a.c

#include <stdint.h>
#include <stdio.h>
#include <string.h>

int main() {
	unsigned char foo_arr[9];
	memset(foo_arr, 0, 9);
	unsigned char *foo = foo_arr;
	uint8_t a = 0xDE;
	uint64_t b = 0xDEEFBEADDEEFBEADLL;
	*((uint64_t *) (foo + 1)) = b, *foo = a;
	printf("[");
	for( int i = 0; i < 9; i++ ) {
		printf("0x%x", foo[i]);
		if( i != 8 ) printf(", ");
	}
	printf("]\n");
}