gh-134486: Fix missing alloca symbol in _ctypes on NetBSD.

collinfunk · collinfunk · commit 46b0d9db807d · 2025-05-21T22:13:59.000-07:00
Previously the module would fail to load because the ``alloca`` symbol
was undefined. Now we check for GCC/Clang builtins for systems who do
not define ``alloca`` in headers.
diff --git a/Misc/NEWS.d/next/Build/2025-05-21-22-13-30.gh-issue-134486.yvdL6f.rst b/Misc/NEWS.d/next/Build/2025-05-21-22-13-30.gh-issue-134486.yvdL6f.rst
@@ -0,0 +1,2 @@
+The ``_ctypes`` module now performs a more portable test for the definition
+of ``alloca``.
diff --git a/Modules/_ctypes/callbacks.c b/Modules/_ctypes/callbacks.c
@@ -11,18 +11,9 @@
 #include "pycore_call.h"          // _PyObject_CallNoArgs()
 #include "pycore_runtime.h"       // _Py_ID()
 
-#ifdef MS_WIN32
-#  include <malloc.h>
-#endif
-
 #include <ffi.h>
 #include "ctypes.h"
 
-#ifdef HAVE_ALLOCA_H
-/* AIX needs alloca.h for alloca() */
-#include <alloca.h>
-#endif
-
 /**************************************************************/
 
 static int
diff --git a/Modules/_ctypes/callproc.c b/Modules/_ctypes/callproc.c
@@ -77,16 +77,8 @@ module _ctypes
 #include <mach-o/dyld.h>
 #endif
 
-#ifdef MS_WIN32
-#include <malloc.h>
-#endif
-
 #include <ffi.h>
 #include "ctypes.h"
-#ifdef HAVE_ALLOCA_H
-/* AIX needs alloca.h for alloca() */
-#include <alloca.h>
-#endif
 
 #ifdef _Py_MEMORY_SANITIZER
 #include <sanitizer/msan_interface.h>
diff --git a/Modules/_ctypes/ctypes.h b/Modules/_ctypes/ctypes.h
@@ -1,5 +1,17 @@
-#if defined (__SVR4) && defined (__sun)
+/* Get a definition of alloca. */
+#if (defined (__SVR4) && defined (__sun)) || defined(HAVE_ALLOCA_H)
 #   include <alloca.h>
+#elif defined(MS_WIN32)
+#   include <malloc.h>
+#endif
+
+/* If the system does not define it we have to hope for a compiler builtin. */
+#ifndef alloca
+#   if defined __GNUC__ || (__clang_major__ >= 4)
+#      define alloca __builtin_alloca
+#   else
+#     error "Could not define alloca on your platform."
+#   endif
 #endif
 
 #include <stdbool.h>

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,2 @@`
	`1`	+The ``_ctypes`` module now performs a more portable test for the definition
	`2`	+of ``alloca``.