Re: [Xen-devel] [PATCH] libs/gnttab: introduce BUILD_BUG_ON

[Paulina Szubarczyk <paulinaszubarczyk@xxxxxxxxx>]

On 07/13/2016 11:25 AM, Wei Liu wrote:
> The implementation is taken from libxc.
>
> Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
> ---
> Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
> Cc: Paulina Szubarczyk <paulinaszubarczyk@xxxxxxxxx>
>
> I could have put it in a header file accessible to all libraries under
> libs but this construct is only relevant to xengnttab library at the
> moment so it's put under gnttab/private.h. It can be easily moved to
> a common place when other libraries under libs require it.
>
> This patch is necessary to unblock Paulina on her gnttab copy work.
> ---
>   tools/libs/gnttab/private.h | 7 +++++++
>   1 file changed, 7 insertions(+)
>
> diff --git a/tools/libs/gnttab/private.h b/tools/libs/gnttab/private.h
> index d286c86..da487f2 100644
> --- a/tools/libs/gnttab/private.h
> +++ b/tools/libs/gnttab/private.h
> @@ -4,6 +4,13 @@
>   #include <xentoollog.h>
>   #include <xengnttab.h>
>
> +/* Force a compilation error if condition is true */
> +#if __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 6)
> +#define BUILD_BUG_ON(p) ({ _Static_assert(!(p), "!(" #p ")"); })
> +#else
> +#define BUILD_BUG_ON(p) ((void)sizeof(struct { int:-!!(p); }))
> +#endif
> +
>   struct xengntdev_handle {
>       xentoollog_logger *logger, *logger_tofree;
>       int fd;
Hi Wei,

thank you for the help with the grant copy patch. I have just rebuild 
Xen and there is a conflict with definition of BUILD_BUG_ON for mini-os 
build:
In file included from minios.c:33:0:
private.h:9:0: error: "BUILD_BUG_ON" redefined [-Werror]
 #define BUILD_BUG_ON(p) ({ _Static_assert(!(p), "!(" #p ")"); })
 ^
In file included from minios.c:25:0:
xen/extras/mini-os-remote/include/lib.h:58:0: note: this is the location 
of the previous definition
 #define BUILD_BUG_ON(cond) ({ _Static_assert(!(cond), "!(" #cond ")"); })
 ^
I thought about wrapping the code in #ifndef BUILD_BUG_ON #endif.

Paulina

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