Re: 1.3.22-1 on XP: malloc returns overlapping buffers

[Larry Hall <cygwin-lh at cygwin dot com>]

roconnor wrote:

> I am finding that under some circumstances a buffer returned by malloc
> will overlap with a buffer returned by a previous call to malloc that
> has not been freed.  I was able to reduce it to the following test
> case.  Running under cygwin 1.3.22-1 on Windows XP Professional
> Version 2002 SP1 it reports an overlap of 4824 bytes on two different
> machines, as well as on a third machine running Windows 2000 5.00.2195
> SP4.  On Windows NT 4.0.1381, it finds no overlap.
>
> Am I doing something wrong or is there a bug in malloc or XP?  More
> details below.
>
> ------------------------------------------------------------------------
>
> #include <stdio.h>
> #include <stdlib.h>
>
> int
> main (int argc, char **argv)
> {
>   char *mm = 0, *p;
>   int size = 8000, overlap;
>
>   p = malloc (1);
>
>   while (mm < p) {
>     mm = malloc (16777216);
>     if (mm == 0) {
>       printf ("not enough memory to run test\n");
>       exit (0);
>     }
>     printf ("malloc (16777216) = %d\n", (int)mm);
>   }
>
>   while ((p = malloc (size))) {
>     overlap = (int)p + size - (int)mm;
>     if (p < mm && overlap > 0) {
>       printf ("overlap = %d\n", overlap);
>       exit (1);
>     }
>   }
>   return 0;
> }
>
> ------------------------------------------------------------------------


This works OK for me on W2K SP1 with cygwin 1.5.x.  Maybe you want to
upgrade to this (i.e. the test version) and see if you still see the
problem.


--
Larry Hall                              http://www.rfk.com
RFK Partners, Inc.                      (508) 893-9779 - RFK Office
838 Washington Street                   (508) 893-9889 - FAX
Holliston, MA 01746


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