Vladimir Oleynik pointed out that va_start() twice in the same function isn't portable (with ppc 4xx as an example of a platform it doesn't work on). This is why va_copy exists.

/* vi: set sw=4 ts=4: */
/*
 * hello.c - A hello world program.
 */

#include "toys.h"

int hello_main(void)
{
	printf("Hello world\n");
	return 0;
}