Re: [PATCH] string_copying.7: don't grant strl{cpy,cat} magic

[Lennart Jablonka <humm@ljabl.com>]

Quoth Matthew House:
>On Sat, Jul 29, 2023 at 8:29 AM Alejandro Colomar <alx@kernel.org> wrote:
>> I lied.  I should have said that it writes what is safe to write, and
>> then uses a somewhat "safer" version of undefined behavior (compared
>> to other string copying functions).  The standard differentiates
>> "bounded UB", which doesn't perform out-of-bounds stores, from
>> "critical UB", which performs them.  In usual jargon, UB is UB, and
>> there's no mild form of UB; however, the standard prescribes a bounded
>> form of UB.  However, I'm not sure compilers --and specifically GCC--
>> follow such a prescription of bounded UB, so it's better to consider
>> all UB to be critical UB, just to fall on the safe side.
>
>Do you have a source for this? As far as I am aware, the standards have
>always followed the "UB is UB" philosophy, which is why standards-oriented
>people keep trying to reiterate it. I've never heard of anything like
>"bounded UB" vs. "critical UB". C17 draft N2176 provides no such
>distinction in its definition:

Quoth Alejandro Colomar:
>References:
>
><https://port70.net/~nsz/c/c11/n1570.html#L.2>

Looks like a reference to me.

Yes, UB is UB.  The optional Annex L on Analyzability does define 
bounded and unbounded UB.  No, you don’t care about them.  Yes, 
that is standard terminology.  No, your implementation doesn’t 
define __STDC_ANALYZABLE__.  Yes, that terminology can be useful.