From: Florian Weimer <fw@deneb.enyo.de>
To: Andreas Schwab <schwab@linux-m68k.org>
Cc: Zack Weinberg via Libc-alpha <libc-alpha@sourceware.org>,
Carlos O'Donell <carlos@redhat.com>,
Zack Weinberg <zack@owlfolio.org>
Subject: Re: “Undefined behavior” considered harmful (was Re: Bug 29863 - Segmentation fault in memcmp-sse2.S…)
Date: Fri, 30 Dec 2022 14:28:07 +0100 [thread overview]
Message-ID: <87bknl3tso.fsf@mid.deneb.enyo.de> (raw)
In-Reply-To: <87y1qp97j4.fsf@igel.home> (Andreas Schwab's message of "Thu, 29 Dec 2022 23:20:15 +0100")
* Andreas Schwab:
> On Dez 29 2022, Zack Weinberg via Libc-alpha wrote:
>
>> 1. The C standard uses “undefined behavior” far more liberally than it
>> ought to. In many cases of existing UB the committee could define
>> the behavior (possibly as implementation-defined or unspecified)
>> without any actual negative consequences. It seems the committee
>> *is* moving in this direction as of C2x, for instance by dropping
>> the allowances for non-twos-complement signed arithmetic, but they
>> could and should go a lot farther down that road.
>
> That's not removing an undefined behavior, it's removing an
> implementation choice.
Right, arithmetic is still not twos-complement, it's only about
representation. Same with C++.
(I associate twos-complement signed *arithmetic* with the obvious
(unsigned) overflow behavior.)
next prev parent reply other threads:[~2022-12-30 13:28 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-12-13 18:20 Bug 29863 - Segmentation fault in memcmp-sse2.S if memory contents can concurrently change Narayanan Iyer
2022-12-13 18:31 ` Andrew Pinski
2022-12-13 18:39 ` Narayanan Iyer
2022-12-13 18:39 ` Cristian Rodríguez
2022-12-13 19:08 ` Noah Goldstein
2022-12-13 19:13 ` Narayanan Iyer
2022-12-13 19:25 ` Noah Goldstein
2022-12-13 20:56 ` Zack Weinberg
2022-12-13 23:29 ` Carlos O'Donell
2022-12-14 2:28 ` Zack Weinberg
2022-12-14 4:16 ` Carlos O'Donell
2022-12-14 14:16 ` Zack Weinberg
2022-12-14 17:36 ` Paolo Bonzini
2022-12-29 7:09 ` Zack Weinberg
2022-12-29 19:32 ` “Undefined behavior” considered harmful (was Re: Bug 29863 - Segmentation fault in memcmp-sse2.S…) Zack Weinberg
2022-12-29 22:20 ` Andreas Schwab
2022-12-30 13:28 ` Florian Weimer [this message]
2022-12-30 15:09 ` Florian Weimer
2022-12-13 22:52 ` Bug 29863 - Segmentation fault vs invalid results, memory models, and control/data dependencies Carlos O'Donell
2022-12-14 12:03 ` Florian Weimer
2022-12-13 21:20 ` Bug 29863 - Segmentation fault in memcmp-sse2.S if memory contents can concurrently change Florian Weimer
2022-12-13 22:59 ` Noah Goldstein
2022-12-14 12:06 ` Florian Weimer
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