[3.13] pythonGH-127429: fix sysconfig data generation on cross-builds (pythonGH-127430)

(cherry picked from commit 2950bc5)

Co-authored-by: Filipe Laíns 🇵🇸 <lains@riseup.net>

Author: FFY00

Lib/sysconfig/__init__.py

@@ -173,7 +173,9 @@ def joinuser(*args):
 _PY_VERSION = sys.version.split()[0]
 _PY_VERSION_SHORT = f'{sys.version_info[0]}.{sys.version_info[1]}'
 _PY_VERSION_SHORT_NO_DOT = f'{sys.version_info[0]}{sys.version_info[1]}'
+_PREFIX = os.path.normpath(sys.prefix)
 _BASE_PREFIX = os.path.normpath(sys.base_prefix)
+_EXEC_PREFIX = os.path.normpath(sys.exec_prefix)
 _BASE_EXEC_PREFIX = os.path.normpath(sys.base_exec_prefix)
 # Mutex guarding initialization of _CONFIG_VARS.
 _CONFIG_VARS_LOCK = threading.RLock()
@@ -323,14 +325,22 @@ def get_default_scheme():
 
 def get_makefile_filename():
     """Return the path of the Makefile."""
+
+    # GH-127429: When cross-compiling, use the Makefile from the target, instead of the host Python.
+    if cross_base := os.environ.get('_PYTHON_PROJECT_BASE'):
+        return os.path.join(cross_base, 'Makefile')
+
     if _PYTHON_BUILD:
         return os.path.join(_PROJECT_BASE, "Makefile")
+
     if hasattr(sys, 'abiflags'):
         config_dir_name = f'config-{_PY_VERSION_SHORT}{sys.abiflags}'
     else:
         config_dir_name = 'config'
+
     if hasattr(sys.implementation, '_multiarch'):
         config_dir_name += f'-{sys.implementation._multiarch}'
+
     return os.path.join(get_path('stdlib'), config_dir_name, 'Makefile')
 
 
@@ -468,29 +478,47 @@ def get_path(name, scheme=get_default_scheme(), vars=None, expand=True):
 def _init_config_vars():
     global _CONFIG_VARS
     _CONFIG_VARS = {}
+
+    prefix = _PREFIX
+    exec_prefix = _EXEC_PREFIX
+    base_prefix = _BASE_PREFIX
+    base_exec_prefix = _BASE_EXEC_PREFIX
+
+    try:
+        abiflags = sys.abiflags
+    except AttributeError:
+        abiflags = ''
+
+    if os.name == 'posix':
+        _init_posix(_CONFIG_VARS)
+        # If we are cross-compiling, load the prefixes from the Makefile instead.
+        if '_PYTHON_PROJECT_BASE' in os.environ:
+            prefix = _CONFIG_VARS['prefix']
+            exec_prefix = _CONFIG_VARS['exec_prefix']
+            base_prefix = _CONFIG_VARS['prefix']
+            base_exec_prefix = _CONFIG_VARS['exec_prefix']
+            abiflags = _CONFIG_VARS['ABIFLAGS']
+
     # Normalized versions of prefix and exec_prefix are handy to have;
     # in fact, these are the standard versions used most places in the
     # Distutils.
+
     _PREFIX = os.path.normpath(sys.prefix)
     _EXEC_PREFIX = os.path.normpath(sys.exec_prefix)
-    _CONFIG_VARS['prefix'] = _PREFIX  # FIXME: This gets overwriten by _init_posix.
-    _CONFIG_VARS['exec_prefix'] = _EXEC_PREFIX  # FIXME: This gets overwriten by _init_posix.
+    _CONFIG_VARS['prefix'] = prefix
+    _CONFIG_VARS['exec_prefix'] = exec_prefix
     _CONFIG_VARS['py_version'] = _PY_VERSION
     _CONFIG_VARS['py_version_short'] = _PY_VERSION_SHORT
     _CONFIG_VARS['py_version_nodot'] = _PY_VERSION_SHORT_NO_DOT
-    _CONFIG_VARS['installed_base'] = _BASE_PREFIX
-    _CONFIG_VARS['base'] = _PREFIX
-    _CONFIG_VARS['installed_platbase'] = _BASE_EXEC_PREFIX
-    _CONFIG_VARS['platbase'] = _EXEC_PREFIX
+    _CONFIG_VARS['installed_base'] = base_prefix
+    _CONFIG_VARS['base'] = prefix
+    _CONFIG_VARS['installed_platbase'] = base_exec_prefix
+    _CONFIG_VARS['platbase'] = exec_prefix
     _CONFIG_VARS['projectbase'] = _PROJECT_BASE
     _CONFIG_VARS['platlibdir'] = sys.platlibdir
     _CONFIG_VARS['implementation'] = _get_implementation()
     _CONFIG_VARS['implementation_lower'] = _get_implementation().lower()
-    try:
-        _CONFIG_VARS['abiflags'] = sys.abiflags
-    except AttributeError:
-        # sys.abiflags may not be defined on all platforms.
-        _CONFIG_VARS['abiflags'] = ''
+    _CONFIG_VARS['abiflags'] = abiflags
     try:
         _CONFIG_VARS['py_version_nodot_plat'] = sys.winver.replace('.', '')
     except AttributeError:
@@ -499,8 +527,6 @@ def _init_config_vars():
     if os.name == 'nt':
         _init_non_posix(_CONFIG_VARS)
         _CONFIG_VARS['VPATH'] = sys._vpath
-    if os.name == 'posix':
-        _init_posix(_CONFIG_VARS)
     if _HAS_USER_BASE:
         # Setting 'userbase' is done below the call to the
         # init function to enable using 'get_config_var' in

Lib/sysconfig/__main__.py

@@ -5,6 +5,7 @@
     _PYTHON_BUILD,
     _get_sysconfigdata_name,
     get_config_h_filename,
+    get_config_var,
     get_config_vars,
     get_default_scheme,
     get_makefile_filename,
@@ -204,7 +205,7 @@ def _generate_posix_vars():
         sys.modules[name] = module
 
     pybuilddir = f'build/lib.{get_platform()}-{get_python_version()}'
-    if hasattr(sys, "gettotalrefcount"):
+    if get_config_var('Py_DEBUG') == '1':
         pybuilddir += '-pydebug'
     os.makedirs(pybuilddir, exist_ok=True)
     destfile = os.path.join(pybuilddir, name + '.py')
@@ -215,6 +216,8 @@ def _generate_posix_vars():
         f.write('build_time_vars = ')
         _print_config_dict(vars, stream=f)
 
+    print(f'Written {destfile}')
+
     # Create file used for sys.path fixup -- see Modules/getpath.c
     with open('pybuilddir.txt', 'w', encoding='utf8') as f:
         f.write(pybuilddir)

Misc/NEWS.d/next/Library/2024-11-29-23-02-43.gh-issue-127429.dQf2w4.rst

@@ -0,0 +1,3 @@
+Fixed bug where, on cross-builds, the :mod:`sysconfig` POSIX data was being
+generated with the host Python's ``Makefile``. The data is now generated from
+current build's ``Makefile``.

configure

@@ -1614,8 +1614,8 @@ if test "$cross_compiling" = yes; then
   RUNSHARED=
 fi
 
+# HOSTRUNNER - Program to run CPython for the host platform
 AC_MSG_CHECKING([HOSTRUNNER])
-AC_ARG_VAR([HOSTRUNNER], [Program to run CPython for the host platform])
 if test -z "$HOSTRUNNER"
 then
   AS_CASE([$ac_sys_system/$ac_sys_emscripten_target],