Re: [Tinycc-devel] Re: malloc(0)

[Rogelio M. Serrano Jr.]

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Well for now the tcc_malloc(0) will return NULL; TCC works fine for me
now.

Except for the uclibc linked TCC of course. Im still testing my TCC build
in a uclibc only system. It seems that there is a lot of glibc dependence
in TCC.


On Mon, 23 Sep 2002, Charlie Gordon wrote:

> Hello folks!
>
> Here comes one of my favorites: libc behaviour at the limits!
>
> - ANSI C 1990 does not specify precisely what the semantics of malloc(0)
>   it only says that free(NULL) is legitimate, and realloc(ptr,0) should free
> ptr.
> - a quick note here on free(NULL): whenever you implement a wrapper on
> malloc/free
>   make it adhere to this convention, it is very useful and becomes quite
> natural;
>   I only test for NULL ptr before calling free() in cases where the function
> call
>   would be too costly, a rare occasion.  As a matter of fact, very few C++
> addicts
>   know that its perfectly fine to 'delete' a NULL pointer.
> - ISO/IEC 9899:1999 is more specific on the malloc(0) issue: section 7.20.3
> pg 324
>   read: "if the size of the space request is zero, the behaviour is
> implementation-
>   defined: either a null pointer is returned, or the behaviour is as the
> size
>   were some nonzero value, except that the returned pointer shall not be
> used
>   to access an object.
> - tcc returns non NULL for malloc(0) because it allocates 1 more byte than
>   requested to ensure that malloc'd areas are never contiguous.  This is
> needed
>   for bound checking.  ISO reads in section 7.20.3 that each successful
> allocation
>   shall yield a pointer to an object disjoint from any other object, yet
> that
>   order and contiguity of storage is unspecified.
>
> Conclusion: do not rely on implementation defined behaviour. Both glibc and
> ulibc
> are OK on this issue, TCC internal libc can implement one or the other,
> preferably
> glibc's, but not necessarily.
>
> There are a lot of small details like these to polish in the C language,
> keep contributing to tcc by testing it to the limits!
>
> Chqrlie.
>
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