python
@@ -666,34 +666,34 @@ def get_platform():
 
     # Set for cross builds explicitly
     if "_PYTHON_HOST_PLATFORM" in os.environ:
-        return os.environ["_PYTHON_HOST_PLATFORM"]
-
-    # Try to distinguish various flavours of Unix
-    osname, host, release, version, machine = os.uname()
-
-    # Convert the OS name to lowercase, remove '/' characters, and translate
-    # spaces (for "Power Macintosh")
-    osname = osname.lower().replace('/', '')
-    machine = machine.replace(' ', '_')
-    machine = machine.replace('/', '-')
-
-    if osname[:5] == "linux":
-        if sys.platform == "android":
-            osname = "android"
-            release = get_config_var("ANDROID_API_LEVEL")
-
-            # Wheel tags use the ABI names from Android's own tools.
-            machine = {
-                "x86_64": "x86_64",
-                "i686": "x86",
-                "aarch64": "arm64_v8a",
-                "armv7l": "armeabi_v7a",
-            }[machine]
-        else:
-            # At least on Linux/Intel, 'machine' is the processor --
-            # i386, etc.
-            # XXX what about Alpha, SPARC, etc?
-            return  f"{osname}-{machine}"
+        osname, _, machine = os.environ["_PYTHON_HOST_PLATFORM"].partition('-')
+        release = None
+    else:
+        # Try to distinguish various flavours of Unix
+        osname, host, release, version, machine = os.uname()
+
+        # Convert the OS name to lowercase, remove '/' characters, and translate
+        # spaces (for "Power Macintosh")
+        osname = osname.lower().replace('/', '')
+        machine = machine.replace(' ', '_')
+        machine = machine.replace('/', '-')
+
+    if osname == "android" or sys.platform == "android":
+        osname = "android"
+        release = get_config_var("ANDROID_API_LEVEL")
+
+        # Wheel tags use the ABI names from Android's own tools.
+        machine = {
+            "x86_64": "x86_64",
+            "i686": "x86",
+            "aarch64": "arm64_v8a",
+            "armv7l": "armeabi_v7a",
+        }[machine]
+    elif osname == "linux":
+        # At least on Linux/Intel, 'machine' is the processor --
+        # i386, etc.
+        # XXX what about Alpha, SPARC, etc?
+        return  f"{osname}-{machine}"
     elif osname[:5] == "sunos":
         if release[0] >= "5":           # SunOS 5 == Solaris 2
             osname = "solaris"
@@ -725,7 +725,7 @@ def get_platform():
                                                 get_config_vars(),
                                                 osname, release, machine)
 
-    return f"{osname}-{release}-{machine}"
+    return '-'.join(map(str, filter(None, (osname, release, machine))))
 
 
 def get_python_version():

@@ -0,0 +1,128 @@
+import json
+import os
+import sys
+import sysconfig
+import string
+import unittest
+
+from test.support import is_android, is_apple_mobile, is_emscripten, is_wasi
+
+
+class FormatTestsBase:
+    @property
+    def contents(self):
+        """Install details file contents. Should be overriden by subclasses."""
+        raise NotImplementedError
+
+    @property
+    def data(self):
+        """Parsed install details file data, as a Python object."""
+        return json.loads(self.contents)
+
+    def key(self, name):
+        """Helper to fetch subsection entries.
+
+        It takes the entry name, allowing the usage of a dot to separate the
+        different subsection names (eg. specifying 'a.b.c' as the key will
+        return the value of self.data['a']['b']['c']).
+        """
+        value = self.data
+        for part in name.split('.'):
+            value = value[part]
+        return value
+
+    def test_parse(self):
+        self.data
+
+    def test_top_level_container(self):
+        self.assertIsInstance(self.data, dict)
+        for key, value in self.data.items():
+            with self.subTest(key=key):
+                if key in ('schema_version', 'base_prefix', 'base_interpreter', 'platform'):
+                    self.assertIsInstance(value, str)
+                elif key in ('language', 'implementation', 'abi', 'suffixes', 'libpython', 'c_api', 'arbitrary_data'):
+                    self.assertIsInstance(value, dict)
+
+    def test_base_prefix(self):
+        self.assertIsInstance(self.key('base_prefix'), str)
+
+    def test_base_interpreter(self):
+        """Test the base_interpreter entry.
+
+        The generic test wants the key to be missing. If your implementation
+        provides a value for it, you should override this test.
+        """
+        with self.assertRaises(KeyError):
+            self.key('base_interpreter')
+
+    def test_platform(self):
+        self.assertEqual(self.key('platform'), sysconfig.get_platform())
+
+    def test_language_version(self):
+        allowed_characters = string.digits + string.ascii_letters + '.'
+        value = self.key('language.version')
+
+        self.assertLessEqual(set(value), set(allowed_characters))
+        self.assertTrue(sys.version.startswith(value))
+
+    def test_language_version_info(self):
+        value = self.key('language.version_info')
+
+        self.assertEqual(len(value), sys.version_info.n_fields)
+        for part_name, part_value in value.items():
+            with self.subTest(part=part_name):
+                self.assertEqual(part_value, getattr(sys.version_info, part_name))
+
+    def test_implementation(self):
+        for key, value in self.key('implementation').items():
+            with self.subTest(part=key):
+                if key == 'version':
+                    self.assertEqual(len(value), len(sys.implementation.version))
+                    for part_name, part_value in value.items():
+                        self.assertEqual(getattr(sys.implementation.version, part_name), part_value)
+                else:
+                    self.assertEqual(getattr(sys.implementation, key), value)
+
+
+needs_installed_python = unittest.skipIf(
+    sysconfig.is_python_build(),
+    'This test can only run in an installed Python',
+)
+
+
+@unittest.skipIf(os.name != 'posix', 'Feature only implemented on POSIX right now')
+@unittest.skipIf(is_wasi or is_emscripten, 'Feature not available on WebAssembly builds')
+class CPythonBuildDetailsTests(unittest.TestCase, FormatTestsBase):
+    """Test CPython's install details file implementation."""
+
+    @property
+    def location(self):
+        if sysconfig.is_python_build():
+            projectdir = sysconfig.get_config_var('projectbase')
+            with open(os.path.join(projectdir, 'pybuilddir.txt')) as f:
+                dirname = os.path.join(projectdir, f.read())
+        else:
+            dirname = sysconfig.get_path('stdlib')
+        return os.path.join(dirname, 'build-details.json')
+
+    @property
+    def contents(self):
+        with open(self.location, 'r') as f:
+            return f.read()
+
+    @needs_installed_python
+    def test_location(self):
+        self.assertTrue(os.path.isfile(self.location))
+
+    # Override generic format tests with tests for our specific implemenation.
+
+    @needs_installed_python
+    @unittest.skipIf(is_android or is_apple_mobile, 'Android and iOS run tests via a custom testbed method that changes sys.executable')
+    def test_base_interpreter(self):
+        value = self.key('base_interpreter')
+
+        self.assertEqual(os.path.realpath(value), os.path.realpath(sys.executable))
+
+
+if __name__ == '__main__':
+    unittest.main()
@@ -728,7 +728,7 @@ list-targets:
 
 .PHONY: build_all
 build_all:	check-clean-src check-app-store-compliance $(BUILDPYTHON) platform sharedmods \
-		gdbhooks Programs/_testembed scripts checksharedmods rundsymutil
+		gdbhooks Programs/_testembed scripts checksharedmods rundsymutil build-details.json
 
 .PHONY: build_wasm
 build_wasm: check-clean-src $(BUILDPYTHON) platform sharedmods \
@@ -934,6 +934,9 @@ pybuilddir.txt: $(PYTHON_FOR_BUILD_DEPS)
 		exit 1 ; \
 	fi
 
+build-details.json: pybuilddir.txt
+	$(RUNSHARED) $(PYTHON_FOR_BUILD) $(srcdir)/Tools/build/generate-build-details.py `cat pybuilddir.txt`/build-details.json
+
 # Build static library
 $(LIBRARY): $(LIBRARY_OBJS)
 	-rm -f $@
@@ -2644,6 +2647,7 @@ libinstall:	all $(srcdir)/Modules/xxmodule.c
 	done
 	$(INSTALL_DATA) `cat pybuilddir.txt`/_sysconfigdata_$(ABIFLAGS)_$(MACHDEP)_$(MULTIARCH).py $(DESTDIR)$(LIBDEST); \
 	$(INSTALL_DATA) `cat pybuilddir.txt`/_sysconfig_vars_$(ABIFLAGS)_$(MACHDEP)_$(MULTIARCH).json $(DESTDIR)$(LIBDEST); \
+	$(INSTALL_DATA) `cat pybuilddir.txt`/build-details.json $(DESTDIR)$(LIBDEST); \
 	$(INSTALL_DATA) $(srcdir)/LICENSE $(DESTDIR)$(LIBDEST)/LICENSE.txt
 	@ # If app store compliance has been configured, apply the patch to the
 	@ # installed library code. The patch has been previously validated against

diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2025-02-13-02-39-42.gh-issue-107956.dLguDW.rst b/Misc/NEWS.d/next/Core_and_Builtins/2025-02-13-02-39-42.gh-issue-107956.dLguDW.rst
@@ -0,0 +1,2 @@
+A ``build-details.json`` file is now install in the platform-independent
+standard library directory (:pep:`739` implementation).
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,2 @@
		A ``build-details.json`` file is now install in the platform-independent
		standard library directory (:pep:`739` implementation).