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Preventing a tapscript from accessing user space.


What prevents a tapscript from attempting to access user space directly? For example:
if $arg is a pointer to a struct in user space (presumably passed to the kernel via some system call).
What prevents me from doing i=$arg->j in the tapscript.


Also when I looked at the code generated by stap I was hoping to see deref() used but that is not what I found.
I could have missed something...


On i386 the above example works ok because we can just access the user space, it works but it is not correct.
On s390 I can't do that I must use something like get_user(), but I cant do that ether because get_user() calls might_sleep() and the probe is running with interrupts off.


--
David Wilder
IBM Linux Technology Center
Beaverton, Oregon, USA dwilder@us.ibm.com
(503)578-3789



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