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Subject[095/205] compiler-gcc.h: gcc-4.5 needs noclone and noinline on __naked functions
2.6.34-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Mikael Pettersson <mikpe@it.uu.se>

commit 9c695203a7ddbe49dba5f22f4c941d24f47475df upstream.

A __naked function is defined in C but with a body completely implemented
by asm(), including any prologue and epilogue. These asm() bodies expect
standard calling conventions for parameter passing. Older GCCs implement
that correctly, but 4.[56] currently do not, see GCC PR44290. In the
Linux kernel this breaks ARM, causing most arch/arm/mm/copypage-*.c
modules to get miscompiled, resulting in kernel crashes during bootup.

Part of the kernel fix is to augment the __naked function attribute to
also imply noinline and noclone. This patch implements that, and has been
verified to fix boot failures with gcc-4.5 compiled 2.6.34 and 2.6.35-rc1
kernels. The patch is a no-op with older GCCs.

Signed-off-by: Mikael Pettersson <mikpe@it.uu.se>
Signed-off-by: Khem Raj <raj.khem@gmail.com>
Cc: Russell King <rmk@arm.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
include/linux/compiler-gcc.h | 10 +++++++++-
include/linux/compiler-gcc4.h | 4 ++++
2 files changed, 13 insertions(+), 1 deletion(-)

--- a/include/linux/compiler-gcc.h
+++ b/include/linux/compiler-gcc.h
@@ -58,8 +58,12 @@
* naked functions because then mcount is called without stack and frame pointer
* being set up and there is no chance to restore the lr register to the value
* before mcount was called.
+ *
+ * The asm() bodies of naked functions often depend on standard calling conventions,
+ * therefore they must be noinline and noclone. GCC 4.[56] currently fail to enforce
+ * this, so we must do so ourselves. See GCC PR44290.
*/
-#define __naked __attribute__((naked)) notrace
+#define __naked __attribute__((naked)) noinline __noclone notrace

#define __noreturn __attribute__((noreturn))

@@ -85,3 +89,7 @@
#define _gcc_header(x) __gcc_header(linux/compiler-gcc##x.h)
#define gcc_header(x) _gcc_header(x)
#include gcc_header(__GNUC__)
+
+#if !defined(__noclone)
+#define __noclone /* not needed */
+#endif
--- a/include/linux/compiler-gcc4.h
+++ b/include/linux/compiler-gcc4.h
@@ -48,6 +48,10 @@
* unreleased. Really, we need to have autoconf for the kernel.
*/
#define unreachable() __builtin_unreachable()
+
+/* Mark a function definition as prohibited from being cloned. */
+#define __noclone __attribute__((__noclone__))
+
#endif

#endif



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