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Message-ID: <c5c35b74-bc56-e0f1-3608-05aac48f1be3@mirbsd.de>
Date: Sat, 21 Jun 2025 00:06:41 +0200 (CEST)
From: Thorsten Glaser <tg@...bsd.de>
To: Alejandro Colomar <alx@...nel.org>
cc: libc-alpha@...rceware.org, bug-gnulib@....org, musl@...ts.openwall.com,
наб <nabijaczleweli@...ijaczleweli.xyz>,
Douglas McIlroy <douglas.mcilroy@...tmouth.edu>,
Paul Eggert <eggert@...ucla.edu>, Robert Seacord <rcseacord@...il.com>,
Elliott Hughes <enh@...gle.com>, Bruno Haible <bruno@...sp.org>,
JeanHeyd Meneide <phdofthehouse@...il.com>, Rich Felker <dalias@...c.org>,
Adhemerval Zanella Netto <adhemerval.zanella@...aro.org>,
Joseph Myers <josmyers@...hat.com>, Florian Weimer <fweimer@...hat.com>,
Laurent Bercot <ska-dietlibc@...rnet.org>, Andreas Schwab <schwab@...e.de>,
Eric Blake <eblake@...hat.com>, Vincent Lefevre <vincent@...c17.net>,
Mark Harris <mark.hsj@...il.com>, Collin Funk <collin.funk1@...il.com>,
Wilco Dijkstra <Wilco.Dijkstra@....com>, DJ Delorie <dj@...hat.com>,
Cristian Rodríguez <cristian@...riguez.im>,
Siddhesh Poyarekar <siddhesh@...plt.org>, Sam James <sam@...too.org>,
Mark Wielaard <mark@...mp.org>, "Maciej W. Rozycki" <macro@...hat.com>,
Martin Uecker <ma.uecker@...il.com>,
Christopher Bazley <chris.bazley.wg14@...il.com>, eskil@...ession.se
Subject: Re: alx-0029r1 - Restore the traditional realloc(3) specification
On Fri, 20 Jun 2025, Alejandro Colomar wrote:
> There are two kinds of code that call realloc(p,0). One
> hard-codes the 0, and is used as a replacement of free(p). This
> code ignores the return value, since it's unimportant. This
> code currently produces a leak of 0 bytes plus associated
> metadata on platforms such as musl libc, where it returns a
> non-null pointer.
16 bytes or so on OpenBSD and derivatives, which return individual
suitably-aligned pointers into pages mapped as inaccessible (so that
accesses of the returned pointer of a 0-byte {m,re}alloc fail) plus,
again, metadata.
+1 on warning on that.
> For consistency, all the other allocation functions are updated
> to both return an .
an…?
FWIW, I’m in favour of the proposed change, but I don’t have any
stakes in this, I don’t think I wrote anything that mallocs or
reallocs 0 ever. Plus I’d likely not have to change… much.
(I now see that, in the case realloc() is passed a pointer the
implementation cannot find in its pool, an error is written (and
if an option is set, the execution terminated), and NULL is
returned without setting errno, but that’s UB already anyway.)
Also no need to Cc me, I get this via the musl mailing list, in
which I have some interest (dalias generally knows his stuff).
bye,
//mirabilos
--
22:20⎜<asarch> The crazy that persists in his craziness becomes a master
22:21⎜<asarch> And the distance between the craziness and geniality is
only measured by the success 18:35⎜<asarch> "Psychotics are consistently
inconsistent. The essence of sanity is to be inconsistently inconsistent
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