The patch titled
Subject: compiler.h: add support for function attribute assume_aligned
has been added to the -mm tree. Its filename is
compilerh-add-support-for-function-attribute-assume_aligned.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/compilerh-add-support-for-function-attribute-assume_aligned.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/compilerh-add-support-for-function-attribute-assume_aligned.patch
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------------------------------------------------------
From: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>
Subject: compiler.h: add support for function attribute assume_aligned
gcc 4.9 added the function attribute assume_aligned, indicating to the
caller that the returned pointer may be assumed to have a certain minimal
alignment. This is useful if, for example, the return value is passed to
memset(). Add a shorthand macro for that.
Signed-off-by: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Pekka Enberg <penberg@xxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/compiler-gcc.h | 17 +++++++++++++++++
include/linux/compiler.h | 8 ++++++++
2 files changed, 25 insertions(+)
diff -puN include/linux/compiler-gcc.h~compilerh-add-support-for-function-attribute-assume_aligned include/linux/compiler-gcc.h
--- a/include/linux/compiler-gcc.h~compilerh-add-support-for-function-attribute-assume_aligned
+++ a/include/linux/compiler-gcc.h
@@ -210,6 +210,23 @@
#define __visible __attribute__((externally_visible))
#endif
+
+#if GCC_VERSION >= 40900
+/*
+ * __assume_aligned(n, k): Tell the optimizer that the returned
+ * pointer can be assumed to be k modulo n. The second argument is
+ * optional (default 0), so we use a variadic macro to make the
+ * shorthand.
+ *
+ * Beware: Do not apply this to functions which may return
+ * ERR_PTRs. Also, it is probably unwise to apply it to functions
+ * returning extra information in the low bits (but in that case the
+ * compiler should see some alignment anyway, when the return value is
+ * massaged by 'flags = ptr & 3; ptr &= ~3;').
+ */
+#define __assume_aligned(a, ...) __attribute__((__assume_aligned__(a, ## __VA_ARGS__)))
+#endif
+
/*
* GCC 'asm goto' miscompiles certain code sequences:
*
diff -puN include/linux/compiler.h~compilerh-add-support-for-function-attribute-assume_aligned include/linux/compiler.h
--- a/include/linux/compiler.h~compilerh-add-support-for-function-attribute-assume_aligned
+++ a/include/linux/compiler.h
@@ -393,6 +393,14 @@ static __always_inline void __write_once
#define __visible
#endif
+/*
+ * Assume alignment of return value.
+ */
+#ifndef __assume_aligned
+#define __assume_aligned(a, ...)
+#endif
+
+
/* Are two types/vars the same type (ignoring qualifiers)? */
#ifndef __same_type
# define __same_type(a, b) __builtin_types_compatible_p(typeof(a), typeof(b))
_
Patches currently in -mm which might be from linux@xxxxxxxxxxxxxxxxxx are
compilerh-add-support-for-function-attribute-assume_aligned.patch
slabh-sprinkle-__assume_aligned-attributes.patch
lib-dynamic_debugc-use-kstrdup_const.patch
lib-vsprintfc-handle-invalid-format-specifiers-more-robustly.patch
lib-vsprintfc-also-improve-sanity-check-in-bstr_printf.patch
lib-vsprintfc-remove-special-handling-in-pointer.patch
test_printf-test-printf-family-at-runtime.patch
lib-introduce-kvasprintf_const.patch
kobject-use-kvasprintf_const-for-formatting-name.patch
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