On Thu, 10 Dec 2009 13:44:50 -0800 chavey@xxxxxxxxxx wrote: > Fix compiler warning "discards qualifiers from pointer target type", > by allowing explicit discard of const qualifier thru type casting. > The const_cast() macro is taken from a patch from Kaveh R. Ghazi > [PATCH]: Fix problematic -Wcast-qual cases using new CONST_CAST macro > posted on > http://old.nabble.com/-PATCH-:-Fix-problematic--Wcast-qual-cases-using-new-CONST_CAST--macro-td11824676.html > The proposed __nowarn__ keyword has not yet been implemented, > (see http://gcc.gnu.org/ml/gcc-patches/2009-11/msg01261.html). > > > Signed-off-by: Laurent Chavey <chavey@xxxxxxxxxx> > --- > include/linux/kernel.h | 12 ++++++++++++ > net/ipv4/netfilter/ipt_ULOG.c | 2 +- > net/netfilter/xt_time.c | 2 +- > 3 files changed, 14 insertions(+), 2 deletions(-) > > diff --git a/include/linux/kernel.h b/include/linux/kernel.h > index 3fa4c59..0246771 100644 > --- a/include/linux/kernel.h > +++ b/include/linux/kernel.h > @@ -710,4 +710,16 @@ struct sysinfo { > # define REBUILD_DUE_TO_FTRACE_MCOUNT_RECORD > #endif > > +/* Cast away const-ness to pass -Wcast-qual */ This comment simply doesn't make sense. I don't think it adequately explains why the macro exists, how and when one should use it, etc. > +#ifdef __GNUC__ > +union gcc_constcast > +{ union gcc_constcast { > + const void *cv; > + void *v; > +}; > +#define const_cast(X) ((__extension__(union gcc_constcast)(const void *)(X)).v) > +#else > +#define const_cast(X) ((void *)(X)) > +#endif Why don't we just use the simple version on all compilers? What's the advantage in using the gcc-specific extension? And I was wrong - this should be implemented in linux/compiler.h. We have infrastructure there to separate gcc-specific and non-gcc implementations of the same interface. Finally, are we sure that __extension__(union gcc_constcast) is available on all gcc versions mentioned in Documentation/Changes? If not, this patch should use include/linux/compiler-gcc4.h, etc. -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
