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Message-ID:	<3CE41EB8.619484D9@yahoo.com>
Date:	Thu, 16 May 2002 17:03:52 -0400
From:	CBFalconer <cbfalconer AT yahoo DOT com>
Organization:	Ched Research
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To:	djgpp-workers AT delorie DOT com
Subject:	Re: Malloc/free DJGPP code
References:	<10205161914 DOT AA17309 AT clio DOT rice DOT edu>
Reply-To:	djgpp-workers AT delorie DOT com

Charles Sandmann wrote:
> 
> > > It cannot be told to supply a negative increment, thus reducing
> > > the portion supplied (question, not statement)?
> >
> > The DJGPP implementation of sbrk does accept a negative argument, but
> > it doesn't return that memory to the system.
> 
> Correct, it just internally changes the pointer but knows internally
> that it's still there and available.
> 
> When you have multiple memory zones, which may not be contiguous,
> if you pass a negative argument which spans those zones really bad
> things happen.  So negative arguments only work for the unixy sbrk,
> or standard sbrk for increments which don't step over a block
> boundary.
> 
> It might be possible to make sbrk() return these blocks to DPMI, but
> I have no plans to revisit that ugly assembler code unless something's
> badly broken.

It should be totally unnecessary, because the malloc code is the
only access to sbrk provided in the whole system (barring emacs). 
However I see no sbrk documentation as to what is valid/invalid
etc. 


-- 
Chuck F (cbfalconer AT yahoo DOT com) (cbfalconer AT worldnet DOT att DOT net)
   Available for consulting/temporary embedded and systems.
   <http://cbfalconer.home.att.net>  USE worldnet address!

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