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Message-ID: <9ce5fc2a-fc8d-4f84-8d69-9ea37cefc356@cs.ucla.edu>
Date: Fri, 31 Oct 2025 14:33:22 -0600
From: Paul Eggert <eggert@...ucla.edu>
To: Alejandro Colomar <alx@...nel.org>
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>, "Paul E. McKenney"
<paulmck@...nel.org>, Thiago Macieira <thiago@...ieira.org>
Subject: Re: Re: realloci(): A realloc() variant that works in-place
On 10/31/25 14:13, Alejandro Colomar wrote:
> Consider that realloci() would be significantly cheaper than realloc(3),
Not in the case where the object doesn't move: they should be about the
same speed. And when the object grows so much that it does need to move,
the V7 realloc approach should be a bit faster because you need to make
just one call into the memory subsystem, not three (realloci + malloc +
free).
> That would make sanitizers and static analyzers unable to verify lots of
> code
No, just the opposite. Currently sanitizers etc. spend useless work
checking for C23 rules that don't correspond to any hardware or
correctness needs; they're simply rules imposed by the C committee. This
checking is counterproductive to real-world software development.
If we fixed the realloc spec to better match how actual production
hardware behaves, we could fix sanitizers to spend their time flagging
real bugs instead of wasting their time (and developers' time)
generating false alarms.
> I wouldn't categorize it as hard to explain:
Oh, it's not hard to specify a realloci API, or to implement it. What's
hard is explaining its motivation: why it's needed and what it's good
for. It's motivated by specialized applications that most programmers
don't know about and don't need to. And these specialized applications
would be better served by a 7th Edition Unix realloc.
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