setjmp: read the manual

[Doug Gwyn <gwyn>]

I am afraid I don't follow Sun's logic.  All that is required is to
unravel the call stack frames by following the back-pointers.  The
VAX built-in support for this stuff is not used on any UNIXes I am
familiar with.  When someone does a longjmp the odds are very good
that it is not in the inside of a tight loop, so the extra time
taken to unwind the stack frame to fix up clobbered registers should
not be an efficiency issue, unless your call frames have a variable
amount of information and no internal clue about how much.