Add unitialized_var() macro for suppressing gcc warnings

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>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

4 files changed, 15 insertions, 1 deletions

diff --git a/include/linux/compiler-gcc3.h b/include/linux/compiler-gcc3.h
index 1698b845761f..ecd621fd27d2 100644
--- a/include/linux/compiler-gcc3.h
+++ b/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 --git a/include/linux/compiler-gcc4.h b/include/linux/compiler-gcc4.h
index 6f5cc6f0e7a6..fd0cc7c4a636 100644
--- a/include/linux/compiler-gcc4.h
+++ b/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 --git a/include/linux/compiler-intel.h b/include/linux/compiler-intel.h
index 1d1c3ceaff4e..a436eea43912 100644
--- a/include/linux/compiler-intel.h
+++ b/include/linux/compiler-intel.h
@@ -22,3 +22,5 @@
     (typeof(ptr)) (__ptr + (off)); })
 
 #endif
+
+#define uninitialized_var(x) x
diff --git a/mm/memory.c b/mm/memory.c
index c252aae544e9..1d647ab0ee72 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1455,7 +1455,7 @@ static int apply_to_pte_range(struct mm_struct *mm, pmd_t *pmd,
         pte_t *pte;
         int err;
         struct page *pmd_page;
-        spinlock_t *ptl = ptl;          /* Suppress gcc warning */
+        spinlock_t *uninitialized_var(ptl);
 
         pte = (mm == &init_mm) ?
                 pte_alloc_kernel(pmd, addr) :