Re: Differences between man-pages and libc manual safety markings

[Alexandre Oliva <aoliva-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

On Nov  1, 2014, Torvald Riegel <triegel-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> wrote:

> It's not surprising that this matters today (ie, when you made the
> choices), and it's not like we've been aware of this since just
> yesterday.

> That's why I'm arguing for being conservative

That goes both ways.  While strcpy coded for current standards might
wish to make such optimizations, old code written for earlier standards
that did not make allowances for the proposed strcpy optimization would
break.  So we have to be conservative in strcpy to avoid breaking valid
old programs (per the standards they were written for), and this implies
not making the proposed optimization, which brings us back to the
conclusion that the ctermid(NULL) implementation is MT-Safe.  And
AS-Safe, too.

> it helps to be cautious when making assumptions about things that may
> easily change in the future and that you can't predict.

Per the above, this one property of strcpy is not one that can *easily*
change.  Quite the opposite.  It takes a lot of wording contortionism to
make writing garbage fit into the strcpy contract even under current
standards.

> In our case here, if you feel like what you require from the strcpy
> implementation is very complex

I don't.  The requirements are the common requirements that apply to all
historical standards that have specified strcpy.  Nothing beyond that.
Now that's not much of a strong or surprising assumption, is it?

> Or, don't go for specifying assumptions about strcpy in the ctermid
> docs, but rather try to solve it at the other end by documenting that
> strcpy has to work well under concurrent execution, in particular under
> concurrent but "idempotent" copies to a memory range.

My take is that requirement is already coded in early C standards.c

-- 
Alexandre Oliva, freedom fighter    http://FSFLA.org/~lxoliva/
You must be the change you wish to see in the world. -- Gandhi
Be Free! -- http://FSFLA.org/   FSF Latin America board member
Free Software Evangelist|Red Hat Brasil GNU Toolchain Engineer
--
To unsubscribe from this list: send the line "unsubscribe linux-man" in
the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html