simple trick to disable rand() on x64

disable_rand.c

/*
 * enferex trick to disable rand() on x64
 * @_hugsy_
 */

#include <stdlib.h>
#include <time.h>
#include <dlfcn.h>
#include <stdio.h>
#include <string.h>

unsigned long get_rdi(void){
	unsigned long x;
	__asm__(
		"mov %%rdi, %0"
		: "=r"(x)
	);
	return x;
}

void rand_many_times(void)
{
        int i;
	for (i=0; i<3; i++) {
		printf("Calling rand(): ret = %#x\n", rand());
	}
        return;
}

int main(int argc, char** argv, char** envp)
{
	void *p;
	unsigned long *unsafe_state;
	unsigned long randtbl;

	srand(time(NULL));
	unsafe_state = (unsigned long *)get_rdi();
	randtbl = (*unsafe_state)-0x10;

	printf("unsafe_state @%#lx\n", (unsigned long)unsafe_state);
	printf("randtbl @%#lx\n", randtbl);

	printf("Before wipe\n");
        rand_many_times();

        printf("Erasing randtbl\n");
	memset((void*)randtbl, 0, 0x80);

	printf("After wipe\n");
        rand_many_times(); // rand() will always return 0

	return 0;
}