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 08:43:08 +0200 |
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On Saturday 14 of April 2012, Linus Torvalds wrote: > On Fri, Apr 13, 2012 at 4:18 PM, Lubos Lunak <l.lunak@suse.cz> wrote: > >> 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++ > > Please don't continue to spread this total bogosity. > > The reason C++ cannot use "(void *)0" has nothing to do with "stronger > type safety". That's a total idiotic lie by C++ apologists, and I hate > hearing it repeated over and over again. > > And it really *is* a lie. The C++ type system isn't even "stronger",
$ cat b.c void foo() { int* a; void* b; char c; a = b = &c; } $ gcc -Wall b.c -c $ g++ -Wall b.c -c b.c: In function ‘void foo()’: b.c:6:14: error: invalid conversion from ‘void*’ to ‘int*’
> it's just different, and it's actively *broken* wrt NULL. Always has > been. > > The sane thing to do for C++ would always have been to recognize that > "(void *)0" is not a "void pointer" - it's just NULL.
As much as I agree that it was stupid to copy the special-casing of 0 from C and they should have instead special-cased (void*)0, the reality is that it took them until C++11 to add that to the standard, and even there they did it differently, so C++ now has to live with the legacy of NULL being possibly implemented in a stupid way.
The reality is also that g++ people recognized this quite some time back, implemented NULL in a sane way, and kernel headers still replace that implementation with one that, as you yourself say, is technically wrong. So how about my patch that fixes that? The rest is a discussion about things that should have been but are not and is completely pointless by now.
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.
Signed-off-by: Luboš Luňák <l.lunak@suse.cz> --- include/linux/stddef.h | 12 +++++++++--- 1 files changed, 9 insertions(+), 3 deletions(-)
diff --git a/include/linux/stddef.h b/include/linux/stddef.h index 6a40c76..a75f4b9 100644 --- a/include/linux/stddef.h +++ b/include/linux/stddef.h @@ -3,12 +3,18 @@ #include <linux/compiler.h> -#undef NULL #if defined(__cplusplus) -#define NULL 0 +#ifndef NULL +#ifdef __GNUG__ +#define NULL __null #else -#define NULL ((void *)0) +#define NULL 0 #endif +#endif +#else /* __cplusplus */ +#undef NULL +#define NULL ((void *)0) +#endif /* __cplusplus */ #ifdef __KERNEL__ -- 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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