This Change Adds initial Support for LongFiles in the VM,

They are:
1. Wrappers for OS APIs which  take or return PATHS

2. Fixing the usage of following Api's:

GetEnvironmentVariableW
SearchPathW
GetShortPathNameW
GetLongPathNameW
GetModuleFileName

Work remaining:
Remove fixed size buffers in the VM

18 files changed, 362 insertions, 302 deletions

diff --git a/src/vm/appdomain.cpp b/src/vm/appdomain.cpp
index 9ab8c7dbc0..a841423ace 100644
--- a/src/vm/appdomain.cpp
+++ b/src/vm/appdomain.cpp
@@ -4770,12 +4770,10 @@ void SystemDomain::GetDevpathW(__out_ecount_opt(1) LPWSTR* pDevpath, DWORD* pdwD
 
         if(m_fDevpath == FALSE) {
             DWORD dwPath = 0;
-            dwPath = WszGetEnvironmentVariable(APPENV_DEVPATH, 0, 0);
+            PathString m_pwDevpathholder; 
+            dwPath = WszGetEnvironmentVariable(APPENV_DEVPATH, m_pwDevpathholder);
             if(dwPath) {
-                m_pwDevpath = (WCHAR*) new WCHAR[dwPath];
-                m_dwDevpath = WszGetEnvironmentVariable(APPENV_DEVPATH,
-                                                        m_pwDevpath,
-                                                        dwPath);
+                m_pwDevpath = m_pwDevpathholder.GetCopyOfUnicodeString();
             }
             else {
                 RegKeyHolder userKey;
@@ -13831,14 +13829,30 @@ DWORD* SetupCompatibilityFlags()
         SO_TOLERANT;
     } CONTRACTL_END;
 
-    WCHAR buf[2] = { '\0', '\0' };
+    LPCWSTR buf;
+    bool return_null = true;
 
     FAULT_NOT_FATAL(); // we can simply give up
 
-    if (WszGetEnvironmentVariable(W("UnsupportedCompatSwitchesEnabled"), buf, COUNTOF(buf)) == 0)
-        return NULL;
+    BEGIN_SO_INTOLERANT_CODE_NO_THROW_CHECK_THREAD(SetLastError(COR_E_STACKOVERFLOW); return NULL;)
+    InlineSString<4> bufString;
+    
+    if (WszGetEnvironmentVariable(W("UnsupportedCompatSwitchesEnabled"), bufString) != 0)
+    {
+        buf = bufString.GetUnicode();
+        if (buf[0] != '1' || buf[1] != '\0')
+        {
+            return_null = true;
+        }
+        else
+        {
+            return_null = false;
+        }
+
+    }
+    END_SO_INTOLERANT_CODE
 
-    if (buf[0] != '1' || buf[1] != '\0')
+    if (return_null)
         return NULL;
 
     static const LPCWSTR rgFlagNames[] = {
@@ -13852,17 +13866,21 @@ DWORD* SetupCompatibilityFlags()
         return NULL;
     ZeroMemory(pFlags, size * sizeof(DWORD));
 
+    BEGIN_SO_INTOLERANT_CODE_NO_THROW_CHECK_THREAD(SetLastError(COR_E_STACKOVERFLOW); return NULL;)
+    InlineSString<4> bufEnvString;
     for (int i = 0; i < COUNTOF(rgFlagNames); i++)
     {
-        if (WszGetEnvironmentVariable(rgFlagNames[i], buf, COUNTOF(buf)) == 0)
+        if (WszGetEnvironmentVariable(rgFlagNames[i], bufEnvString) == 0)
             continue;
 
+        buf = bufEnvString.GetUnicode();
         if (buf[0] != '1' || buf[1] != '\0')
             continue;
 
         pFlags[i / 32] |= 1 << (i % 32);
     }
-
+    END_SO_INTOLERANT_CODE
+    
     return pFlags;
 }
 
diff --git a/src/vm/assemblynative.cpp b/src/vm/assemblynative.cpp
index 5720c201ed..c89e927404 100644
--- a/src/vm/assemblynative.cpp
+++ b/src/vm/assemblynative.cpp
@@ -2364,8 +2364,8 @@ void QCALLTYPE AssemblyNative::CreateVersionInfoResource(LPCWSTR    pwzFilename,
     const void  *pvData=0;              // Pointer to the resource.
     ULONG       cbData;                 // Size of the resource data.
     ULONG       cbWritten;
-    WCHAR       szFile[MAX_PATH_FNAME+1];     // File name for resource file.
-    WCHAR       szPath[MAX_LONGPATH+1];     // Path name for resource file.
+    PathString       szFile;     // File name for resource file.
+    PathString       szPath;     // Path name for resource file.
     HandleHolder hFile;
 
     res.SetInfo(pwzFilename, 
@@ -2387,9 +2387,9 @@ void QCALLTYPE AssemblyNative::CreateVersionInfoResource(LPCWSTR    pwzFilename,
     // messages including the path/file name</TODO>
 
     // Persist to a file.
-    if (!WszGetTempPath(MAX_LONGPATH, szPath))
+    if (!WszGetTempPath(szPath))
         COMPlusThrowWin32();
-    if (!WszGetTempFileName(szPath, W("RES"), 0, szFile))
+    if (!WszGetTempFileName(szPath.GetUnicode(), W("RES"), 0, szFile))
         COMPlusThrowWin32();
 
     hFile = WszCreateFile(szFile, GENERIC_READ|GENERIC_WRITE, 0, NULL, OPEN_EXISTING, 0, NULL);
diff --git a/src/vm/ceemain.cpp b/src/vm/ceemain.cpp
index d6391056ab..e2419ac88f 100644
--- a/src/vm/ceemain.cpp
+++ b/src/vm/ceemain.cpp
@@ -2978,9 +2978,9 @@ static BOOL CacheCommandLine(__in LPWSTR pCmdLine, __in_opt LPWSTR* ArgvW)
     }
 
     if (ArgvW != NULL && ArgvW[0] != NULL) {
-        WCHAR wszModuleName[MAX_LONGPATH];
-        WCHAR wszCurDir[MAX_LONGPATH];
-        if (!WszGetCurrentDirectory(MAX_LONGPATH, wszCurDir))
+        PathString wszModuleName;
+        PathString wszCurDir;
+        if (!WszGetCurrentDirectory(wszCurDir))
             return FALSE;
 
 #ifdef _PREFAST_
@@ -2991,17 +2991,17 @@ static BOOL CacheCommandLine(__in LPWSTR pCmdLine, __in_opt LPWSTR* ArgvW)
         // usage of PathCombine is safe if we ensure that buffer specified by
         // parameter1 can accomodate buffers specified by paramater2, parameter3
         // and one path separator
-        if (lstrlenW(wszCurDir) + lstrlenW(ArgvW[0]) + 1 >= COUNTOF(wszModuleName))
-            return FALSE;
+        COUNT_T wszModuleName_len = wszCurDir.GetCount() + lstrlenW(ArgvW[0]);
+        WCHAR* wszModuleName_buf = wszModuleName.OpenUnicodeBuffer(wszModuleName_len);
 
-        if (PathCombine(wszModuleName, wszCurDir, ArgvW[0]) == NULL)
+        if (PathCombine(wszModuleName_buf, wszCurDir, ArgvW[0]) == NULL)
             return FALSE;
-
+        wszModuleName.CloseBuffer();
 #ifdef _PREFAST_
 #pragma warning(pop)
 #endif
 
-        size_t len = wcslen(wszModuleName);
+        size_t len = wszModuleName.GetCount();
         _ASSERT(g_pCachedModuleFileName== NULL);
         g_pCachedModuleFileName = new WCHAR[len+1];
         wcscpy_s(g_pCachedModuleFileName, len+1, wszModuleName);
@@ -3824,7 +3824,7 @@ BOOL STDMETHODCALLTYPE EEDllMain( // TRUE on success, FALSE on error.
                 CoreClrCallbacks cccallbacks;
                 cccallbacks.m_hmodCoreCLR               = (HINSTANCE)g_pMSCorEE;
                 cccallbacks.m_pfnIEE                    = IEE;
-                cccallbacks.m_pfnGetCORSystemDirectory  = GetCORSystemDirectoryInternal;
+                cccallbacks.m_pfnGetCORSystemDirectory  = GetCORSystemDirectoryInternaL;
                 cccallbacks.m_pfnGetCLRFunction         = GetCLRFunction;
 
                 InitUtilcode(cccallbacks);
@@ -4279,30 +4279,47 @@ static HRESULT InitializeIPCManager(void)
     {
         // We failed to create the IPC block because it has already been created. This means that
         // two mscoree's have been loaded into the process.
-        WCHAR strFirstModule[256];
-        WCHAR strSecondModule[256];
-
-        // Get the name and path of the first loaded MSCOREE.DLL.
-        if (!hInstIPCBlockOwner || !WszGetModuleFileName(hInstIPCBlockOwner, strFirstModule, 256))
-            wcscpy_s(strFirstModule, COUNTOF(strFirstModule), W("<Unknown>"));
-
-        // Get the name and path of the second loaded MSCOREE.DLL.
-        if (!WszGetModuleFileName(g_pMSCorEE, strSecondModule, 256))
-            wcscpy_s(strSecondModule, COUNTOF(strSecondModule), W("<Unknown>"));
+        PathString strFirstModule;
+        PathString strSecondModule;
+        EX_TRY
+        {
+            // Get the name and path of the first loaded MSCOREE.DLL.
+            if (!hInstIPCBlockOwner || !WszGetModuleFileName(hInstIPCBlockOwner, strFirstModule))
+                strFirstModule.Set(W("<Unknown>"));
 
+            // Get the name and path of the second loaded MSCOREE.DLL.
+            if (!WszGetModuleFileName(g_pMSCorEE, strSecondModule))
+               strSecondModule.Set(W("<Unknown>"));
+        }
+        EX_CATCH_HRESULT(hr);
         // Load the format strings for the title and the message body.
         EEMessageBoxCatastrophic(IDS_EE_TWO_LOADED_MSCOREE_MSG, IDS_EE_TWO_LOADED_MSCOREE_TITLE, strFirstModule, strSecondModule);
         goto errExit;
     }
     else
     {
-        if (!WszGetModuleFileName(GetModuleInst(), (PWSTR)
-                                  g_pIPCManagerInterface->
-                                  GetInstancePath(),
-                                  MAX_LONGPATH))
+        PathString temp;
+        if (!WszGetModuleFileName(GetModuleInst(),
+                                  temp
+                                  ))
         {
             hr = HRESULT_FROM_GetLastErrorNA();
         }
+        else
+        {
+            EX_TRY
+            {
+                if (temp.GetCount() + 1 > MAX_LONGPATH)
+                {
+                    hr = E_FAIL;
+                }
+                else
+                {
+                    wcscpy_s((PWSTR)g_pIPCManagerInterface->GetInstancePath(),temp.GetCount() + 1,temp);
+                }
+            }
+            EX_CATCH_HRESULT(hr);
+        }
     }
 
     // Generate public IPCBlock for our PID.
@@ -4915,11 +4932,12 @@ HRESULT CorCommandLine::ReadClickOnceEnvVariables()
     EX_TRY
     {
         // Find out if this is a ClickOnce application being activated.
-        DWORD cAppFullName = WszGetEnvironmentVariable(g_pwzClickOnceEnv_FullName, NULL, 0);
+        PathString m_pwszAppFullNameHolder;
+        DWORD cAppFullName = WszGetEnvironmentVariable(g_pwzClickOnceEnv_FullName, m_pwszAppFullNameHolder);
         if (cAppFullName > 0) {
             // get the application full name.
-            m_pwszAppFullName = new WCHAR[cAppFullName];
-            WszGetEnvironmentVariable(g_pwzClickOnceEnv_FullName, m_pwszAppFullName, cAppFullName);
+            m_pwszAppFullName = m_pwszAppFullNameHolder.GetCopyOfUnicodeString();
+                       
             // reset the variable now that we read it so child processes
             // do not think they are a clickonce app.
             WszSetEnvironmentVariable(g_pwzClickOnceEnv_FullName, NULL);
@@ -4933,7 +4951,8 @@ HRESULT CorCommandLine::ReadClickOnceEnvVariables()
                 _itow_s(dwManifestPaths, buf.OpenUnicodeBuffer(size), size, 10);
                 buf.CloseBuffer();
                 manifestFile.Append(buf);
-                if (WszGetEnvironmentVariable(manifestFile.GetUnicode(), NULL, 0) > 0)
+                SString temp;
+                if (WszGetEnvironmentVariable(manifestFile.GetUnicode(), temp) > 0)
                     dwManifestPaths++;
                 else
                     break;
@@ -4946,10 +4965,11 @@ HRESULT CorCommandLine::ReadClickOnceEnvVariables()
                 _itow_s(i, buf.OpenUnicodeBuffer(size), size, 10);
                 buf.CloseBuffer();
                 manifestFile.Append(buf);
-                DWORD cManifestPath = WszGetEnvironmentVariable(manifestFile.GetUnicode(), NULL, 0);
+                PathString m_ppwszManifestPathsHolder;
+                DWORD cManifestPath = WszGetEnvironmentVariable(manifestFile.GetUnicode(), m_ppwszManifestPathsHolder);
                 if (cManifestPath > 0) {
-                    m_ppwszManifestPaths[i] = new WCHAR[cManifestPath];
-                    WszGetEnvironmentVariable(manifestFile.GetUnicode(), m_ppwszManifestPaths[i], cManifestPath);
+                    
+                    m_ppwszManifestPaths[i] = m_ppwszManifestPathsHolder.GetCopyOfUnicodeString();
                     WszSetEnvironmentVariable(manifestFile.GetUnicode(), NULL); // reset the env. variable.
                 }
             }
@@ -4964,7 +4984,8 @@ HRESULT CorCommandLine::ReadClickOnceEnvVariables()
                 _itow_s(dwActivationData, buf.OpenUnicodeBuffer(size), size, 10);
                 buf.CloseBuffer();
                 activationData.Append(buf);
-                if (WszGetEnvironmentVariable(activationData.GetUnicode(), NULL, 0) > 0)
+                SString temp;
+                if (WszGetEnvironmentVariable(activationData.GetUnicode(), temp) > 0)
                     dwActivationData++;
                 else
                     break;
@@ -4977,10 +4998,10 @@ HRESULT CorCommandLine::ReadClickOnceEnvVariables()
                 _itow_s(i, buf.OpenUnicodeBuffer(size), size, 10);
                 buf.CloseBuffer();
                 activationData.Append(buf);
-                DWORD cActivationData = WszGetEnvironmentVariable(activationData.GetUnicode(), NULL, 0);
+                PathString m_ppwszActivationDataHolder;
+                DWORD cActivationData = WszGetEnvironmentVariable(activationData.GetUnicode(), m_ppwszActivationDataHolder);
                 if (cActivationData > 0) {
-                    m_ppwszActivationData[i] = new WCHAR[cActivationData];
-                    WszGetEnvironmentVariable(activationData.GetUnicode(), m_ppwszActivationData[i], cActivationData);
+                    m_ppwszActivationData[i] = m_ppwszActivationDataHolder.GetCopyOfUnicodeString();
                     WszSetEnvironmentVariable(activationData.GetUnicode(), NULL); // reset the env. variable.
                 }
             }
diff --git a/src/vm/codeman.cpp b/src/vm/codeman.cpp
index 9374a2c8a9..4f99539215 100644
--- a/src/vm/codeman.cpp
+++ b/src/vm/codeman.cpp
@@ -1386,10 +1386,12 @@ static void LoadAndInitializeJIT(LPCWSTR pwzJitName, OUT HINSTANCE* phJit, OUT I
     HRESULT hr = E_FAIL;
 
 #ifdef FEATURE_MERGE_JIT_AND_ENGINE
-    WCHAR CoreClrFolder[MAX_LONGPATH + 1];
+    PathString CoreClrFolderHolder;
     extern HINSTANCE g_hThisInst;
-    if (WszGetModuleFileName(g_hThisInst, CoreClrFolder, MAX_LONGPATH))
+    if (WszGetModuleFileName(g_hThisInst, CoreClrFolderHolder))
     {
+        DWORD len = CoreClrFolderHolder.GetCount();
+        WCHAR* CoreClrFolder = CoreClrFolderHolder.OpenUnicodeBuffer(len);
         WCHAR *filePtr = wcsrchr(CoreClrFolder, DIRECTORY_SEPARATOR_CHAR_W);
         if (filePtr)
         {
@@ -1401,6 +1403,7 @@ static void LoadAndInitializeJIT(LPCWSTR pwzJitName, OUT HINSTANCE* phJit, OUT I
                 hr = S_OK;
             }
         }
+        CoreClrFolderHolder.CloseBuffer();
     }
 #else
     hr = g_pCLRRuntime->LoadLibrary(pwzJitName, phJit);
diff --git a/src/vm/corhost.cpp b/src/vm/corhost.cpp
index 2a7cf45249..f0e90291b7 100644
--- a/src/vm/corhost.cpp
+++ b/src/vm/corhost.cpp
@@ -2471,10 +2471,9 @@ HRESULT CorHost2::ExecuteMain(
         AppDomain *pDomain = GetAppDomain();
         _ASSERTE(pDomain);
 
-        WCHAR wzExeFileName[_MAX_PATH];
-        DWORD cchExeFileName = _MAX_PATH;
-        cchExeFileName = WszGetModuleFileName(nullptr, wzExeFileName, cchExeFileName);
-        if (cchExeFileName == _MAX_PATH)
+        PathString wzExeFileName;
+         
+        if (WszGetModuleFileName(nullptr, wzExeFileName) == 0)
             IfFailThrow(E_UNEXPECTED);
 
         LPWSTR wzExeSimpleFileName = nullptr;
diff --git a/src/vm/dwbucketmanager.hpp b/src/vm/dwbucketmanager.hpp
index 48746d4816..a3aef9b2a8 100644
--- a/src/vm/dwbucketmanager.hpp
+++ b/src/vm/dwbucketmanager.hpp
@@ -323,7 +323,6 @@ private:
     void FindFaultingMethodInfo();
     OBJECTREF GetRealExceptionObject();
     WCHAR* GetParamBufferForIndex(BucketParameterIndex paramIndex);
-    int CopyStringToBucket(__out_ecount(targetMaxLength) LPWSTR pTargetParam, int targetMaxLength, __in_z LPCWSTR pSource, bool cannonicalize = false);
     void LogParam(__in_z LPCWSTR paramValue, BucketParameterIndex paramIndex);
     
 protected:
@@ -349,7 +348,7 @@ protected:
 
 public:
     BaseBucketParamsManager(GenericModeBlock* pGenericModeBlock, TypeOfReportedError typeOfError, PCODE initialFaultingPc, Thread* pFaultingThread, OBJECTREF* pThrownException);
-
+    static int CopyStringToBucket(__out_ecount(targetMaxLength) LPWSTR pTargetParam, int targetMaxLength, __in_z LPCWSTR pSource, bool cannonicalize = false);
     // function that consumers should call to populate the GMB
     virtual void PopulateBucketParameters() = 0;
 };
@@ -485,10 +484,10 @@ void BaseBucketParamsManager::GetAppName(__out_ecount(maxLength) WCHAR* targetPa
     CONTRACTL_END;
 
     HMODULE hModule = WszGetModuleHandle(NULL);
-    WCHAR appPath[MAX_LONGPATH];
-    DWORD cchAppPath = NumItems(appPath);
+    PathString appPath;
+    
 
-    if (GetCurrentModuleFileName(appPath, &cchAppPath) == S_OK)
+    if (GetCurrentModuleFileName(appPath) == S_OK)
     {
         CopyStringToBucket(targetParam, maxLength, appPath);
     }
@@ -509,13 +508,13 @@ void BaseBucketParamsManager::GetAppVersion(__out_ecount(maxLength) WCHAR* targe
     CONTRACTL_END;
 
     HMODULE hModule = WszGetModuleHandle(NULL);
-    WCHAR appPath[MAX_LONGPATH];
-    DWORD cchAppPath = NumItems(appPath);
+    PathString appPath;
+    
 
     WCHAR verBuf[23] = {0};
     USHORT major, minor, build, revision;
 
-    if ((GetCurrentModuleFileName(appPath, &cchAppPath) == S_OK) && SUCCEEDED(DwGetFileVersionInfo(appPath, major, minor, build, revision)))
+    if ((GetCurrentModuleFileName(appPath) == S_OK) && SUCCEEDED(DwGetFileVersionInfo(appPath, major, minor, build, revision)))
     {
         _snwprintf_s(targetParam,
             maxLength,
diff --git a/src/vm/dwreport.cpp b/src/vm/dwreport.cpp
index 15a58c0701..77669b2f14 100644
--- a/src/vm/dwreport.cpp
+++ b/src/vm/dwreport.cpp
@@ -214,15 +214,6 @@ BOOL RegisterOutOfProcessWatsonCallbacks()
     CONTRACTL_END;
     
     WCHAR wszDACName[] = MAIN_DAC_MODULE_NAME_W W(".dll");
-    WCHAR wszDACPath[MAX_LONGPATH];
-    DWORD dwSize = 0;
-
-    if ((FAILED(::GetCORSystemDirectoryInternal(wszDACPath, NumItems(wszDACPath), &dwSize))) || 
-        (wcscat_s(wszDACPath, _countof(wszDACPath), wszDACName) != 0))
-    {
-        return FALSE;
-    }
-
     WerModuleHolder hWerModule(WER_MODULE_NAME_W);
 
 #ifdef FEATURE_CORESYSTEM
@@ -250,8 +241,23 @@ BOOL RegisterOutOfProcessWatsonCallbacks()
     {
        return FALSE;
     }
+    HRESULT hr = S_OK;
 
-    HRESULT hr = (*pFnWerRegisterRuntimeExceptionModule)(wszDACPath, (PDWORD)g_pMSCorEE);
+    EX_TRY
+    {
+        PathString wszDACPath;
+        if (SUCCEEDED(::GetCORSystemDirectoryInternaL(wszDACPath)))
+        {
+            wszDACPath.Append(wszDACName);
+            hr = (*pFnWerRegisterRuntimeExceptionModule)(wszDACPath, (PDWORD)g_pMSCorEE);
+        }
+        else {
+            hr = E_FAIL;
+        }
+
+    }
+    EX_CATCH_HRESULT(hr);
+    
     if (FAILED(hr))
     {
         STRESS_LOG0(LF_STARTUP, 
@@ -562,9 +568,9 @@ HRESULT DwCheckCompany(                 // S_OK or error.
 //   None
 //------------------------------------------------------------------------------
 int DwGetAppDescription(                // Number of characters written.
-    __in_z LPWSTR wszFilePath,          // Path to the executable.
-    __inout_ecount(cchBuf) WCHAR *pBuf, // Put description here.
-    int     cchBuf)                     // Size of buf, wide chars.
+    __in_z LPCWSTR wszFilePath,          // Path to the executable.
+    SString& pBuf // Put description here.
+    )                     // Size of buf, wide chars.
 {
     CONTRACTL
     {
@@ -663,8 +669,17 @@ int DwGetAppDescription(                // Number of characters written.
     }
 
     // Copy back the description.
-    size = (int)size > cchBuf-1 ? cchBuf-1 : size;
-    wcsncpy_s(pBuf, cchBuf, fileDescription, size);
+    EX_TRY
+    {
+        wcsncpy_s(pBuf.OpenUnicodeBuffer(size), size, fileDescription, size);
+        pBuf.CloseBuffer(size);
+    }
+        EX_CATCH
+    {
+        size = 0;
+    }
+    EX_END_CATCH(SwallowAllExceptions);
+    
 
     return size;
 } // int DwGetAppDescription()
@@ -685,7 +700,7 @@ int DwGetAppDescription(                // Number of characters written.
 //   None
 //------------------------------------------------------------------------------
 int DwGetAssemblyVersion(               // Number of characters written.
-    __in_z LPWSTR  wszFilePath,         // Path to the executable.
+    __in_z LPCWSTR  wszFilePath,         // Path to the executable.
     __inout_ecount(cchBuf) WCHAR *pBuf, // Put description here.
     int cchBuf)                     // Size of buf, wide chars.
 {
@@ -1469,88 +1484,99 @@ BOOL RunWatson(
     memset(&startupInfo, 0, sizeof(STARTUPINFOW));
     startupInfo.cb = sizeof(STARTUPINFOW);
 
+    HRESULT hr = S_OK;
+    PathString watsonAppName;
+    PathString watsonCommandLine;
+    EX_TRY
+    {
+        do
+        {
 
-    WCHAR watsonAppName[MAX_LONGPATH];
-    WCHAR watsonCommandLine[MAX_LONGPATH+1];
 
-    {
-#if !defined(FEATURE_CORECLR)
-        // Use the version of DW20.exe that lives in the system directory.
-        DWORD ret;
+        
 
-        if (FAILED(GetCORSystemDirectoryInternal(watsonAppName, NumItems(watsonAppName), &ret)))
-        {
-            return false;
-        }
-        if (wcsncat_s(watsonAppName, NumItems(watsonAppName), kWatsonImageNameOnVista, _TRUNCATE) != 0)
-        {
-            return false;
-        }
-#else // FEATURE_CORECLR
-        HKEYHolder hKey;
-        // Look for key \\HKLM\Software\Microsoft\PCHealth\ErrorReporting\DW\Installed"
-        DWORD ret = WszRegOpenKeyEx(HKEY_LOCAL_MACHINE,
-                                    kWatsonPath,
-                                    0,
-                                    KEY_READ | kWatsonRegKeyOptions,
-                                    &hKey);
-
-        if (ERROR_SUCCESS != ret)
         {
-            return false;
-        }
+    #if !defined(FEATURE_CORECLR)
+            // Use the version of DW20.exe that lives in the system directory.
+            DWORD ret;
 
+            if (FAILED(GetCORSystemDirectoryInternaL(watsonAppName)))
+            {
+                hr = E_FAIL;
+                break;
+            }
+            watsonCommandLine.Set(watsonAppName);
+            watsonCommandLine.Append(kWatsonImageNameOnVista);
+
+    #else // FEATURE_CORECLR
+            HKEYHolder hKey;
+            // Look for key \\HKLM\Software\Microsoft\PCHealth\ErrorReporting\DW\Installed"
+            DWORD ret = WszRegOpenKeyEx(HKEY_LOCAL_MACHINE,
+                                        kWatsonPath,
+                                        0,
+                                        KEY_READ | kWatsonRegKeyOptions,
+                                        &hKey);
+
+            if (ERROR_SUCCESS != ret)
+            {
+                hr = E_FAIL;
+                break;
+            }
 
-        // Look in ...\DW\Installed for dw0200 (dw0201 on ia64).  This will be
-        //  the full path to the executable.
-        DWORD size = NumItems(watsonAppName);
-        ret = WszRegQueryValueEx(hKey,
-                                    kWatsonValue,
-                                    NULL,
-                                    NULL,
-                                    reinterpret_cast< LPBYTE >(watsonAppName),
-                                    &size);
 
-    
-        if (ERROR_SUCCESS != ret)
-        {
-            return false;
-        }
-#endif // ! FEATURE_CORECLR
+            // Look in ...\DW\Installed for dw0200 (dw0201 on ia64).  This will be
+            //  the full path to the executable.
+
+            ClrRegReadString(hKey, kWatsonValue, watsonAppName);
+
+    #endif // ! FEATURE_CORECLR
 
-        _snwprintf_s(watsonCommandLine,
-                   NumItems(watsonCommandLine)-1,
-                   _TRUNCATE,
-                   W("dw20.exe -x -s %lu"),
-                   PtrToUlong(hWatsonSharedMemory));
-        watsonCommandLine[NumItems(watsonCommandLine) - 1] = W('\0');
+            COUNT_T len = watsonCommandLine.GetCount();
+            WCHAR* buffer = watsonCommandLine.OpenUnicodeBuffer(len);
+            _snwprintf_s(buffer,
+                       len,
+                       _TRUNCATE,
+                       W("dw20.exe -x -s %lu"),
+                       PtrToUlong(hWatsonSharedMemory));
+            watsonCommandLine.CloseBuffer();
+
+        }
+        } while (false);
     }
+    EX_CATCH_HRESULT(hr);
 
 
+    if (hr != S_OK)
     {
-        BOOL ret = WszCreateProcess(watsonAppName,
-                                    watsonCommandLine,
-                                    NULL,
-                                    NULL,
-                                    TRUE,
-                                    NULL,
-                                    NULL,
-                                    NULL,
-                                    &startupInfo,
-                                    &processInformation);
+        return false;
+    }
 
-        if (FALSE == ret)
         {
-            //
-            // Watson failed to start up.
-            //
-            // This can happen if e.g. Watson wasn't installed on the machine.
-            //
-            HRESULT hr = HRESULT_FROM_GetLastErrorNA();
-            return false;
+            BOOL ret = WszCreateProcess(watsonAppName,
+                                        watsonCommandLine,
+                                        NULL,
+                                        NULL,
+                                        TRUE,
+                                        NULL,
+                                        NULL,
+                                        NULL,
+                                        &startupInfo,
+                                        &processInformation);
+
+            if (FALSE == ret)
+            {
+                //
+                // Watson failed to start up.
+                //
+                // This can happen if e.g. Watson wasn't installed on the machine.
+                //
+                 return  E_FAIL;
+                 
+            }
+
         }
 
-    }
+    
 
     // Wait for watson to finish.
     //
@@ -2426,9 +2452,11 @@ FaultReportResult DoFaultReportWorker(      // Was Watson attempted, successful?
     pWatsonSharedMemory->bfmsoctdsLetRun = offerFlags;
 
     {
+        PathString wzModuleFileName;
         DWORD dwRet = WszGetModuleFileName(NULL,
-	                                       pWatsonSharedMemory->wzModuleFileName,
-	                                       NumItems(pWatsonSharedMemory->wzModuleFileName));
+	                                       wzModuleFileName);
+        BaseBucketParamsManager::CopyStringToBucket(pWatsonSharedMemory->wzModuleFileName, NumItems(pWatsonSharedMemory->wzModuleFileName), wzModuleFileName);
+        
         _ASSERTE(0 != dwRet);
         if (0 == dwRet)
         {
@@ -2455,24 +2483,24 @@ FaultReportResult DoFaultReportWorker(      // Was Watson attempted, successful?
     // do this just by using the executable name.
     //
     {
-        WCHAR   buf[_MAX_PATH];         // Buffer for path for description.
-        WCHAR   *pName = buf;           // Pointer to filename or description.
+        PathString   buf;         // Buffer for path for description.
+        LPCWSTR   pName ;           // Pointer to filename or description.
         int     size;                   // Size of description.
         HMODULE hModule;                // Handle to module.
         DWORD   result;                 // Return code
 
         // Get module name.
         hModule = WszGetModuleHandle(NULL);
-        result = WszGetModuleFileName(hModule, buf, NumItems(buf));
+        result = WszGetModuleFileName(hModule, buf);
 
         if (result == 0)
         {   // Couldn't get module name.  This should never happen.
-            wcscpy_s(buf, COUNTOF(buf), W("<<unknown>>"));
+            pName = W("<<unknown>>");
         }
         else
         {   // re-use the buf for pathname and description.
-            size = DwGetAppDescription(buf, buf, NumItems(buf));
-
+            size = DwGetAppDescription(buf, buf);
+            pName = buf.GetUnicode();
             // If the returned size was zero, buf wasn't changed, and still contains the path.
             //  find just the filename part.
             if (size == 0)
diff --git a/src/vm/dwreport.h b/src/vm/dwreport.h
index a2750cefe7..44306689ea 100644
--- a/src/vm/dwreport.h
+++ b/src/vm/dwreport.h
@@ -58,7 +58,7 @@ BOOL IsWatsonEnabled();
 BOOL RegisterOutOfProcessWatsonCallbacks();
 
 int DwGetAssemblyVersion(               // Number of characters written.
-    __in_z LPWSTR  wszFilePath,         // Path to the executable.
+    __in_z LPCWSTR  wszFilePath,         // Path to the executable.
     __inout_ecount(cchBuf) WCHAR *pBuf, // Put description here.
     int cchBuf);
 
diff --git a/src/vm/eeconfig.cpp b/src/vm/eeconfig.cpp
index e322a63f5e..973a4f4235 100644
--- a/src/vm/eeconfig.cpp
+++ b/src/vm/eeconfig.cpp
@@ -835,12 +835,12 @@ HRESULT EEConfig::sync()
             {
                 bGCStressAndHeapVerifyAllowed = false;
                 
-                WCHAR wszFileName[_MAX_PATH];
-                if (WszGetModuleFileName(NULL, wszFileName, _MAX_PATH) != 0)
+                PathString wszFileName;
+                if (WszGetModuleFileName(NULL, wszFileName) != 0)
                 {
                     // just keep the name
-                    LPWSTR pwszName = wcsrchr(wszFileName, W('\\'));
-                    pwszName = (pwszName == NULL) ? wszFileName : (pwszName + 1);
+                    LPCWSTR pwszName = wcsrchr(wszFileName, W('\\'));
+                    pwszName = (pwszName == NULL) ? wszFileName.GetUnicode() : (pwszName + 1);
                     
                     if (SString::_wcsicmp(pwszName,pszGCStressExe) == 0)
                     {
@@ -1619,46 +1619,62 @@ HRESULT EEConfig::SetupConfiguration()
     // AppX process check to make sure no app.config file
     // exists unless launched with AO_DESIGNMODE.
     // ----------------------------------------------------
+    
+    do
     {
-        WCHAR wzProcExe[_MAX_PATH];
-        size_t cchProcExe = COUNTOF(wzProcExe);
-
-        // Get name of file used to create process
-        if (g_pCachedModuleFileName)
-        {
-            IfFailRet(StringCchCopy(wzProcExe, COUNTOF(wzProcExe), g_pCachedModuleFileName));
-            IfFailRet(StringCchLength(wzProcExe, COUNTOF(wzProcExe), &cchProcExe));
-        }
-        else
+        size_t cchProcExe=0;
+        PathString wzProcExe;
+        EX_TRY
         {
-            cchProcExe = WszGetModuleFileName(NULL, wzProcExe, COUNTOF(wzProcExe));
 
-            if (cchProcExe == 0)
+
+
+            // Get name of file used to create process
+            if (g_pCachedModuleFileName)
             {
-                return HRESULT_FROM_GetLastError();
+                wzProcExe.Set(g_pCachedModuleFileName);
+                cchProcExe = wzProcExe.GetCount();
             }
-        }
+            else
+            {
+                cchProcExe = WszGetModuleFileName(NULL, wzProcExe);
 
-        if (cchProcExe != 0)
-        {
-            IfFailRet(StringCchCat(wzProcExe, COUNTOF(wzProcExe), CONFIGURATION_EXTENSION));
+                if (cchProcExe == 0)
+                {
+                    hr = HRESULT_FROM_GetLastError();
+                    break;
+                }
+            }
 
-            if (AppX::IsAppXProcess() && !AppX::IsAppXDesignMode())
+            if (cchProcExe != 0)
             {
-                if (clr::fs::Path::Exists(wzProcExe))
+                wzProcExe.Append(CONFIGURATION_EXTENSION);
+
+                if (AppX::IsAppXProcess() && !AppX::IsAppXDesignMode())
                 {
-                    return CLR_E_APP_CONFIG_NOT_ALLOWED_IN_APPX_PROCESS;
+                    if (clr::fs::Path::Exists(wzProcExe))
+                    {
+                        hr = CLR_E_APP_CONFIG_NOT_ALLOWED_IN_APPX_PROCESS;
+                        break;
+                    }
                 }
             }
-
+        }
+        EX_CATCH_HRESULT(hr);
+        if (cchProcExe != 0)
+        {
             IfFailParseError(wzProcExe, true, AppendConfigurationFile(wzProcExe, version));
 
             // We really should return a failure hresult if the app config file is bad, but that
             // would be a breaking change. Not sure if it's worth it yet.
             hr = S_OK;
+            break;
         }
-    }
+    } while (false);
+    
 
+    if (hr != S_OK)
+        return hr;
     // ----------------------------------------------------
     // Import machine.config, if needed.
     // ----------------------------------------------------
diff --git a/src/vm/eepolicy.cpp b/src/vm/eepolicy.cpp
index c67d06d596..8c3f2ec625 100644
--- a/src/vm/eepolicy.cpp
+++ b/src/vm/eepolicy.cpp
@@ -530,11 +530,11 @@ void SafeExitProcess(UINT exitCode, BOOL fAbort = FALSE, ShutdownCompleteAction
         if (CLRConfig::GetConfigValue(CLRConfig::UNSUPPORTED_BreakOnBadExit))
         {
             // Workaround for aspnet
-            WCHAR  wszFilename[_MAX_PATH];
+            PathString  wszFilename;
             bool bShouldAssert = true;
-            if (WszGetModuleFileName(NULL, wszFilename, _MAX_PATH))
+            if (WszGetModuleFileName(NULL, wszFilename))
             {
-                _wcslwr_s(wszFilename, COUNTOF(wszFilename));
+                wszFilename.LowerCase();
                 
                 if (wcsstr(wszFilename, W("aspnet_compiler"))) 
                 {
diff --git a/src/vm/eventreporter.cpp b/src/vm/eventreporter.cpp
index e07a6401cd..567f4f5d51 100644
--- a/src/vm/eventreporter.cpp
+++ b/src/vm/eventreporter.cpp
@@ -47,8 +47,8 @@ EventReporter::EventReporter(EventReporterType type)
     m_eventType = type;
 
     HMODULE hModule = WszGetModuleHandle(NULL);
-    WCHAR appPath[MAX_LONGPATH];
-    DWORD ret = WszGetModuleFileName(hModule, appPath, NumItems(appPath));
+    PathString appPath;
+    DWORD ret = WszGetModuleFileName(hModule, appPath);
 
     fBufferFull = FALSE;
 
@@ -65,7 +65,7 @@ EventReporter::EventReporter(EventReporterType type)
     if (ret != 0)
     {
         // If app name has a '\', consider the part after that; otherwise consider whole name.
-        WCHAR* appName =  wcsrchr(appPath, W('\\'));
+        LPCWSTR appName =  wcsrchr(appPath, W('\\'));
         appName = appName ? appName+1 : appPath;
         m_Description.Append(appName);
         m_Description.Append(W("\n"));
@@ -808,8 +808,8 @@ void EventReporter::GetCoreCLRInstanceProductVersion(DWORD * pdwMajor, DWORD * p
     _ASSERTE(hModRuntime != NULL);
 
     // Get the path to the runtime
-    WCHAR runtimePath[MAX_LONGPATH];
-    DWORD ret = WszGetModuleFileName(hModRuntime, runtimePath, NumItems(runtimePath));
+    PathString runtimePath;
+    DWORD ret = WszGetModuleFileName(hModRuntime, runtimePath);
     if (ret != 0)
     {
         // Got the path - get the file version from the path
diff --git a/src/vm/eventtrace.cpp b/src/vm/eventtrace.cpp
index e6a25cc853..5e35f9a2b8 100644
--- a/src/vm/eventtrace.cpp
+++ b/src/vm/eventtrace.cpp
@@ -4869,7 +4869,7 @@ VOID ETW::InfoLog::RuntimeInformation(INT32 type)
             PCWSTR szDtraceOutput1=W(""),szDtraceOutput2=W("");
             UINT8 startupMode = 0;
             UINT startupFlags = 0;
-            WCHAR dllPath[MAX_LONGPATH+1] = {0};
+            PathString dllPath;
             UINT8 Sku = 0;
             _ASSERTE(g_fEEManagedEXEStartup ||   //CLR started due to a managed exe
                 g_fEEIJWStartup ||               //CLR started as a mixed mode Assembly
@@ -4899,7 +4899,7 @@ VOID ETW::InfoLog::RuntimeInformation(INT32 type)
             LPCGUID comGUID=&g_EEComObjectGuid;
 
             PCWSTR lpwszCommandLine = W("");
-            PCWSTR lpwszRuntimeDllPath = (PCWSTR)dllPath;
+            
 
 #ifndef FEATURE_CORECLR
             startupFlags = CorHost2::GetStartupFlags();
@@ -4954,12 +4954,12 @@ VOID ETW::InfoLog::RuntimeInformation(INT32 type)
                 startupMode = ETW::InfoLog::InfoStructs::Other;
             }
 
-            _ASSERTE (NumItems(dllPath) > MAX_LONGPATH);
+          
             // if WszGetModuleFileName fails, we return an empty string
-            if (!WszGetModuleFileName(GetCLRModule(), dllPath, MAX_LONGPATH)) {
-                dllPath[0] = 0;
+            if (!WszGetModuleFileName(GetCLRModule(), dllPath)) {
+                dllPath.Set(W("\0"));
             }
-            dllPath[MAX_LONGPATH] = 0;
+            
 
             if(type == ETW::InfoLog::InfoStructs::Callback)
             {
@@ -4977,7 +4977,7 @@ VOID ETW::InfoLog::RuntimeInformation(INT32 type)
                                                   startupMode,
                                                   lpwszCommandLine,
                                                   comGUID,
-                                                  lpwszRuntimeDllPath );
+                                                  dllPath );
             }
             else
             {
@@ -4995,7 +4995,7 @@ VOID ETW::InfoLog::RuntimeInformation(INT32 type)
                                                 startupMode,
                                                 lpwszCommandLine,
                                                 comGUID,
-                                                lpwszRuntimeDllPath );
+                                                dllPath );
             }
         }
     } EX_CATCH { } EX_END_CATCH(SwallowAllExceptions);
diff --git a/src/vm/mdaassistants.cpp b/src/vm/mdaassistants.cpp
index de81a82f83..cc598c0a6c 100644
--- a/src/vm/mdaassistants.cpp
+++ b/src/vm/mdaassistants.cpp
@@ -995,12 +995,12 @@ void MdaPInvokeLog::LogPInvoke(NDirectMethodDesc* pMD, HINSTANCE hMod)
         StackSString sszEntryPoint;
         sszEntryPoint.SetUTF8(pMD->GetEntrypointName());
 
-        WCHAR szDllFullName[_MAX_PATH] = {0};
+        PathString szDllFullName ;
         WCHAR szDrive[_MAX_PATH] = {0};
         WCHAR szPath[_MAX_PATH] = {0};
         WCHAR szFileName[_MAX_PATH] = {0};
         WCHAR szExt[_MAX_PATH] = {0};
-        WszGetModuleFileName(hMod, szDllFullName, _MAX_PATH);      
+        WszGetModuleFileName(hMod, szDllFullName);      
         SplitPath(szDllFullName, szDrive, _MAX_PATH, szPath, _MAX_PATH, szFileName, _MAX_PATH, szExt, _MAX_PATH);
 
         StackSString sszDllName;
@@ -1869,16 +1869,14 @@ void MdaLoaderLock::ReportViolation(HINSTANCE hInst)
         MdaXmlMessage msg(this->AsMdaAssistant(), TRUE, &pXml);
 
         DWORD cName = 0;
-        WCHAR szName[_MAX_PATH * 2];
+        PathString szName;
         if (hInst)
         {
-            cName = _MAX_PATH * 2 - 1;
-            cName = WszGetModuleFileName(hInst, szName, cName);
+            cName = WszGetModuleFileName(hInst, szName);
         }
 
         if (cName)
         {
-            szName[cName] = W('\0');
             msg.SendMessagef(MDARC_LOADER_LOCK_DLL, szName);
         }
         else
diff --git a/src/vm/peimage.cpp b/src/vm/peimage.cpp
index 27904ff476..cb1dd50c9d 100644
--- a/src/vm/peimage.cpp
+++ b/src/vm/peimage.cpp
@@ -422,15 +422,8 @@ void PEImage::GetPathFromDll(HINSTANCE hMod, SString &result)
     }
     CONTRACTL_END;
 
-    DWORD ret;
-    DWORD length = MAX_LONGPATH;
-    do
-    {
-        WCHAR *buffer = result.OpenUnicodeBuffer(length);
-        ret = WszGetModuleFileName(hMod, buffer, length);
-        result.CloseBuffer(ret);
-        length *= 2;
-    } while (ret == 0);
+    WszGetModuleFileName(hMod, result);   
+    
 }
 #endif // !FEATURE_PAL
 
diff --git a/src/vm/peimage.inl b/src/vm/peimage.inl
index 343b2bbbd9..c2f6957ba0 100644
--- a/src/vm/peimage.inl
+++ b/src/vm/peimage.inl
@@ -592,25 +592,9 @@ inline PTR_PEImage PEImage::FindByLongPath(LPCWSTR pPath)
     }
     CONTRACTL_END;
 
-    InlineSString<MAX_PATH> sLongPath;
-    // Note: GetLongPathName  return the number of characters written NOT INCLUDING the
-    //       null character on success, and on failure returns the buffer size required
-    //       INCLUDING the null. This means the result must not be equal to MAX_PATH -
-    //       it must be greater or less then.
-    COUNT_T nLen = WszGetLongPathName(pPath, sLongPath.OpenUnicodeBuffer(MAX_PATH-1), MAX_PATH);
-    CONSISTENCY_CHECK(nLen != MAX_PATH);
-
-    // If this was insufficient buffer, then try again with a reallocated buffer
-    if (nLen > MAX_PATH)
-    {
-        // Close the buffer before reopening
-        sLongPath.CloseBuffer();
-        INDEBUG(SIZE_T nOldLen = nLen;)
-        nLen = WszGetLongPathName(pPath, sLongPath.OpenUnicodeBuffer(nLen-1), nLen);
-        CONSISTENCY_CHECK(nLen == (nOldLen - 1));
-    }
-    sLongPath.CloseBuffer(nLen);
-
+    PathString sLongPath;
+    COUNT_T nLen = WszGetLongPathName(pPath, sLongPath);
+   
     // Check for any kind of error other than an insufficient buffer result.
     if (nLen == 0)
     {
@@ -619,7 +603,7 @@ inline PTR_PEImage PEImage::FindByLongPath(LPCWSTR pPath)
             ThrowHR(hr);
         return (PEImage*)INVALIDENTRY;
     }
-    return FindByPath(sLongPath);
+    return FindByPath(sLongPath.GetUnicode());
 }
 
 /*static*/
@@ -634,24 +618,8 @@ inline PTR_PEImage PEImage::FindByShortPath(LPCWSTR pPath)
     }
     CONTRACTL_END;
 
-    InlineSString<MAX_PATH> sShortPath;
-    // Note: GetLongPathName  return the number of characters written NOT INCLUDING the
-    //       null character on success, and on failure returns the buffer size required
-    //       INCLUDING the null. This means the result must not be equal to MAX_PATH -
-    //       it must be greater or less then.
-    COUNT_T nLen = WszGetShortPathName(pPath, sShortPath.OpenUnicodeBuffer(MAX_PATH-1), MAX_PATH);
-    CONSISTENCY_CHECK(nLen != MAX_PATH);
-
-    // If this was insufficient buffer, then try again with a reallocated buffer
-    if (nLen > MAX_PATH)
-    {
-        // Close the buffer before reopening
-        sShortPath.CloseBuffer();
-        INDEBUG(SIZE_T nOldLen = nLen;)
-        nLen = WszGetShortPathName(pPath, sShortPath.OpenUnicodeBuffer(nLen-1), nLen);
-        CONSISTENCY_CHECK(nLen == (nOldLen - 1));
-    }
-    sShortPath.CloseBuffer(nLen);
+    PathString sShortPath;
+    COUNT_T nLen = WszGetShortPathName(pPath, sShortPath);
 
     // Check for any kind of error other than an insufficient buffer result.
     if (nLen == 0)
@@ -661,7 +629,7 @@ inline PTR_PEImage PEImage::FindByShortPath(LPCWSTR pPath)
             ThrowHR(hr);
         return (PEImage*)INVALIDENTRY;
     }
-    return FindByPath(sShortPath);
+    return FindByPath(sShortPath.GetUnicode());
 }
 #endif // !FEATURE_CORECLR
 
diff --git a/src/vm/peimagelayout.cpp b/src/vm/peimagelayout.cpp
index 3868386860..8fdf554557 100644
--- a/src/vm/peimagelayout.cpp
+++ b/src/vm/peimagelayout.cpp
@@ -319,9 +319,9 @@ RawImageLayout::RawImageLayout(const void *mapped, PEImage* pOwner, BOOL bTakeOw
     if (bTakeOwnership)
     {
 #ifndef FEATURE_PAL
-        WCHAR wszDllName[MAX_LONGPATH];
-        WszGetModuleFileName((HMODULE)mapped, wszDllName, MAX_LONGPATH);
-        wszDllName[MAX_LONGPATH - 1] = W('\0');
+        PathString wszDllName;
+        WszGetModuleFileName((HMODULE)mapped, wszDllName);
+        
         m_LibraryHolder=CLRLoadLibraryEx(wszDllName,NULL,GetLoadWithAlteredSearchPathFlag());
 #else // !FEATURE_PAL
         _ASSERTE(!"bTakeOwnership Should not be used on FEATURE_PAL");
diff --git a/src/vm/securitypolicy.cpp b/src/vm/securitypolicy.cpp
index 082be54f88..fe1da90b8d 100644
--- a/src/vm/securitypolicy.cpp
+++ b/src/vm/securitypolicy.cpp
@@ -1,9 +1,6 @@
 // Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-// See the LICENSE file in the project root for more information.
-// 
-
-//
+//The .NET Foundation licenses this file to you under the MIT license.
+//See the LICENSE file in the project root for more information.
 
 
 #include "common.h"
@@ -676,12 +673,11 @@ void QCALLTYPE SecurityPolicy::_GetLongPathName(LPCWSTR wszPath, QCall::StringHa
     BEGIN_QCALL;
 
 #if !defined(PLATFORM_UNIX)
-    WCHAR wszBuffer[MAX_LONGPATH + 1];
-    ZeroMemory(wszBuffer, sizeof(wszBuffer));
+    PathString wszBuffer;
                 
-    if (SecurityPolicy::GetLongPathNameHelper( wszPath, wszBuffer, MAX_LONGPATH ) != 0)
+    if (SecurityPolicy::GetLongPathNameHelper( wszPath, wszBuffer ) != 0)
     {
-        retLongPath.Set( wszBuffer );
+        retLongPath.Set( wszBuffer.GetUnicode() );
     }
 #endif // !PLATFORM_UNIX
 
@@ -689,15 +685,15 @@ void QCALLTYPE SecurityPolicy::_GetLongPathName(LPCWSTR wszPath, QCall::StringHa
 }
 
 #if !defined(PLATFORM_UNIX)
-size_t SecurityPolicy::GetLongPathNameHelper( const WCHAR* wszShortPath, __inout_ecount(cchBuffer) __inout_z WCHAR* wszBuffer, DWORD cchBuffer )
+size_t GetLongPathNameHelperthatThrows(const WCHAR* wszShortPath, SString& wszBuffer)
 {
-    CONTRACTL {
-        NOTHROW;
-        GC_NOTRIGGER;
-        MODE_ANY;
+    CONTRACTL{
+        THROWS;
+    GC_NOTRIGGER;
+    MODE_ANY;
     } CONTRACTL_END;
 
-    DWORD size = WszGetLongPathName(wszShortPath, wszBuffer, cchBuffer);
+    DWORD size = WszGetLongPathName(wszShortPath, wszBuffer);
 
     if (size == 0)
     {
@@ -707,66 +703,87 @@ size_t SecurityPolicy::GetLongPathNameHelper( const WCHAR* wszShortPath, __inout
         // trying GetLongPathName on every subdirectory until
         // it succeeds or we run out of string.
 
-        WCHAR wszIntermediateBuffer[MAX_LONGPATH];
+        size_t len = wcslen(wszShortPath);
+        NewArrayHolder<WCHAR> wszIntermediateBuffer = new (nothrow) WCHAR[len + 1];
 
-        if (wcslen( wszShortPath ) >= MAX_LONGPATH)
+        if (wszIntermediateBuffer == NULL)
+        {
             return 0;
+        }
 
-        wcscpy_s( wszIntermediateBuffer, COUNTOF(wszIntermediateBuffer), wszShortPath );
+        wcscpy_s(wszIntermediateBuffer, len + 1, wszShortPath);
 
-        size_t index = wcslen( wszIntermediateBuffer );
+        size_t index = len;
 
         do
         {
-            while (index > 0 && (wszIntermediateBuffer[index-1] != W('\\') && wszIntermediateBuffer[index-1] != W('/')))
+            while (index > 0 && (wszIntermediateBuffer[index - 1] != W('\\') && wszIntermediateBuffer[index - 1] != W('/')))
                 --index;
 
             if (index == 0)
                 break;
 
-            #ifdef _PREFAST_
-            #pragma prefast(push)
-            #pragma prefast(disable:26001, "suppress prefast warning about underflow by doing index-1 which is checked above.")
-            #endif // _PREFAST_
-            
-            wszIntermediateBuffer[index-1] = W('\0');
+#ifdef _PREFAST_
+#pragma prefast(push)
+#pragma prefast(disable:26001, "suppress prefast warning about underflow by doing index-1 which is checked above.")
+#endif // _PREFAST_
+
+            wszIntermediateBuffer[index - 1] = W('\0');
 
-            #ifdef _PREFAST_
-            #pragma prefast(pop)
-            #endif
+#ifdef _PREFAST_
+#pragma prefast(pop)
+#endif
 
-            size = WszGetLongPathName(wszIntermediateBuffer, wszBuffer, MAX_LONGPATH);
+            size = WszGetLongPathName(wszIntermediateBuffer, wszBuffer);
 
             if (size != 0)
             {
-                size_t sizeBuffer = wcslen( wszBuffer );
 
-                if (sizeBuffer + wcslen( &wszIntermediateBuffer[index] ) > MAX_LONGPATH - 2)
-                {
-                    return 0;
-                }
-                else
-                {
-                    if (wszBuffer[sizeBuffer-1] != W('\\') && wszBuffer[sizeBuffer-1] != W('/'))
-                        wcscat_s( wszBuffer, cchBuffer, W("\\") );
-                    wcscat_s( wszBuffer, cchBuffer, &wszIntermediateBuffer[index] );
-                    return (DWORD)wcslen( wszBuffer );
-                }
+                int sizeBuffer = wszBuffer.GetCount();
+
+                if (wszBuffer[sizeBuffer - 1] != W('\\') && wszBuffer[sizeBuffer - 1] != W('/'))
+                    wszBuffer.Append(W("\\"));
+
+                wszBuffer.Append(&wszIntermediateBuffer[index]);
+
+
+                return (DWORD)wszBuffer.GetCount();
+
             }
-        }
-        while( true );
+        } while (true);
 
         return 0;
     }
-    else if (size > MAX_LONGPATH)
+    else
     {
-        return 0;
+        return (DWORD)wszBuffer.GetCount();
     }
-    else
+}
+size_t SecurityPolicy::GetLongPathNameHelper(const WCHAR* wszShortPath, SString& wszBuffer)
+{
+    CONTRACTL{
+        NOTHROW;
+    GC_NOTRIGGER;
+    MODE_ANY;
+    } CONTRACTL_END;
+
+    HRESULT hr = S_OK;
+    size_t retval = 0;
+
+    EX_TRY
     {
-        return wcslen( wszBuffer );
+        retval = GetLongPathNameHelperthatThrows(wszShortPath,wszBuffer);
     }
+    EX_CATCH_HRESULT(hr);
+
+    if (hr != S_OK)
+    {
+        retval = 0;
+    }
+
+    return retval;
 }
+
 #endif // !PLATFORM_UNIX
 
 void QCALLTYPE SecurityPolicy::GetDeviceName(LPCWSTR wszDriveLetter, QCall::StringHandleOnStack retDeviceName)
diff --git a/src/vm/securitypolicy.h b/src/vm/securitypolicy.h
index cf2b10f21c..ba77bcbda8 100644
--- a/src/vm/securitypolicy.h
+++ b/src/vm/securitypolicy.h
@@ -198,7 +198,7 @@ namespace SecurityPolicy
     BOOL WasStrongNameEvidenceUsed(OBJECTREF evidence);
 #endif
     // Like WszGetLongPathName, but it works with nonexistant files too
-    size_t GetLongPathNameHelper( const WCHAR* wszShortPath, __inout_ecount(cchBuffer) __inout_z WCHAR* wszBuffer, DWORD cchBuffer );
+    size_t GetLongPathNameHelper( const WCHAR* wszShortPath, SString& wszBuffer);
 
 #ifdef FEATURE_CAS_POLICY
     extern CrstStatic s_crstPolicyInit;