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

[Ljubomir Josifovski <lbj at cre dot canon dot co dot uk>]

On Wed, Aug 20, 2003 at 04:07:11PM -0400, 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;
> }
> 
> ------------------------------------------------------------------------

lbj@lbjlaptop:/tmp/q
$ gcc test.c -o test.exe
lbj@lbjlaptop:/tmp/q
$ gcc -mno-cygwin test.c -o test_no-cygwin.exe
lbj@lbjlaptop:/tmp/q
$ ./test.exe
malloc (16777216) = 6553608
malloc (16777216) = 23396360
malloc (16777216) = 40239112
malloc (16777216) = 57081864
malloc (16777216) = 73924616
malloc (16777216) = 90767368
malloc (16777216) = 107610120
malloc (16777216) = 124452872
malloc (16777216) = 141295624
malloc (16777216) = 570687496
overlap = 4920
lbj@lbjlaptop:/tmp/q
$ ./test_no-cygwin.exe
malloc (16777216) = 4456480
lbj@lbjlaptop:/tmp/q

Win2K, 512MB RAM, cygwin 1.3.22.

-- 
Ljubomir Josifovski

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