Messages in this thread | | | Date | Thu, 30 Mar 2017 09:17:07 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH] x86/debug: define BUG() againfor !CONFIG_BUG |
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* Peter Zijlstra <peterz@infradead.org> wrote:
> 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 ?
I think we'll get a U2D crash in this case, without any bug information.
I.e. only marginally debuggable, but it's a deterministic outcome - instead of the crazy GCC code generation variant of the day when the warning triggers, or the similarly crazy infinite loop hang.
I'm not entirely sure though, I don't think many people actually _use_ CONFIG_BUG=n, it's essentially a crazy thing to do even on constrainted hardware. Debugging and maintenance costs almost always trump marginal hardware costs of a bit more debugging code.
Thanks,
Ingo
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