[PATCH 3.2 064/164] compiler: Define OPTIMIZER_HIDE_VAR

[Ben Hutchings]

3.2.65-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Ben Hutchings <ben@xxxxxxxxxxxxxxx>

Part of upstream commit fe8c8a126806 ('crypto: more robust
crypto_memneq'), needed by commit d4c5efdb9777 ('random: add and use
memzero_explicit() for clearing data').

--- 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
--- 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
 
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -164,6 +164,10 @@ void ftrace_likely_update(struct ftrace_
     (typeof(ptr)) (__ptr + (off)); })
 #endif
 
+#ifndef OPTIMIZER_HIDE_VAR
+#define OPTIMIZER_HIDE_VAR(var) barrier()
+#endif
+
 #endif /* __KERNEL__ */
 
 #endif /* __ASSEMBLY__ */

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