/* stack guard gap testing - 2017/06/17 - w.tarreau */

#include <sys/mman.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <alloca.h>
#include <fcntl.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

static volatile void *stack_h, *stack_l, *stack_last;
static volatile void *heap_h, *heap_l, *heap_last;
static volatile void *anon_h, *anon_l, *anon_last;

char buf[256];
int len;

void dump()
{

	printf("stack=%p [%p-%p] (%lu total bytes)\n", stack_last, stack_l, stack_h, (long)(stack_h-stack_l));
	printf("heap~=%p [%p-%p] (%lu total bytes)\n", heap_last, heap_l, heap_h, (long)(heap_h-heap_l));
	printf("anon~=%p [%p-%p] (%lu total bytes)\n", anon_last, anon_l, anon_h, (long)(anon_h-anon_l));
	printf("heap...stack=%lu bytes\n", (long)(stack_h - heap_l));
	printf("heap+anon+stack=%lu bytes\n", (long)(stack_h-stack_l+heap_h-heap_l+anon_h-anon_l));
	close(0);
	open("/proc/self/maps", O_RDONLY);
	while ((len = read(0, buf, sizeof(buf))) > 0)
		write(1, buf, len);
	close(0);
}

void segv(int sig, siginfo_t *si, void *uc)
{
	printf("SEGV caught\n");
	dump();
	exit(1);
}

main(int argc, char **argv)
{
	void *p;
	int round;
	long step = -65536;
	stack_t ss;
	struct sigaction sa;

	if (argc > 1)
		step = atol(argv[1]);

	ss.ss_flags = 0;
	ss.ss_size = SIGSTKSZ;
	ss.ss_sp = malloc(ss.ss_size);
	sigaltstack(&ss, NULL);

	sa.sa_handler = NULL;
	sa.sa_sigaction = segv;
	sa.sa_flags = SA_ONESHOT | SA_ONSTACK;
	sigemptyset(&sa.sa_mask);
	sigaction(SIGSEGV, &sa, NULL);

	stack_h = NULL;
	round = 0;
	while (1) {
		if (step > 0) {
			p = mmap(0, step, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
			if (p == MAP_FAILED)
				break;
			anon_last = p;

			if (!anon_l || p < anon_l)
				anon_l = p;

			if (!anon_h || p > anon_h)
				anon_h = p;
		}
		else {
			/* use sbrk() nor malloc to ensure libc doesn't use mmap() under us */
			p = sbrk(0);
			if (sbrk(-step) == (void *)-1) {
				/* continue with mmap() */
				step = -step;
				continue;
				//break;
			}

			heap_last = p;

			if (!heap_l || p < heap_l)
				heap_l = p;

			if (!heap_h || p > heap_h)
				heap_h = p;
		}

		round++;
		getchar();

		p = alloca(abs(step));
		stack_last = p;
		*(char *)p = 0;

		//memset(p, 0, step);

		if (!stack_l || p < stack_l)
			stack_l = p;

		if (!stack_h || p > stack_h)
			stack_h = p;
	}
	printf("mmap() failed\n");
	dump();
	printf("rounds: %d\n", round);
}