windows: build statically linked libffi

Up until this point, static builds for Python 3.8 have been broken
because of issues linking libffi. This commit unbusts things.

We teach libffi to build a static library. This entailed changing
some defines so declspec(dllexport) isn't used. We also had to opt in
to a statically linked CRT. And disable a shared library.

With the static libffi.lib being produced, we had to teach our hacks
to the static build configuration to link it.

With all that in place, we're able to build a statically linked Python
3.8!

Author: indygreg

cpython-windows/build.py

@@ -622,7 +622,13 @@ def copy_link_to_lib(p: pathlib.Path):
 """
 
 
-def hack_props(td: pathlib.Path, pcbuild_path: pathlib.Path, arch: str, static: bool):
+def hack_props(
+    td: pathlib.Path,
+    pcbuild_path: pathlib.Path,
+    arch: str,
+    static: bool,
+    building_libffi: bool,
+):
     # TODO can we pass props into msbuild.exe?
 
     # Our dependencies are in different directories from what CPython's
@@ -724,18 +730,37 @@ def hack_props(td: pathlib.Path, pcbuild_path: pathlib.Path, arch: str, static:
                 b"<_DLLSuffix>-1_1-%s</_DLLSuffix>" % suffix,
             )
 
+    libffi_props = pcbuild_path / "libffi.props"
+
+    if static and building_libffi:
+        # For some reason the built .lib doesn't have the -7 suffix in
+        # static build mode. This is possibly a side-effect of CPython's
+        # libffi build script not officially supporting static-only builds.
+        static_replace_in_file(
+            libffi_props,
+            b"<AdditionalDependencies>libffi-7.lib;%(AdditionalDependencies)</AdditionalDependencies>",
+            b"<AdditionalDependencies>libffi.lib;%(AdditionalDependencies)</AdditionalDependencies>",
+        )
+
 
 def hack_project_files(
     td: pathlib.Path,
     cpython_source_path: pathlib.Path,
     build_directory: str,
     static: bool,
+    building_libffi: bool,
 ):
     """Hacks Visual Studio project files to work with our build."""
 
     pcbuild_path = cpython_source_path / "PCbuild"
 
-    hack_props(td, pcbuild_path, build_directory, static=static)
+    hack_props(
+        td,
+        pcbuild_path,
+        build_directory,
+        static=static,
+        building_libffi=building_libffi,
+    )
 
     # Our SQLite directory is named weirdly. This throws off version detection
     # in the project file. Replace the parsing logic with a static string.
@@ -797,6 +822,24 @@ def hack_project_files(
         br'<ClCompile Include="$(opensslIncludeDir)\openssl\applink.c">',
     )
 
+    pythoncore_proj = pcbuild_path / "pythoncore.vcxproj"
+
+    # normally the _ctypes extension/project pulls in libffi via
+    # <Link><AdditionalDependencies>. However, as part of converting this
+    # extension to static, we lose the transitive dependency. Here, we
+    # hack pythoncore as a one-off to add the dependency. Ideally we would
+    # handle this when hacking the extension's project. But it is easier to
+    # do here.
+    if static and building_libffi:
+        libffi_path = td / "libffi" / "libffi.lib"
+        static_replace_in_file(
+            pythoncore_proj,
+            b"<AdditionalDependencies>version.lib;shlwapi.lib;ws2_32.lib;%(AdditionalDependencies)</AdditionalDependencies>",
+            b"<AdditionalDependencies>version.lib;shlwapi.lib;ws2_32.lib;"
+            + bytes(libffi_path)
+            + b";%(AdditionalDependencies)</AdditionalDependencies>",
+        )
+
     if static:
         for extension, entry in sorted(CONVERT_TO_BUILTIN_EXTENSIONS.items()):
             if entry.get("ignore_static"):
@@ -810,7 +853,6 @@ def hack_project_files(
 
     # pythoncore.vcxproj produces libpython. Typically pythonXY.dll. We change
     # it to produce a static library.
-    pythoncore_proj = pcbuild_path / "pythoncore.vcxproj"
     pyproject_props = pcbuild_path / "pyproject.props"
 
     # Need to replace Py_ENABLE_SHARED with Py_NO_ENABLE_SHARED so symbol
@@ -1314,7 +1356,11 @@ def build_openssl(
 
 
 def build_libffi(
-    python: str, arch: str, sh_exe: pathlib.Path, dest_archive: pathlib.Path
+    python: str,
+    arch: str,
+    sh_exe: pathlib.Path,
+    dest_archive: pathlib.Path,
+    static: bool,
 ):
     with tempfile.TemporaryDirectory(prefix="libffi-build-") as td:
         td = pathlib.Path(td)
@@ -1355,6 +1401,23 @@ def build_libffi(
             / "prepare_libffi.bat"
         )
 
+        if static:
+            # We replace FFI_BUILDING_DLL with FFI_BUILDING so
+            # declspec(dllexport) isn't used.
+            # We add USE_STATIC_RTL to force static linking of the crt.
+            static_replace_in_file(
+                prepare_libffi,
+                b"CPPFLAGS='-DFFI_BUILDING_DLL'",
+                b"CPPFLAGS='-DFFI_BUILDING -DUSE_STATIC_RTL'",
+            )
+
+            # We also need to tell configure to only build a static library.
+            static_replace_in_file(
+                prepare_libffi,
+                b"--build=$BUILD --host=$HOST;",
+                b"--build=$BUILD --host=$HOST --disable-shared;",
+            )
+
         env = dict(os.environ)
         env["LIBFFI_SOURCE"] = str(ffi_source_path)
         env["VCVARSALL"] = str(find_vcvarsall_path())
@@ -1776,7 +1839,13 @@ def build_cpython(
 
         builtin_extensions = parse_config_c(config_c)
 
-        hack_project_files(td, cpython_source_path, build_directory, static=static)
+        hack_project_files(
+            td,
+            cpython_source_path,
+            build_directory,
+            static=static,
+            building_libffi=libffi_archive is not None,
+        )
         hack_source_files(cpython_source_path, static=static)
 
         if pgo:
@@ -2114,7 +2183,13 @@ def main():
                 "libffi-%s-%s.tar" % (target_triple, args.profile)
             )
             if not libffi_archive.exists():
-                build_libffi(args.python, arch, pathlib.Path(args.sh), libffi_archive)
+                build_libffi(
+                    args.python,
+                    arch,
+                    pathlib.Path(args.sh),
+                    libffi_archive,
+                    "static" in args.profile,
+                )
         else:
             libffi_archive = None