From: Rich Felker <dalias@aerifal.cx>
To: musl@lists.openwall.com
Subject: Re: malloc(0) behaviour
Date: Tue, 15 Jan 2013 08:46:34 -0500 [thread overview]
Message-ID: <20130115134634.GX20323@brightrain.aerifal.cx> (raw)
In-Reply-To: <20130115110618.GA4468@port70.net>
On Tue, Jan 15, 2013 at 12:06:18PM +0100, Szabolcs Nagy wrote:
> * Igmar Palsenberg <igmar@palsenberg.com> [2013-01-15 09:31:24 +0100]:
> > > fundamental reasons too. Basically they all come down to interactions
> > > between the requirements of malloc and realloc, and the fact that
> > > returning a null pointer from realloc means failure (and thus that the
> > >
> > > http://www.open-std.org/jtc1/sc22/wg14/www/docs/dr_400.htm
> > > http://austingroupbugs.net/view.php?id=400
> > > http://sourceware.org/bugzilla/show_bug.cgi?id=12547
> >
> > While the above is clear to me, returning a pointer that can't hold anything just seems wrong to me.
>
> i don't think we have too many options here,
> the standards and historical practices has
> various inconsistencies and musl has the least
> broken one
>
> but we can do a theoretical discussion about
> the merits of malloc(0)!=0:
>
> i'm surprised that it "seems wrong" to you,
> you can access the amount of bytes you requested
> through the returned pointer p, evaluating
> p+size is valid, p is suitably aligned for all
> objects and it can be freed.
> these assumptions are broken if malloc(0)==0
>
> if the standard made malloc(0) work in ansi c
> then it would save some branch logic and would
> made the world a safer place
> (because in a fair amount of code that gets
> array length from external source no special
> casing would be needed for length==0)
In fairness, there's hardly any difference between the work involved
in:
if (size < LIMIT)
and
if (size-1 < LIMIT-1)
The latter catches 0 and treats it as invalid.
> > I'll wrap malloc() to include an abort in my case :)
>
> but don't do that in library code that may be
> used in a long running process: allocation failures
> should be reported to let the caller handle it
I think he meant malloc(0) would abort to indicate that, in the rules
of his project, malloc(0) is a programming error. This is not such a
bad idea..
Rich
next prev parent reply other threads:[~2013-01-15 13:46 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-01-14 17:17 Igmar Palsenberg
2013-01-14 18:05 ` Rich Felker
2013-01-14 22:22 ` Strake
2013-01-14 23:05 ` Rich Felker
2013-01-15 8:32 ` Igmar Palsenberg
2013-01-15 12:53 ` Rob Landley
2013-01-15 22:18 ` Igmar Palsenberg
2013-01-15 8:31 ` Igmar Palsenberg
2013-01-15 11:06 ` Szabolcs Nagy
2013-01-15 12:33 ` Igmar Palsenberg
2013-01-15 13:48 ` Rich Felker
2013-01-15 22:28 ` Igmar Palsenberg
2013-01-15 23:22 ` Rob
2013-01-16 7:46 ` Igmar Palsenberg
2013-01-15 13:46 ` Rich Felker [this message]
2013-01-15 12:52 ` Rob Landley
2013-01-14 23:37 ` Rob Landley
2013-01-15 0:24 ` Rich Felker
2013-01-15 12:17 ` Rob Landley
2013-01-15 9:01 ` Igmar Palsenberg
2013-01-15 12:58 ` Rob Landley
2013-01-15 14:54 ` dladdr() pierre
2013-01-15 18:48 ` dladdr() Rich Felker
2013-01-16 11:00 ` dladdr() pierre
2013-01-16 12:51 ` dladdr() Szabolcs Nagy
2013-01-16 14:24 ` dladdr() musl
2013-01-16 15:20 ` dladdr() pierre
2013-01-16 16:49 ` dladdr() Rich Felker
2013-01-16 17:42 ` dladdr() musl
2013-01-21 2:03 ` dladdr() Rich Felker
2013-01-21 6:58 ` dladdr() pierre
2013-01-21 18:35 ` dladdr() Rich Felker
2013-01-22 6:27 ` dladdr() pierre
2013-01-22 13:07 ` dladdr() Szabolcs Nagy
2013-01-22 13:40 ` dladdr() pierre
2013-01-22 13:51 ` dladdr() Rich Felker
2013-01-22 14:59 ` dladdr() pierre
2013-01-22 16:11 ` dladdr() Szabolcs Nagy
2013-01-22 23:43 ` dladdr() Rich Felker
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