dtrace backtracing

[Frank Ch. Eigler]

Hi -

FYI, piecing information together, it appears that both kernel- and
user-side backtrace functions in dtrace work by:

a) assuming that everything is compiled with frame pointers
b) assuming that the stack frames are not corrupted
c) walking the stack frame pointers to populate an array of PC value
   for call sites
d) passing said array to dtrace userspace in the trace stream
e) dtrace userspace mapping the PC array to symbolic data later
   by looking up ELF symbol tables
f) assuming that this deferred mapping is still valid


- FChE