tt> implementation saves all possibly pointer-valued registers
into the buffer, as opposed to trying to unwind the stack at
<TT>longjmp</tt> time.  The <TT>setjmp_test</tt> test tries to determine this,
but often doesn't get it right.
<P>
In GC6.x versions of the collector, tracing of registers
was more commonly handled
with assembly code.  In GC7, this is generally to be avoided.
<P>
Most commonly <TT>os_dep.c</tt> will not require attention, but see below.
<H2>Thread support</h2>
Supporting threads requir