Python 3.10 has made it mandatory that the 'string+length` formats use ssize_t
instead of int, so define the magic symbol and upcast the ints from the libfdt
API to ssize_t.

Upstream-Status: Pending
Signed-off-by: Ross Burton <ross.burton@arm.com>

diff --git a/pylibfdt/libfdt.i b/pylibfdt/libfdt.i
index 51ee801..075ef70 100644
--- a/pylibfdt/libfdt.i
+++ b/pylibfdt/libfdt.i
@@ -1044,9 +1044,9 @@ typedef uint32_t fdt32_t;
 		$result = Py_None;
 	else
         %#if PY_VERSION_HEX >= 0x03000000
-            $result = Py_BuildValue("y#", $1, *arg4);
+            $result = Py_BuildValue("y#", $1, (Py_ssize_t)*arg4);
         %#else
-            $result = Py_BuildValue("s#", $1, *arg4);
+            $result = Py_BuildValue("s#", $1, (Py_ssize_t)*arg4);
         %#endif
 }
 
diff --git a/pylibfdt/setup.py b/pylibfdt/setup.py
index ef40f15..88ff7d1 100755
--- a/pylibfdt/setup.py
+++ b/pylibfdt/setup.py
@@ -42,6 +42,7 @@ def get_version():
 libfdt_module = Extension(
     '_libfdt',
     sources=[os.path.join(srcdir, 'libfdt.i')],
+    define_macros=[('PY_SSIZE_T_CLEAN', None)],
     include_dirs=[os.path.join(srcdir, '../libfdt')],
     libraries=['fdt'],
     library_dirs=[os.path.join(top_builddir, 'libfdt')],