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Date:      Mon, 27 Feb 2012 22:22:17 -0800
From:      Marc Abramowitz <msabramo@gmail.com>
To:        freebsd-questions@freebsd.org
Subject:   DTrace userland
Message-ID:  <CAAgNOZ2niHqw6SLWUkmTch-bKh1HPYrUX20QvLYPF-SKZ7wg8A@mail.gmail.com>

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I'm using FreeBSD 9.0 on amd64 in VMware Fusion and trying to DTrace
userland programs. I think I must be doing something wrong.

I recompiled my kernel and world, following the instructions at
http://wiki.freebsd.org/DTrace and I've read
http://wiki.freebsd.org/DTrace/userland:

The test.c pid provider example worked fine for me:

$ sudo dtrace -s pid.d -c ./test
dtrace: script 'pid.d' matched 2 probes
dtrace: buffer size lowered to 1m
CPU     ID                    FUNCTION:NAME
  0  43030                       main:entry
  0  43031                      sleep:entry
  0  43031                      sleep:entry
  0  43031                      sleep:entry

As does a simple probe of test.c specified with the -n option:

[marca@freebsd9-0 ~]$ sudo dtrace -n 'pid$target:test:main:entry' -c ./test
dtrace: description 'pid$target:test:main:entry' matched 1 probe
dtrace: buffer size lowered to 1m
CPU     ID                    FUNCTION:NAME
  0  43030                       main:entry

When I start trying to dtrace other programs, things don't go so well...

$ sudo dtrace -n ":::entry" -c /usr/local/bin/python
Python 2.4.5 (#2, Dec  5 2011, 15:19:09)
[GCC 4.2.1 20070831 patched [FreeBSD]] on freebsd9
Type "help", "copyright", "credits" or "license" for more information.
>>> import os
>>> os.getpid()
1603
>>>
dtrace: failed to control pid 1603: process exited with status 0

$ sudo dtrace -n 'pid$target:::entry' -c '/bin/cat hello_world.txt'
dtrace: description 'pid$target:::entry' matched 3315 probes
dtrace: buffer size lowered to 1m
CPU     ID                    FUNCTION:NAME
  0  43448                 _rtld_bind:entry
  0  43903              rlock_acquire:entry
  0  43125        def_thread_set_flag:entry
(Had to hit Ctrl-C to exit; it never displayed hello_world.txt to stdout)

[marca@freebsd9-0 /usr/ports/sysutils/coreutils]$ sudo make install
...
[marca@freebsd9-0 /usr/ports/sysutils/coreutils]$ sudo dtrace -n
'pid$target:::entry' -c '/usr/local/bin/gcat config.log'
dtrace: description 'pid$target:::entry' matched 3823 probes
dtrace: buffer size lowered to 1m
CPU     ID                    FUNCTION:NAME
  0  43524                 _rtld_bind:entry
  0  43979              rlock_acquire:entry
  0  43201        def_thread_set_flag:entry
^C

$ sudo dtrace -n 'pid$target:cat:main:entry' -c '/bin/cat hello_world.txt'
causes a kernel panic.
According to the core.txt file, it was a "Fatal trap 10: trace trap while
in kernel mode" and here's the KDB backtrace:

KDB: stack backtrace:
#0 0xffffffff8089025e at kdb_backtrace+0x5e
#1 0xffffffff80858ce7 at panic+0x187
#2 0xffffffff80b4bf20 at trap_fatal+0x290
#3 0xffffffff80b4c540 at trap+0x180
#4 0xffffffff80b36963 at calltrap+0x8
#5 0xffffffff8162583d at dtrace_assfail+0x2d
#6 0xffffffff8188aa2e at fasttrap_provider_free+0x1de
#7 0xffffffff8188ad13 at fasttrap_pid_cleanup_cb+0x1c3
#8 0xffffffff8086dfa1 at softclock+0x3a1
#9 0xffffffff8082d724 at intr_event_execute_handlers+0x104
#10 0xffffffff8082eee4 at ithread_loop+0xa4
#11 0xffffffff8082a34f at fork_exit+0x11f
#12 0xffffffff80b36e8e at fork_trampoline+0xe

[marca@freebsd9-0 /usr/ports/sysutils/coreutils]$ sudo dtrace -n
'pid$target:gcat::entry' -c '/usr/local/bin/gcat config.log'
(Another kernel panic)

I can provide full crash dumps if necessary.

Any idea what's going on here?

Cheers,
Marc



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