6142431810
To support probing module init functions, kprobe-tracer allows user to define a probe on non-existed function when it is given with a module name. This also enables user to set a probe on a function on a specific module, even if a same name (but different) function is locally defined in another module. The module name must be in the front of function name and separated by a ':'. e.g. btrfs:btrfs_init_sysfs Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: Arnaldo Carvalho de Melo <acme@redhat.com> Link: http://lkml.kernel.org/r/20110627072656.6528.89970.stgit@fedora15 Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
172 lines
6.9 KiB
Text
172 lines
6.9 KiB
Text
Kprobe-based Event Tracing
|
|
==========================
|
|
|
|
Documentation is written by Masami Hiramatsu
|
|
|
|
|
|
Overview
|
|
--------
|
|
These events are similar to tracepoint based events. Instead of Tracepoint,
|
|
this is based on kprobes (kprobe and kretprobe). So it can probe wherever
|
|
kprobes can probe (this means, all functions body except for __kprobes
|
|
functions). Unlike the Tracepoint based event, this can be added and removed
|
|
dynamically, on the fly.
|
|
|
|
To enable this feature, build your kernel with CONFIG_KPROBE_TRACING=y.
|
|
|
|
Similar to the events tracer, this doesn't need to be activated via
|
|
current_tracer. Instead of that, add probe points via
|
|
/sys/kernel/debug/tracing/kprobe_events, and enable it via
|
|
/sys/kernel/debug/tracing/events/kprobes/<EVENT>/enabled.
|
|
|
|
|
|
Synopsis of kprobe_events
|
|
-------------------------
|
|
p[:[GRP/]EVENT] [MOD:]SYM[+offs]|MEMADDR [FETCHARGS] : Set a probe
|
|
r[:[GRP/]EVENT] [MOD:]SYM[+0] [FETCHARGS] : Set a return probe
|
|
-:[GRP/]EVENT : Clear a probe
|
|
|
|
GRP : Group name. If omitted, use "kprobes" for it.
|
|
EVENT : Event name. If omitted, the event name is generated
|
|
based on SYM+offs or MEMADDR.
|
|
MOD : Module name which has given SYM.
|
|
SYM[+offs] : Symbol+offset where the probe is inserted.
|
|
MEMADDR : Address where the probe is inserted.
|
|
|
|
FETCHARGS : Arguments. Each probe can have up to 128 args.
|
|
%REG : Fetch register REG
|
|
@ADDR : Fetch memory at ADDR (ADDR should be in kernel)
|
|
@SYM[+|-offs] : Fetch memory at SYM +|- offs (SYM should be a data symbol)
|
|
$stackN : Fetch Nth entry of stack (N >= 0)
|
|
$stack : Fetch stack address.
|
|
$retval : Fetch return value.(*)
|
|
+|-offs(FETCHARG) : Fetch memory at FETCHARG +|- offs address.(**)
|
|
NAME=FETCHARG : Set NAME as the argument name of FETCHARG.
|
|
FETCHARG:TYPE : Set TYPE as the type of FETCHARG. Currently, basic types
|
|
(u8/u16/u32/u64/s8/s16/s32/s64), "string" and bitfield
|
|
are supported.
|
|
|
|
(*) only for return probe.
|
|
(**) this is useful for fetching a field of data structures.
|
|
|
|
Types
|
|
-----
|
|
Several types are supported for fetch-args. Kprobe tracer will access memory
|
|
by given type. Prefix 's' and 'u' means those types are signed and unsigned
|
|
respectively. Traced arguments are shown in decimal (signed) or hex (unsigned).
|
|
String type is a special type, which fetches a "null-terminated" string from
|
|
kernel space. This means it will fail and store NULL if the string container
|
|
has been paged out.
|
|
Bitfield is another special type, which takes 3 parameters, bit-width, bit-
|
|
offset, and container-size (usually 32). The syntax is;
|
|
|
|
b<bit-width>@<bit-offset>/<container-size>
|
|
|
|
|
|
Per-Probe Event Filtering
|
|
-------------------------
|
|
Per-probe event filtering feature allows you to set different filter on each
|
|
probe and gives you what arguments will be shown in trace buffer. If an event
|
|
name is specified right after 'p:' or 'r:' in kprobe_events, it adds an event
|
|
under tracing/events/kprobes/<EVENT>, at the directory you can see 'id',
|
|
'enabled', 'format' and 'filter'.
|
|
|
|
enabled:
|
|
You can enable/disable the probe by writing 1 or 0 on it.
|
|
|
|
format:
|
|
This shows the format of this probe event.
|
|
|
|
filter:
|
|
You can write filtering rules of this event.
|
|
|
|
id:
|
|
This shows the id of this probe event.
|
|
|
|
|
|
Event Profiling
|
|
---------------
|
|
You can check the total number of probe hits and probe miss-hits via
|
|
/sys/kernel/debug/tracing/kprobe_profile.
|
|
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 kprobe_events
|
|
as below.
|
|
|
|
echo 'p:myprobe do_sys_open dfd=%ax filename=%dx flags=%cx mode=+4($stack)' > /sys/kernel/debug/tracing/kprobe_events
|
|
|
|
This sets a kprobe on the top of do_sys_open() function with recording
|
|
1st to 4th arguments as "myprobe" event. Note, which register/stack entry is
|
|
assigned to each function argument depends on arch-specific ABI. If you unsure
|
|
the ABI, please try to use probe subcommand of perf-tools (you can find it
|
|
under tools/perf/).
|
|
As this example shows, users can choose more familiar names for each arguments.
|
|
|
|
echo 'r:myretprobe do_sys_open $retval' >> /sys/kernel/debug/tracing/kprobe_events
|
|
|
|
This sets a kretprobe on the return point of do_sys_open() function with
|
|
recording return value as "myretprobe" event.
|
|
You can see the format of these events via
|
|
/sys/kernel/debug/tracing/events/kprobes/<EVENT>/format.
|
|
|
|
cat /sys/kernel/debug/tracing/events/kprobes/myprobe/format
|
|
name: myprobe
|
|
ID: 780
|
|
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:unsigned long __probe_ip; offset:12; size:4; signed:0;
|
|
field:int __probe_nargs; offset:16; size:4; signed:1;
|
|
field:unsigned long dfd; offset:20; size:4; signed:0;
|
|
field:unsigned long filename; offset:24; size:4; signed:0;
|
|
field:unsigned long flags; offset:28; size:4; signed:0;
|
|
field:unsigned long mode; offset:32; size:4; signed:0;
|
|
|
|
|
|
print fmt: "(%lx) dfd=%lx filename=%lx flags=%lx mode=%lx", REC->__probe_ip,
|
|
REC->dfd, REC->filename, REC->flags, REC->mode
|
|
|
|
You can see that the event has 4 arguments as in the expressions you specified.
|
|
|
|
echo > /sys/kernel/debug/tracing/kprobe_events
|
|
|
|
This clears all probe points.
|
|
|
|
Or,
|
|
|
|
echo -:myprobe >> kprobe_events
|
|
|
|
This clears probe points selectively.
|
|
|
|
Right after definition, each event is disabled by default. For tracing these
|
|
events, you need to enable it.
|
|
|
|
echo 1 > /sys/kernel/debug/tracing/events/kprobes/myprobe/enable
|
|
echo 1 > /sys/kernel/debug/tracing/events/kprobes/myretprobe/enable
|
|
|
|
And you can see the traced information via /sys/kernel/debug/tracing/trace.
|
|
|
|
cat /sys/kernel/debug/tracing/trace
|
|
# tracer: nop
|
|
#
|
|
# TASK-PID CPU# TIMESTAMP FUNCTION
|
|
# | | | | |
|
|
<...>-1447 [001] 1038282.286875: myprobe: (do_sys_open+0x0/0xd6) dfd=3 filename=7fffd1ec4440 flags=8000 mode=0
|
|
<...>-1447 [001] 1038282.286878: myretprobe: (sys_openat+0xc/0xe <- do_sys_open) $retval=fffffffffffffffe
|
|
<...>-1447 [001] 1038282.286885: myprobe: (do_sys_open+0x0/0xd6) dfd=ffffff9c filename=40413c flags=8000 mode=1b6
|
|
<...>-1447 [001] 1038282.286915: myretprobe: (sys_open+0x1b/0x1d <- do_sys_open) $retval=3
|
|
<...>-1447 [001] 1038282.286969: myprobe: (do_sys_open+0x0/0xd6) dfd=ffffff9c filename=4041c6 flags=98800 mode=10
|
|
<...>-1447 [001] 1038282.286976: myretprobe: (sys_open+0x1b/0x1d <- do_sys_open) $retval=3
|
|
|
|
|
|
Each line shows when the kernel hits an event, and <- SYMBOL means kernel
|
|
returns from SYMBOL(e.g. "sys_open+0x1b/0x1d <- do_sys_open" means kernel
|
|
returns from do_sys_open to sys_open+0x1b).
|
|
|