Re: [Xen-devel] [PATCH] compat/memory: fix build with old gcc

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Wed, 2014-01-15 at 10:41 +0000, Jan Beulich wrote:
> struct xen_add_to_physmap_batch's size field being uint16_t causes old
> compiler versions to warn about the pointless range check done inside
> compat_handle_okay().
> 
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> Tested-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

As far as the release goes this is fine IMHO.

> --- a/xen/common/compat/memory.c
> +++ b/xen/common/compat/memory.c
> @@ -206,18 +206,20 @@ int compat_memory_op(unsigned int cmd, X
>          {
>              unsigned int limit = (COMPAT_ARG_XLAT_SIZE - sizeof(*nat.atpb))
>                                   / (sizeof(nat.atpb->idxs.p) + 
> sizeof(nat.atpb->gpfns.p));
> +            /* Use an intermediate variable to suppress warnings on old gcc: 
> */
> +            unsigned int size = cmp.atpb.size;
>              xen_ulong_t *idxs = (void *)(nat.atpb + 1);
>              xen_pfn_t *gpfns = (void *)(idxs + limit);
>  
>              if ( copy_from_guest(&cmp.atpb, compat, 1) ||
> -                 !compat_handle_okay(cmp.atpb.idxs, cmp.atpb.size) ||
> -                 !compat_handle_okay(cmp.atpb.gpfns, cmp.atpb.size) ||
> -                 !compat_handle_okay(cmp.atpb.errs, cmp.atpb.size) )
> +                 !compat_handle_okay(cmp.atpb.idxs, size) ||
> +                 !compat_handle_okay(cmp.atpb.gpfns, size) ||
> +                 !compat_handle_okay(cmp.atpb.errs, size) )
>                  return -EFAULT;
>  
>              end_extent = start_extent + limit;
> -            if ( end_extent > cmp.atpb.size )
> -                end_extent = cmp.atpb.size;
> +            if ( end_extent > size )
> +                end_extent = size;
>  
>              idxs -= start_extent;
>              gpfns -= start_extent;
> 
> 
> 
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> http://lists.xen.org/xen-devel



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