[3.13.y.z extended stable] Patch "compiler: define OPTIMIZER_HIDE_VAR() macro" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    compiler: define OPTIMIZER_HIDE_VAR() macro

to the linux-3.13.y-queue branch of the 3.13.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.13.y-queue

This patch is scheduled to be released in version 3.13.11.11.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.13.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 3ba7f806ba7b209ba49771c326239724da87e57f Mon Sep 17 00:00:00 2001
From: Cesar Eduardo Barros <cesarb at cesarb.eti.br>
Date: Mon, 25 Nov 2013 22:00:41 -0200
Subject: compiler: define OPTIMIZER_HIDE_VAR() macro

[ 3.13-stable only: OPTIMIZER_HIDE_VAR() macro
  extracted from fe8c8a1 "crypto: more robust crypto_memneq" ]

[...] dummy inline assembly
(based on RELOC_HIDE) to block the problematic kinds of optimization,
while still allowing other optimizations to be applied to the code.

Signed-off-by: Cesar Eduardo Barros <cesarb at cesarb.eti.br>
[ kamal: 3.13-stable prereq for
  d4c5efd "random: add and use memzero_explicit() for clearing data" ]
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 include/linux/compiler-gcc.h   | 3 +++
 include/linux/compiler-intel.h | 7 +++++++
 include/linux/compiler.h       | 4 ++++
 3 files changed, 14 insertions(+)

diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
index 24545cd..02ae99e 100644
--- a/include/linux/compiler-gcc.h
+++ b/include/linux/compiler-gcc.h
@@ -37,6 +37,9 @@
     __asm__ ("" : "=r"(__ptr) : "0"(ptr));		\
     (typeof(ptr)) (__ptr + (off)); })

+/* Make the optimizer believe the variable can be manipulated arbitrarily. */
+#define OPTIMIZER_HIDE_VAR(var) __asm__ ("" : "=r" (var) : "0" (var))
+
 #ifdef __CHECKER__
 #define __must_be_array(arr) 0
 #else
diff --git a/include/linux/compiler-intel.h b/include/linux/compiler-intel.h
index dc1bd3d..5529c52 100644
--- a/include/linux/compiler-intel.h
+++ b/include/linux/compiler-intel.h
@@ -15,6 +15,7 @@
  */
 #undef barrier
 #undef RELOC_HIDE
+#undef OPTIMIZER_HIDE_VAR

 #define barrier() __memory_barrier()

@@ -23,6 +24,12 @@
      __ptr = (unsigned long) (ptr);				\
     (typeof(ptr)) (__ptr + (off)); })

+/* This should act as an optimization barrier on var.
+ * Given that this compiler does not have inline assembly, a compiler barrier
+ * is the best we can do.
+ */
+#define OPTIMIZER_HIDE_VAR(var) barrier()
+
 /* Intel ECC compiler doesn't support __builtin_types_compatible_p() */
 #define __must_be_array(a) 0

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 92669cd..a2329c5 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -170,6 +170,10 @@ void ftrace_likely_update(struct ftrace_branch_data *f, int val, int expect);
     (typeof(ptr)) (__ptr + (off)); })
 #endif

+#ifndef OPTIMIZER_HIDE_VAR
+#define OPTIMIZER_HIDE_VAR(var) barrier()
+#endif
+
 /* Not-quite-unique ID. */
 #ifndef __UNIQUE_ID
 # define __UNIQUE_ID(prefix) __PASTE(__PASTE(__UNIQUE_ID_, prefix), __LINE__)
--
1.9.1