--- a/config/check_js_msg_encoding.py
+++ b/config/check_js_msg_encoding.py
@@ -8,17 +8,19 @@
 #
 # JSErrorFormatString.format member should be in ASCII encoding.
 #----------------------------------------------------------------------------
 
 from __future__ import print_function
 
 import os
 import sys
-from check_utils import get_all_toplevel_filenames
+
+from mozversioncontrol import get_repository_from_env
+
 
 scriptname = os.path.basename(__file__);
 expected_encoding = 'ascii'
 
 # The following files don't define JSErrorFormatString.
 ignore_files = [
     'dom/base/domerr.msg',
     'js/xpconnect/src/xpc.msg',
@@ -40,20 +42,23 @@ def check_single_file(filename):
             log_fail(filename, 'not in {} encoding'.format(expected_encoding))
 
     log_pass(filename, 'ok')
     return True
 
 def check_files():
     result = True
 
-    for filename in get_all_toplevel_filenames():
+    repo = get_repository_from_env()
+    root = repo.path
+
+    for filename in repo.get_files_in_working_directory():
         if filename.endswith('.msg'):
             if filename not in ignore_files:
-                if not check_single_file(filename):
+                if not check_single_file(os.path.join(root, filename)):
                     result = False
 
     return result
 
 def main():
     if not check_files():
         sys.exit(1)
 

--- a/config/check_macroassembler_style.py
+++ b/config/check_macroassembler_style.py
@@ -20,19 +20,20 @@
 # proper methods annotations.
 #----------------------------------------------------------------------------
 
 from __future__ import print_function
 
 import difflib
 import os
 import re
-import subprocess
 import sys
-from check_utils import get_all_toplevel_filenames
+
+from mozversioncontrol import get_repository_from_env
+
 
 architecture_independent = set([ 'generic' ])
 all_architecture_names = set([ 'x86', 'x64', 'arm', 'arm64', 'mips32', 'mips64' ])
 all_shared_architecture_names = set([ 'x86_shared', 'mips_shared', 'arm', 'arm64' ])
 
 reBeforeArg = "(?<=[(,\s])"
 reArgType = "(?P<type>[\w\s:*&]+)"
 reArgName = "(?P<name>\s\w+)"
@@ -126,17 +127,17 @@ def get_macroassembler_definitions(filen
         fileAnnot = get_file_annotation(filename)
     except:
         return []
 
     style_section = False
     code_section = False
     lines = ''
     signatures = []
-    with open(os.path.join('../..', filename)) as f:
+    with open(filename) as f:
         for line in f:
             if '//{{{ check_macroassembler_style' in line:
                 style_section = True
             elif '//}}} check_macroassembler_style' in line:
                 style_section = False
             if not style_section:
                 continue
 
@@ -166,17 +167,17 @@ def get_macroassembler_definitions(filen
                 continue
 
     return signatures
 
 def get_macroassembler_declaration(filename):
     style_section = False
     lines = ''
     signatures = []
-    with open(os.path.join('../..', filename)) as f:
+    with open(filename) as f:
         for line in f:
             if '//{{{ check_macroassembler_style' in line:
                 style_section = True
             elif '//}}} check_macroassembler_style' in line:
                 style_section = False
             if not style_section:
                 continue
 
@@ -233,23 +234,27 @@ def generate_file_content(signatures):
 
 def check_style():
     # We read from the header file the signature of each function.
     decls = dict()      # type: dict(signature => ['x86', 'x64'])
 
     # We infer from each file the signature of each MacroAssembler function.
     defs = dict()       # type: dict(signature => ['x86', 'x64'])
 
+    repo = get_repository_from_env()
+
     # Select the appropriate files.
-    for filename in get_all_toplevel_filenames():
+    for filename in repo.get_files_in_working_directory():
         if not filename.startswith('js/src/jit/'):
             continue
         if 'MacroAssembler' not in filename:
             continue
 
+        filename = os.path.join(repo.path, filename)
+
         if filename.endswith('MacroAssembler.h'):
             decls = append_signatures(decls, get_macroassembler_declaration(filename))
         else:
             defs = append_signatures(defs, get_macroassembler_definitions(filename))
 
     # Compare declarations and definitions output.
     difflines = difflib.unified_diff(generate_file_content(decls),
                                      generate_file_content(defs),

--- a/config/check_spidermonkey_style.py
+++ b/config/check_spidermonkey_style.py
@@ -35,20 +35,20 @@
 #   isolation, but don't try to do any order checking between such blocks.
 #----------------------------------------------------------------------------
 
 from __future__ import print_function
 
 import difflib
 import os
 import re
-import subprocess
 import sys
-import traceback
-from check_utils import get_all_toplevel_filenames
+
+from mozversioncontrol import get_repository_from_env
+
 
 # We don't bother checking files in these directories, because they're (a) auxiliary or (b)
 # imported code that doesn't follow our coding style.
 ignored_js_src_dirs = [
    'js/src/config/',            # auxiliary stuff
    'js/src/ctypes/libffi/',     # imported code
    'js/src/devtools/',          # auxiliary stuff
    'js/src/editline/',          # imported code
@@ -244,18 +244,20 @@ def check_style():
     # - "js/src/vm/String.h"        -> "vm/String.h"
 
     non_js_dirnames = ('mfbt/',
                        'memory/mozalloc/',
                        'mozglue/')  # type: tuple(str)
     non_js_inclnames = set()        # type: set(inclname)
     js_names = dict()               # type: dict(filename, inclname)
 
+    repo = get_repository_from_env()
+
     # Select the appropriate files.
-    for filename in get_all_toplevel_filenames():
+    for filename in repo.get_files_in_working_directory():
         for non_js_dir in non_js_dirnames:
             if filename.startswith(non_js_dir) and filename.endswith('.h'):
                 inclname = 'mozilla/' + filename.split('/')[-1]
                 non_js_inclnames.add(inclname)
 
         if filename.startswith('js/public/') and filename.endswith('.h'):
             inclname = 'js/' + filename[len('js/public/'):]
             js_names[filename] = inclname
@@ -280,17 +282,17 @@ def check_style():
         inclname = js_names[filename]
         file_kind = FileKind.get(filename)
         if file_kind == FileKind.C or file_kind == FileKind.CPP or \
            file_kind == FileKind.H or file_kind == FileKind.INL_H:
             included_h_inclnames = set()    # type: set(inclname)
 
             # This script is run in js/src/, so prepend '../../' to get to the root of the Mozilla
             # source tree.
-            with open(os.path.join('../..', filename)) as f:
+            with open(os.path.join(repo.path, filename)) as f:
                 do_file(filename, inclname, file_kind, f, all_inclnames, included_h_inclnames)
 
         edges[inclname] = included_h_inclnames
 
     find_cycles(all_inclnames, edges)
 
     # Compare expected and actual output.
     difflines = difflib.unified_diff(expected_output, actual_output,

deleted file mode 100644
--- a/config/check_utils.py
+++ /dev/null
@@ -1,31 +0,0 @@
-# vim: set ts=8 sts=4 et sw=4 tw=99:
-# 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/.
-
-import subprocess
-
-def get_all_toplevel_filenames():
-    '''Get a list of all the files in the (Mercurial or Git) repository.'''
-    failed_cmds = []
-    try:
-        cmd = ['hg', 'manifest', '-q']
-        all_filenames = subprocess.check_output(cmd, universal_newlines=True,
-                                                stderr=subprocess.PIPE).split('\n')
-        return all_filenames
-    except:
-        failed_cmds.append(cmd)
-
-    try:
-        # Get the relative path to the top-level directory.
-        cmd = ['git', 'rev-parse', '--show-cdup']
-        top_level = subprocess.check_output(cmd, universal_newlines=True,
-                                                stderr=subprocess.PIPE).split('\n')[0]
-        cmd = ['git', 'ls-files', '--full-name', top_level]
-        all_filenames = subprocess.check_output(cmd, universal_newlines=True,
-                                                stderr=subprocess.PIPE).split('\n')
-        return all_filenames
-    except:
-        failed_cmds.append(cmd)
-
-    raise Exception('failed to run any of the repo manifest commands', failed_cmds)

--- a/python/mozversioncontrol/mozversioncontrol/__init__.py
+++ b/python/mozversioncontrol/mozversioncontrol/__init__.py
@@ -71,16 +71,21 @@ class Repository(object):
         '''
         raise NotImplementedError
 
     def forget_add_remove_files(self, path):
         '''Undo the effects of a previous add_remove_files call for `path`.
         '''
         raise NotImplementedError
 
+    def get_files_in_working_directory(self):
+        """Obtain a list of managed files in the working directory."""
+        raise NotImplementedError
+
+
 class HgRepository(Repository):
     '''An implementation of `Repository` for Mercurial repositories.'''
     def __init__(self, path):
         super(HgRepository, self).__init__(path, 'hg')
         self._env[b'HGPLAIN'] = b'1'
 
     def get_modified_files(self):
         # Use --no-status to print just the filename.
@@ -94,16 +99,22 @@ class HgRepository(Repository):
         args = ['addremove', path]
         if self.tool_version >= b'3.9':
             args = ['--config', 'extensions.automv='] + args
         self._run(*args)
 
     def forget_add_remove_files(self, path):
         self._run('forget', path)
 
+    def get_files_in_working_directory(self):
+        # Can return backslashes on Windows. Normalize to forward slashes.
+        return list(p.replace('\\', '/') for p in
+                    self._run('files', '-0').split('\0'))
+
+
 class GitRepository(Repository):
     '''An implementation of `Repository` for Git repositories.'''
     def __init__(self, path):
         super(GitRepository, self).__init__(path, 'git')
 
     def get_modified_files(self):
         return self._run('diff', '--diff-filter=M', '--name-only').splitlines()
 
@@ -111,18 +122,46 @@ class GitRepository(Repository):
         return self._run('diff', '--diff-filter=A', '--name-only').splitlines()
 
     def add_remove_files(self, path):
         self._run('add', path)
 
     def forget_add_remove_files(self, path):
         self._run('reset', path)
 
+    def get_files_in_working_directory(self):
+        return self._run('ls-files', '-z').split('\0')
+
+
+class InvalidRepoPath(Exception):
+    """Represents a failure to find a VCS repo at a specified path."""
+
+
 def get_repository_object(path):
     '''Get a repository object for the repository at `path`.
     If `path` is not a known VCS repository, raise an exception.
     '''
     if os.path.isdir(os.path.join(path, '.hg')):
         return HgRepository(path)
     elif os.path.exists(os.path.join(path, '.git')):
         return GitRepository(path)
     else:
-        raise Exception('Unknown VCS, or not a source checkout: %s' % path)
+        raise InvalidRepoPath('Unknown VCS, or not a source checkout: %s' %
+                              path)
+
+
+def get_repository_from_env():
+    """Obtain a repository object by looking at the environment."""
+    def ancestors(path):
+        while path:
+            yield path
+            path, child = os.path.split(path)
+            if child == '':
+                break
+
+    for path in ancestors(os.getcwd()):
+        try:
+            return get_repository_object(path)
+        except InvalidRepoPath:
+            continue
+
+    raise Exception('Could not find Mercurial or Git checkout for %s' %
+                    os.getcwd())