From: Rich Felker <dalias@aerifal.cx>
To: musl@lists.openwall.com
Subject: Re: malloc(0) behaviour
Date: Tue, 15 Jan 2013 08:48:02 -0500 [thread overview]
Message-ID: <20130115134802.GY20323@brightrain.aerifal.cx> (raw)
In-Reply-To: <4FA1FD0D-5C34-4DE0-AF27-1F48BB194005@palsenberg.com>
On Tue, Jan 15, 2013 at 01:33:07PM +0100, Igmar Palsenberg wrote:
>
>
> >> 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
>
> That's there to access if size is 0 ? Sure, you can access :
>
> struct foo {
> };
This is a constraint violation. C does not allow empty structs, and
even if it did, they would not have size 0, since no type or object
ever has size 0 in C.
>
> which is size 0. I do wonder what that gives me in practice. That is, not counting the fact that :
>
> if (size == 0)
> size = 1;
>
> was a common practice in malloc() implementations a while ago.
Of course, this is the canonical, simplest way to make malloc(0)
return a unique pointer.
Rich
next prev parent reply other threads:[~2013-01-15 13:48 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 [this message]
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
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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