crashpad/util/mach/mig_fix.py

#!/usr/bin/env python3

# Copyright 2019 The Crashpad Authors
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

import argparse
import os
import re
import sys

from mig_gen import MigInterface


def _make_generated_comments_deterministic(contents):
    """Replaces generated code comments with determenistic ones.

    This is what is generated by mig (only in .c files):
    /*
     * IDENTIFICATION:
     * stub generated Mon Jan 17 15:28:03 2022
     * with a MiG generated by bootstrap_cmds-122
     * OPTIONS:
     */

    We look for two specific lines and replace them like so:
    /*
     * IDENTIFICATION:
     * stub generated <suppressed by mig_fix.py>
     * with a MiG generated by <suppressed by mig_fix.py>
     * OPTIONS:
     */
    """

    return re.sub(r'^( \* (?:stub generated|with a MiG generated by) ).+$',
                  r'\1<suppressed by mig_fix.py>',
                  contents,
                  count=2,
                  flags=re.MULTILINE)


def _fix_user_implementation(implementation, fixed_implementation, header,
                             fixed_header):
    """Rewrites a MIG-generated user implementation (.c) file.

    Rewrites the file at |implementation| by adding “__attribute__((unused))” to
    the definition of any structure typedefed as “__Reply” by searching for the
    pattern unique to those structure definitions. These structures are in fact
    unused in the user implementation file, and this will trigger a
    -Wunused-local-typedefs warning in gcc unless removed or marked with the
    “unused” attribute. Also changes header references to point to the new
    header filename, if changed. Replaces generated code comments with
    deterministic ones.

    If |fixed_implementation| is None, overwrites the original; otherwise, puts
    the result in the file at |fixed_implementation|.
    """

    file = open(implementation, 'r+' if fixed_implementation is None else 'r')
    contents = file.read()

    pattern = re.compile('^(\t} __Reply);$', re.MULTILINE)
    contents = pattern.sub(r'\1 __attribute__((unused));', contents)

    if fixed_header is not None:
        contents = contents.replace(
            '#include "%s"' % os.path.basename(header),
            '#include "%s"' % os.path.basename(fixed_header))

    # Replace generated code comments with determenistic ones.
    contents = _make_generated_comments_deterministic(contents)

    if fixed_implementation is None:
        file.seek(0)
        file.truncate()
    else:
        file.close()
        file = open(fixed_implementation, 'w')
    file.write(contents)
    file.close()


def _fix_server_implementation(implementation, fixed_implementation, header,
                               fixed_header):
    """Rewrites a MIG-generated server implementation (.c) file.

    Rewrites the file at |implementation| by replacing “mig_internal” with
    “mig_external” on functions that begin with “__MIG_check__”. This makes
    these functions available to other callers outside this file from a linkage
    perspective. It then returns, as a list of lines, declarations that can be
    added to a header file, so that other files that include that header file
    will have access to these declarations from a compilation perspective. Also
    changes header references to point to the new header filename, if changed.
    Replaces generated code comments with deterministic ones.

    If |fixed_implementation| is None or not provided, overwrites the original;
    otherwise, puts the result in the file at |fixed_implementation|.
    """

    file = open(implementation, 'r+' if fixed_implementation is None else 'r')
    contents = file.read()

    # Find interesting declarations.
    declaration_pattern = re.compile(
        '^mig_internal (kern_return_t __MIG_check__.*)$', re.MULTILINE)
    declarations = declaration_pattern.findall(contents)

    # Remove “__attribute__((__unused__))” from the declarations, and call them
    # “mig_external” or “extern” depending on whether “mig_external” is defined.
    attribute_pattern = re.compile(r'__attribute__\(\(__unused__\)\) ')
    declarations = [
        '''\
#ifdef mig_external
mig_external
#else
extern
#endif
''' + attribute_pattern.sub('', x) + ';\n' for x in declarations
    ]

    # Rewrite the declarations in this file as “mig_external”.
    contents = declaration_pattern.sub(r'mig_external \1', contents)

    # Crashpad never implements the mach_msg_server() MIG callouts. To avoid
    # needing to provide stub implementations, set KERN_FAILURE as the RetCode
    # and abort().
    routine_callout_pattern = re.compile(
        r'OutP->RetCode = (([a-zA-Z0-9_]+)\(.+\));')
    routine_callouts = routine_callout_pattern.findall(contents)
    for routine in routine_callouts:
        contents = contents.replace(routine[0], 'KERN_FAILURE; abort()')

    # Include the header for abort().
    contents = '#include <stdlib.h>\n' + contents

    if fixed_header is not None:
        contents = contents.replace(
            '#include "%s"' % os.path.basename(header),
            '#include "%s"' % os.path.basename(fixed_header))

    # Replace generated code comments with determenistic ones.
    contents = _make_generated_comments_deterministic(contents)

    if fixed_implementation is None:
        file.seek(0)
        file.truncate()
    else:
        file.close()
        file = open(fixed_implementation, 'w')
    file.write(contents)
    file.close()
    return declarations


def _fix_header(header, fixed_header, declarations=[]):
    """Rewrites a MIG-generated header (.h) file.

    Rewrites the file at |header| by placing it inside an “extern "C"” block, so
    that it declares things properly when included by a C++ compilation unit.
    |declarations| can be a list of additional declarations to place inside the
    “extern "C"” block after the original contents of |header|.

    If |fixed_header| is None or not provided, overwrites the original;
    otherwise, puts the result in the file at |fixed_header|.
    """

    file = open(header, 'r+' if fixed_header is None else 'r')
    contents = file.read()
    declarations_text = ''.join(declarations)
    contents = '''\
#ifdef __cplusplus
extern "C" {
#endif

%s
%s
#ifdef __cplusplus
}
#endif
''' % (contents, declarations_text)

    if fixed_header is None:
        file.seek(0)
        file.truncate()
    else:
        file.close()
        file = open(fixed_header, 'w')
    file.write(contents)
    file.close()


def fix_interface(interface, fixed_interface=None):
    if fixed_interface is None:
        fixed_interface = MigInterface(None, None, None, None)

    _fix_user_implementation(interface.user_c, fixed_interface.user_c,
                             interface.user_h, fixed_interface.user_h)
    server_declarations = _fix_server_implementation(interface.server_c,
                                                     fixed_interface.server_c,
                                                     interface.server_h,
                                                     fixed_interface.server_h)
    _fix_header(interface.user_h, fixed_interface.user_h)
    _fix_header(interface.server_h, fixed_interface.server_h,
                server_declarations)


def main(args):
    parser = argparse.ArgumentParser()
    parser.add_argument('user_c')
    parser.add_argument('--fixed_user_c', default=None)
    parser.add_argument('server_c')
    parser.add_argument('--fixed_server_c', default=None)
    parser.add_argument('user_h')
    parser.add_argument('--fixed_user_h', default=None)
    parser.add_argument('server_h')
    parser.add_argument('--fixed_server_h', default=None)
    parsed = parser.parse_args(args)

    interface = MigInterface(parsed.user_c, parsed.server_c, parsed.user_h,
                             parsed.server_h)
    fixed_interface = MigInterface(parsed.fixed_user_c, parsed.fixed_server_c,
                                   parsed.fixed_user_h, parsed.fixed_server_h)
    fix_interface(interface, fixed_interface)


if __name__ == '__main__':
    sys.exit(main(sys.argv[1:]))