Hi,
James Carlson wrote:
David Finberg writes:
On Thu, 12 Feb 2009, James Carlson wrote:
J writes:
There doesn't seem to be any Dtrace hooks for monitoring ddi put/get. I
think this would be a great feature for developers as they would be
able to monitor hardware access at the register level. Is there any
reason why these hooks do not exist already?
This is CR 4969919.
Yes, it's extremely annoying when debugging drivers, and the RE has
suggested that it be closed as "will not fix."
For the sun4v hypervisor hcalls, I've built special versions that use
save/restore instead of leafs so I could simply dtrace them. Could we add
a build flag and extra code for low speed versions of ddi_put/get?
The people who really want it probably don't mind switching kernels, since
they're probably running debug anyways.
I think the argument against that idea is that the whole point of
dtrace is to be able to instrument a production system. If you have
to rebuild the kernel, then you've wandered off the reservation.
I guess I don't quite see why these special functions can't be
instrumented deliberately with SDTs instead of relying on FBT. It
should be possible even though this is assembly code.
Maybe there's a good reason that wasn't considered as an option to
solve the underlying problem, and the RE just wants to close out the
bug instead. It'd be helpful if he'd comment here, as I don't
understand enough of the issues, so I've cc'd him. ;-}
I agree with James. The mutex_enter code is a good place to look to see a
way to do this in assembler. I don't have access to source at the minute,
but I think the lockstat provider replaces the ret at the end of mutex_enter
and simply falls into lockstat_wrapper code. You wouldn't catch the
call into
the function, but you could see what is happening at the return.
max
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