On 01/19/2017 03:07 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 <m...@redhat.com> > Reviewed-by: Markus Armbruster <arm...@redhat.com> > --- > include/qemu/osdep.h | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-)
Reviewed-by: Eric Blake <ebl...@redhat.com>
>
> diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
> index 689f253..56c9e22 100644
> --- a/include/qemu/osdep.h
> +++ b/include/qemu/osdep.h
> @@ -198,8 +198,15 @@ extern int daemon(int, int);
> #define DIV_ROUND_UP(n,d) (((n) + (d) - 1) / (d))
> #endif
>
> +/*
> + * &(x)[0] is always a pointer - if it's same type as x then the argument is
> a
> + * pointer, not an array.
> + */
> +#define QEMU_IS_ARRAY(x) (!__builtin_types_compatible_p(typeof(x), \
> + typeof(&(x)[0])))
> #ifndef ARRAY_SIZE
> -#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
> +#define ARRAY_SIZE(x) ((sizeof(x) / sizeof((x)[0])) + \
> + QEMU_BUILD_BUG_ON_ZERO(!QEMU_IS_ARRAY(x)))
We've got some double-negation going on here ("cause a build bug if the
negation of QEMU_IS_ARRAY() is not 0") which takes some mental
gymnastics, but it is the correct result. [I kind of like that gnulib
uses positive logic in its 'verify(x)' meaning "verify that x is true,
or cause a build error"; compared to the negative logic in the kernal
'BUILD_BUG_ON[_ZERO](x)' meaning "cause a build bug if x is non-zero" -
but that's personal preference and not something for qemu to change]
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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