Bug 1542830: Part 3 - Add ntdll_freestanding.lib to freestanding; r=mhowell,froydnj

The `freestanding` library is built with specific compiler flags to signify
that it is indeed freestanding code. That is, it does not depend on a
standard library.

One of the requirements of freestanding code is that the toolchain still
expects implementations of `memcpy`, `memmove`, `memcmp`, and `memset`.

I did briefly implement my own naive versions of these functions, but that
solution is less than ideal since the implementations must be `extern` and are
thus picked up by the entire `firefox.exe` binary. This denies the rest of
`firefox.exe` the benefit of optimized implementations. On Windows, the
sandbox is linked into `firefox.exe`, so we cannot just shrug and
assume that naive implementations will not have any effect on anything.

There are, however, optimized implementations of these functions that are
exported by `ntdll.dll`. They are not included in the `ntdll.lib` that is
included in the Windows SDK. Using `llvm-dlltool`, we can build an import
library containing the missing entries and then add that library to `OS_LIBS`.

Differential Revision: https://phabricator.services.mozilla.com/D43157

--HG--
extra : moz-landing-system : lando

browser/app/moz.build

@@ -86,6 +86,15 @@ if CONFIG['OS_ARCH'] == 'WINNT':
         'version.dll',
     ]
 
+    if CONFIG['CC_TYPE'] == 'clang-cl':
+        libpath_flag = '-LIBPATH:'
+    else:
+        libpath_flag = '-L'
+
+    WIN32_EXE_LDFLAGS += [
+        libpath_flag + OBJDIR + '/winlauncher/freestanding',
+    ]
+
 if CONFIG['MOZ_SANDBOX'] and CONFIG['OS_ARCH'] == 'Darwin':
     USE_LIBS += [
         'mozsandbox',

browser/app/winlauncher/freestanding/gen_ntdll_freestanding_lib.py

@@ -0,0 +1,30 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+from __future__ import absolute_import
+
+import os
+import subprocess
+import tempfile
+
+
+def main(output_fd, def_file, llvm_dlltool, *llvm_dlltool_args):
+    # llvm-dlltool can't output to stdout, so we create a temp file, use that
+    # to write out the lib, and then copy it over to output_fd
+    (tmp_fd, tmp_output) = tempfile.mkstemp()
+    os.close(tmp_fd)
+
+    try:
+        cmd = [llvm_dlltool]
+        cmd.extend(llvm_dlltool_args)
+        cmd += ['-d', def_file, '-l', tmp_output]
+
+        subprocess.check_call(cmd)
+
+        with open(tmp_output, 'rb') as tmplib:
+            output_fd.write(tmplib.read())
+    finally:
+        os.remove(tmp_output)

browser/app/winlauncher/freestanding/moz.build

@@ -43,8 +43,22 @@ CXXFLAGS += [ SRCDIR + '/Freestanding.h' ]
 
 OS_LIBS += [
     'ntdll',
+    'ntdll_freestanding',
 ]
 
+ntdll_freestanding_lib = '%sntdll_freestanding.%s' % (CONFIG['LIB_PREFIX'],
+                                                      CONFIG['LIB_SUFFIX'])
+
+GENERATED_FILES += [
+    ntdll_freestanding_lib,
+]
+
+ntdll_freestanding_gen = GENERATED_FILES[ntdll_freestanding_lib]
+ntdll_freestanding_gen.script = 'gen_ntdll_freestanding_lib.py'
+ntdll_freestanding_gen.inputs = ['ntdll_freestanding.def']
+ntdll_freestanding_gen.flags = [CONFIG['LLVM_DLLTOOL']] + \
+                               CONFIG['LLVM_DLLTOOL_FLAGS']
+
 DisableStlWrapping()
 
 with Files('**'):

browser/app/winlauncher/freestanding/ntdll_freestanding.def

@@ -0,0 +1,25 @@
+; This Source Code Form is subject to the terms of the Mozilla Public
+; License, v. 2.0. If a copy of the MPL was not distributed with this
+; file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+LIBRARY ntdll
+
+; When we compile with -freestanding, the compiler still requires implementation
+; of the four functions listed below.
+;
+; We could implement our own naive versions of these functions, but that
+; solution is less than ideal since the implementations must be extern and are
+; thus picked up by the entire firefox.exe binary. This denies the rest of
+; firefox.exe the benefit of optimized implementations. On Windows the
+; sandbox is linked into firefox.exe, so we cannot just shrug and
+; assume that a naive implementation will not have any effect on anything.
+;
+; There are, however, optimized implementations of these functions that are
+; exported by ntdll.dll. OTOH, they are not included in the ntdll.lib
+; import library. This .def file is used to build an import library that "fills
+; in the blanks" and allows us to link into the ntdll implementations.
+EXPORTS
+    memcmp
+    memcpy
+    memmove
+    memset

python/mozbuild/mozbuild/frontend/data.py

@@ -1209,6 +1209,7 @@ class GeneratedFile(ContextDerived):
         suffixes = (
             '.h',
             '.inc',
+            context.config.substs['LIB_SUFFIX'],
             '.py',
             '.rs',
             # We need to compile Java to generate JNI wrappers for native code