Calculate the size of a memory page on your system.

pagesize.c

#define _GNU_SOURCE

#include <signal.h>
#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <unistd.h>
#include <ucontext.h>

volatile int done;
uint8_t * volatile top,
        * volatile bottom,
        * volatile iter,
        * volatile iter_orig;

volatile int fault_count = 0;

static void segv_action(int sig, siginfo_t* info, void* arg_context) {
	ucontext_t* context = (ucontext_t*)arg_context;

	printf("Orig Iter: %p -- Iter: %p -- Fault Addr: %p\n", iter_orig, iter, info->si_addr);

	done = 1;
	iter = iter_orig;

	if (top == NULL) {
		top = info->si_addr;
	} else if (bottom == NULL) {
		bottom = info->si_addr + 1;
	}

	context->uc_mcontext.gregs[REG_RAX] = (long long)iter_orig;

	if (++fault_count >= 4) {
		exit(1);
	}
}

int main(int argc, char** argv) {
	struct sigaction action;
	action.sa_handler   = NULL;
	action.sa_sigaction = segv_action;
	action.sa_flags     = SA_SIGINFO;
	action.sa_restorer  = NULL;

	printf("System reports a page size of %d\n", getpagesize());

	sigaction(11, &action, NULL);

	top = bottom = NULL;
	iter_orig = iter = malloc(1);

	done = 0;
	while (0 == done) {
		uint8_t x = *(iter++);
	}

	done = 0;
	while (done == 0) {
		uint8_t x = *(iter--);
	}

	printf("Top of page: %p\n", top);
	printf("Bottom of page: %p\n", bottom);
	printf("Calculated page size: 0x%lx\n", top - bottom);

	return 0;
}