120 | /sys/kernel/debug/tracing/trace. | ||
121 | |||
122 | cat /sys/kernel/debug/tracing/trace | ||
123 | # tracer: nop | ||
124 | # | ||
125 | # TASK-PID CPU# TIMESTAMP FUNCTION | ||
126 | # | | | | | | ||
127 | <...>-1447 [001] 1038282.286875: do_sys_open+0x0/0xd6: 0x3 0x7fffd1ec4440 0x8000 0x0 | ||
128 | <...>-1447 [001] 1038282.286878: sys_openat+0xc/0xe <- do_sys_open: 0xfffffffffffffffe 0xffffffff81367a3a | ||
129 | <...>-1447 [001] 1038282.286885: do_sys_open+0x0/0xd6: 0xffffff9c 0x40413c 0x8000 0x1b6 | ||
130 | <...>-1447 [001] 1038282.286915: sys_open+0x1b/0x1d <- do_sys_open: 0x3 0xffffffff81367a3a | ||
131 | <...>-1447 [001] 1038282.286969: do_sys_open+0x0/0xd6: 0xffffff9c 0x4041c6 0x98800 0x10 | ||
132 | <...>-1447 [001] 1038282.286976: sys_open+0x1b/0x1d <- do_sys_open: 0x3 0xffffffff81367a3a | ||
133 | |||
134 | |||
135 | Each line shows when the kernel hits a probe, and <- SYMBOL means kernel | ||
136 | returns from SYMBOL(e.g. "sys_open+0x1b/0x1d <- do_sys_open" means kernel | ||
137 | returns from do_sys_open to sys_open+0x1b). | ||
138 | |||
139 | |||