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

Andrew Morton
2007-04-29T09:25:28Z

On Sun, 29 Apr 2007 08:50:49 +0200 Borislav Petkov <bbpetkov@yahoo.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@yahoo.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@yahoo.de>
Signed-off-by: Andrew Morton <akpm@linux-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
_