Comment # 7 on bug 1188327 from Richard Biener

(In reply to Takashi Iwai from comment #6)
> FWIW, ecc_swap_digits() handles the u64 array, so copying would be needed
> there instead of the caller.  (And there are two calls of ecc_swap_digits()
> in 
> ecdsa_set_pub_key()).
> 
> If performance matters, we'd need two versions of ecc_swap_digits() for
> aligned and unaligned.  But all calls of ecc_swap_digits() in ecdsa.c look
> suspicious wrt alignment.

Instead of a memcpy you can also use

typedef u64 unaligned_u64 __attribute__((aligned(1)));

  *(unaligned_u64 *)digits

that avoids the memcpy (which should be similarly optimized in most cases,
but you'd need to check).  It might of course be slow when the target
cannot do unaligned accesses as it will to shifting/masking/etc. to
produce the u64 value which might not actually be needed as 'u64' (without
knowing the code in question)