#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <stdio.h>
#include <errno.h>
#include <sys/time.h>
#include <sys/resource.h>
#include <sys/stat.h>
#include <fcntl.h>

#define TRIES 2

void *
get_stack_addr();

void print_layout(pid_t pid)
{
	char maps_file[128];
	char buf[BUFSIZ];
	int fd;
	int bytes;
	snprintf(maps_file, sizeof(maps_file)-1, "/proc/%d/maps", pid);
	
	fd = open(maps_file, O_RDONLY);
	printf("%u MEMORY layout\n", pid);
	while((bytes = read(fd, buf, sizeof(buf)))>0)
	{
		buf[bytes]='\0';
		printf("%s", buf);
	}
	printf("END\n");
}

main()
{
    size_t len;
    int i;
    void *v1, *v, *vold;
    void *stacktop;
    void *mina, *maxa;
    struct rlimit stack_limit;
    pid_t pid=getpid();
    

    // len = 17179869184;
    // len = 34359738368;

   // did not infringe
    // len = 100000L  * 4096;

    len = 20000L  * 4096 * 1024;

    stacktop = get_stack_addr();
    getrlimit(RLIMIT_STACK, &stack_limit);

    //printf("stacktop is %lx\n",(long) stacktop);

    mina = (void*)0xFFFFFFFFFFFFFFFFL;
    maxa = 0;

    vold = 0;
    for (i=0; i<TRIES; i++) {
      	v = mmap (NULL, len, PROT_READ | PROT_WRITE,
            MAP_SHARED | MAP_ANONYMOUS | MAP_NORESERVE, -1, (off_t)0);
      	if (v == MAP_FAILED) {	printf("failed, errno=%d\n",errno); abort(); } 

	if (v < mina)       mina = v;
	if (v + len > maxa) maxa = v + len;

	vold = v;

  }

  unsigned long delta = (unsigned long)stacktop - (unsigned long)maxa;
  if (delta<stack_limit.rlim_cur)
  {
	printf("%u: mmaps zone %lx - %lx stack %lx delta %ld\n", pid,
				(unsigned long)mina, (unsigned long)maxa,
				(unsigned long)stacktop, 
				delta);
	printf("Dangerous layout!\n");
	print_layout(pid);
	abort();
  }
  return 0;
}

void *
get_stack_addr()
{
    char fname[BUFSIZ], fmt_str[BUFSIZ];
    FILE *fp;
    long val;
    int i;

    // find the stack starting addr in /proc/<PID>/stat

    sprintf(fname,"/proc/%d/stat",getpid());
    if (!(fp = fopen(fname, "r"))) {
        printf("Error opening %s\n",fname);
	abort();
    }

    // create format string.  The stack starting addr is param #28
    // we don't care about the first 27 parameters.

    strcpy(fmt_str,"%*d %*s %*c");
    for (i=4;i<28;i++) {
      strcat(fmt_str," %*d");
    }
    strcat(fmt_str," %lu");

    fscanf(fp,fmt_str,&val);
    fclose(fp);

    return (void *)val;
}