Move memory zeroing to a compiled function in a new source file. Cast

the pointer to volatile before writing to it. At least for various
versions of GCC, Clang, and ICC on x86-64, this does cause the
compiler to emit a simple byte-at-a-time loop, and at least in non-LTO
builds the compiler won't optimize the call away. For dealing with
LTO, probably would have to do some kind of complicated side-effect.

3 files changed, 38 insertions, 11 deletions

diff --git a/src/utils/info.txt b/src/utils/info.txt
index a1079d47b..5bf1b9a54 100644
--- a/src/utils/info.txt
+++ b/src/utils/info.txt
@@ -9,6 +9,7 @@ charset.cpp
 cpuid.cpp
 parsing.cpp
 version.cpp
+zero_mem.cpp
 </source>
 
 <header:internal>
diff --git a/src/utils/mem_ops.h b/src/utils/mem_ops.h
index fc59c90d6..92a130310 100644
--- a/src/utils/mem_ops.h
+++ b/src/utils/mem_ops.h
@@ -1,6 +1,6 @@
 /*
 * Memory Operations
-* (C) 1999-2009 Jack Lloyd
+* (C) 1999-2009,2012 Jack Lloyd
 *
 * Distributed under the terms of the Botan license
 */
@@ -14,15 +14,11 @@
 namespace Botan {
 
 /**
-* Copy memory
-* @param out the destination array
-* @param in the source array
-* @param n the number of elements of in/out
+* Zeroize memory
+* @param ptr a pointer to memory to zero out
+* @param n the number of bytes pointed to by ptr
 */
-template<typename T> inline void copy_mem(T* out, const T* in, size_t n)
-   {
-   std::memmove(out, in, sizeof(T)*n);
-   }
+BOTAN_DLL void zero_mem(void* ptr, size_t n);
 
 /**
 * Zeroize memory
@@ -31,8 +27,18 @@ template<typename T> inline void copy_mem(T* out, const T* in, size_t n)
 */
 template<typename T> inline void clear_mem(T* ptr, size_t n)
    {
-   if(n) // avoid glibc warning if n == 0
-      std::memset(ptr, 0, sizeof(T)*n);
+   zero_mem(ptr, sizeof(T)*n);
+   }
+
+/**
+* Copy memory
+* @param out the destination array
+* @param in the source array
+* @param n the number of elements of in/out
+*/
+template<typename T> inline void copy_mem(T* out, const T* in, size_t n)
+   {
+   std::memmove(out, in, sizeof(T)*n);
    }
 
 /**
diff --git a/src/utils/zero_mem.cpp b/src/utils/zero_mem.cpp
new file mode 100644
index 000000000..e812ced0c
--- /dev/null
+++ b/src/utils/zero_mem.cpp
@@ -0,0 +1,20 @@
+/*
+* Zero Memory
+* (C) 2012 Jack Lloyd
+*
+* Distributed under the terms of the Botan license
+*/
+
+#include <botan/mem_ops.h>
+
+namespace Botan {
+
+void zero_mem(void* ptr, size_t n)
+   {
+   volatile byte* p = reinterpret_cast<volatile byte*>(ptr);
+
+   for(size_t i = 0; i != n; ++i)
+      p[i] = 0;
+   }
+
+}