Came across this article http://duartes.org/gustavo/blog/post/anatomy-of-a-program-in-memory/, and the pictorial illustration is very clear. Here’s a short program to confirm the layout:

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#include <stdio.h>
#include <stdlib.h>
#include <sys/mman.h>
#include <errno.h>
#include <unistd.h>

int main()
{
  int x;
  printf("%p\n", &x);
  void *p = mmap(NULL, 1, PROT_READ|PROT_WRITE,
      MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
  printf("%p\n", p);
  
  printf("%p\n", sbrk(0));

  malloc(1);
  printf("%p\n", sbrk(0));

  malloc(1);
  printf("%p\n", sbrk(0));

  return 0;
}

The output on my box is:

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0x7ffdb10979a8
0x7fb6f6cde000
0x7fb6f6cdd000
0x2030000
0x2051000
0x2051000

Some observation (mentioned in the article):

  • stack starts from high address
  • mmap region is placed below stack, and grows downwards
  • mmap anonymous memory is page (4k) align
  • heap starts from low address, and grows upwards