[asterisk-dev] Re: [svn-commits] rizzo: trunk r48389 - /trunk/main/manager.c

[Russell Bryant]

svn-commits at lists.digium.com wrote:
> Author: rizzo
> Date: Mon Dec 11 12:11:58 2006
> New Revision: 48389
> 
> URL: http://svn.digium.com/view/asterisk?view=rev&rev=48389
> Log:
> make sure the argument to ast_malloc() is > 0.
> 
> Long explaination:
> 
> The behaviour of the underlying malloc(0) differs depending on the
> operating system.  Some return NULL (SysV behaviour); some still
> allocate a small chunk of memory and return a valid pointer (e.g.
> traditional BSD); some (e.g. FreeBSD 6.x) return a non-null pointer
> that causes a memory fault if used, even just for reading.
> 
> Given the above variety, better never call malloc(0).

Autoconf actually has a macro to check for this behavior.  However, I'm thinking 
that maybe the safest, and least obfuscated thing to do is to just modify the 
ast_*() memory allocation wrappers to check for an argument of zero and allocate 
a single byte in that case.


For reference ...

[Macro] AC FUNC MALLOC

If the malloc function is compatible with the gnu C library malloc (i.e., 
‘malloc (0)’ returns a valid pointer), define HAVE_MALLOC to 1. Otherwise define 
HAVE_MALLOC to 0, ask for an AC_LIBOBJ replacement for ‘malloc’, and define 
malloc to rpl_malloc so that the native malloc is not used in the main project.
Typically, the replacement file ‘malloc.c’ should look like (note the ‘#undef 
malloc’):

#if HAVE_CONFIG_H
# include <config.h>
#endif
#undef malloc
#include <sys/types.h>

void *malloc ();

/* Allocate an N-byte block of memory from the heap.
    If N is zero, allocate a 1-byte block. */

void *
rpl_malloc (size_t n)
{
    if (n == 0)
       n = 1;
    return malloc (n);
}


-- 
Russell Bryant
Software Engineer
Digium, Inc.
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