Index: include/llvm/Support/DynamicLibrary.h
===================================================================
--- include/llvm/Support/DynamicLibrary.h
+++ include/llvm/Support/DynamicLibrary.h
@@ -14,6 +14,8 @@
 #ifndef LLVM_SUPPORT_DYNAMICLIBRARY_H
 #define LLVM_SUPPORT_DYNAMICLIBRARY_H
 
+#include "llvm/ADT/SmallString.h"
+
 #include <string>
 
 namespace llvm {
@@ -43,10 +45,16 @@
     // Opaque data used to interface with OS-specific dynamic library handling.
     void *Data;
 
-    explicit DynamicLibrary(void *data = &Invalid) : Data(data) {}
+    llvm::SmallString<128> Filename;
+
+    DynamicLibrary(llvm::StringRef filename, void *data = &Invalid)
+        : Data(data), Filename(filename) {}
+
   public:
+    DynamicLibrary() { Data = &Invalid; }
+
     /// Returns true if the object refers to a valid library.
-    bool isValid() { return Data != &Invalid; }
+    bool isValid() const { return Data != &Invalid; }
 
     /// Searches through the library for the symbol \p symbolName. If it is
     /// found, the address of that symbol is returned. If not, NULL is returned.
Index: lib/Support/DynamicLibrary.cpp
===================================================================
--- lib/Support/DynamicLibrary.cpp
+++ lib/Support/DynamicLibrary.cpp
@@ -56,8 +56,11 @@
 DynamicLibrary DynamicLibrary::getPermanentLibrary(const char *filename,
                                                    std::string *errMsg) {
   SmartScopedLock<true> lock(*SymbolsMutex);
-
-  void *handle = dlopen(filename, RTLD_LAZY|RTLD_GLOBAL);
+  int flags = RTLD_LAZY | RTLD_GLOBAL;
+#if defined(__APPLE__)
+  flags |= RTLD_FIRST;
+#endif
+  void *handle = dlopen(filename, flags);
   if (!handle) {
     if (errMsg) *errMsg = dlerror();
     return DynamicLibrary();
@@ -78,13 +81,28 @@
   if (!OpenedHandles->insert(handle).second)
     dlclose(handle);
 
-  return DynamicLibrary(handle);
+  return DynamicLibrary(filename, handle);
 }
 
 void *DynamicLibrary::getAddressOfSymbol(const char *symbolName) {
   if (!isValid())
     return nullptr;
-  return dlsym(Data, symbolName);
+  void *symbol_addr = dlsym(Data, symbolName);
+  if (!symbol_addr)
+    return nullptr;
+
+#if !defined(__APPLE__)
+  // This platform doesn't support limiting searches only to this shared
+  // library, so manually limit the search to this library by checking
+  // that the path of the module that this symbol lives in matches that
+  // which the module was dlopen'ed with.
+  Dl_info info;
+  if (!dladdr(symbol_addr, &info) || !info.dli_fname)
+    return nullptr;
+  if (0 != strcmp(info.dli_fname, Filename.c_str()))
+    return nullptr;
+#endif
+  return symbol_addr;
 }
 
 #else
Index: lib/Support/Windows/DynamicLibrary.inc
===================================================================
--- lib/Support/Windows/DynamicLibrary.inc
+++ lib/Support/Windows/DynamicLibrary.inc
@@ -81,7 +81,7 @@
     EnumerateLoadedModules(GetCurrentProcess(), ELM_Callback, 0);
     // Dummy library that represents "search all handles".
     // This is mostly to ensure that the return value still shows up as "valid".
-    return DynamicLibrary(&OpenedHandles);
+    return DynamicLibrary(filename, &OpenedHandles);
   }
 
   SmallVector<wchar_t, MAX_PATH> filenameUnicode;
@@ -106,7 +106,7 @@
   if (!OpenedHandles->insert(a_handle).second)
     FreeLibrary(a_handle);
 
-  return DynamicLibrary(a_handle);
+  return DynamicLibrary(filename, a_handle);
 }
 
 // Stack probing routines are in the support library (e.g. libgcc), but we don't