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On OS X 10.4 and newer, we have to use dlsym because the old NS* interface has
been deprecated. The patch checks for HAVE_DLFCN_H instead of switching on
the OS version.

There is one additional quirk: although OS X prefixes global symbols with an
underscore, dlsym expects its argument NOT to have a leading underscore. As a
hack, we simply strip it off in lookupSymbol. Something a bit more elaborate
might be cleaner.

Also noticed a few others from RtsAPI were missing, so I added them all

When -fbreak-on-exception is set, an exception will cause GHCi to
suspend the current computation and return to the prompt, where the
history of the current evaluation can be inspected (if we are in
:trace).  This isn't on by default, because the behaviour could be
confusing: for example, ^C will cause a breakpoint.  It can be very
useful for finding the cause of a "head []" or a "fromJust Nothing",
though.

This is the result of Bernie Pope's internship work at MSR Cambridge,
with some subsequent improvements by me.  The main plan was to

 (a) Reduce the overhead for breakpoints, so we could enable 
     the feature by default without incurrent a significant penalty
 (b) Scatter more breakpoint sites throughout the code

Currently we can set a breakpoint on almost any subexpression, and the
overhead is around 1.5x slower than normal GHCi.  I hope to be able to
get this down further and/or allow breakpoints to be turned off.

This patch also fixes up :print following the recent changes to
constructor info tables.  (most of the :print tests now pass)

We now support single-stepping, which just enables all breakpoints.

  :step <expr>     executes <expr> with single-stepping turned on
  :step            single-steps from the current breakpoint

The mechanism is quite different to the previous implementation.  We
share code with the HPC (haskell program coverage) implementation now.
The coverage pass annotates source code with "tick" locations which
are tracked by the coverage tool.  In GHCi, each "tick" becomes a
potential breakpoint location.

Previously breakpoints were compiled into code that magically invoked
a nested instance of GHCi.  Now, a breakpoint causes the current
thread to block and control is returned to GHCi.

See the wiki page for more details and the current ToDo list:

  http://hackage.haskell.org/trac/ghc/wiki/NewGhciDebugger

Initial support for loading x86_64 Mach-O files

... so that GHCi doesn't complain about duplicate symbols when two C modules define the same static variable.

MERGE TO STABLE.

The __i686.get_pc_thunk symbols generated by gcc's PIC code generator are weak definitions that appear in every object file, so we need to deal with them.

MERGE TO STABLE.

We recently discovered that they aren't a win any more, and just cost
code size.

This patch adds data constructor names into their info tables. 
This is useful in the ghci debugger. It replaces the old scheme which
was based on tracking data con names in the linker. 

David Kirkman and Peter Tanski noticed that a line had been removed during
a patch merge which meant that oc->image pointed to the wrong place and
ultimately caused an error from realloc.

Specifically, this disables the special support in the RTS for looking up the datacon name corresponding to an address. 
Correspondingly, the debugging commads in GHCi will not be available, and neither will the '-fdebugging' flag

This patch extends the RTS linker and the dynamic linker so that it is possible to find out the datacon of a closure in heap at runtime:
- The RTS linker now carries a hashtable 'Address->Symbol' for data constructors
- The Persistent Linker State in the dynamic linker is extended in a similar way.

Finally, these two sources of information are consulted by:

> Linker.recoverDataCon :: a -> TcM Name

Original patch by brianlsmith@gmail.com

StableRoots opened new possibilities in the world
of plugins with their ability to link partially
applied closures against object code.
Exporting '(fn pluginwideState)' severely reduced
the complexity of HIDE's plugin system. The previous
system of global variables was both fragile and hard
to scale.

Good bye, StableRoots. We sure had some fun.

Apparently, the original fix never really worked due to typos and oversights.

In preparation for parallel GC, split up the monolithic GC.c file into
smaller parts.  Also in this patch (and difficult to separate,
unfortunatley):
  
  - Don't include Stable.h in Rts.h, instead just include it where
    necessary.
  
  - consistently use STATIC_INLINE in source files, and INLINE_HEADER
    in header files.  STATIC_INLINE is now turned off when DEBUG is on,
    to make debugging easier.
  
  - The GC no longer takes the get_roots function as an argument.
    We weren't making use of this generalisation.

Changes to the RTLD_DEFAULT semantics broke the trick we used to ensure
libc symbols were available to the ghci linker, in OpenBSD 4.0. We can
fix this by linking the ghc binary itself with --export-dynamic on this
system, removing the need for any magic Linker.c games.

GHCi now works on OpenBSD 4.0

Contributed by Eric Mertens <emertens at gmail.com>