[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20250619214030.GH1827@brightrain.aerifal.cx>
Date: Thu, 19 Jun 2025 17:40:30 -0400
From: Rich Felker <dalias@...c.org>
To: Thorsten Glaser <tg@...bsd.de>
Cc: musl@...ts.openwall.com, Alejandro Colomar <alx@...nel.org>,
linux-man@...r.kernel.org, libc-alpha@...rceware.org,
Paul Eggert <eggert@...ucla.edu>, Bruno Haible <bruno@...sp.org>,
bug-gnulib@....org
Subject: Re: [v2] malloc.3: Clarify realloc(3) standards conformance
On Thu, Jun 19, 2025 at 05:38:15PM +0200, Thorsten Glaser wrote:
> On Thu, 19 Jun 2025, Rich Felker wrote:
>
> >> + The glibc implementation of realloc() is not consistent with
> >> + that, and as a consequence, it is dangerous to call
> >> + realloc(p, 0) in glibc.
> >
> >It's not dangerous if you know what it's doing. Rather it's
> >non-portable.
>
> Nope.
>
> It’s actually dangerous in all libcs.
>
> GCC is a repeat offender of taking things that are Undefined
> Behaviour in C (and GCC 15 even defaults to C23) and optimising
> in a way that breaks programs and libraries that depend on the
> behaviour of the respektive system and libc, which they even
> guarantee.
>
> This is an unperiodic reminder that GCC lacks a -std=posix2024
> and similar.
>
> This is also why I was a bit angry that C23 made it UB. Had
> they made it unspecified (POSIX verbiage) / IB (C verbiage),
> implementations could actually do things and compilers would
> not be allowed to break things that rely on it, i.e. it would
> merely have been unportable. But when ISO C says UB it’s not
> unportable, it’s dangerous.
OK, this is a legitimate point in support of "dangerous", but it only
applies with -std=c23 or similar. When targeting an older version of
the language standard, the UB does not apply. It would be interesting
to know if GCC and/or LLVM have any particular intent on this yet. My
hope would be that they wait to react until a better consensus is
achieved.
Rich
Powered by blists - more mailing lists
Confused about mailing lists and their use?
Read about mailing lists on Wikipedia
and check out these
guidelines on proper formatting of your messages.
