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Date: Tue, 13 Jun 2017 00:33:00 +0300
From: Konstantin Belousov <kostikbel@gmail.com>
To: Mark Johnston <markj@FreeBSD.org>
Cc: src-committers@freebsd.org, svn-src-all@freebsd.org,
 svn-src-head@freebsd.org
Subject: Re: svn commit: r319868 - in head/sys: kern sys
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On Mon, Jun 12, 2017 at 01:47:05PM -0700, Mark Johnston wrote:
> On Mon, Jun 12, 2017 at 11:29:52PM +0300, Konstantin Belousov wrote:
> > On Mon, Jun 12, 2017 at 08:14:44PM +0000, Mark Johnston wrote:
> > > +int
> > > +uuidcmp(const struct uuid *uuid1, const struct uuid *uuid2)
> > > +{
> > > +
> > > +	return (memcmp(uuid1, uuid2, sizeof(struct uuid)));
> > > +}
> > 
> > This is unsafe.  The function operation depends on the ABI properties
> > that there is no padding either between members, or at the end of
> > the structure.  Why not use by-member comparision ?
> 
> I interpreted the CTASSERT at the beginning of kern_uuid.c as a
> guarantee that no such padding will be present. kern_uuid.c also defines
> an alternate representation, struct uuid_private, and casts between the
> two.

I agree, your addition is consistent with the other code in kern_uuid.c,
which already depends on these features.  At least it contradicts
to what compiler authors try to teach C language users.

BTW, does uuid_private low/mid/hi union split of ll depend on endianess ?