Messages in this thread | | | Subject | Re: [PATCH] compiler.h: don't use temporary variable in __compiletime_assert() | From | Johannes Berg <> | Date | Tue, 13 May 2014 11:26:24 +0200 |
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Hi James,
> Subject: [PATCH] compiler.h: avoid sparse errors in > __compiletime_error_fallback() > > Usually, BUG_ON and friends aren't even evaluated in sparse, but > recently compiletime_assert_atomic_type() was added, and that now > results in a sparse warning every time it is used. > > The reason turns out to be the temporary variable, after it sparse no > longer considers the value to be a constant, and results in a warning > and an error. The error is the more annoying part of this as it > suppresses any further warnings in the same file, hiding other problems. > > Unfortunately the condition cannot be simply expanded out to avoid the > temporary variable since it breaks compiletime_assert on old versions of > GCC such as GCC 4.2.4 which the latest metag compiler is based on. > > Therefore #ifndef __CHECKER__ out the __compiletime_error_fallback which > uses the potentially negative size array to trigger a conditional > compiler error, so that sparse doesn't see it. > > Signed-off-by: James Hogan <james.hogan@imgtec.com> > Cc: Johannes Berg <johannes.berg@intel.com> > Cc: Daniel Santos <daniel.santos@pobox.com> > Cc: Luciano Coelho <luciano.coelho@intel.com> > Cc: Peter Zijlstra <peterz@infradead.org> > Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> > Cc: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Johannes Berg <johannes@sipsolutions.net>
> It's not particularly pretty, if you can think of a better solution that > doesn't break old GCC I'm all ears.
> #ifndef __compiletime_error > # define __compiletime_error(message) > -# define __compiletime_error_fallback(condition) \ > +/* > + * Sparse complains of variable sized arrays due to the temporary variable in > + * __compiletime_assert. Unfortunately we can't just expand it out to make > + * sparse see a constant array size without breaking compiletime_assert on old > + * versions of GCC (e.g. 4.2.4), so hide the array from sparse altogether. > + */ > +# ifndef __CHECKER__ > +# define __compiletime_error_fallback(condition) \ > do { ((void)sizeof(char[1 - 2 * condition])); } while (0) > -#else > +# endif > +#endif > +#ifndef __compiletime_error_fallback > # define __compiletime_error_fallback(condition) do { } while (0) > #endif
That's pretty much what I had in mind, I may have expressed it a bit differently but the end result is the same.
Thanks, johannes
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