Re: [Qemu-devel] [PATCH v2 4/4] ARRAY_SIZE: check that argument is an array

[Michael S. Tsirkin]

On Thu, Jan 19, 2017 at 08:53:34AM -0600, Eric Blake wrote:
> On 01/18/2017 02:55 PM, Michael S. Tsirkin wrote:
> > It's a familiar pattern: some code uses ARRAY_SIZE, then refactoring
> > changes the argument from an array to a pointer to a dynamically
> > allocated buffer.  Code keeps compiling but any ARRAY_SIZE calls now
> > return the size of the pointer divided by element size.
> > 
> > Let's add build time checks to ARRAY_SIZE before we allow more
> > of these in the code-base.
> > 
> > Signed-off-by: Michael S. Tsirkin <address@hidden>
> > ---
> >  include/qemu/osdep.h | 8 +++++++-
> 
> >  
> >  #ifndef ARRAY_SIZE
> > -#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
> > +/*
> > + * &(x)[0] is always a pointer - if it's same type as x then the argument 
> > is a
> > + * pointer, not an array as expected.
> > + */
> > +#define ARRAY_SIZE(x) ((sizeof(x) / sizeof((x)[0])) + 
> > QEMU_BUILD_BUG_ON_ZERO( \
> > +                        __builtin_types_compatible_p(typeof(x), \
> 
> Are we sure that __builtin_types_compatible_p() is supported for all
> versions of gcc and clang that we support, or does this need further
> #ifdefs?
> 
> 
> -- 
> Eric Blake   eblake redhat com    +1-919-301-3266
> Libvirt virtualization library http://libvirt.org
> 


We seem to use it without ifdefs elsewhere.

-- 
MST