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Message-ID: <294157776.ifERbkFSEj@tjmaciei-mobl5>
Date: Fri, 31 Oct 2025 09:02:42 -0700
From: Thiago Macieira <thiago@...ieira.org>
To: Alejandro Colomar <alx@...nel.org>, Thorsten Glaser <tg@...bsd.de>
Cc: libc-alpha@...rceware.org, musl@...ts.openwall.com,
"A. Wilcox" <AWilcox@...cox-tech.com>,
Lénárd Szolnoki <cpp@...ardszolnoki.com>,
Collin Funk <collin.funk1@...il.com>,
Arthur O'Dwyer <arthur.j.odwyer@...il.com>,
Jonathan Wakely <jwakely@...hat.com>, Alejandro Colomar <alx@...nel.org>
Subject: Re: Re: realloci(): A realloc() variant that works in-place
On Friday, 31 October 2025 08:45:09 Pacific Daylight Time Thorsten Glaser
wrote:
> >In C, I've sometimes seen programmers trying to check if realloc(3)
> >moved or not, to skip some work. That's a micro-optimization that I've
> >never written myself, so I won't defend it. But for some reason, some
> >programmers keep wanting to do it.
>
> Huh. That one if is probably more effort than just doing the
> arithmetics always… if it’s not actually UB…
The conclusion among C++ developers is that using the previous pointer in any
way is UB. Therefore, you simply cannot know if the area was moved or not.
--
Thiago Macieira - thiago (AT) macieira.info - thiago (AT) kde.org
Principal Engineer - Intel Data Center - Platform & Sys. Eng.
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