diff --git a/Misc/NEWS.d/next/Security/2020-07-03-17-21-37.bpo-29778.cR_fGS.rst b/Misc/NEWS.d/next/Security/2020-07-03-17-21-37.bpo-29778.cR_fGS.rst
@@ -0,0 +1,2 @@
diff --git a/PC/getpathp.c b/PC/getpathp.c
@@ -118,7 +118,6 @@

static wchar_t prefix[MAXPATHLEN+1];
static wchar_t progpath[MAXPATHLEN+1];
-static wchar_t dllpath[MAXPATHLEN+1];
static wchar_t *module_search_path = NULL;


@@ -150,24 +149,37 @@ reduce(wchar_t *dir)
static int
change_ext(wchar_t *dest, const wchar_t *src, const wchar_t *ext)
{
-    size_t src_len = wcsnlen_s(src, MAXPATHLEN+1);
-    size_t i = src_len;
-    if (i >= MAXPATHLEN+1)
-        Py_FatalError("buffer overflow in getpathp.c's reduce()");

-    while (i > 0 && src[i] != '.' && !is_sep(src[i]))
-        --i;

-    if (i == 0) {
-        dest[0] = '\0';
-        return -1;
-    }

-    if (is_sep(src[i]))
-        i = src_len;

-    if (wcsncpy_s(dest, MAXPATHLEN+1, src, i) ||
-        wcscat_s(dest, MAXPATHLEN+1, ext)) {
        dest[0] = '\0';
        return -1;
    }
@@ -304,6 +316,20 @@ search_for_prefix(wchar_t *argv0_path, const wchar_t *landmark)
    return 0;
}

#ifdef Py_ENABLE_SHARED

/* a string loaded from the DLL at startup.*/
@@ -467,15 +493,6 @@ get_progpath(void)
    wchar_t *path = _wgetenv(L"PATH");
    wchar_t *prog = Py_GetProgramName();

-#ifdef Py_ENABLE_SHARED
-    extern HANDLE PyWin_DLLhModule;
-    /* static init of progpath ensures final char remains \0 */
-    if (PyWin_DLLhModule)
-        if (!GetModuleFileNameW(PyWin_DLLhModule, dllpath, MAXPATHLEN))
-            dllpath[0] = 0;
-#else
-    dllpath[0] = 0;
-#endif
    if (GetModuleFileNameW(NULL, modulepath, MAXPATHLEN)) {
        canonicalize(progpath, modulepath);
        return;
@@ -693,7 +710,7 @@ calculate_path(void)
    {
        wchar_t spbuffer[MAXPATHLEN+1];

-        if ((dllpath[0] && !change_ext(spbuffer, dllpath, L"._pth") && exists(spbuffer)) ||
            (progpath[0] && !change_ext(spbuffer, progpath, L"._pth") && exists(spbuffer))) {

            if (!read_pth_file(spbuffer, prefix, &Py_IsolatedFlag, &Py_NoSiteFlag)) {
@@ -737,7 +754,11 @@ calculate_path(void)
    }

    /* Calculate zip archive path from DLL or exe path */
-    change_ext(zip_path, dllpath[0] ? dllpath : progpath, L".zip");

    if (pythonhome == NULL || *pythonhome == '\0') {
        if (zip_path[0] && exists(zip_path)) {
@@ -919,8 +940,6 @@ calculate_path(void)
}


-/* External interface */
-
void
Py_SetPath(const wchar_t *path)
{
@@ -981,25 +1000,39 @@ int
_Py_CheckPython3()
{
    wchar_t py3path[MAXPATHLEN+1];
-    wchar_t *s;
-    if (python3_checked)
        return hPython3 != NULL;
    python3_checked = 1;

    /* If there is a python3.dll next to the python3y.dll,
-       assume this is a build tree; use that DLL */
-    wcscpy(py3path, dllpath);
-    s = wcsrchr(py3path, L'\\');
-    if (!s)
-        s = py3path;
-    wcscpy(s, L"\\python3.dll");
-    hPython3 = LoadLibraryExW(py3path, NULL, LOAD_WITH_ALTERED_SEARCH_PATH);
-    if (hPython3 != NULL)
-        return 1;

-    /* Check sys.prefix\DLLs\python3.dll */
    wcscpy(py3path, Py_GetPrefix());
-    wcscat(py3path, L"\\DLLs\\python3.dll");
-    hPython3 = LoadLibraryExW(py3path, NULL, LOAD_WITH_ALTERED_SEARCH_PATH);
    return hPython3 != NULL;
}
diff --git a/PCbuild/pyproject.props b/PCbuild/pyproject.props
@@ -24,12 +24,12 @@
    <_PlatformPreprocessorDefinition>_WIN32;</_PlatformPreprocessorDefinition>
    <_PlatformPreprocessorDefinition Condition="$(Platform) == 'x64'">_WIN64;_M_X64;</_PlatformPreprocessorDefinition>
    <_PydPreprocessorDefinition Condition="$(TargetExt) == '.pyd'">Py_BUILD_CORE_MODULE;</_PydPreprocessorDefinition>
  </PropertyGroup>
  <ItemDefinitionGroup>
    <ClCompile>
      <AdditionalIncludeDirectories>$(PySourcePath)Include;$(PySourcePath)PC;$(IntDir);%(AdditionalIncludeDirectories)</AdditionalIncludeDirectories>
-      <PreprocessorDefinitions>WIN32;$(_PlatformPreprocessorDefinition)$(_DebugPreprocessorDefinition)$(_PydPreprocessorDefinition)%(PreprocessorDefinitions)</PreprocessorDefinitions>
-
      <Optimization>MaxSpeed</Optimization>
      <IntrinsicFunctions>true</IntrinsicFunctions>
      <StringPooling>true</StringPooling>

diff --git a/PCbuild/python.props b/PCbuild/python.props
@@ -175,6 +175,8 @@

    <!-- The name of the resulting pythonXY.dll (without the extension) -->
    <PyDllName>python$(MajorVersionNumber)$(MinorVersionNumber)$(PyDebugExt)</PyDllName>

    <!-- The version and platform tag to include in .pyd filenames -->
    <PydTag Condition="$(ArchName) == 'win32'">.cp$(MajorVersionNumber)$(MinorVersionNumber)-win32</PydTag>