Messages in this thread Patch in this message | | | From | Lubos Lunak <> | Subject | Re: [PATCH][RESEND] do not redefine userspace's NULL #define | Date | Sat, 14 Apr 2012 01:18:51 +0200 |
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On Saturday 14 of April 2012, Linus Torvalds wrote: > On Fri, Apr 13, 2012 at 3:01 PM, Peter Seebach > > Maybe the thing to do would be to ensure that NULL goes to __null, > > then define that to be ((void *) 0) if the compiler doesn't provide > > it? The magic behavior of __null seems like it'd be preferable > > where it is available. > > So if gcc guarantees that __null has the correct semantics, I could > imagine replacing the kernel ((void *)0) with __null.
__null apparently exists only with g++, C does not have the stronger type safety that prevents ((void*)0) from being usable in C++, so __null is not needed there. So this is really only about userspace C++ code.
So how about this one? It does not change anything in the C mode and keeps it the way you want, and it fixes the C++ mode.
8<----- headers: do not redefine userspace's NULL #define when compiling C++ code
GCC's NULL is actually __null when compiling C++, which allows detecting some questionable NULL usage and warn about it, so do not redefine NULL to 0. Use the 0 definition only if NULL does not exists, to keep kernel headers self-contained (and GCC's stddef.h will possibly redefine it later to __null). In C mode ((void*)0) works fine.
Signed-off-by: Luboš Luňák <l.lunak@suse.cz> --- include/linux/stddef.h | 4 +++- 1 files changed, 3 insertions(+), 1 deletions(-)
diff --git a/include/linux/stddef.h b/include/linux/stddef.h index 6a40c76..13dfc92 100644 --- a/include/linux/stddef.h +++ b/include/linux/stddef.h @@ -3,10 +3,12 @@ #include <linux/compiler.h> -#undef NULL #if defined(__cplusplus) +#ifndef NULL #define NULL 0 +#endif #else +#undef NULL #define NULL ((void *)0) #endif -- 1.7.7
-- Lubos Lunak l.lunak@suse.cz -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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