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Message-ID: <20250617145104.GX1827@brightrain.aerifal.cx>
Date: Tue, 17 Jun 2025 10:51:04 -0400
From: Rich Felker <dalias@...c.org>
To: enh <enh@...gle.com>
Cc: Alejandro Colomar <alx@...nel.org>, Florian Weimer <fweimer@...hat.com>,
Adhemerval Zanella Netto <adhemerval.zanella@...aro.org>,
musl@...ts.openwall.com, libc-alpha@...rceware.org,
Joseph Myers <josmyers@...hat.com>,
наб <nabijaczleweli@...ijaczleweli.xyz>,
Paul Eggert <eggert@...ucla.edu>,
Robert Seacord <rcseacord@...il.com>,
Bruno Haible <bruno@...sp.org>, bug-gnulib@....org,
JeanHeyd Meneide <phdofthehouse@...il.com>
Subject: Re: Re: BUG: realloc(p,0) should be consistent with malloc(0)
On Tue, Jun 17, 2025 at 10:07:07AM -0400, enh wrote:
> On Mon, Jun 16, 2025 at 5:44 PM Alejandro Colomar <alx@...nel.org> wrote:
> >
> > Hi Florian,
> >
> > On Mon, Jun 16, 2025 at 09:35:01PM +0200, Florian Weimer wrote:
> > > * Adhemerval Zanella Netto:
> > >
> > > > I have re-read the whole thread and it seems that most maintainers are OK
> > > > with this change and agree that current POSIX's realloc spec has some
> > > > drawbacks (albeit it still allows current glic behavior).
> > > >
> > > > The only one involved in the previous thread that raised some objection to
> > > > this change was Joseph [1], but I will let to say if he still think this
> > > > potential change to glibc is ill-advised.
> > >
> > > I objected then, and I'm objecting now as well.
> > >
> > > My rationale has not changed:
> > >
> > > <https://inbox.sourceware.org/libc-alpha/8734kl1pim.fsf@oldenburg.str.redhat.com/>
> > >
> > > I believe Siddhesh's proposed patch as the time was mostly a device to
> > > drive the discussion to a conclusion, which it did.
> >
> > I'll quote your rationale from the link:
> >
> > | * Siddhesh Poyarekar:
> > | | Nope, please read the threads carefully; I actually said that I won't
> > | | sustain an objection if I'm the only one holding that opinion.
> > |
> > | I'm still objecting, I don't think this change is valuable.
> > |
> > | I'm open to looking at this again once the C standard fully specifies
> > | the behavior of zero-sized objects, the return value of malloc (0), and
> > | so on.
> >
> > I'm working on that. I have a proposal for mandating that malloc(0),
> > but I can't present it until realloc(p, 0) is fixed. And the
> > C Committee has refused to fix realloc(p, 0) by decree, so until the
> > remaining implementations that are broken fix their implementations, we
> > can't think of having the standard fixed.
> >
> > Since glibc and Bionic are the two implementations that are currently
> > broken, could you please fix your implementations? I'm sure the
> > C Committee will be much easier to convince if the implentations have
> > changed in a clear direction.
> >
> > But if the committee says we're not fixing ISO C until the
> > implementations are fixed, and the implementations (you) refuse to
> > accept the fix until the committee standardizes something, then we'll
> > have the problem forever.
>
> is it really a problem though? you're basically asking to _add_ an
> incompatibility with existing versions of glibc/bionic (so, you know,
> "basically every non-Windows computer out there").
>
> from my perspective:
>
> pros:
> + code would then behave the same on android and ios
> cons:
> - code would behave differently on different versions of android
> - code would behave differently on the host
> unknowns:
> ? what does Windows do?
> ? does anyone actually care?
>
> not having heard anyone but you bring this up in the last 15 years
> (despite it apparently being an android/ios difference), i'm inclined
> to assume this is a non-problem that's not worth the disruption of
> changing anything...
I'm not sure what you mean by "not having heard anyone but you bring
this up in the last 15 years". This has been a recurring issue on the
glibc bug tracker and in C and POSIX committees, and comes up all the
time with users of the language not understanding what the standard
says or if/how implementations are conforming. There have been
multiple bug reports against different versions of the wording in
different versions of the C and POSIX standards, and it's a perpetual
source of disagreements.
Indeed fixing the bug will not make any immediate improvement. For
decades applications will still need to assume they might be running
on a system with the broken (inconsistent) behavior like glibc or
Bionic, or apply a wrapper to fix it (ala gnulib). But maybe
eventually that can become a bad chapter of history we leave behind.
One thing I kinda would like to think about is if there's a way we can
signal at compile-time (without run tests that don't work for cross
compiling) that realloc is non-broken and doesn't need gnulib-style
wrapping/replacement. My hope is that such a mechanism would follow
the principles of the "Macro-based advertisement of libc extensions"
proposal on libc-coord.
Rich
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