User Function Boundary Tracing

The simplest mode of operation for the pid provider is as the user space analogue to the fbt provider. The following example program traces all function entries and returns that are made from a single function. The $1 macro variable (the first operand on the command line) is the process ID for the process to trace. The $2 macro variable (the second operand on the command line) is the name of the function from which to trace all function calls.

#!/usr/sbin/dtrace -s

#pragma D option flowindent

pid$1::$2:entry
{
        self->trace = 1;
}

pid$1::$2:return
/self->trace/
{
        self->trace = 0;
}

pid$1:::entry,
pid$1:::return
/self->trace/
{
}

Type in the above example script and save it in a file named userfunc.d, and then chmod it to be executable. This script produces output similar to the following example:

# ./userfunc.d 15032 execute
dtrace: script './userfunc.d' matched 11594 probes
  0  -> execute                               
  0    -> execute                             
  0      -> Dfix                              
  0      <- Dfix                              
  0      -> s_strsave                         
  0        -> malloc                          
  0        <- malloc                          
  0      <- s_strsave                         
  0      -> set                               
  0        -> malloc                          
  0        <- malloc                          
  0      <- set                               
  0      -> set1                              
  0        -> tglob                           
  0        <- tglob                           
  0      <- set1                              
  0      -> setq                              
  0        -> s_strcmp                        
  0        <- s_strcmp                        
...

The pid provider can only be used on processes that are already running. You can use the $target macro variable (see Chapter 9, Scripting) and the dtrace -c and -p options to create and grab processes of interest and instrument them using DTrace. For example, the following D script can be used to determine the distribution of function calls made to libc by a particular subject process:

pid$target:libc.so::entry
{
        @[probefunc] = count();
}

To determine the distribution of such calls made by the date(1) command, save the script in a file named libc.d and execute the following command:

# dtrace -s libc.d -c date
dtrace: script 'libc.d' matched 2476 probes
Fri Jul 30 14:08:54 PDT 2004
dtrace: pid 109196 has exited

  pthread_rwlock_unlock                                             1
  _fflush_u                                                         1
  rwlock_lock                                                       1
  rw_write_held                                                     1
  strftime                                                          1
  _close                                                            1
  _read                                                             1
  __open                                                            1
  _open                                                             1
  strstr                                                            1
  load_zoneinfo                                                     1

...
  _ti_bind_guard                                                   47
  _ti_bind_clear                                                   94