From ce2584379f31cfc44bbe770bb78430950a24156e Mon Sep 17 00:00:00 2001
From: Ben Hutchings <ben@decadent.org.uk>
Date: Thu, 11 Dec 2014 02:43:02 +0000
Subject: [PATCH] compiler: Define OPTIMIZER_HIDE_VAR

Part of upstream commit fe8c8a126806 ('crypto: more robust
crypto_memneq'), needed by commit d4c5efdb9777 ('random: add and use
memzero_explicit() for clearing data').
---
 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 5633053ac7c2..9ac1a7a977c2 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 cba9593c4047..1a97cac7dcb2 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 320d6c94ff84..7c7546bf1c10 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -164,6 +164,10 @@ 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
+
 #endif /* __KERNEL__ */
 
 #endif /* __ASSEMBLY__ */
-- 
2.39.2