DTrace on FreeBSD

Adding support to the kernel

Note: as of May 2012, DTrace support is enabled by default in GENERIC, and the steps below are not needed. If you are using a custom kernel config, make sure that all the lines below are present.

  1. Enable building of debug symbols
    makeoptions DEBUG="-g"       # build kernel with gdb(1) debug symbols
  2. For FreeBSD versions earlier than 10.0, add:

    options KDTRACE_HOOKS      # all architectures - enable general DTrace hooks
    options DDB_CTF            # all architectures - kernel ELF linker loads CTF data
  3. For AMD64 (all versions), add:

    options KDTRACE_FRAME        # amd64 - ensure frames are compiled in
  4. For FreeBSD 9.0 or later, WITH_CTF=1 must be defined in the kernel config:

    makeoptions WITH_CTF=1

    Note: It will not be picked up from make.conf or src.conf for the kernel build.

Rebuild and install the kernel

  1. For FreeBSD 9 or later
    make buildkernel KERNCONF=DTRACE
  2. For FreeBSD 8-STABLE or earlier
    make buildkernel WITH_CTF=1 KERNCONF=DTRACE
  3. Install the kernel and reboot
    make installkernel KERNCONF=DTRACE
    shutdown -r now

Getting Started

Note: You'll need to su to root in order to use DTrace, which may be fixed once we add a more comprehensive fine-grained privilege policy.

  1. Load some or all DTrace kernel modules:
    kldload dtraceall
  2. Confirm that you have piles of available DTrace hooks:
    dtrace -l | head
  3. Confirm that the kernel was compiled correctly with tracing by running a DTrace one liner.
    dtrace -n 'syscall:::entry { @num[execname] = count(); }'
    If you see an error stemming from one of the DTrace files in /usr/lib, such as this:
    dtrace: invalid probe specifier syscall:::entry { @num[execname] = count(); }: "/usr/lib/dtrace/psinfo.d", line 37: failed to copy type of 'pr_uid': Type information is in parent and unavailable
    then you do not have DTrace properly compiled in. Go back and check your work.

Userland DTrace

FreeBSD 9.0 or later

  1. For userland DTrace support add the following to your make.conf (or src.conf if you want it just for the base system):
    STRIP=
    CFLAGS+=-fno-omit-frame-pointer
    This allows stack traces to work and display even more information.
  2. Rebuild and install world with 'WITH_CTF=1' in either make.conf (if you also want to have it for ports) or src.conf:
    make buildworld
    shutdown -r NOW
    boot -s
    make installworld
    reboot

FreeBSD 8-STABLE or earlier

  1. For userland DTrace support add the following to your make.conf:
    STRIP=
    CFLAGS+=-fno-omit-frame-pointer
    This allows stack traces to work and display even more information.
  2. Rebuild and install world:
    make WITH_CTF=1 buildworld
    shutdown -r NOW
    boot -s
    make installworld

Hints

Resources


CategoryDTrace

DTrace (last edited 2014-02-13 02:29:19 by RuiPaulo)