Re: Being more anal about iospace accesses..

[Brian Gerst]

Jörn Engel wrote:
> On Wed, 15 September 2004 09:30:42 -0700, Linus Torvalds wrote:
>
> > For example, if you don't know (or, more importantly - don't care) what 
> > kind of IO interface you use, you can now do something like
> >
> > 	void __iomem * map = pci_iomap(dev, bar, maxbytes);
> > 	...
> > 	status = ioread32(map + DRIVER_STATUS_OFFSET);
>
>
> C now supports pointer arithmetic with void*?  I hope the width of a
> void is not architecture dependent, that would introduce more subtle
> bugs.
>
> Jörn

http://gcc.gnu.org/onlinedocs/gcc-3.4.2/gcc/Pointer-Arith.html#Pointer-Arith

5.18 Arithmetic on void- and Function-Pointers

In GNU C, addition and subtraction operations are supported on pointers 
to void and on pointers to functions. This is done by treating the size 
of a void or of a function as 1.

A consequence of this is that sizeof is also allowed on void and on 
function types, and returns 1.

The option -Wpointer-arith requests a warning if these extensions are used.

--
				Brian Gerst
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