From owner-freebsd-current  Sat Nov 23  3:19:22 2002
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Date: Sat, 23 Nov 2002 22:32:17 +1100 (EST)
From: Bruce Evans <bde@zeta.org.au>
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To: David Schultz <dschultz@uclink.Berkeley.EDU>
Cc: "M. Warner Losh" <imp@bsdimp.com>,
	<marc@informatik.uni-bremen.de>, <freebsd-current@FreeBSD.ORG>
Subject: Re: malloc(0) broken?
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On Sat, 23 Nov 2002, David Schultz wrote:

> Thus spake Bruce Evans <bde@zeta.org.au>:
> > ...  C90 has a bogus requirement that
> > the pointer for malloc(0) be "unique", whatever that means.  C99 only
> > requires that the objects pointed to by the results of malloc() be
> > disjoint, and this is satisfied by FreeBSD's behaviour of returning the
> > same magic pointer for each instance of malloc(0).
>
> In FreeBSD, malloc(0) returns a distinct pointer each time by
> making a 16-byte allocation.  I seem to recall that it may have
> returned a single magic pointer at one time, so what you say might
> have been correct some time ago.

Actually, it is correct now.  malloc(0) returns the constant invalid
pointer ZEROSIZEPTR (0x800 on i386's), but it returned a distinct pointer
before the ZEROSIZEPTR stuff was added in rev.1.60 of libc/stdlib/malloc.c.
(All this is without the malloc option V which causes malloc(0) to return
a null pointer.)

Bruce


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