diff --git a/include/dxc/Support/WinAdapter.h b/include/dxc/Support/WinAdapter.h
index 52afcbfefd..72567aadd3 100644
--- a/include/dxc/Support/WinAdapter.h
+++ b/include/dxc/Support/WinAdapter.h
@@ -42,9 +42,6 @@
 #define C_ASSERT(expr) static_assert((expr), "")
 #define ATLASSERT assert
 
-#define CoTaskMemAlloc malloc
-#define CoTaskMemFree free
-
 #define ARRAYSIZE(array) (sizeof(array) / sizeof(array[0]))
 
 #define _countof(a) (sizeof(a) / sizeof(*(a)))
@@ -216,6 +213,10 @@
 #define UInt32Add UIntAdd
 #define Int32ToUInt32 IntToUInt
 
+#ifndef DXC_API_IMPORT
+#define DXC_API_IMPORT __attribute__((visibility("default")))
+#endif
+
 //===--------------------- HRESULT Related Macros -------------------------===//
 
 #define S_OK ((HRESULT)0L)
@@ -935,9 +936,17 @@ class CHeapPtr : public CHeapPtrBase<T, Allocator> {
 
 //===--------------------------- BSTR Allocation --------------------------===//
 
-void SysFreeString(BSTR bstrString);
+extern "C" DXC_API_IMPORT void __stdcall SysFreeString(BSTR bstrString);
 // Allocate string with length prefix
-BSTR SysAllocStringLen(const OLECHAR *strIn, UINT ui);
+extern "C" DXC_API_IMPORT BSTR __stdcall SysAllocStringLen(const OLECHAR *strIn,
+                                                           UINT ui);
+extern "C" DXC_API_IMPORT UINT __stdcall SysStringByteLen(BSTR bstr);
+extern "C" DXC_API_IMPORT UINT __stdcall SysStringLen(BSTR pbstr);
+
+//===-------------------------- CoTask Allocation -------------------------===//
+
+extern "C" DXC_API_IMPORT LPVOID __stdcall CoTaskMemAlloc(SIZE_T cb);
+extern "C" DXC_API_IMPORT void __stdcall CoTaskMemFree(LPVOID pv);
 
 //===--------------------- UTF-8 Related Types ----------------------------===//
 
diff --git a/lib/DxcSupport/WinAdapter.cpp b/lib/DxcSupport/WinAdapter.cpp
index 27bd7c3c7e..78de917b6c 100644
--- a/lib/DxcSupport/WinAdapter.cpp
+++ b/lib/DxcSupport/WinAdapter.cpp
@@ -47,14 +47,14 @@ void CAllocator::Free(void *p) throw() { free(p); }
 
 //===--------------------------- BSTR Allocation --------------------------===//
 
-void SysFreeString(BSTR bstrString) {
+DXC_API_IMPORT void __stdcall SysFreeString(BSTR bstrString) {
   if (bstrString)
     free((void *)((uintptr_t)bstrString - sizeof(uint32_t)));
 }
 
 // Allocate string with length prefix
 // https://docs.microsoft.com/en-us/previous-versions/windows/desktop/automat/bstr
-BSTR SysAllocStringLen(const OLECHAR *strIn, UINT ui) {
+DXC_API_IMPORT BSTR __stdcall SysAllocStringLen(const OLECHAR *strIn, UINT ui) {
   uint32_t *blobOut =
       (uint32_t *)malloc(sizeof(uint32_t) + (ui + 1) * sizeof(OLECHAR));
 
@@ -75,6 +75,23 @@ BSTR SysAllocStringLen(const OLECHAR *strIn, UINT ui) {
   return strOut;
 }
 
+DXC_API_IMPORT UINT __stdcall SysStringByteLen(BSTR bstr) {
+  if (!bstr)
+    return 0;
+
+  return ((UINT *)bstr)[-1];
+}
+
+DXC_API_IMPORT UINT __stdcall SysStringLen(BSTR pbstr) {
+  return SysStringByteLen(pbstr) / 4;
+}
+
+//===-------------------------- CoTask Allocation -------------------------===//
+
+DXC_API_IMPORT LPVOID __stdcall CoTaskMemAlloc(SIZE_T cb) { return malloc(cb); }
+
+DXC_API_IMPORT void __stdcall CoTaskMemFree(LPVOID pv) { free(pv); }
+
 //===---------------------- Char converstion ------------------------------===//
 
 const char *CPToLocale(uint32_t CodePage) {
diff --git a/tools/clang/tools/dxcompiler/dxcapi.cpp b/tools/clang/tools/dxcompiler/dxcapi.cpp
index d35140b626..255836824c 100644
--- a/tools/clang/tools/dxcompiler/dxcapi.cpp
+++ b/tools/clang/tools/dxcompiler/dxcapi.cpp
@@ -9,13 +9,15 @@
 //                                                                           //
 ///////////////////////////////////////////////////////////////////////////////
 
-#include "dxc/Support/WinIncludes.h"
-
+#ifndef DXC_API_IMPORT
 #ifdef _WIN32
 #define DXC_API_IMPORT __declspec(dllexport)
 #else
 #define DXC_API_IMPORT __attribute__ ((visibility ("default")))
 #endif
+#endif
+
+#include "dxc/Support/WinIncludes.h"
 
 #include "dxc/dxcisense.h"
 #include "dxc/dxctools.h"