prex(1)
NAME
prex - control tracing and manipulate probe points in a pro-
cess or the kernel
SYNOPSIS
prex [-o trace_file_name] [-l libraries] [-s kbytes_size]
cmd [cmd-args...]
prex [-o trace_file_name] [-l libraries] [-s kbytes_size]
-p pid
prex -k [-s kbytes_size]
DESCRIPTION
The prex command is the part of the Solaris tracing archi-
tecture that controls probes in a process or the kernel. See
tracing(3TNF) for an overview of this tracing architecture,
including example source code using it.
prex is the application used for external control of probes.
It automatically preloads the libtnfprobe library. prex
locates all the probes in a target executable or the kernel
and provides an interface for the user to manipulate them.
It allows a probe to be turned on for tracing, debugging, or
both. Tracing generates a TNF (Trace Normal Form) trace file
that can be converted to ASCII by tnfdump(1) and used for
performance analysis. Debugging generates a line to standard
error whenever the probe is hit at run time.
prex does not work on static executables. It only works on
dynamic executables.
Invoking prex
There are three ways to invoke prex:
1. Use prex to start the target application cmd. In this
case, the target application need not be built with a
dependency on libtnfprobe. See TNF_PROBE(3TNF). prex sets
the environment variable LD_PRELOAD to load libtnfprobe
into the target process. See ld(1). prex then uses the
environment variable PATH to find the target application.
2. Attach prex to a running application. In this case, the
running target application should have libtnfprobe
already linked in. Alternatively, the user may manually
set LD_PRELOAD to include libtnfprobe.so.1 prior to
invoking the target.
3. Use prex with the -k option to set prex to kernel mode.
prex can then be used to control probes in the Solaris
kernel. In kernel mode, additional commands are defined,
and some commands that are valid in other modes are
invalid. See Kernel Mode below.
Control File Format and Command Language
In a future release of prex, the command language may be
moved to a syntax that is supported by an existing scripting
language like ksh(1). In the meantime, the interface to prex
is uncommitted.
o Commands should be in ASCII.
o Each command is terminated with the NEWLINE character.
o A command can be continued onto the next line by end-
ing the previous line with the backslash ("\") charac-
ter.
o Tokens in a command must be separated by whitespace
(one or more spaces or tabs).
o The "#" character implies that the rest of the line is
a comment.
Basic prex Commands
Command Result
% prex a.out Attaches prex to your pro-
gram and starts prex.
prex> enable $all Enables all the probes.
prex> quit resume Quits prex and resumes exe-
cution of program.
Control File Search Path
There are two different methods of communicating with prex:
o By specifications in a control file. During start-up,
prex searches for a file named .prexrc in the direc-
tories specified below. prex does not stop at the
first one it finds. This way a user can override any
defaults that are set up. The search order is:
$HOME/
./
o By typing commands at the prex prompt.
The command language for both methods is the same and is
specified in USAGE. The commands that return output will not
make sense in a control file. The output will go to standard
output.
When using prex on a target process, the target will be in
one of two states, running or stopped. This can be detected
by the presence or absence of the prex> prompt. If the
prompt is absent, it means that the target process is run-
ning. Typing Control-C will stop the target pr ocess and
return the user to the prompt. There is no guarantee that
Control-C will return to a prex prompt immediately. For
example, if the target process is stopped on a job control
stop (SIGSTOP), then Control-C in prex will wait until the
target has been continued (SIGCONT). See Signals to Target
Program below for more information on signals and the target
process.
OPTIONS
The following options are supported:
-k kernel mode: prex is used to control probes in the
Solaris kernel. In kernel mode, additional commands
are defined, and some commands valid in other modes
are invalid. See Kernel Mode below.
-l libraries
The libraries mentioned are linked in to the target
application using LD_PRELOAD (see ld(1)). This option
cannot be used when attaching to a running process.
The argument to the -l option should be a space-
separated string enclosed in double quotes. Each token
in the string is a library name. It follows the
LD_PRELOAD rules on how libraries should be specified
and where they will be found.
-o trace_file_name
File to be used for the trace output. trace_file_name
is assumed to be relative to the current working
directory of prex (that is, the directory that the
user was in when prex was started).
If prex attaches to a process that is already tracing,
the new trace_file_name (if provided) will not be
used. If no trace_file_name is specified, the default
is /$TMPDIR/trace-pid where pid is the process id of
the target program. If TMPDIR is not set, /tmp is
used.
-s kbytes_size
Maximum size of the output trace file in Kbytes. The
default size of the trace kbytes_size is 4096 (2**10)
bytes or 4 Mbytes for normal usage, and 384 or 384
kbytes in kernel mode. The minimum size that can be
specified is 128 Kbytes. The trace file can be thought
of as a least recently used circular buffer. Once the
file has been filled, newer events will overwrite the
older ones.
USAGE
This section describes the usage of the prex utility.
Grammar
Probes are specified by a list of space-separated selectors.
Selectors are of the form:
attribute=value
(See TNF_PROBE(3TNF)). The "attribute=" is optional. If it
is not specified, it defaults to "keys=".
The attribute or value (generically called "spec") can be
any of the following:
IDENT Any sequence of letters, digits, _, \, ., % not begin-
ning with a digit. IDENT implies an exact match.
QUOTED_STR
Usually used to escape reserved words (any commands in
the command language). QUOTED_STR implies an exact
match and has to be enclosed in single quotes (' ').
REGEXP
An ed(1) regular expression pattern match. REGEXP has
to be enclosed in slashes (/ /), A / can be included
in a REGEXP by escaping it with a backslash \.
The following grammar explains the syntax.
selector_list ::= | /* empty */
selector_list selector
selector ::= spec=spec | /* whitespace around `=' opt */
spec
spec ::= IDENT |
QUOTED_STR |
REGEXP
The terminals in the above grammar are:
IDENT = [a-zA-Z_\.%]{[a-zA-Z0-9_\.%]}+
QUOTED_STR = '[^\n']*' /* any string in single quotes */
REGEXP = /[^\n/]*/ /* regexp's have to be in / / */
This is a list of the remaining grammar that is needed to
understand the syntax of the command language (defined in
next subsection):
filename ::= QUOTED_STR /* QUOTED_STR defined above */
spec_list ::= /* empty */ |
spec_list spec /* spec defined above */
fcn_handle ::= &IDENT /* IDENT defined above */
set_name ::= $IDENT /* IDENT defined above */
Command Language
1. Set Creation and Set Listing
create $set_name selector_list
list sets # list the defined sets
create can be used to define a set which contains probes
that match the selector_list. The set $all is pre-defined
as /.*/ and it matches all the probes.
2. Function Listing
list fcns # list the available fcn_handle
The user can list the different functions that can be
connected to probe points. Currently, only the debug
function called &debug is available.
3. Commands to Connect and Disconnect Probe Functions
connect &fcn_handle $set_name
connect &fcn_handle selector_list
clear $set_name
clear selector_list
The connect command is used to connect probe functions
(which must be prefixed by `&') to probes. The probes are
specified either as a single set (with a `$'), or by
explicitly listing the probe selectors in the command.
The probe function has to be one that is listed by the
list fcns command. This command does not enable the
probes.
The clear command is used to disconnect all connected
probe functions from the specified probes.
4. Commands to Toggle the Tracing Mode
trace $set_name
trace selector_list
untrace $set_name
untrace selector_list
The trace and untrace commands are used to toggle the
tracing action of a probe point (that is, whether a probe
will emit a trace record or not if it is hit). This com-
mand does not enable the probes specified. Probes have
tracing on by default. The most efficient way to turn off
tracing is by using the disable command. untrace is use-
ful if you want debug output but no tracing. If so, set
the state of the probe to enabled, untraced, and the
debug function connected.
5. Commands to Enable and Disable Probes
enable $set_name
enable selector_list
disable $set_name
disable selector_list
The enable and disable commands are used to control
whether the probes perform the action that they have been
set up for. To trace a probe, it has to be both enabled
and traced (using the trace command). Probes are disabled
by default. The list history command is used to list the
probe control commands issued: connect, clear, trace,
untrace, enable, and disable. These are the commands
that are executed whenever a new shared object is brought
in to the target program by dlopen(3DL). See the subsec-
tion, dlopen'ed Libraries, below for more information.
The following table shows the actions that result from
specific combinations of tracing, enabling, and connect-
ing:
Enabled or Tracing State Debug State Results
Disabled (On/Off) (Connected/Cleared) In
------------------------------------------------------------
Enabled On Connected Tracing and
Debugging
Enabled On Cleared Tracing only
Enabled Off Connected Debugging only
Enabled Off Cleared Nothing
Disabled On Connected Nothing
Disabled On Cleared Nothing
Disabled Off Connected Nothing
Disabled Off Cleared Nothing
6. List History
list history # lists probe control command history
The list history command displays a list of the probe
control commands previously issued in the tracing ses-
sion, for example, connect, clear, trace, disable. Com-
mands in the history list are executed wherever a new
shared object is brought into the target program by
dlopen(3DL).
7. Commands to List Probes, List Values, or List Trace File
Name
list spec_list probes $set_name # list probes $all
list spec_list probes selector_list # list name probes file=test.c
list values spec_list # list values keys given in spec_list
list tracefile # list tracefile
The first two commands list the selected attributes and
values of the specified probes. They can be used to check
the state of a probe. The third command lists the various
values associated with the selected attributes. The
fourth command lists the current tracefile.
8. Help Command
help topic
To get a list of the help topics that are available,
invoke the help command with no arguments. If a topic
argument is specified, help is printed for that topic.
9. Source a File
source filename
The source command can be used to source a file of prex
commands. source can be nested (that is, a file can
source another file). filename is a quoted string.
10.
Process Control
continue # resumes the target process
quit kill # quit prex, kill target
quit resume # quit prex, continue target
quit suspend # quit prex, leave target suspended
quit # quit prex (continue or kill target)
The default quit will continue the target process if prex
attached to it. Instead, if prex had started the target
program, quit will kill the target process.
dlopen'ed Libraries
Probes in shared objects that are brought in by dlopen(3DL)
are automatically set up according to the command history of
prex. When a shared object is removed by a dlclose(3DL),
prex again needs to refresh its understanding of the probes
in the target program. This implies that there is more work
to do for dlopen(3DL) and dlclose(3DL) -so they will take
slightly longer. If a user is not interested in this feature
and doesn't want to interfere with dlopen(3DL) and
dlclose(3DL), detach prex from the target to inhibit this
feature.
Signals to Target Program
prex does not interfere with signals that are delivered
directly to the target program. However, prex receives all
signals normally generated from the terminal, for example,
Control-C (SIGINT), and Control-Z (SIGSTOP), and does not
forward them to the target program. To signal the target
program, use the kill(1) command from a shell.
Interactions with Other Applications
Process managing applications like dbx, truss(1), and prex
cannot operate on the same target program simultaneously.
prex will not be able to attach to a target which is being
controlled by another application. A user can trace and
debug a program serially by the following method: first
attach prex to target (or start target through prex), set up
the probes using the command language, and then type quit
suspend. The user can then attach dbx to the suspended pro-
cess and debug it. A user can also suspend the target by
sending it a SIGSTOP signal, and then by typing quit resume
to prex. In this case, the user should also send a SIGCONT
signal after invoking dbx on the stopped process (else dbx
will be hung).
Failure of Event Writing Operations
There are a few failure points that are possible when writ-
ing out events to a trace file, for example, system call
failures. These failures result in a failure code being set
in the target process. The target process continues nor-
mally, but no trace records are written. Whenever a user
enters Control-C to prex to get to a prex prompt, prex will
check the failure code in the target and inform the user if
there was a tracing failure.
Target Executing a Fork or exec
If the target program does a fork(2), any probes that the
child encounters will cause events to be logged to the same
trace file. Events are annotated with a process id, so it
will be possible to determine which process a particular
event came from. In multi-threaded programs, there is a race
condition with a thread doing a fork while the other threads
are still running. For the trace file not to get corrupted,
the user should either use fork1(2), or make sure that all
other threads are quiescent when doing a fork(2),
If the target program itself (not any children it may
fork(2)) does an exec(2), prex detaches from the target and
exits. The user can reconnect prex with prex -p pid.
A vfork(2) is generally followed quickly by an exec(2) in
the child, and in the interim, the child borrows the
parent's process while the parent waits for the exec(2). Any
events logged by the child from the parent process will
appear to have been logged by the parent.
Kernel Mode
Invoking prex with the -k flag causes prex to run in kernel
mode. In kernel mode, prex controls probes in the Solaris
kernel. See tnf_kernel_probes(4) for a list of available
probes in the Solaris kernel. A few prex commands are una-
vailable in kernel mode; many other commands are valid in
kernel mode only.
The -l, -o, and -p command-line options are not valid in
kernel mode (that is, they may not be combined with the -k
flag).
The rest of this section describes the differences in the
prex command language when running prex in kernel mode.
1. prex will not stop the kernel
When prex attaches to a running user program, it stops
the user program. Obviously, it cannot do this when
attaching to the kernel. Instead, prex provides a
``tracing master switch'': no probes will have any
effect unless the tracing master switch is on. This
allows the user to iteratively select probes to enable,
then enable them all at once by turning on the master
switch.
The command
ktrace [ on | off ]
is used to inspect and set the value of the master
switch. Without an argument, prex reports the current
state of the master switch.
Since prex will not stop or kill the kernel, the
quit resume
and
quit kill
commands are not valid in kernel mode.
2. No functions may be attached to probes in the kernel
In particular, the debug function is unavailable in ker-
nel mode.
3. Trace output is written to an in-core buffer
In kernel mode, a trace output file is not generated
directly, in order to allow probes to be placed in time-
critical code. Instead, trace output is written to an
in-core buffer, and copied out by a separate program,
tnfxtract(1).
The in-core buffer is not automatically created. The fol-
lowing prex command controls buffer allocation and deal-
location:
buffer [ alloc [ size ] | dealloc ]
Without an argument, the buffer command reports the size
of the currently allocated buffer, if any. With an argu-
ment of alloc [size], prex allocates a buffer of the
given size. size is in bytes, with an optional suffix of
'k' or 'm' specifying a multiplier of 1024 or 1048576,
respectively. If no size is specified, the size speci-
fied on the command line with the -s option is used as a
default. If the -s command line option was not used, the
``default default'' is 384 kilobytes.
With an argument of dealloc, prex deallocates the trace
buffer in the kernel.
prex will reject attempts to turn the tracing master
switch on when no buffer is allocated, and to deallocate
the buffer when the tracing master switch is on. prex
will refuse to allocate a buffer when one is already
allocated; use buffer dealloc first.
prex will not allocate a buffer larger than one-half of a
machine's physical memory.
4. prex supports per-process probe enabling in the kernel
In kernel mode, it is possible to select a set of
processes for which probes are enabled. No trace output
will be written when other processes traverse these probe
points. This is called "process filter mode". By default,
process filter mode is off, and all processes cause the
generation of trace records when they hit an enabled
probe.
Some kernel events such as interrupts cannot be associ-
ated with a particular user process. By convention,
these events are considered to be generated by process id
0.
prex provides commands to turn process filter mode on and
off, to get the current status of the process filter mode
switch, to add and delete processes (by process id) from
the process filter set, and to list the current process
filter set.
The process filter set is maintained even when process
filter mode is off, but has no effect unless process
filter mode is on.
When a process in the process filter set exits, its pro-
cess id is automatically deleted from the process filter
set.
The command:
pfilter [ on | off | add pidlist | delete pidlist ]
controls the process filter switch, and process filter
set membership. With no arguments, pfilter prints the
current process filter set and the state of the process
filter mode switch:
on or off
set the state of the process filter mode switch.
add pidlist
delete pidlist
add or delete processes from the process filter
set. pidlist is a comma-separated list of one or
more process ids.
EXAMPLES
See tracing(3TNF) for complete examples showing, among other
things, the use of prex to do simple probe control.
When either the process or kernel is started, all probes are
disabled.
Example 1: Set creation and set listing
create $out name=/out/ # $out = probes with "out" in
# value of "name" attribute
create $foo /page/ name=biodone # $foo = union of
# probes with "page" in value of keys attribute
# probes with "biodone" as value of "name" attribute
list sets # list the defined sets
list fcns # list the defined probe fcns
Example 2: Commands to trace and connect probe functions
trace foobar='on' # exact match on foobar attribute
trace $all # trace all probes (predefined set $all)
connect &debug $foo # connect debug func to probes in $foo
Example 3: Commands to enable and disable probes
enable $all # enable all probes
enable /vm/ name=alloc # enable the specified probes
disable $foo # disable probes in set $foo
list history # list probe control commands issued
Example 4: Process control
continue # resumes the target process
^C # stop target; give control to prex
quit resume # exit prex, leave process running
# and resume execution of program
Example 5: Kernel mode
buffer alloc 2m # allocate a 2 Megabyte buffer
enable $all # enable all probes
trace $all # trace all probes
ktrace on # turn tracing on
ktrace off # turn tracing back off
pfilter on # turn process filter mode on
pfilter add 1379 # add pid 1379 to process filter
ktrace on # turn tracing on
# (only pid 1379 will be traced)
FILES
.prexrc
local prex initialization file
~/.prexrc
user's prex initialization file
/proc/nnnnn
process files
ATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:
____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|_____________________________|_____________________________|
| Availability | SUNWtnfc (32-bit) |
|_____________________________|_____________________________|
| | SUNWtnfcx (64-bit) |
|_____________________________|_____________________________|
SEE ALSO
ed(1), kill(1), ksh(1), ld(1), tnfdump(1), tnfxtract(1),
truss(1), exec(2), fork(2), fork1(2), vfork(2),
TNF_DECLARE_RECORD(3TNF), TNF_PROBE(3TNF), dlclose(3DL),
dlopen(3DL), gethrtime(3C), libtnfctl(3TNF),
tnf_process_disable(3TNF), tracing(3TNF),
tnf_kernel_probes(4), attributes(5)
NOTES
Currently, the only probe function that is available is the
&debug function. When this function is executed, it prints
out the arguments sent in to the probe as well as the value
associated with the sunw%debug attribute in the detail field
(if any) to stderr.
For example, for the following probe point:
TNF_PROBE_2(input_values, "testapp main",
"sunw%debug 'have read input values successfully'",
tnf_long, int_input, x,
tnf_string, string_input, input);
If x was 100 and input was the string "success", then the
output of the debug probe function would be:
probe input_values; sunw%debug "have read input values successfully";
int_input=100; string_input="success";
Some non-SPARC hardware lacks a true high-resolution timer,
causing gethrtime() to return the same value multiple times
in succession. This can lead to problems in how some tools
interpret the trace file. This situation can be improved by
interposing a version of gethrtime(), which causes these
successive values to be artificially incremented by one
nanosecond:
hrtime_t
gethrtime()
{
static mutex_t lock;
static hrtime_t (*real_gethrtime)(void) = NULL;
static hrtime_t last_time = 0;
hrtime_t this_time;
if (real_gethrtime == NULL) {
real_gethrtime =
(hrtime_t (*)(void)) dlsym(RTLD_NEXT, "gethrtime");
}
this_time = real_gethrtime();
mutex_lock(&lock);
if (this_time <= last_time)
this_time = ++last_time;
else
last_time = this_time;
mutex_unlock(&lock);
return (this_time);
}
Of course, this does not increase the resolution of the
timer, so timestamps for individual events are still rela-
tively inaccurate. But this technique maintains ordering, so
that if event A causes event B, B never appears to happen
before or at the same time as A.
dbx is available with the Sun Workshop Products.
BUGS
prex should issue a notification when a process id has been
automatically deleted from the filter set.
There is a known bug in prex which can result in this mes-
sage:
Tracing shut down in target program due to an internal
error - Please restart prex and target
When prex runs as root, and the target process is not root,
and the tracefile is placed in a directory where it cannot
be removed and re-created (a directory with the sticky bit
on, like /tmp),mm then the target process will not be able
to open the tracefile when it needs to. This results in
tracing being disabled.
Changing any of the circumstances listed above should fix
the problem. Either don't run prex as root, or run the tar-
get process as root, or specify the tracefile in a directory
other than /tmp.
Man(1) output converted with
man2html