expected calloc out put

[Steven Munroe]

Sharyathi Nagesh <sharyath@in.ibm.com> writes:

>	ltp test suite tests for 2 successive calloc()s like this 
>=====================
>#include<stdio.h>
>#include<stdlib.h>
>#include<errno.h>
>#define MAX 8092*8092
>int main()
>{
>        char *ptr1,*ptr2;
>        ptr1=calloc(MAX,1);
>        perror("calloc 1:");
>        ptr2=ptr1;
>        free(ptr1);
>        perror("free ");
>        ptr1=calloc(MAX,1);
>        perror(" calloc 2");
>        if(ptr1 == ptr2)
>                printf("\n Success");
>        else
>                printf("\n Failure");
>}
>=====================
>fails in ppc 64 specifically. The test suite fails as ptr1 is not equal
>to ptr2. Is calloc() expected to return same values on successive
>allocation? as man page doesn't suggest any thing on this.

Your allocation is large enought to exceed the MMAP_THRESHOLD and use an
annonymous mmap for the storage. In this case the free is just an unmap
and the 2nd calloc is a new mmap. So it is the kernel choosing the address.

So what kernel and which distro are you running? RedHat? Fedora? 
This might be execshield randomizing mmap addresses.