*BSD support in 6.8.3

[Simon Marlow]

Don Stewart wrote:
> marlowsd:
>> Hi Folks,
>>
>> 6.8.3 is nearing release, and we have an outstanding bug affecting the 
>> GHCi on the BSDs:
>>
>>   http://hackage.haskell.org/trac/ghc/ticket/2013
>>
>> We need someone to help out with this.  The patch in the ticket apparently 
>> works, but can't be committed as is because it isn't correctly #ifdef'd 
>> and will presumably break other platforms.  Also it needs to be tested on 
>> OpenBSD/NetBSD in addition to FreeBSD.
>>
>> I don't have access to a *BSD machine right now, and I don't have the time 
>> available to set one up.  If someone can donate a temporary account then 
>> that would be helpful, but most helpful would be if someone could work 
>> with us to get this bug fixed in time for 6.8.3 (i.e. the next few days). 
>> Otherwise, we have to release with the bug still in, which would be bad.
> 
> So, try the patch to get the patch to compile against ghc
> 6.8.3-snapshot, and see if it works on OpenBSD?

It's not just a case of testing the patch, there are a couple of issues to 
address:

  - it has a couple of wired-in addresses: one place to load object files,
    another to put jump tables at.  This is necessary because *BSD doesn't
    have the MAP_32BIT flag for mmap().  However, the particular wired-in
    addresses needed will probably vary on the different *BSDs.  Someone
    needs to look at the memory map and make sure we're picking sensible
    addresses.

  - the patch doesn't #ifdef its changes, so it'll break other platforms
    (easy to fix).

Also the code has changed in HEAD, and we need a completely different patch 
there (although the same idea applies, pick an address and use MAP_FIXED).

Cheers,
	Simon