Marek Vasut <marek.va...@gmail.com> wrote on 2012/04/02 17:23:03: > > Dear Joakim Tjernlund, > > > Marek Vasut <marek.va...@gmail.com> wrote on 2012/04/02 16:42:30: > > > Dear Joakim Tjernlund, > > > > > > > Marek Vasut <marek.va...@gmail.com> wrote on 2012/04/02 16:05:13: > > > > > Dear Joakim Tjernlund, > > > > > > > > > > > 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. > > > > > > > > > > But kernel has something mapped there to trap these pointers I > > > > > believe. > > > > > > > > So? That only means that the kernel has extra protection if someone > > > > tries to deference such a ptr. You are not required to do that(nice to > > > > have though) You don have any protection for deferencing NULL either I > > > > think? > > > > > > Can't GCC track it? > > > > Track what? NULL ptrs? I don't think so. Possibly when you have a static > > NULL ptr but not in the general case. > > Well of course.
What did you mean then with "Can't GCC track it?" then? Just a bad joke? > > > I am getting tired of this discussion now. I am just trying to tell you > > that no sane impl. of malloc() these days return NULL for malloc(0). > > And I got your point. Though for u-boot, this would be the best solution > actually. Anyone who uses memory allocated by malloc(0) is insane. No, you don't get the point. If you did you would not have have made the "insane" remark. > > > Even > > though standards allow it they don't consider malloc(0) an error, glibc > > will not update errno in this case. > > There's no errno in uboot I'm aware of ;-) Just pointing out that malloc(0) is not an error even if malloc returns NULL in glibc/standards. malloc(0) represents the empty set, just like 0 does in math and it is sometimes useful. Jocke _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot
