Re: xen3pae on 5.0_stable/i386

[Jean-Yves Migeon <jeanyves.migeon%free.fr@localhost>]

On 01/23/10 14:08, David Laight wrote:
> On Sat, Jan 23, 2010 at 12:32:31PM +0100, Jean-Yves Migeon wrote:
> > On 01/23/10 09:13, Christoph Egger wrote:
> > > On 23.01.10 02:53, Jean-Yves Migeon wrote:
> > >
> > > Jean, Manuel: We should introduce helper macros which hide the
> > > needed casts completely. This makes new code less error prone.
> >
> > It is something that is worth considering, although not as easy to fix
> > as it seems.
>
> macros don't normally force you to write the correct code - especially
> if they cast their arguments.

Functions either in this case. See below.

> inline functions can help, as can embedding an integral type within
> a structure - and then passing the structure by value.

Even if you have a function with a "correct" prototype, it can go wrong.

#include <stdio.h>

/* Some typedefs for clarity */
typedef unsigned long xen_pfn_t; /* as defined by Xen */
typedef unsigned long long paddr_t; /* 64 bits PDE/PTE for PAE */

paddr_t
pfn_to_paddr(xen_pfn_t pfn) {
        return pfn << PAGE_SHIFT;
}

int main(void) {
        xen_pfn_t pfn  = 0xf0000000;
        paddr_t   pfn2 = 0xf0000000ULL;
        printf("1: %llx\n", pfn_to_paddr(pfn));
        printf("2: %llx\n", pfn_to_paddr(pfn2));
        return 0;
}

--
Jean-Yves Migeon
jeanyves.migeon%free.fr@localhost