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From: sandmann AT clio DOT rice DOT edu (Charles Sandmann)
Message-Id: <10202120441.AA22905@clio.rice.edu>
Subject: Re: Alignment problem
To: rudd AT cyberoptics DOT com
Date: Mon, 11 Feb 2002 22:41:28 -0600 (CST)
Cc: eliz AT is DOT elta DOT co DOT il, djgpp-workers AT delorie DOT com
In-Reply-To: <3C684B4A.3AC31AA2@cyberoptics.com> from "Eric Rudd" at Feb 11, 2002 04:52:58 PM
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Here's a malloc.c patch vs 2.03 (not CVS - but should apply OK there 
with a line number offset).  It only gets called if you have a new
sbrk() block and it's unaligned - so normally no additional memory or
cpu overhead.  Note: sbrk(1..7) bytes should always be internally
handled by sbrk() and not do any DPMI calls.

Note, I can't make it fail normally so I added some sbrk(1) and sbrk(4)
calls into a test program and malloc always returned 8 byte aligned.

*** malloc.c_	Wed Dec  5 14:52:52 2001
--- malloc.c	Mon Feb 11 22:22:32 2002
*************** malloc(size_t size)
*** 208,215 ****
--- 208,222 ----
      rv = (BLOCK *)((char *)rv - 4);
    }
    else
    {
+     int align_bytes = (int)rv & (ALIGN-1);
+     if(align_bytes)
+     {
+       align_bytes = ALIGN - align_bytes;
+       if(sbrk(align_bytes) == (void *)((char *)rv + chunk_size) )
+         rv = (BLOCK *)((char *)rv + align_bytes);
+     }
      expected_sbrk = (BLOCK *)((char *)rv + chunk_size);
  #if DEBUG
      printf("    disconnected sbrk\n");
  #endif