Invalid pointer traps (S/6000)

[Marc Brandis]

I noticed that when a program under AIX on the S/6000 reads through an invalid
pointer, no exception is reported but instead the value 0 is returned. On write,
the exception is reported. This seems to be true for the whole address range
from 0 up to 7fffffff.

As I understand the hardware documentation, the MMU does in fact detect the
illegal access, so the whole thing can only be a matter of the operating system.

Is there a way to turn this off so that all accesses to unmapped pages report
an exception, not only writes?

Thanks for any pointers.


Marc-Michael Brandis
Computer Systems Laboratory, ETH-Zentrum (Swiss Federal Institute of Technology)
CH-8092 Zurich, Switzerland
email: brandis at inf.ethz.ch