summaryrefslogtreecommitdiff
path: root/Documentation/trace/kprobetrace.rst
diff options
context:
space:
mode:
Diffstat (limited to 'Documentation/trace/kprobetrace.rst')
-rw-r--r--Documentation/trace/kprobetrace.rst83
1 files changed, 50 insertions, 33 deletions
diff --git a/Documentation/trace/kprobetrace.rst b/Documentation/trace/kprobetrace.rst
index 55993055902c..bf9cecb69fc9 100644
--- a/Documentation/trace/kprobetrace.rst
+++ b/Documentation/trace/kprobetrace.rst
@@ -6,21 +6,21 @@ Kprobe-based Event Tracing
Overview
--------
-These events are similar to tracepoint based events. Instead of Tracepoint,
+These events are similar to tracepoint-based events. Instead of tracepoints,
this is based on kprobes (kprobe and kretprobe). So it can probe wherever
kprobes can probe (this means, all functions except those with
__kprobes/nokprobe_inline annotation and those marked NOKPROBE_SYMBOL).
-Unlike the Tracepoint based event, this can be added and removed
+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_EVENTS=y.
-Similar to the events tracer, this doesn't need to be activated via
+Similar to the event 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>/enable.
+/sys/kernel/tracing/kprobe_events, and enable it via
+/sys/kernel/tracing/events/kprobes/<EVENT>/enable.
-You can also use /sys/kernel/debug/tracing/dynamic_events instead of
+You can also use /sys/kernel/tracing/dynamic_events instead of
kprobe_events. That interface will provide unified access to other
dynamic events too.
@@ -28,19 +28,21 @@ Synopsis of kprobe_events
-------------------------
::
- p[:[GRP/]EVENT] [MOD:]SYM[+offs]|MEMADDR [FETCHARGS] : Set a probe
- r[MAXACTIVE][:[GRP/]EVENT] [MOD:]SYM[+0] [FETCHARGS] : Set a return probe
- -:[GRP/]EVENT : Clear a probe
+ p[:[GRP/][EVENT]] [MOD:]SYM[+offs]|MEMADDR [FETCHARGS] : Set a probe
+ r[MAXACTIVE][:[GRP/][EVENT]] [MOD:]SYM[+0] [FETCHARGS] : Set a return probe
+ p[:[GRP/][EVENT]] [MOD:]SYM[+0]%return [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.
+ SYM%return : Return address of the symbol
MEMADDR : Address where the probe is inserted.
MAXACTIVE : Maximum number of instances of the specified function that
can be probed simultaneously, or 0 for the default value
- as defined in Documentation/kprobes.txt section 1.3.1.
+ as defined in Documentation/trace/kprobes.rst section 1.3.1.
FETCHARGS : Arguments. Each probe can have up to 128 args.
%REG : Fetch register REG
@@ -56,32 +58,43 @@ Synopsis of kprobe_events
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), hexadecimal types
- (x8/x16/x32/x64), "string", "ustring" and bitfield
- are supported.
-
- (\*1) only for the probe on function entry (offs == 0).
- (\*2) only for return probe.
+ (x8/x16/x32/x64), "char", "string", "ustring", "symbol", "symstr"
+ and bitfield are supported.
+
+ (\*1) only for the probe on function entry (offs == 0). Note, this argument access
+ is best effort, because depending on the argument type, it may be passed on
+ the stack. But this only support the arguments via registers.
+ (\*2) only for return probe. Note that this is also best effort. Depending on the
+ return value type, it might be passed via a pair of registers. But this only
+ accesses one register.
(\*3) this is useful for fetching a field of data structures.
(\*4) "u" means user-space dereference. See :ref:`user_mem_access`.
+.. _kprobetrace_types:
+
Types
-----
-Several types are supported for fetch-args. Kprobe tracer will access memory
+Several types are supported for fetchargs. Kprobe tracer will access memory
by given type. Prefix 's' and 'u' means those types are signed and unsigned
respectively. 'x' prefix implies it is unsigned. Traced arguments are shown
in decimal ('s' and 'u') or hexadecimal ('x'). Without type casting, 'x32'
or 'x64' is used depends on the architecture (e.g. x86-32 uses x32, and
x86-64 uses x64).
+
These value types can be an array. To record array data, you can add '[N]'
(where N is a fixed number, less than 64) to the base type.
-E.g. 'x16[4]' means an array of x16 (2bytes hex) with 4 elements.
+E.g. 'x16[4]' means an array of x16 (2-byte hex) with 4 elements.
Note that the array can be applied to memory type fetchargs, you can not
apply it to registers/stack-entries etc. (for example, '$stack1:x8[8]' is
wrong, but '+8($stack):x8[8]' is OK.)
+
+Char type can be used to show the character value of traced arguments.
+
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. "ustring" type is an alternative of string for user-space.
-See :ref:`user_mem_access` for more info..
+See :ref:`user_mem_access` for more info.
+
The string array type is a bit different from other types. For other base
types, <base-type>[1] is equal to <base-type> (e.g. +0(%di):x32[1] is same
as +0(%di):x32.) But string[1] is not equal to string. The string type itself
@@ -94,9 +107,14 @@ offset, and container-size (usually 32). The syntax is::
Symbol type('symbol') is an alias of u32 or u64 type (depends on BITS_PER_LONG)
which shows given pointer in "symbol+offset" style.
+On the other hand, symbol-string type ('symstr') converts the given address to
+"symbol+offset/symbolsize" style and stores it as a null-terminated string.
+With 'symstr' type, you can filter the event with wildcard pattern of the
+symbols, and you don't need to solve symbol name by yourself.
For $comm, the default type is "string"; any other type is invalid.
.. _user_mem_access:
+
User Memory Access
------------------
Kprobe events supports user-space memory access. For that purpose, you can use
@@ -113,8 +131,8 @@ space. 'ustring' is a shortcut way of performing the same task. That is,
Note that kprobe-event provides the user-memory access syntax but it doesn't
use it transparently. This means if you use normal dereference or string type
-for user memory, it might fail, and may always fail on some archs. The user
-has to carefully check if the target data is in kernel or user space.
+for user memory, it might fail, and may always fail on some architectures. The
+user has to carefully check if the target data is in kernel or user space.
Per-Probe Event Filtering
-------------------------
@@ -143,7 +161,7 @@ trigger:
Event Profiling
---------------
You can check the total number of probe hits and probe miss-hits via
-/sys/kernel/debug/tracing/kprobe_profile.
+/sys/kernel/tracing/kprobe_profile.
The first column is event name, the second is the number of probe hits,
the third is the number of probe miss-hits.
@@ -153,11 +171,11 @@ You can add and enable new kprobe events when booting up the kernel by
"kprobe_event=" parameter. The parameter accepts a semicolon-delimited
kprobe events, which format is similar to the kprobe_events.
The difference is that the probe definition parameters are comma-delimited
-instead of space. For example, adding myprobe event on do_sys_open like below
+instead of space. For example, adding myprobe event on do_sys_open like below::
p:myprobe do_sys_open dfd=%ax filename=%dx flags=%cx mode=+4($stack)
-should be below for kernel boot parameter (just replace spaces with comma)
+should be below for kernel boot parameter (just replace spaces with comma)::
p:myprobe,do_sys_open,dfd=%ax,filename=%dx,flags=%cx,mode=+4($stack)
@@ -167,7 +185,7 @@ Usage examples
To add a probe as a new event, write a new definition to kprobe_events
as below::
- echo 'p:myprobe do_sys_open dfd=%ax filename=%dx flags=%cx mode=+4($stack)' > /sys/kernel/debug/tracing/kprobe_events
+ echo 'p:myprobe do_sys_open dfd=%ax filename=%dx flags=%cx mode=+4($stack)' > /sys/kernel/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
@@ -177,15 +195,15 @@ 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
+ echo 'r:myretprobe do_sys_open $retval' >> /sys/kernel/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.
+/sys/kernel/tracing/events/kprobes/<EVENT>/format.
::
- cat /sys/kernel/debug/tracing/events/kprobes/myprobe/format
+ cat /sys/kernel/tracing/events/kprobes/myprobe/format
name: myprobe
ID: 780
format:
@@ -208,7 +226,7 @@ You can see the format of these events via
You can see that the event has 4 arguments as in the expressions you specified.
::
- echo > /sys/kernel/debug/tracing/kprobe_events
+ echo > /sys/kernel/tracing/kprobe_events
This clears all probe points.
@@ -223,8 +241,8 @@ 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
+ echo 1 > /sys/kernel/tracing/events/kprobes/myprobe/enable
+ echo 1 > /sys/kernel/tracing/events/kprobes/myretprobe/enable
Use the following command to start tracing in an interval.
::
@@ -233,10 +251,10 @@ Use the following command to start tracing in an interval.
Open something...
# echo 0 > tracing_on
-And you can see the traced information via /sys/kernel/debug/tracing/trace.
+And you can see the traced information via /sys/kernel/tracing/trace.
::
- cat /sys/kernel/debug/tracing/trace
+ cat /sys/kernel/tracing/trace
# tracer: nop
#
# TASK-PID CPU# TIMESTAMP FUNCTION
@@ -252,4 +270,3 @@ And you can see the traced information via /sys/kernel/debug/tracing/trace.
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).
-