Build wheels using QEMU emulation

cibuildwheel/__main__.py

@@ -79,6 +79,12 @@ def main() -> None:
                             considered the 'project' and is copied into the Docker container on
                             Linux. Default: the working directory.
                         ''')
+    parser.add_argument('--use-binfmt',
+                        default=False,
+                        action='store_true',
+                        help='''
+                            Use QEMU Emulation to run the Docker images of other architectures.
+                        ''')
 
     parser.add_argument('--print-build-identifiers',
                         action='store_true',
@@ -168,8 +174,11 @@ def main() -> None:
         print('cibuildwheel: Could not find setup.py, setup.cfg or pyproject.toml at root of package', file=sys.stderr)
         exit(2)
 
+    # qemu is only available on linux platforms
+    use_binfmt = args.use_binfmt and platform == 'linux'
+
     if args.print_build_identifiers:
-        print_build_identifiers(platform, build_selector)
+        print_build_identifiers(platform, build_selector, use_binfmt)
         exit(0)
 
     manylinux_images: Optional[Dict[str, str]] = None
@@ -216,6 +225,7 @@ def main() -> None:
         environment=environment,
         dependency_constraints=dependency_constraints,
         manylinux_images=manylinux_images,
+        use_binfmt=use_binfmt
     )
 
     # Python is buffering by default when running on the CI platforms, giving problems interleaving subprocess call output with unflushed calls to 'print'
@@ -284,10 +294,10 @@ def print_preamble(platform: str, build_options: BuildOptions) -> None:
     print('\nHere we go!\n')
 
 
-def print_build_identifiers(platform: str, build_selector: BuildSelector) -> None:
+def print_build_identifiers(platform: str, build_selector: BuildSelector, use_binfmt: bool) -> None:
     python_configurations: List[Any] = []
     if platform == 'linux':
-        python_configurations = cibuildwheel.linux.get_python_configurations(build_selector)
+        python_configurations = cibuildwheel.linux.get_python_configurations(build_selector, use_binfmt)
     elif platform == 'windows':
         python_configurations = cibuildwheel.windows.get_python_configurations(build_selector)
     elif platform == 'macos':

cibuildwheel/linux.py

@@ -33,6 +33,17 @@ def matches_platform(identifier: str) -> bool:
     return False
 
 
+def matches_qemu_capable(identifier: str) -> bool:
+    arch = identifier.split('_')[-1]
+    qemu_platform = Path(f"/proc/sys/fs/binfmt_misc/qemu-{arch}")
+
+    if not qemu_platform.exists():
+        return False
+
+    contents = open(qemu_platform, "r").readlines()
+    return contents[0].strip() == "enabled"
+
+
 class PythonConfiguration(NamedTuple):
     version: str
     identifier: str
@@ -43,7 +54,7 @@ def path(self):
         return PurePath(self.path_str)
 
 
-def get_python_configurations(build_selector: BuildSelector) -> List[PythonConfiguration]:
+def get_python_configurations(build_selector: BuildSelector, use_binfmt: bool = False) -> List[PythonConfiguration]:
     python_configurations = [
         PythonConfiguration(version='2.7', identifier='cp27-manylinux_x86_64', path_str='/opt/python/cp27-cp27m'),
         PythonConfiguration(version='2.7', identifier='cp27-manylinux_x86_64', path_str='/opt/python/cp27-cp27mu'),
@@ -79,7 +90,8 @@ def get_python_configurations(build_selector: BuildSelector) -> List[PythonConfi
         PythonConfiguration(version='3.9', identifier='cp39-manylinux_s390x', path_str='/opt/python/cp39-cp39'),
     ]
     # skip builds as required
-    return [c for c in python_configurations if matches_platform(c.identifier) and build_selector(c.identifier)]
+    return [c for c in python_configurations if (matches_platform(c.identifier)
+            or (use_binfmt and matches_qemu_capable(c.identifier))) and build_selector(c.identifier)]
 
 
 def build(options: BuildOptions) -> None:
@@ -92,8 +104,12 @@ def build(options: BuildOptions) -> None:
               file=sys.stderr)
         exit(2)
 
+    if options.use_binfmt:
+        log.step('Installing binfmt...')
+        subprocess.check_output(['docker', 'run', '--rm', '--privileged', 'docker/binfmt:a7996909642ee92942dcd6cff44b9b95f08dad64'])
+
     assert options.manylinux_images is not None
-    python_configurations = get_python_configurations(options.build_selector)
+    python_configurations = get_python_configurations(options.build_selector, options.use_binfmt)
     platforms = [
         ('cp', 'manylinux_x86_64', options.manylinux_images['x86_64']),
         ('cp', 'manylinux_i686', options.manylinux_images['i686']),

cibuildwheel/util.py

@@ -136,6 +136,7 @@ class BuildOptions(NamedTuple):
     test_requires: List[str]
     test_extras: str
     build_verbosity: int
+    use_binfmt: bool
 
 
 resources_dir = Path(__file__).resolve().parent / 'resources'