Will,

The current method of using soft_calls was nothing more than a hack
I put in to avoid our constantly getting bitten by undetected stack 
overflows causing memory corruption.   Due to a design/implementation
flaw in the awt, such overflows can be caused by some applications
making use of awt facilities in an unforeseen way.  Other applications
(pizza) also make careless use of recursion.

As Tim pointed out, he performs faster inlined stack checking in the 
custom version with certain architecture-specific instruction 
templates for the JIT.  I would like to see this in the public version.  
For architectures for which those templates aren't provided we must fall
back to the slower soft call method.

As for hardware checking, first I agree with Tim that we it can't
be the only possible way since not all archs have or use an MMU.
This doesn't mean that software checking should be the only possible
way.  If someone implements hardware checking for the architectures
that support it, that would be nice.  We can enable one of the other
depending on the architecture, like we already do for NullPointerExceptions.