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Re: [Qemu-devel] [PATCH v2 4/4] ARRAY_SIZE: check that argument is an ar
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-devel] [PATCH v2 4/4] ARRAY_SIZE: check that argument is an array |
Date: |
Thu, 19 Jan 2017 17:06:59 +0200 |
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