Date: Sat, 23 Nov 2002 03:25:01 -0800 From: David Schultz <dschultz@uclink.Berkeley.EDU> To: Bruce Evans <bde@zeta.org.au> Cc: "M. Warner Losh" <imp@bsdimp.com>, marc@informatik.uni-bremen.de, freebsd-current@FreeBSD.ORG Subject: Re: malloc(0) broken? Message-ID: <20021123112501.GA302@HAL9000.homeunix.com> In-Reply-To: <20021123221927.I49462-100000@gamplex.bde.org> References: <20021123104135.GA13619@HAL9000.homeunix.com> <20021123221927.I49462-100000@gamplex.bde.org>
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Thus spake Bruce Evans <bde@zeta.org.au>: > 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.) Aah, what I ``seemed to recall'' is actually the behavior in -CURRENT, and what I described applies to 3.X and 4.X. Thanks for the clarification. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
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