NAME¶

perf-probe - Define new dynamic tracepoints

SYNOPSIS¶

perf probe [options] --add=PROBE [...]
or
perf probe [options] PROBE
or
perf probe [options] --del=[GROUP:]EVENT [...]
or
perf probe --list
or
perf probe [options] --line=LINE
or
perf probe [options] --vars=PROBEPOINT

DESCRIPTION¶

This command defines dynamic tracepoint events, by symbol and registers without debuginfo, or by C expressions (C line numbers, C function names, and C local variables) with debuginfo.

OPTIONS¶

-k, --vmlinux=PATH

-m, --module=MODNAME|PATH

-s, --source=PATH

-v, --verbose

-q, --quiet

-a, --add=

-d, --del=

-l, --list

-L, --line=

-V, --vars=

--externs

-F, --funcs

--filter=FILTER

-f, --force

-n, --dry-run

--max-probes=NUM

-x, --exec=PATH

--demangle

--demangle-kernel

In absence of -m/-x options, perf probe checks if the first argument after the options is an absolute path name. If its an absolute path, perf probe uses it as a target module/target user space binary to probe.

PROBE SYNTAX¶

Probe points are defined by following syntax.

1) Define event based on function name


 [EVENT=]FUNC[@SRC][:RLN|+OFFS|%return|;PTN] [ARG ...]

2) Define event based on source file with line number


 [EVENT=]SRC:ALN [ARG ...]

3) Define event based on source file with lazy pattern


 [EVENT=]SRC;PTN [ARG ...]

EVENT specifies the name of new event, if omitted, it will be set the name of the probed function. Currently, event group name is set as probe. FUNC specifies a probed function name, and it may have one of the following options; +OFFS is the offset from function entry address in bytes, :RLN is the relative-line number from function entry line, and %return means that it probes function return. And ;PTN means lazy matching pattern (see LAZY MATCHING). Note that ;PTN must be the end of the probe point definition. In addition, @SRC specifies a source file which has that function. It is also possible to specify a probe point by the source line number or lazy matching by using SRC:ALN or SRC;PTN syntax, where SRC is the source file path, :ALN is the line number and ;PTN is the lazy matching pattern. ARG specifies the arguments of this probe point, (see PROBE ARGUMENT).

PROBE ARGUMENT¶

Each probe argument follows below syntax.

[NAME=]LOCALVAR|$retval|%REG|@SYMBOL[:TYPE]

NAME specifies the name of this argument (optional). You can use the name of local variable, local data structure member (e.g. var→field, var.field2), local array with fixed index (e.g. array[1], var→array[0], var→pointer[2]), or kprobe-tracer argument format (e.g. $retval, %ax, etc). Note that the name of this argument will be set as the last member name if you specify a local data structure member (e.g. field2 for var→field1.field2.) $vars special argument is also available for NAME, it is expanded to the local variables which can access at given probe point. TYPE casts the type of this argument (optional). If omitted, perf probe automatically set the type based on debuginfo. You can specify string type only for the local variable or structure member which is an array of or a pointer to char or unsigned char type.

On x86 systems %REG is always the short form of the register: for example %AX. %RAX or %EAX is not valid.

LINE SYNTAX¶

Line range is described by following syntax.

"FUNC[@SRC][:RLN[+NUM|-RLN2]]|SRC[:ALN[+NUM|-ALN2]]"

FUNC specifies the function name of showing lines. RLN is the start line number from function entry line, and RLN2 is the end line number. As same as probe syntax, SRC means the source file path, ALN is start line number, and ALN2 is end line number in the file. It is also possible to specify how many lines to show by using NUM. Moreover, FUNC@SRC combination is good for searching a specific function when several functions share same name. So, "source.c:100-120" shows lines between 100th to l20th in source.c file. And "func:10+20" shows 20 lines from 10th line of func function.

LAZY MATCHING¶

The lazy line matching is similar to glob matching but ignoring spaces in both of pattern and target. So this accepts wildcards(´*´, ´?´) and character classes(e.g. [a-z], [!A-Z]).

e.g. a=* can matches a=b, a = b, a == b and so on.

This provides some sort of flexibility and robustness to probe point definitions against minor code changes. For example, actual 10th line of schedule() can be moved easily by modifying schedule(), but the same line matching rq=cpu_rq* may still exist in the function.)

FILTER PATTERN¶

The filter pattern is a glob matching pattern(s) to filter variables.
In addition, you can use "!" for specifying filter-out rule. You also can give several rules combined with "&" or "|", and fold those rules as one rule by using "(" ")".

e.g. With --filter "foo* | bar*", perf probe -V shows variables which start with "foo" or "bar". With --filter "!foo* & *bar", perf probe -V shows variables which don’t start with "foo" and end with "bar", like "fizzbar". But "foobar" is filtered out.

EXAMPLES¶

Display which lines in schedule() can be probed:

./perf probe --line schedule

Add a probe on schedule() function 12th line with recording cpu local variable:

./perf probe schedule:12 cpu
or
./perf probe --add=´schedule:12 cpu´

this will add one or more probes which has the name start with "schedule".

Add probes on lines in schedule() function which calls update_rq_clock().

./perf probe ´schedule;update_rq_clock*´
or
./perf probe --add=´schedule;update_rq_clock*´

Delete all probes on schedule().

./perf probe --del=´schedule*´

Add probes at zfree() function on /bin/zsh

./perf probe -x /bin/zsh zfree or ./perf probe /bin/zsh zfree

Add probes at malloc() function on libc

./perf probe -x /lib/libc.so.6 malloc or ./perf probe /lib/libc.so.6 malloc

SEE ALSO¶

perf-trace(1), perf-record(1)