Graeme Russ <graeme.r...@gmail.com> wrote on 2012/04/02 22:28:46: > From: Graeme Russ <graeme.r...@gmail.com> > > On 04/02/2012 05:40 PM, Joakim Tjernlund wrote: > > Hi Grame > > > > Graeme Russ <graeme.r...@gmail.com> wrote on 2012/04/02 09:17:44: > >> > >> Hi Joakim, > >> On Apr 2, 2012 4:55 PM, "Joakim Tjernlund" <joakim.tjernl...@transmode.se> > >> wrote: > >>> > >>>> > >>>> Hi Marek, > >>>> > >>>> On Mon, Apr 2, 2012 at 1:36 PM, Marek Vasut <marek.va...@gmail.com> > >>>> wrote: > >>>>> Dear Mike Frysinger, > >>>>> > >>>>>> On Sunday 01 April 2012 20:25:44 Graeme Russ wrote: > >>>>>>> b) The code calling malloc(0) is making a perfectly legitimate > >>>>>>> assumption > >>>>>>> > >>>>>>> based on how glibc handles malloc(0) > >>>>>> > >>>>>> not really. POSIX says malloc(0) is implementation defined (so it may > >>>>>> return a unique address, or it may return NULL). no userspace code > >>>>>> assuming malloc(0) will return non-NULL is correct. > >>>>> > >>>>> Which is your implementation-defined ;-) But I have to agree with this > >>>>> one. So > >>>>> my vote is for returning NULL. > >>>> > >>>> Also, no userspace code assuming malloc(0) will return NULL is correct > >>>> > >>>> Point being, no matter which implementation is chosen, it is up to the > >>>> caller to not assume that the choice that was made was, in fact, the > >>>> choice that was made. > >>>> > >>>> I.e. the behaviour of malloc(0) should be able to be changed on a whim > >>>> with no side-effects > >>>> > >>>> So I think I should change my vote to returning NULL for one reason and > >>>> one reason only - It is faster during run-time > >>> > >>> Then u-boot will be incompatible with both glibc and the linux kernel, it > >>> seems > >> Forget aboug other implementations... > >> What matters is that the fact that the behaviour is undefined and it is up > >> to the caller to take that into account > > > > Well, u-boot borrows code from both kernel and user space so it would make > > sense if > > malloc(0) behaved the same. Especially for kernel code which tend to depend > > on the > > kernels impl.(just look at Scotts example) > > > >>> to me that any modern impl. of malloc(0) will return a non NULL ptr. > >>> > >>> It does need to be slower, just return ~0 instead, the kernel does > >>> something similar: > >>> if (!size) > >>> return ZERO_SIZE_PTR; > >> That could work, but technically I don't think it complies as it is not a > >> pointer to allocated memory... > > > > It doesn't not have to be allocated memory, just a ptr != NULL which you > > can do free() on. > > As per the spec: > > The malloc function returns either a null pointer or a pointer to the > allocated space. > > The amount of storage allocated by a successful call to the calloc, malloc, > or realloc function when 0 bytes was requested (7.22.3). > > The way I read that, if NULL is not returned, then what is returned is a > pointer to allocated space. If malloc(0) is called, the amount of space > allocated is not determined by the spec
Please read http://lwn.net/Articles/236920/ They have a different view. Jocke _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot