Dear Joakim Tjernlund,
Mike Frysinger vapier@gentoo.org wrote on 2010/10/21 21:51:53:
On Thursday, October 21, 2010 07:45:10 Joakim Tjernlund wrote:
Wolfgang Denk wrote on 2010/10/21 13:32:54:
Joakim Tjernlund you wrote:
- if ((long)bytes < 0) return 0;
- if ((long)bytes <= 0) return 0;
I think you should return some impossible ptr value =! NULL Size 0 not really an error.
It is legal for malloc() to return NULL in case of size==0, and for the sake of simplicity I recommend we do just that.
Yes, but not very useful. Glibc does not return NULL
it is useful for malloc(0) == NULL. the glibc behavior is downright obnoxious. we disable this for uClibc and dont see problems. if
anything, we
catch accidental programming mistakes which then get fixed.
My five cents:
There is a value in having the possibility to express a 0 bytes data set. Consider this simple example: An app read lines from a file and mallocs each line read and builds an array with malloced pointers. The last entry is a NULL ptr to signal EOF. This breaks down for empty lines if malloc(0) returns NULL.
Your example is in the right way, but a bit flawed in its simplicity. Even empty lines need some form of information that they are of length zero, be it a 0x00 in the memory line itself (requiring malloc(length+1)) or that same information in a variable somewhere else: struct line { byte *buf; int length; } lines[...];
As an (undercover) Mathematician: Out of principle I would say that malloc(0) should return a non-NULL pointer of an area where exactly 0 bytes may be used. And, of course, free() of that area shall not fail or crash the system.
Not to mention error handling, as I recall, a malloc(0) that returns NULL does not set errno which screws error handling. One have to bend over just to cope with this.
why exactly do you want malloc(0) to return valid memory ? i would
rather
have u-boot return an error.
In the case of u-boot, where a driver or whatever should never really need to allocate zero memory, such a programming error should be made obvious by at least a warning message.
Ideally it should return a ptr to invalid memory so you get a SEGV if you try to defer the ptr but I take anything over a NULL ptr.
Makes sense only if any access outside of any allocated memory would behave the same, otherwise this is a special case again.
Best Regards, Reinhard