#include <stdio.h>
#include <limits.h>
#include <sys/resource.h>

#ifndef PAGE_SIZE
#include <unistd.h>
#define PAGE_SIZE sysconf(_SC_PAGE_SIZE)
#endif

/* get the stack [start,end] of the main thread:
   start is heuristic (smallest possible based on current rlimit
   and current mappings, but stack size is limited for sanity)
   end is precise, parsing /proc may fail */
static int getstack(size_t *start, size_t *end)
{
	size_t limit, prevend;
	struct rlimit r;
	FILE *f;
	char buf[PATH_MAX+80], s[8];
	int n;

	f = fopen("/proc/self/maps", "re");
	if (!f)
		return -1;
	n = 0;
	while (fgets(buf, sizeof buf, f)) {
		n = sscanf(buf, "%zx-%zx %*s %*s %*s %*s %7s", start, end, s);
		if (n >= 2) {
			if (n == 3 && strcmp(s, "[stack]") == 0)
				break;
			prevend = *end;
		}
		n = 0;
	}
	fclose(f);
	if (n == 0)
		return -1;

	limit = 100 << 20; /* 100MB stack limit */
	if (getrlimit(RLIMIT_STACK, &r)==0 && r.rlim_cur < limit)
		limit = r.rlim_cur & -PAGE_SIZE;
	if (limit > *end) limit = *end;
	if (prevend < *end - limit) prevend = *end - limit;
	if (*start > prevend) *start = prevend;
	return 0;
}

int main()
{
	size_t s,e;

	if (getstack(&s, &e)) {
		printf("getstack failed\n");
		return -1;
	}
	printf("%zx-%zx %zu\n", s, e, e-s);
	return 0;
}