Using systemtap to trace into libraries

Systemtap is able to trace into userspace libraries. It’s actually very simple:

#!/usr/bin/stap

global last;

function display_time () {
      now = gettimeofday_us ();
      delta = 0;
      if (last > 0)
            delta = now - last;
      last = now;

      printf ("%d (+%d):", now, delta);
}

probe begin {
      last = 0;
      printf ("ready\n");
}

probe process("/usr/lib*/libguestfs.so.0")
            .function("guestfs_[a-z]*") ? {
      display_time();
      printf ("\t%s %s\n", probefunc(), $$parms);
}

Run this script (as root) and in another terminal run any program that uses libguestfs, and you’ll see this output:

$ sudo /tmp/test.stap
ready
1318252148697989 (+0):	guestfs_create 
1318252148698028 (+39):	guestfs_is_config g=0x123ab50
1318252149060531 (+362503):	guestfs_set_pgroup g=0x123ab50 pgroup=0x1
1318252149060588 (+57):	guestfs_add_drive g=0x123ab50 filename=0x123ad50
1318252149060648 (+60):	guestfs_safe_malloc g=0x123ab50 nbytes=0x8
1318252149060668 (+20):	guestfs_safe_realloc g=0x123ab50 ptr=0x123add0 nbytes=0x10
1318252149060689 (+21):	guestfs_safe_strdup g=0x123ab50 str=0x368567df1b
1318252149060705 (+16):	guestfs_safe_realloc g=0x123ab50 ptr=0x123add0 nbytes=0x18
1318252149060719 (+14):	guestfs_safe_strdup g=0x123ab50 str=0x7fffea8473f0
1318252149060736 (+17):	guestfs_is_config g=0x123ab50
1318252149060749 (+13):	guestfs_launch g=0x123ab50
[etc.]