Re: [libunwind] Cursor copying

[David Mosberger]

>>>>> On Mon, 16 Aug 2004 12:29:07 +0100, "Thomas Hallgren" <address@hidden> 
>>>>> said:

  Thomas> The libunwind overview mentions how bidirectional iteration
  Thomas> can be achieved using cursor copies. I'd like to know how to
  Thomas> safely copy a cursor.

Yes.

  Thomas> A mere memcpy seems unsafe since the cursor contains a
  Thomas> pointer to an unw_context_t. The copy needs a state of its
  Thomas> own doesn't it?

A shallow copy (i.e., mmcpy) is safe provided the underlying
machine-state remains valid.  For local unwinding, that means the
unw_context_t with which the original cursor was created must remain
valid.

  Thomas> A suggestion could be to include a copy function in the
  Thomas> libunwind.  Something like this:

  Thomas> unw_copy_cursor(unw_cursor_t* from, unw_cursor_t* to,
  Thomas>                 unw_context_t* toContext);

  Thomas> The reason for passing the 'to' and 'toContext' is of course
  Thomas> to avoid the need for memory allocation.

Hmmh, can you say a bit more why you need this?  I'm not terribly fond
of adding routines which mention unw_context_t, since those by
definition work for local unwinding only.  From my perspective, it
would be preferable if applications could manage the life-time of
unw_context_t so it's never necessary to copy such a structure.

        --david