Re: malloc attributes and realloc

[Jeff Sturm <jsturm at one-point dot com>]

On Thu, 1 Jan 2004, Joseph S. Myers wrote:
> Can __attribute__((__malloc__)) safely be used on realloc-type functions?

My non-expert understanding is "no"...

> /* Reallocate memory without fail.  This works like xmalloc.  Note,
>    realloc type functions are not suitable for attribute malloc since
>    they may return the same address across multiple calls. */

This comment is misleading.  The pointer address returned by a malloc-type
function isn't significant to alias analysis.  What *is* significant is
that malloc returns memory initialized with zeros, so that it cannot
alias anything.  (Moreover, malloc itself can return the same address
twice if a call to free intervenes between calls to malloc.)

Since the return value of realloc() aliases whatever its first argument
aliases, a literal reading of the documentation of the malloc attribute
indicates that it is inappropriate for the declaration of realloc.

Jeff