Re: free() does not call sbrk()

[Jeff Johnston <jjohnstn at redhat dot com>]

On 15/09/09 03:29 PM, Martin Walter wrote:
> > ...
> > For a discussion on the design see: http://g.oswego.edu/dl/html/malloc.html
> > which is referenced in libc/stdlib/mallocr.c
>
> Thanks for clarification!
>
> > My simple test of mallocing a block of 4000 and freeing it back again in an
> > infinite loop results in the same pointer being given back each time and no
> > increment in memory usage.  I do not know why you are not seeing similar
> > behavior for your test.  Is there something else in your loop other than
> > malloc/free? (mine has a printf as well)
>
> Actually no. Please take a look at my code:

I believe the culprit has to be UART_write which is not a part of 
newlib.  I took your code and ran it with an mn10300-elf newlib build 
(using a simulator) and for x86-linux newlib locally on my x86-linux 
machine.  I replaced the UART_write call with a direct "write" syscall 
and it works just as expected; the same pointer each time.

-- Jeff J.

> #include "UART.h"
> #include<stdio.h>
> #include<stdlib.h>
> #include<string.h>
>
> static void alloc (int size)
> {
>          char buf[128];
>          int len;
>
>          char *ptr = malloc (size);
>          if (ptr != NULL)
>          {
>                  len = sprintf (buf, "ptr: %d\r\n", (int)ptr);
>                  UART_write(0, buf, len);
>                  free (ptr);
>          }
> }
>
> int main (int argc, char *argv[])
> {
>          register int i;
>
>          for (i = 0; i<  10; ++i)
>                  alloc (4000);
>
>          return 0;
> }
>
> And the output:
>
> ptr: 2016
> ptr: 6024
> ptr: 10032
> ptr: 14040
> ptr: 18048
> ptr: 22056
> ptr: 26064
> ptr: 30072
> ptr: 34080
> ptr: 38088
>
> Kind regards,
> Martin