Re: [Xen-ia64-devel] [PATCH 1/7][SMP] add volatile to mpt_table

[Isaku Yamahata <yamahata@xxxxxxxxxxxxx>]

On Thu, Jun 15, 2006 at 10:35:53AM -0600, Al Stone wrote:
> On Thu, 2006-06-15 at 11:58 +0900, Isaku Yamahata wrote:
> >  diff -r d33add81096b -r ad418fdb1981 xen/arch/ia64/xen/xenmem.c
> >  --- a/xen/arch/ia64/xen/xenmem.c        Wed Jun 14 16:05:45 2006
> -0600
> >  +++ b/xen/arch/ia64/xen/xenmem.c        Thu Jun 15 11:33:14 2006
> +0900
> >  @@ -35,7 +35,7 @@ unsigned long max_page;
> >   /*
> >    * Set up the page tables.
> >    */
> >  -unsigned long *mpt_table;
> >  +volatile unsigned long *mpt_table;
> > 
> >   void
> >   paging_init (void)
> >  @@ -140,7 +140,7 @@ create_mpttable_page_table (u64 start, u
> >   create_mpttable_page_table (u64 start, u64 end, void *arg)
> >   {
> >          unsigned long address, start_page, end_page;
> >  -       unsigned long *map_start, *map_end;
> >  +       volatile unsigned long *map_start, *map_end;
> >          pgd_t *pgd;
> >          pud_t *pud;
> >          pmd_t *pmd;
> 
> [snip...]
> 
> I don't understand why map_start and map_end need to be
> volatile here.  They only seem to be copying volatile
> values for later use so there is no need for them to be
> volatile; did I miss something?

The below two lines follows.

        map_start = mpt_table + (__pa(start) >> PAGE_SHIFT);
        map_end   = mpt_table + (__pa(end) >> PAGE_SHIFT);

Gcc produces warnings without volatile.

-- 
yamahata

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