[uClibc]Re: fressh-0.3 works on mipsel. Thanks!

Erik Andersen andersen at codepoet.org
Thu Oct 17 10:59:37 UTC 2002

On Mon Sep 30, 2002 at 12:27:31PM +0100, Matthew Bloch wrote:
> Here we go, try compiling this program under uClibc and glibc:

First, my appologies for not seeing this email sooner.  I just
realized that I never replied.

> ------------------------------- realloc0.c ---------------------------------
> #include <stdlib.h>
> int main(int argc, char **argv)
> {
>     void *ptr = NULL;
>     ptr = realloc(ptr, 0);
>     printf("pointer = %p\n", ptr);
>     return 0;
> }
> ----------------------------------------------------------------------------
> glibc prints a valid pointer, uClibc prints (nil).  I suggest that this is a 
> uClibc bug because glibc's behaviour is explicit in that "If you pass a null 
> pointer for PTR, `realloc' behaves just like `malloc (NEWSIZE)'".  uClibc 
> will happily return a valid pointer for malloc(0) but realloc(NULL, 0) does 
> not behave the same way.

Not true.  Regardless of whether uClibc is compiled to include
"malloc-930716" or "malloc", calling malloc(0) returns a NULL.

> Also I only found this bug in uClibc after fixing a bug in the fressh buffer 
> allocation routine which relied on an uninitialised pointer being zero; 
> updated complete patch attached.

Here's the deal.  According to SuSv3:

	If ptr is a null pointer, realloc() shall be equivalent
	to malloc() for the specified size.


	If the size of the space requested is 0, the behavior is
	implementation-defined: the value returned shall be
	either a null pointer or a unique pointer.

So yes, there is a behavior difference between glibc and uClibc.
This is a legitimate, since the standards specify this case to be
implementation-defined.  Glibc returns a live pointer (pointing
to some live storage space), which IMHO is terribly stupid and
enables poor programming since people may actually try and _use_
that pointer, and they may actually succeed.  uClibc returns a
NULL, which guarantees a richly deserved segfault if someone uses
the NULL pointer.


Erik B. Andersen             http://codepoet-consulting.com/
--This message was written using 73% post-consumer electrons--

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