Messages in this thread |  | | Date | Thu, 27 Feb 2014 11:00:32 -0800 | From | Greg Kroah-Hartman <> | Subject | Re: [PATCH 1/3] typecheck: introduce assign_if() and assign_if_enabled() |
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On Mon, Feb 24, 2014 at 11:08:25AM -0600, Josh Cartwright wrote: > The assign_if() and assign_if_enable() macros are intended to be used > in static initializers for function pointers, where the pointer is > expected to be NULL when a compile-time condition does not hold. > > These macros allow for implementing this behavior, without requiring the > functions be wrapped in #ifdef conditionals, and while providing > typesafety regardless of the value of the conditional. > > For example, the following pattern is common: > > #ifdef CONFIG_FOO > static void foo_callback(void) > { > } > #else > #define foo_callback NULL > #endif > > static struct foo_object foo_obj = { > .callback = foo_callback, > }; > > Usage of assign_if_enabled() allows for achieving the same effect > without the preprocessor conditional, and in addition, allowing the > compiler to typecheck the function regardless of CONFIG_FOO. > > static void foo_callback(void) > { > } > > static struct foo_object foo_obj = { > .callback = assign_if_enabled(CONFIG_FOO, foo_callback), > }; > > Cc: Andrew Morton <akpm@linux-foundation.org> > Signed-off-by: Josh Cartwright <joshc@codeaurora.org> > --- > include/linux/typecheck.h | 18 ++++++++++++++++++ > 1 file changed, 18 insertions(+) > > diff --git a/include/linux/typecheck.h b/include/linux/typecheck.h > index eb5b74a..04134c7 100644 > --- a/include/linux/typecheck.h > +++ b/include/linux/typecheck.h > @@ -21,4 +21,22 @@ > (void)__tmp; \ > }) > > +/* > + * Intended for use in static object initializers, > + * assign_if(const_expr, function) evaluates to 'function' if 'const_expr', > + * otherwise NULL. > + * > + * The type of the assign_if() expression is typeof(function), and therefore > + * can provide typechecking regardless of 'const_expr'. > + * > + * gcc considers 'function' to be used and will not generate a 'defined but not > + * used' warning when not 'const_expr', however, gcc is smart enough to > + * eliminate 'function' if assign_if() is the only reference. > + */
What version of gcc started doing this? Does llvm also do this?
thanks,
greg k-h
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