NAME¶

uftrace-live - Trace functions in a command during live execution

SYNOPSIS¶

uftrace [live] [options] COMMAND [command-options]

DESCRIPTION¶

This command runs COMMAND and prints its functions with time and thread info. This is basically the same as running the uftrace record and uftrace replay commands in turn, but it does not save a data file. This command accepts most options that are accepted by the record or replay commands.

COMMON OPTIONS¶

-F FUNC, --filter=FUNC

Set filter to trace selected functions and their children functions. This option can be used more than once. See FILTERS.

-N FUNC, --notrace=FUNC

Set filter not to trace selected functions and their children functions. This option can be used more than once. See FILTERS.

-C FUNC, --caller-filter=FUNC

Set filter to trace callers of selected functions only. This option can be used more than once. See FILTERS.

-T TRG, --trigger=TRG

Set trigger on selected functions. This option can be used more than once. See TRIGGERS.

-D DEPTH, --depth=DEPTH

Set global trace limit in nesting level. See FILTERS.

-t TIME, --time-filter=TIME

Do not show functions which run under the time threshold. If some functions explicitly have the `trace' trigger applied, those are always traced regardless of execution time. See FILTERS.

-Z SIZE, --size-filter=SIZE

Do not show functions smaller than SIZE bytes. See FILTERS.

-L LOCATION, --loc-filter=LOCATION

Set filter to trace selected source locations. This option can be used more than once. Applies to replay command, not record. See FILTERS.

--no-libcall

Do not record library function invocations. Library calls are normally traced by hooking calls to the resolver function of dynamic linker in the PLT. One can disable it with this option.

--no-event

Disable event recording which is used by default. Note that explicit event tracing by --event option is not affected by this. Implies --no-sched.

--no-sched

Disable schedule event recording which is used by default.

--match=TYPE

Use pattern match using TYPE. Possible types are regex and glob. Default is regex.

--disable

DEPRECATED. Use --trace=off instead.

--trace=STATE

Set uftrace tracing STATE. Possible states are on and off. Default is on. This is only meaningful when used with a trace_on trigger or with the agent

--with-syms=DIR

Read symbol data from the .sym files in DIR directory instead of the binary. This can be useful to deal with stripped binaries. The file name of the main binary should be the same when saved and used.

LIVE OPTIONS¶

--list-event

Show available events in the process.

--report

Show live-report before replay.

--record

Do not discard the recorded data.

-p PID, --pid=PID

Switch to client mode. Forward the supported tracing options to a running target with given PID. See AGENT.

RECORD OPTIONS¶

-A SPEC, --argument=SPEC

Record function arguments. This option can be used more than once. See ARGUMENTS.

-R SPEC, --retval=SPEC

Record function return values. This option can be used more than once. See ARGUMENTS.

-P FUNC, --patch=FUNC

Patch FUNC dynamically. This is only applicable binaries built by gcc with -pg -mfentry -mnop-mcount or clang with -fxray-instrument. This option can be used more than once. See DYNAMIC TRACING.

-U FUNC, --unpatch=FUNC

Do not apply dynamic patching for FUNC. This option can be used more than once. See DYNAMIC TRACING.

-E EVENT, --event=EVENT

Enable event tracing. The event should be available on the system.

-S SCRIPT_PATH, --script=SCRIPT_PATH

Run a given script to do additional work at the entry and exit of function during target program execution. The type of script is detected by the postfix such as `.py' for python. See SCRIPT EXECUTION.

-W, --watch=POINT

Add watch point to display POINT if the value is changed. See WATCH POINT.

-a, --auto-args

Automatically record arguments and return values of known functions. These are usually functions in standard (C language or system) libraries but if debug info is available it includes functions in the user program.

-l, --nest-libcall

Trace function calls between libraries. By default, uftrace only record library call from the main executable. Implies --force.

-k, --kernel

Trace kernel functions as well as user functions. Only kernel entry/exit functions will be traced by default. Use the --kernel-depth option to override this.

-K DEPTH, --kernel-depth=DEPTH

Set kernel max function depth separately. Implies --kernel.

--clock=CLOCK

Set clock source for timestamp recording. CLOCK can be one of `mono', `mono_raw', or `boot'. Default is `mono'.

--signal=TRG

Set trigger on selected signals rather than functions. But there are restrictions so only a few of trigger actions are support for signals. The available actions are: trace_on, trace_off, finish. This option can be used more than once. See TRIGGERS.

--nop

Do not record and replay any functions. This is a no-op and only meaningful for performance comparisons.

--force

Allow running uftrace even if some problems occur. When uftrace record finds no mcount symbol (which is generated by compiler) in the executable, it quits with an error message since uftrace can not trace the program. However, it is possible that the user is only interested in functions within a dynamically-linked library, in which case this option can be used to cause uftrace to run the program regardless. Also, the -A/--argument and -R/--retval options work only for binaries built with -pg, so uftrace will normally exit when it tries to run binaries built without that option. This option ignores the warning and goes on tracing without the argument and/or return value.

--time

Print running time of children in time(1)-style.

-e, --estimate-return

Record only ENTRY data for each function. This option is useful when the target program deals with stack in some way. Normally uftrace modifies task’s execution stack frame to hook return from the function. However sometimes it makes troubles and it’s hard to handle all the cases properly. This option tells uftrace not to hook return address in order to prevent those problems. The return time is estimated as a half of execution time of two consecutive functions.

RECORD CONFIG OPTIONS¶

--libmcount-path=PATH

Load libmcount libraries from this path. This is mostly for testing purposes.

-b SIZE, --buffer=SIZE

Size of internal buffer in which trace data will be saved. Default size is 128k.

--kernel-buffer=SIZE

Set kernel tracing buffer size. The default value (in the kernel) is 1408k.

--no-pltbind

Do not bind dynamic symbol address. This option uses the LD_BIND_NOT environment variable to trace library function calls which might be missing due to concurrent (first) accesses. It is not meaningful to use this option with the --no-libcall option.

--max-stack=DEPTH

Set the max function stack depth for tracing. Default is 1024.

--num-thread=NUM

Use NUM threads to record trace data. Default is 1/4 of online CPUs (but when full kernel tracing is enabled, it will use the full number of CPUs).

--libmcount-single

Use single thread version of libmcount for faster recording. This is ignored if the target program links with the pthread library.

--rt-prio=PRIO

Boost priority of recording threads to real-time (FIFO) with priority of PRIO. This is particularly useful for high-volume data such as full kernel tracing.

--keep-pid

Retain same pid for traced program. For some daemon processes, it is important to have same pid when forked. Running under uftrace normally changes pid as it calls fork() again internally. Note that it might corrupt terminal setting so it’d be better using it with --no-pager option.

--no-randomize-addr

Disable ASLR (Address Space Layout Randomization). It makes the target process fix its address space layout.

-g, --agent

Spawn an agent thread in the target. At runtime, the agent receives external commands and can change supported tracing options. See AGENT.

REPLAY OPTIONS¶

-f FIELD, --output-fields=FIELD

Customize field in the output. Possible values are: duration, tid, time, delta, elapsed and addr. Multiple fields can be set by using comma. Special field of `none' can be used (solely) to hide all fields. Default is `duration,tid'. See FIELDS.

--flat

Print flat format rather than C-like format. This is usually for debugging and testing purpose.

--column-view

Show each task in separate column. This makes easy to distinguish functions in different tasks.

--column-offset=DEPTH

When --column-view option is used, this option specifies the amount of offset between each task. Default is 8.

--task-newline

Interleave a new line when task is changed. This makes easy to distinguish functions in different tasks.

--no-comment

Do not show comments of returned functions.

--libname

Show library name along with function name.

--no-args

Do not show function arguments and return value.

COMMON ANALYSIS OPTIONS¶

-H FUNC, --hide=FUNC

Set filter not to trace selected functions. It doesn’t affect their subtrees, but hides only the given functions. This option can be used more than once. See FILTERS.

--kernel-full

Show all kernel functions called outside of user functions.

--kernel-only

Show kernel functions only without user functions.

--event-full

Show all (user) events outside of user functions.

--demangle=TYPE

Demangle C++ symbol names. Possible values are “full”, “simple” and “no”. Default is “simple” which ignores function arguments and template parameters.

-r RANGE, --time-range=RANGE

Only show functions executed within the time RANGE. The RANGE can be <start>~<stop> (separated by “~”) and one of <start> and <stop> can be omitted. The <start> and <stop> are timestamp or elapsed time if they have <time_unit> postfix, for example `100us'. However, it is highly recommended to use only elapsed time because there is no way to know the timestamp before actually running the program. The timestamp or elapsed time can be shown with -f time or -f elapsed option respectively.

FILTERS¶

The uftrace tool supports filtering out uninteresting functions. Filtering is highly recommended since it helps users focus on the interesting functions and reduces the data size. When uftrace is called, it receives two types of function filter; an opt-in filter with -F/--filter and an opt-out filter with -N/--notrace.

These filters can be applied either at record time or replay time. For record time, they can be added and removed at runtime from the client, see AGENT. Removing filters is achieved by specifying the @clear suffix for the -F / --filter or -N / --notrace options.

The first type of filter is opt-in. By default, it doesn’t trace anything. But when one of the specified functions is executed, tracing is started. When the function returns, tracing is stopped again.

For example, consider a simple program which calls a(), b() and c() in turn.

$ cat abc.c
void c(void) {


    /* do nothing */
}
void b(void) {


    c();
}
void a(void) {


    b();
}
int main(void) {


    a();


    return 0;
}
$ gcc -pg -o abc abc.c
    

Normally uftrace will trace all the functions from main() to c().

$ uftrace live ./abc
# DURATION    TID     FUNCTION


 138.494 us [ 1234] | __cxa_atexit();


            [ 1234] | main() {


            [ 1234] |   a() {


            [ 1234] |     b() {


   3.880 us [ 1234] |       c();


   5.475 us [ 1234] |     } /* b */


   6.448 us [ 1234] |   } /* a */


   8.631 us [ 1234] | } /* main */
    

In the above example, the command name live is explicitly used, but it can be omitted because uftrace uses live command by default. So the above command can be reused as uftrace ./abc in short.

But when the -F b filter option is used, it will not trace main() or a() but only b() and c().

$ uftrace -F b ./abc
# DURATION    TID     FUNCTION


            [ 1234] | b() {


   3.880 us [ 1234] |   c();


   5.475 us [ 1234] | } /* b */
    

The second type of filter is opt-out. By default, everything is traced, but when one of the specified functions is executed, tracing stops. When the excluded function returns, tracing is started again.

In the above example, you can omit the function b() and all calls it makes with the -N option.

$ uftrace -N b ./abc
# DURATION    TID     FUNCTION


 138.494 us [ 1234] | __cxa_atexit();


            [ 1234] | main() {


   6.448 us [ 1234] |   a();


   8.631 us [ 1234] | } /* main */
    

You can hide the function b() only without affecting the calls it makes in its subtree functions with -H option.

$ uftrace -H b ./abc
# DURATION    TID     FUNCTION


 138.494 us [ 1234] | __cxa_atexit();


            [ 1234] | main() {


            [ 1234] |   a() {


   3.880 us [ 1234] |     c();


   6.448 us [ 1234] |   } /* a */


   8.631 us [ 1234] | } /* main */
    

The above -H option is especially useful when hiding std namespace functions in C++ programs by using -H ^std:: option setting.

If users only care about specific functions and want to know how they are called, one can use the caller filter. It makes the function as leaf and records the parent functions to the function.

$ uftrace -C b ./abc
# DURATION    TID     FUNCTION


            [ 1234] | main() {


            [ 1234] |   a() {


   5.475 us [ 1234] |     b();


   6.448 us [ 1234] |   } /* a */


   8.631 us [ 1234] | } /* main */
    

In the above example, functions not in the calling path were not shown. Also the function `c' - which is a child of the function `b' - is also hidden.

Caller filters can be added and removed from the client at runtime, using the @clear suffix for the -C / --caller-filter option.

In addition, you can limit the nesting level of functions with the -D option.

$ uftrace -D 3 ./abc
# DURATION    TID     FUNCTION


 138.494 us [ 1234] | __cxa_atexit();


            [ 1234] | main() {


            [ 1234] |   a() {


   5.475 us [ 1234] |     b();


   6.448 us [ 1234] |   } /* a */


   8.631 us [ 1234] | } /* main */
    

In the above example, uftrace only prints functions up to a depth of 3, so leaf function c() was omitted. Note that the -D option works with -F.

Sometimes, it’s useful to see long-running functions only. This is good because there are usually many tiny functions that are not interesting. The -t/--time-filter option implements the time-based filter that only records functions which run longer than the given threshold. In the above example, the user might want to see functions running more than 5 micro-seconds like below:

$ uftrace -t 5us ./abc
# DURATION    TID     FUNCTION


 138.494 us [ 1234] | __cxa_atexit();


            [ 1234] | main() {


            [ 1234] |   a() {


   5.475 us [ 1234] |     b();


   6.448 us [ 1234] |   } /* a */


   8.631 us [ 1234] | } /* main */
    

In addition, you can set filter to record selected source locations with -L option.

$ uftrace -L s-libmain.c --srcline  t-lib
# DURATION     TID     FUNCTION [SOURCE]


            [  5043] | main() { /* /home/uftrace/tests/s-libmain.c:16 */


   6.998 us [  5043] |   foo(); /* /home/uftrace/tests/s-libmain.c:11 */


   9.393 us [  5043] | } /* main */
    

You can set filter with the @hide suffix not to record selected source locations.

$ uftrace -L s-libmain.c@hide --srcline  t-lib
# DURATION     TID     FUNCTION [SOURCE]


            [ 14688] | lib_a() { /* /home/uftrace/tests/s-lib.c:10 */


            [ 14688] |   lib_b() { /* /home/uftrace/tests/s-lib.c:15 */


   1.505 us [ 14688] |     lib_c(); /* /home/uftrace/tests/s-lib.c:20 */


   2.816 us [ 14688] |   } /* lib_b */


   3.181 us [ 14688] | } /* lib_a */
    

The -Z/--size-filter option is to filter functions that has small sizes. It reads ELF symbols size and compare it with the given value. The PLT functions may have no symbol size in the ELF format, in that case the PLT entry size will be used as the size of the function.

$ uftrace -Z 100  t-arg
# DURATION     TID     FUNCTION


            [162500] | main() {


  12.486 us [162500] |   foo();


   0.505 us [162500] |   many();


            [162500] |   pass() {


   0.283 us [162500] |     check();


   1.449 us [162500] |   } /* pass */


  18.478 us [162500] | } /* main */
    

You can also set triggers on filtered functions. See TRIGGERS section below for details.

When kernel function tracing is enabled, you can also set the filters on kernel functions by marking the symbol with the @kernel modifier. The following example will show all user functions and the (kernel) page fault handler.

$ sudo uftrace -k -F '.*page_fault@kernel' ./abc
# DURATION    TID     FUNCTION


           [14721] | main() {


  7.713 us [14721] |   __do_page_fault();


  6.600 us [14721] |   __do_page_fault();


  6.544 us [14721] |   __do_page_fault();


           [14721] |   a() {


           [14721] |     b() {


           [14721] |       c() {


  0.860 us [14721] |         getpid();


  2.346 us [14721] |       } /* c */


  2.956 us [14721] |     } /* b */


  3.340 us [14721] |   } /* a */


 79.086 us [14721] | } /* main */
    

TRIGGERS¶

The uftrace tool supports triggering actions on selected function calls (with or without filters) and/or signals. Currently supported triggers are listed below. The BNF for trigger specification is as follows:

<trigger>    :=  <symbol> "@" <actions>
<actions>    :=  <action>  | <action> "," <actions>
<action>     :=  "depth="<num> | "backtrace" | "trace" | "trace_on" | "trace_off" |


                 "recover" | "color="<color> | "time="<time_spec> | "read="<read_spec> |


                 "finish" | "filter" | "notrace" | "hide" | "clear" [ "="<clear_spec> ]
<time_spec>  :=  <num> [ <time_unit> ]
<time_unit>  :=  "ns" | "nsec" | "us" | "usec" | "ms" | "msec" | "s" | "sec" | "m" | "min"
<read_spec>  :=  "proc/statm" | "page-fault" | "pmu-cycle" | "pmu-cache" | "pmu-branch"
<clear_spec> :=  <action> | <action> "+" <action>
    

The depth trigger is to change filter depth during execution of the function. It can be used to apply different filter depths for different functions. And the backtrace trigger is used to print a stack backtrace at replay time.

The color trigger is to change the color of the function in replay output. The supported colors are red, green, blue, yellow, magenta, cyan, bold, and gray.

The following example shows how triggers work. The global filter maximum depth is 5, but when function b() is called, it is changed to 1, so functions below b() will not be shown.

$ uftrace -D 5 -T 'b@depth=1' ./abc
# DURATION    TID     FUNCTION


 138.494 us [ 1234] | __cxa_atexit();


            [ 1234] | main() {


            [ 1234] |   a() {


   5.475 us [ 1234] |     b();


   6.448 us [ 1234] |   } /* a */


   8.631 us [ 1234] | } /* main */
    

The backtrace trigger is only meaningful in the replay command.

The trace_on and trace_off actions (the _ can be omitted as traceon and traceoff) control whether uftrace records the specified functions or not.

The recover trigger is for some corner cases in which the process accesses the callstack directly. During tracing of the v8 javascript engine, for example, it kept getting segfaults in the garbage collection stage. It was because v8 incorporates the return address into compiled code objects(?). The recover trigger restores the original return address at the function entry point and resets to the uftrace return hook address again at function exit. This was used to work around segfaults by setting the recover trigger on the related function (specifically ExitFrame::Iterate)

The time trigger is to change time filter setting during execution of the function. It can be used to apply different time filter for different functions.

The read trigger is to read some information at runtime. The result will be recorded as (builtin) events at the beginning and the end of a given function. As of now, the following events are supported:

•

“proc/statm”: process memory stat from /proc filesystem

•

“page-fault”: number of page faults using getrusage(2)

•

“pmu-cycle”: cpu cycles and instructions using Linux perf-event syscall

•

“pmu-cache”: (cpu) cache-references and misses using Linux perf-event syscall

•

“pmu-branch”: branch instructions and misses using Linux perf-event syscall

The results are printed as events (comments) like below.

$ uftrace -T a@read=proc/statm ./abc
# DURATION    TID     FUNCTION


            [ 1234] | main() {


            [ 1234] |   a() {


            [ 1234] |     /* read:proc/statm (size=6808KB, rss=776KB, shared=712KB) */


            [ 1234] |     b() {


            [ 1234] |       c() {


   1.448 us [ 1234] |         getpid();


  10.270 us [ 1234] |       } /* c */


  11.250 us [ 1234] |     } /* b */


            [ 1234] |     /* diff:proc/statm (size=+4KB, rss=+0KB, shared=+0KB) */


  18.380 us [ 1234] |   } /* a */


  19.537 us [ 1234] | } /* main */
    

The finish trigger is to end recording. The process can still run, which can be useful to trace non-terminating processes like daemon.

The filter and notrace triggers have same effect as -F/--filter and -N/--notrace options respectively.

The hide trigger has the same effect as -H/--hide option that hides the given functions, but does not affect to the functions in their subtree unlike the notrace trigger.

The clear trigger is to delete existing actions and it’s for agent use case. It can have optional trigger action names connected by “+” (for example, -T myfunc@clear=trace+read). If so it’ll delete the specified actions only otherwise it’ll delete all actions.

Triggers only work for user-level functions for now.

The trigger can be used for signals as well. This is done by signal trigger with --signal option. The syntax is similar to function trigger but only “trace_on”, “trace_off” and “finish” trigger actions are supported.

$ uftrace --signal 'SIGUSR1@finish' ./some-daemon
    

ARGUMENTS¶

The uftrace tool supports recording function arguments and/or return values using the -A/--argument and -R/--retval options respectively. The syntax is very similar to that of triggers:

<argument>    :=  <symbol> [ "@" <specs> ]
<specs>       :=  <spec> | <spec> "," <spec>
<spec>        :=  ( <int_spec> | <float_spec> | <ret_spec> )
<int_spec>    :=  "arg" N [ "/" <format> [ <size> ] ] [ "%" ( <reg> | <stack> ) ]
<float_spec>  :=  "fparg" N [ "/" ( <size> | "80" ) ] [ "%" ( <reg> | <stack> ) ]
<ret_spec>    :=  "retval" [ "/" <format> [ <size> ] ]
<format>      :=  "d" | "i" | "u" | "x" | "o" | "s" | "c" | "f" | "S" | "p"
<size>        :=  "8" | "16" | "32" | "64"
<reg>         :=  <arch-specific register name>  # "rdi", "xmm0", "r0", ...
<stack>       :=  "stack" [ "+" ] <offset>
    

The -A/--argument option takes a symbol name pattern and its optional specs. The spec is started by argN where N is an index of the arguments. The index starts from 1 and corresponds to the argument passing order of the calling convention on the system. Note that the indexes of arguments are separately counted for integer (or pointer) and floating-point type, and they can interfere depending on the calling convention. The argN is for integer arguments and fpargN is for floating-point arguments.

Users can optionally specify a format and size for the arguments and/or return values. The “d” format or without format field, uftrace treats them as `long int' type for integers and `double' for floating-point numbers. The “i” format makes it signed integer type and “u” format is for unsigned type. Both are printed as decimal while “x” format makes it printed as hexadecimal, and “o” format makes it printed as octal. The “s” format is for null-terminated string type and “c” format is for character type. The “f” format is for floating-point type and is meaningful only for return value (generally). Note that fpargN doesn’t take the format field since it’s always floating-point. The “S” format is for std::string, but it only supports libstdc++ library as of yet. Finally, the “p” format is for function pointer. Once the target address is recorded, it will be displayed as function name.

Please beware when using string type arguments since it can crash the program if the (pointer) value is invalid. Actually uftrace tries to keep track of valid ranges of process address space but it might miss some corner cases.

It is also possible to specify a certain register name or stack offset for arguments (but not for return value). The following register names can be used for argument:

•

x86: rdi, rsi, rdx, rcx, r8, r9 (for integer), xmm[0-7] (for floating-point)

•

arm: r[0-3] (for integer), s[0-15] or d[0-7] (for floating-point)

Examples are shown below:

$ uftrace -A main@arg1/x -R main@retval/i32 ./abc
# DURATION    TID     FUNCTION


 138.494 us [ 1234] | __cxa_atexit();


            [ 1234] | main(0x1) {


            [ 1234] |   a() {


            [ 1234] |     b() {


   3.880 us [ 1234] |       c();


   5.475 us [ 1234] |     } /* b */


   6.448 us [ 1234] |   } /* a */


   8.631 us [ 1234] | } = 0; /* main */
$ uftrace -A puts@arg1/s -R puts@retval ./hello
Hello world
# DURATION    TID     FUNCTION


   1.457 us [21534] | __monstartup();


   0.997 us [21534] | __cxa_atexit();


            [21534] | main() {


   7.226 us [21534] |   puts("Hello world") = 12;


   8.708 us [21534] | } /* main */
    

Note that these arguments and return value are recorded only if the executable was built with the -pg option. Executables built with -finstrument-functions will ignore it except for library calls. Recording of arguments and return values only works with user-level functions for now.

If the target program is built with debug info like DWARF, uftrace can identify number of arguments and their types automatically (when built with libdw). Also arguments and return value of some well-known library functions are provided even if the debug info is not available. In these cases user don’t need to specify spec of the arguments and return value manually - just a function name (or pattern) is enough. In fact, manual argspec will suppress the automatic argspec.

For example, the above example can be written like below:

$ uftrace -A . -R main -F main ./hello
Hello world
# DURATION     TID     FUNCTION


            [ 18948] | main(1, 0x7ffeeb7590b8) {


   7.183 us [ 18948] |   puts("Hello world");


   9.832 us [ 18948] | } = 0; /* main */
    

Note that argument pattern (“.”) matches to any character so it recorded all (supported) functions. It shows two arguments for “main” and a single string argument for “puts”. If you simply want to see all arguments and return values of every functions (if supported), use -a/--auto-args option.

FIELDS¶

The uftrace allows for user to customize the replay output with a couple of fields. Here the field means info on the left side of the pipe (|) character. By default it uses duration and tid fields, but you can use other fields in any order like:

$ uftrace -f time,delta,duration,tid,addr ./abc
#     TIMESTAMP      TIMEDELTA  DURATION    TID      ADDRESS     FUNCTION


    75059.205379813              1.374 us [27804]       4004d0 | __monstartup();


    75059.205384184   4.371 us   0.737 us [27804]       4004f0 | __cxa_atexit();


    75059.205386655   2.471 us            [27804]       4006b1 | main() {


    75059.205386838   0.183 us            [27804]       400656 |   a() {


    75059.205386961   0.123 us            [27804]       400669 |     b() {


    75059.205387078   0.117 us            [27804]       40067c |       c() {


    75059.205387264   0.186 us   0.643 us [27804]       4004b0 |         getpid();


    75059.205388501   1.237 us   1.423 us [27804]       40067c |       } /* c */


    75059.205388724   0.223 us   1.763 us [27804]       400669 |     } /* b */


    75059.205388878   0.154 us   2.040 us [27804]       400656 |   } /* a */


    75059.205389030   0.152 us   2.375 us [27804]       4006b1 | } /* main */
    

Each field has following meaning:

•

tid: task id (obtained by gettid(2))

•

duration: function execution time

•

time: timestamp at the execution

•

delta: difference between two timestamp in a task

•

elapsed: elapsed time from the first timestamp

•

addr: address of the function

•

task: task name (comm)

•

module: library or executable name of the function

The default value is `duration,tid'. If given field name starts with “+”, then it’ll be appended to the default fields. So “-f +time” is as same as “-f duration,tid,time”. And it also accepts a special field name of `none' which disables the field display and shows function output only.

DYNAMIC TRACING¶

SCRIPT EXECUTION¶

The uftrace tool supports script execution for each function entry and exit. The supported script types are Python 2.7, Python 3 and Lua 5.1 as of now.

The user can write four functions. `uftrace_entry' and `uftrace_exit' are executed whenever each function is executed at the entry and exit. However `uftrace_begin' and `uftrace_end' are only executed once when the target program begins and ends.

$ cat scripts/simple.py
def uftrace_begin(ctx):


    print("program begins...")
def uftrace_entry(ctx):


    func = ctx["name"]


    print("entry : " + func + "()")
def uftrace_exit(ctx):


    func = ctx["name"]


    print("exit  : " + func + "()")
def uftrace_end():


    print("program is finished")
    

The above script can be executed in record time as follows:

$ uftrace -S scripts/simple.py -F main tests/t-abc
program begins...
entry : main()
entry : a()
entry : b()
entry : c()
entry : getpid()
exit  : getpid()
exit  : c()
exit  : b()
exit  : a()
exit  : main()
program is finished
# DURATION    TID     FUNCTION


            [10929] | main() {


            [10929] |   a() {


            [10929] |     b() {


            [10929] |       c() {


   4.293 us [10929] |         getpid();


  19.017 us [10929] |       } /* c */


  27.710 us [10929] |     } /* b */


  37.007 us [10929] |   } /* a */


  55.260 us [10929] | } /* main */
    

The `ctx' variable is a dictionary type that contains the below information.

/* context information passed to uftrace_entry(ctx) and uftrace_exit(ctx) */
script_context = {


    int       tid;


    int       depth;


    long      timestamp;


    long      duration;    # exit only


    long      address;


    string    name;


    list      args;        # entry only (if available)


    value     retval;      # exit  only (if available)
};
/* context information passed to uftrace_begin(ctx) */
script_context = {


    bool      record;      # True if it runs at record time, otherwise False


    string    version;     # uftrace version info


    list      cmds;        # execution commands
};
    

Each field in `script_context' can be read inside the script. Please see uftrace-script(1) for details about scripting.

AGENT¶

uftrace supports running an agent inside the traced target, which can modify the tracing config at runtime. The agent is disabled by default, and is enabled at start-up using the -g/--agent option. The user can interact with the agent during while the target executes, from uftrace client instance, using the -p/--pid option.

The client currently supports the following features: * toggle tracing * call depth filter * time threshold filter * opt-in and opt-out filters * caller filters

Consider the following program, which calls a() -> b() -> c() twice, and waits for external input in between.

$ cat abc_abc.c
void c(void) {


    /* do nothing */
}
void b(void) {


    c();
}
void a(void) {


    b();
}
int main(void) {


    a();


    wait_for_sigusr1();


    a();


    return 0;
}
$ gcc -pg -o abc_abc abc_abc.c
    

Tracing can be toggled anytime during execution.

$ uftrace --agent --trace=off abc_abc &
$ uftrace --pid $(pidof abc_abc) --trace=on
$ kill -s SIGUSR1 $(pidof abc_abc)
# DURATION     TID     FUNCTION


  10.508 us [ 30324] |   } /* wait_for_sigusr1 */


            [ 30324] |   a() {


            [ 30324] |     b() {


   0.138 us [ 30324] |       c();


   0.757 us [ 30324] |     } /* b */


   1.217 us [ 30324] |   } /* a */


  12.346 us [ 30324] | } /* main */
    

The call depth filter can be increased or decreased from the client.

$ uftrace --agent --depth=2 abc_abc &
$ uftrace --pid $(pidof abc_abc) --depth=4
$ kill -s SIGUSR1 $(pidof abc_abc)
# DURATION     TID     FUNCTION


            [ 32384] | main() {


   0.324 us [ 32384] |   a();


   5.081  s [ 32384] |   wait_for_sigusr1();


            [ 32384] |   a() {


            [ 32384] |     b() {


   0.106 us [ 32384] |       c();


   0.552 us [ 32384] |     } /* b */


   0.862 us [ 32384] |   } /* a */


   5.081  s [ 32384] | } /* main */
    

The time threshold can also be increased or decreased from the client.

$ uftrace --agent --time-filter=0.8us abc_abc &
$ uftrace --pid $(pidof abc_abc) --time-filter=0.5us
$ kill -s SIGUSR1 $(pidof abc_abc)
# DURATION     TID     FUNCTION


            [ 30196] | main() {


   0.805 us [ 30196] |   a();


   6.859  s [ 30196] |   wait_for_sigusr1();


            [ 30196] |   a() {


   0.522 us [ 30196] |     b();


   0.802 us [ 30196] |   } /* a */


   6.859  s [ 30196] | } /* main */
    

The agent can enforce opt-in and opt-out filters, as well as caller filters.

$ uftrace --agent --filter=c abc_abc &
$ uftrace --pid $(pidof abc_abc) --filter=a
$ kill -s SIGUSR1 $(pidof abc_abc)
# DURATION     TID     FUNCTION


   0.398 us [  3679] | c();


            [  3679] | a() {


            [  3679] |   b() {


   0.163 us [  3679] |     c();


   2.099 us [  3679] |   } /* b */


   3.655 us [  3679] | } /* a */
    

Filters can be removed using the @clear suffix.

$ uftrace --agent --caller-filter=a abc_abc &
$ uftrace --pid $(pidof abc_abc) --caller-filter=a@clear
$ kill -s SIGUSR1 $(pidof abc_abc)
# DURATION     TID     FUNCTION


            [  4956] | main() {


   0.821 us [  4956] |   a();


  10.525  s [  4956] |   wait_for_sigusr1();


            [  4956] |   a() {


            [  4956] |     b() {


   0.116 us [  4956] |       c();


   0.573 us [  4956] |     } /* b */


   0.806 us [  4956] |   } /* a */


  10.525  s [  4956] | } /* main */
    

WATCH POINT¶

The uftrace watch point is to display certain value only if it’s changed. It’s conceptually the same as that of a debugger’s but only works at function entry and exit so it might miss some updates.

As of now, the following watch points are supported:

•

“cpu” : cpu number current task is running on

Like read triggers, the result is displayed as event (comment):

$ uftrace -W cpu tests/t-abc
# DURATION     TID     FUNCTION


            [ 19060] | main() {


            [ 19060] |   /* watch:cpu (cpu=8) */


            [ 19060] |   a() {


            [ 19060] |     b() {


            [ 19060] |       c() {


   2.365 us [ 19060] |         getpid();


   8.002 us [ 19060] |       } /* c */


   8.690 us [ 19060] |     } /* b */


   9.350 us [ 19060] |   } /* a */


  12.479 us [ 19060] | } /* main */
    

SEE ALSO¶

uftrace-record(1), uftrace-replay(1), uftrace-report(1), uftrace-script(1)

AUTHORS¶

Namhyung Kim <namhyung@gmail.com>.