Re: [PATCH] x86/debug: define BUG() againfor !CONFIG_BUG

[Peter Zijlstra]

On Wed, Mar 29, 2017 at 11:16:31PM +0200, Arnd Bergmann wrote:
> The latest change to the BUG() macro inadvertently reverted the earlier
> commit b06dd879f5db ("x86: always define BUG() and HAVE_ARCH_BUG, even
> with !CONFIG_BUG") that sanitized the behavior with CONFIG_BUG=n.
> 
> I noticed this as some warnings have appeared again that were previously
> fixed as a side effect of that patch:
> 
> kernel/seccomp.c: In function '__seccomp_filter':
> kernel/seccomp.c:670:1: error: no return statement in function returning non-void [-Werror=return-type]
> 
> drivers/gpu/drm/i915/intel_sprite.c: In function 'intel_check_sprite_plane':
> drivers/gpu/drm/i915/intel_sprite.c:936:20: error: 'src_h' may be used uninitialized in this function [-Werror=maybe-uninitialized]
>    src->y2 = (src_y + src_h) << 16;
>              ~~~~~~~^~~~~~~~
> drivers/gpu/drm/i915/intel_sprite.c:934:20: error: 'src_w' may be used uninitialized in this function [-Werror=maybe-uninitialized]
>    src->x2 = (src_x + src_w) << 16;
>              ~~~~~~~^~~~~~~~
> drivers/gpu/drm/i915/intel_sprite.c:936:20: error: 'src_y' may be used uninitialized in this function [-Werror=maybe-uninitialized]
>    src->y2 = (src_y + src_h) << 16;
>              ~~~~~~~^~~~~~~~
> drivers/gpu/drm/i915/intel_sprite.c:934:20: error: 'src_x' may be used uninitialized in this function [-Werror=maybe-uninitialized]
>    src->x2 = (src_x + src_w) << 16;
>              ~~~~~~~^~~~~~~~
> 
> This combines the two patches and uses the ud2 macro to define BUG()
> in case of CONFIG_BUG=n.

OK, fair enough I suppose. However, I cribbed this from arm64. What does
that do for BUG=n ?