* Michael S. Tsirkin (m...@redhat.com) wrote:
> There are theoretical concerns that some compilers might not trigger
> build failures on attempts to define an array of size -1 and make it a
> variable sized array instead. Let rewrite using a struct with a negative
> bit field size instead as there are no dynamic bit field sizes. This is
> similar to what Linux does.
>
> Signed-off-by: Michael S. Tsirkin <m...@redhat.com>
> ---
> include/qemu/compiler.h | 9 ++++++---
> 1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/include/qemu/compiler.h b/include/qemu/compiler.h
> index 7512082..c6f673e 100644
> --- a/include/qemu/compiler.h
> +++ b/include/qemu/compiler.h
> @@ -85,9 +85,12 @@
> #define typeof_field(type, field) typeof(((type *)0)->field)
> #define type_check(t1,t2) ((t1*)0 - (t2*)0)
>
> -#define QEMU_BUILD_BUG_ON(x) \
> - typedef char glue(qemu_build_bug_on__, __LINE__)[(x) ? -1 : 1] \
> - __attribute__((unused))
> +#define QEMU_BUILD_BUG_ON_STRUCT(x) \
> + struct { \
> + int qemu_build_bug_on : (x) ? -1 : 1; \
> + }
The problem with this is it can't be used as an expression, where as
your previous version could.
I've got a similar case (see previous reply) that needed an expression
bug-on that would evaluate to zero.
Dave
> +#define QEMU_BUILD_BUG_ON(x) typedef QEMU_BUILD_BUG_ON_STRUCT(x) \
> + glue(qemu_build_bug_on__, __LINE__) __attribute__((unused))
>
> #if defined __GNUC__
> # if !QEMU_GNUC_PREREQ(4, 4)
> --
> MST
>
>
--
Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
