[RFC PATCH 1/2] build_bug.h: add wrapper for _Static_assert

[Simon Glass]

On Tue, 18 May 2021 at 03:19, Rasmus Villemoes
<rasmus.villemoes at prevas.dk> wrote:
>
> [Linux commit 6bab69c65013bed5fce9f101a64a84d0385b3946]
>
> BUILD_BUG_ON() is a little annoying, since it cannot be used outside
> function scope.  So one cannot put assertions about the sizeof() a
> struct next to the struct definition, but has to hide that in some more
> or less arbitrary function.
>
> Since gcc 4.6 (which is now also the required minimum), there is support
> for the C11 _Static_assert in all C modes, including gnu89.  So add a
> simple wrapper for that.
>
> _Static_assert() requires a message argument, which is usually quite
> redundant (and I believe that bug got fixed at least in newer C++
> standards), but we can easily work around that with a little macro
> magic, making it optional.
>
> For example, adding
>
>   static_assert(sizeof(struct printf_spec) == 8);
>
> in vsprintf.c and modifying that struct to violate it, one gets
>
> ./include/linux/build_bug.h:78:41: error: static assertion failed: "sizeof(struct printf_spec) == 8"
>  #define __static_assert(expr, msg, ...) _Static_assert(expr, "" msg "")
>
> godbolt.org suggests that _Static_assert() has been support by clang
> since at least 3.0.0.
>
> Signed-off-by: Rasmus Villemoes <rasmus.villemoes at prevas.dk>
> ---
>  include/linux/build_bug.h | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)

Reviewed-by: Simon Glass <sjg at chromium.org>