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

[Eric Blake <eblake@redhat.com>]

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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 <mst@redhat.com>
> ---
>  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


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