Re: CVS commit: src/sys/arch/atari/stand/installboot

[Taylor R Campbell <campbell+netbsd-source-changes-d%mumble.net@localhost>]

   Date: Sat, 15 Nov 2014 13:43:16 +0900
   From: Izumi Tsutsui <tsutsui%ceres.dti.ne.jp@localhost>

   -	uint16_t	 sum;
   +	union {
   +		struct bootblock *bbp;
   +		uint16_t *word;		/* to fill cksum word */
   +	} bbsec;
   ...
   -	sum = 0;
   -	memcpy(bb->bb_xxboot + 255 * sizeof(sum), &sum, sizeof(sum));
   -	sum = 0x1234 - abcksum(bb->bb_xxboot);
   -	memcpy(bb->bb_xxboot + 255 * sizeof(sum), &sum, sizeof(sum));
   +	bbsec.bbp = bb;
   +	bbsec.word[255] = 0;
   +	bbsec.word[255] = 0x1234 - abcksum(bb->bb_xxboot);

Um, that has the same issue as the original code, no?  It still refers
to the content of the struct bootblock object by two different types,
struct bootblock and uint16_t -- passing the pointer through a union
doesn't change that.

What's wrong with the memcpy?

If you don't like the way the memcpy code looks, you could write

set16(bb->bb_xxboot, 255, 0);
set16(bb->bb_xxboot, 255, 0x1234 - abcksum(bb->bb_xxboot));

void
set16(void *p, size_t off, uint16_t v)
{
	memcpy((uint8_t *)p + off*sizeof(uint16_t), &v, sizeof v);
}

I don't see any byte ordering issues here that weren't present before.