compiler-gcc.h: gcc-4.5 needs noclone and noinline on __naked functions

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>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
index 73dcf804bc940e6738f5f0f553f3cf2045f78fd7..0da5b187f1245e8c33fd659420f5e4dca82b9ead 100644 (file)
--- 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

diff --git a/include/linux/compiler-gcc4.h b/include/linux/compiler-gcc4.h
index 94dea3ffbfa19576e2cd8bb59b56658465101b49..fcfa5b9a4317af2b272d06073d7af51019ebf321 100644 (file)
--- 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