Re: Linux 2.4.26-rc2

[Jeff Garzik <jgarzik@pobox.com>]

Eyal Lebedinsky wrote:
> Marcelo Tosatti wrote:
> 
>> The void pointer case in here its being done math on without any 
>> problem. What is the
>> problem with void pointer math 
> 
> 
> There is a problem regarding the C standard. The semantics of 'void *' 
> are well defined
> and only allow for limited use. Basically, you can cast any pointer to 
> and from 'void *',
> but nothing else.
> 
> Pointer math says that 'p+n' means "add to 'p' the value 'n*s' where 's' 
> is the size
> on the element that 'p' points to". A 'void *' does not have a defined 
> element size
> until it is cast. So, ANSI specifically does not allow any arithmetics 
> on 'void *'.
> 
> Some compilers are forgiving and will invent an element size of '1' and 
> allow the
> math. We should not rely on such improper usage.


Void pointer arithmatic is an explicit gcc extension, and used 
extensively throughout the kernel.

	Jeff