cygwin issues

[Boehm, Hans]

> From: Anthony Green [ mailto:green@redhat.com ]

> IIRC, the change was also motivated somewhat by issues 
> related to data in
> shared libraries on either Alpha or PPC Linux.  Do you 
> believe this is a
> non-issue now?
> 
AFAIK, this should work fine.  The only past problem I'm aware of was that
some of the old heuristics for locating the main data segment failed when
the collector was in a shared library.  The collector always walks the list
of shared libraries to find the other data segments.  The code to do so
seems to be fairly portable, though I'm not sure the data structure it
relies on is officially viewed as documented.

(It can optionally look at /proc to find writable mappings instead.  This
seems to be necessary under Linux if you redirect C/C++ allocation to use
GC_malloc, since some very early allocations use a special malloc in the
dynamic loader, and that memory ends up pointing to memory allocated with
the later malloc.  I haven't found a reason to use that feature under Linux
unless malloc itself is redirected.)

Hans