Date: Sat, 23 Nov 2002 22:32:17 +1100 (EST) From: Bruce Evans <bde@zeta.org.au> 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? Message-ID: <20021123221927.I49462-100000@gamplex.bde.org> In-Reply-To: <20021123104135.GA13619@HAL9000.homeunix.com>
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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 To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
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