Re: DTrace SDT Provider not working?

On Sun, Jun 11, 2006 at 10:11:14PM +0200, Marius Nuennerich wrote:
> I added a printf after the first SDT_PROBE I added to kern_timeout.c.
> That prints very often on the console even after boot.
> 
> > The version of code you have has the fbt provider restricted to just a
> > few probes. You could try changing the filter in that to allow it
> > to look at more functions. Be warned though that there are some that
> > aren't safe to instrument. I'm still tracking those down, so enabling
> > all probes with fbt::: is very unwise if you remove the filter I have
> > in there.
> 
> Ok, where can I tune the filter?

Look at the file sys/cddl/dev/fbt/fbt.c and the function
fbt_provide_module_function. You should be able to understand the code. 8-)

> Ok. Thanks for the Hint. It seems like the softclock function is not
> known to fbt by default right now.

That's because I left a version of fbt.c with just about everything
filtered out. I'm in the process of trying to track down which functions
are being called illegally during the execution of a probe. At the moment
I suspect that it is witness in something that needs to have a dtrace
specific version.

> I wonder why sdt:kernel:linker_load_module:entry isn't fired when
> kldload'ing, does it work on your machine(s)?

It does for me. Remember that at this stages it's only single processor
i386 systems that are supported.

> P.S.
> sdt:kernel:callout:entry:
> 0xeb 0x00 0xa1 0xbc 0x75 0x9c 0xc0 0x8b 0x15 0xc0 0x75 0x9c 0xc0 0x09
> 0xc2 0x74 0x13 0x6a 0x00 0x6a 0x00 0x6a 0x00 0x6a 0x00 0x53 0x50 0xff
> 0x15 0x50 0x5d 0x9c 0xc0 0x83 0xc4 0x18 
> 
> Is printed on boot. Is it normal that it is this many Bytes? I thought
> it would just be the jmp (0xeb) directly followed by a one byte
> offset?

The whole sdt implementation needs to change to do it like Sun does
in Solaris. The current implementation was developed before I had added
the support for invalid opcode exceptions.

> P.P.S. Why do you use a near jmp instead of NOPs? Just curious.
> Is there any documentation for implementation details of DTrace,
> haven't found much so far.

The only documentation for the implementation of DTrace is the code
itself. 8-)

--
John Birrell