[RFC PATCH 2/2] global-data.h: add build-time sanity check of sizeof(struct global_data)

[Simon Glass <sjg@chromium.org>]

On Tue, 18 May 2021 at 03:20, Rasmus Villemoes
<rasmus.villemoes@prevas.dk> wrote:
>
> The layout and contents of struct global_data depends on a lot of
> CONFIG_* preprocessor macros, not all of which are entirely converted
> to Kconfig - not to mention weird games played here and there. This
> can result in one translation unit using one definition of struct
> global_data while the actual layout is another.
>
> That can be very hard to debug. But we already have a mechanism that
> can help catch such bugs at build time, namely the asm-offsets
> machinery which is necessary anyway to provide assembly code with the
> necessary constants. So make sure that every C translation unit that
> include global_data.h actually sees the same size of struct
> global_data as that which was seen by the asm-offsets.c TU.
>
> It is likely that this patch will break the build of some boards. For
> example, without the patch from Matt Merhar
> (https://lists.denx.de/pipermail/u-boot/2021-May/450135.html) or some
> other fix, this breaks P2041RDB_defconfig:
>
>   CC      arch/powerpc/lib/traps.o
>   AS      arch/powerpc/cpu/mpc85xx/start.o
> In file included from include/asm-generic/global_data.h:26,
>                  from ./arch/powerpc/include/asm/global_data.h:109,
>                  from include/init.h:21,
>                  from arch/powerpc/lib/traps.c:7:
> include/linux/build_bug.h:99:41: error: static assertion failed: "sizeof(struct global_data) == GD_SIZE"
>    99 | #define __static_assert(expr, msg, ...) _Static_assert(expr, msg)
>       |                                         ^~~~~~~~~~~~~~
> include/linux/build_bug.h:98:34: note: in expansion of macro ?__static_assert?
>    98 | #define static_assert(expr, ...) __static_assert(expr, ##__VA_ARGS__, #expr)
>       |                                  ^~~~~~~~~~~~~~~
> include/asm-generic/global_data.h:470:1: note: in expansion of macro ?static_assert?
>   470 | static_assert(sizeof(struct global_data) == GD_SIZE);
>       | ^~~~~~~~~~~~~
> make[1]: *** [scripts/Makefile.build:266: arch/powerpc/lib/traps.o] Error 1
> make: *** [Makefile:1753: arch/powerpc/lib] Error 2
> make: *** Waiting for unfinished jobs....
>
> Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
> ---
>  include/asm-generic/global_data.h | 5 +++++
>  1 file changed, 5 insertions(+)

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