linux-kernel - [PATCH][RESEND] do not redefine userspace's NULL #define

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Message-Id: <201204132124.21294.l.lunak@suse.cz>
Date:	Fri, 13 Apr 2012 21:24:20 +0200
From:	Lubos Lunak <l.lunak@...e.cz>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Arnd Bergmann <arnd@...db.de>
Subject: [PATCH][RESEND] do not redefine userspace's NULL #define

GCC's NULL is actually __null, which allows detecting some questionable
NULL usage and warn about it. Moreover each platform/compiler should have
its own stddef.h anyway (which is different from linux/stddef.h).
So there's no good reason to override what the compiler provides.
Keep the #define conditionally, in order to keep the headers self-contained.

Signed-off-by: Luboš Luňák <l.lunak@...e.cz>
---

 There have been no further comments after this last version, and I do not see 
how this change should affect anything in either kernel builds or userspace 
builds, except for fixing the issue of overriding the proper NULL definition, 
so I consider this the proper and safe fix.

 include/linux/stddef.h |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/include/linux/stddef.h b/include/linux/stddef.h
index 6a40c76..ce225a9 100644
--- a/include/linux/stddef.h
+++ b/include/linux/stddef.h
@@ -3,12 +3,13 @@

 #include <linux/compiler.h>

-#undef NULL
+#ifndef NULL
 #if defined(__cplusplus)
 #define NULL 0
 #else
 #define NULL ((void *)0)
 #endif
+#endif

 #ifdef __KERNEL__

-- 
1.7.7
-- 
 Lubos Lunak
 l.lunak@...e.cz
--
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