dtrace discuss - Jun 2007 - copyin of stack addresses in a USDT

I have more values I want to pass into a USDT probe than there are availble
arguments in the probe macros.  So I decided to get around this by copying the
data into a structure on the stack and then passing the address of that
structure to the probe.  Likewise in the probe I do a copyin into a D script
structure and then operate on that data.

This seems to work, but after talking to a coworker I was wondering if probes
are actually running concurrently with the applications thus the structure on
the stack could possibly be overwritten/reclaimed before the copyin() in the
probe happens.

--td
--
This message posted from opensolaris.org

>This seems to work, but after talking to a coworker I was wondering if
probes are actually running concurrently with the applications thus the
structure on the stack could possibly be overwritten/reclaimed before the
copyin() in the probe happens.
Copyin and such run in probe context; i.e., they run synchronous with the
execution of the code.

But it is true for all kernel operations that data can change while it
is being copied (and if it''s copied once in your probe and once in a 
syscall, the two copyin results may be different.

Casper