linux-kernel - Re: [PATCH] mm/memory.c: remove warning from an uninitialized spinlock. was: Re: 2.6.21-rc7-mm2

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Date:	Sun, 29 Apr 2007 02:24:40 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	bbpetkov@...oo.de
Cc:	Andy Whitcroft <apw@...dowen.org>, linux-kernel@...r.kernel.org,
	Jeremy Fitzhardinge <jeremy@...source.com>
Subject: Re: [PATCH] mm/memory.c: remove warning from an uninitialized
 spinlock. was: Re: 2.6.21-rc7-mm2

On Sun, 29 Apr 2007 08:50:49 +0200 Borislav Petkov <bbpetkov@...oo.de> wrote:

> Introduce a macro for suppressing gcc from generating a warning about a probable
> unitialized state of a variable.

I ended up doing the below.

It's better to make this a per-compiler-version thing: later versions of
gcc might need different tricks, or might provide __attribute__((stfu)) or
whatever.

Plus I don't know if the x=x trick is needed on the intel compiler, nor if
it even works, so I left ICC alone.




From: Borislav Petkov <bbpetkov@...oo.de>

Introduce a macro for suppressing gcc from generating a warning about a
probable uninitialized state of a variable.

Example:

-	spinlock_t *ptl;
+	spinlock_t *uninitialized_var(ptl);

Not a happy solution, but those warnings are obnoxious.

- Using the usual pointlessly-set-it-to-zero approach wastes several
  bytes of text.

- Using a macro means we can (hopefully) do something else if gcc changes
  cause the `x = x' hack to stop working

- Using a macro means that people who are worried about hiding true bugs
  can easily turn it off.

Signed-off-by: Borislav Petkov <bbpetkov@...oo.de>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
---

 include/linux/compiler-gcc3.h  |    6 ++++++
 include/linux/compiler-gcc4.h  |    6 ++++++
 include/linux/compiler-intel.h |    2 ++
 3 files changed, 14 insertions(+)

diff -puN include/linux/compiler-gcc3.h~add-unitialized_var-macro-for-suppressing-gcc-warnings include/linux/compiler-gcc3.h
--- a/include/linux/compiler-gcc3.h~add-unitialized_var-macro-for-suppressing-gcc-warnings
+++ a/include/linux/compiler-gcc3.h
@@ -13,4 +13,10 @@
 #define __must_check		__attribute__((warn_unused_result))
 #endif
 
+/*
+ * A trick to suppress uninitialized variable warning without generating any
+ * code
+ */
+#define uninitialized_var(x) x = x
+
 #define __always_inline		inline __attribute__((always_inline))
diff -puN include/linux/compiler-gcc4.h~add-unitialized_var-macro-for-suppressing-gcc-warnings include/linux/compiler-gcc4.h
--- a/include/linux/compiler-gcc4.h~add-unitialized_var-macro-for-suppressing-gcc-warnings
+++ a/include/linux/compiler-gcc4.h
@@ -16,3 +16,9 @@
 #define __must_check 		__attribute__((warn_unused_result))
 #define __compiler_offsetof(a,b) __builtin_offsetof(a,b)
 #define __always_inline		inline __attribute__((always_inline))
+
+/*
+ * A trick to suppress uninitialized variable warning without generating any
+ * code
+ */
+#define uninitialized_var(x) x = x
diff -puN include/linux/compiler-intel.h~add-unitialized_var-macro-for-suppressing-gcc-warnings include/linux/compiler-intel.h
--- a/include/linux/compiler-intel.h~add-unitialized_var-macro-for-suppressing-gcc-warnings
+++ a/include/linux/compiler-intel.h
@@ -22,3 +22,5 @@
     (typeof(ptr)) (__ptr + (off)); })
 
 #endif
+
+#define uninitialized_var(x) x
_

-
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