sexec.c

#include <stdio.h>
#include <unistd.h>

int main(int argc, char *argv[])
{
	char buf[512];
	char *args[3] = { argv[0], NULL, NULL };
	int x = (argc > 1 ? atoi(argv[1]) : 0) + 1;
	if (x == 10000)
		return puts("done") && 0;
	snprintf(buf, 512, "%d", x);
	args[1] = buf;
	execv(args[0], args);
}

sprint.c

#include <stdio.h>
#include <unistd.h>

int main(int argc, char *argv[])
{
	char buf[512] = "";
	int x;
top:
	x = (buf[0] ? atoi(buf) : 0) + 1;
	if (x == 10000)
		return puts("done") && 0;
	snprintf(buf, 512, "%d", x);
	goto top;
}

times

theta ~/work/sandbox/sexec$ time ./sexec
done

real    0m4.834s
user    0m1.207s
sys     0m3.540s
theta ~/work/sandbox/sexec$ time ./sprint
done

real    0m0.005s
user    0m0.003s
sys     0m0.000s
theta ~/work/sandbox/sexec$