Okay.

Author: Eclips4

.github/workflows/reusable-san.yml

@@ -52,8 +52,6 @@ jobs:
         else
           sudo ./llvm.sh 20
         fi
-      env:
-        SANITIZER: ${{ inputs.sanitizer }}
 
     - name: Sanitizer option setup
       run: |

Modules/cpython-sys/bindgen-fallback/stdatomic.h

@@ -0,0 +1,44 @@
+/*
+ * Fallback <stdatomic.h> for bindgen.
+ *
+ * Some libclang builds ship a <stdatomic.h> that silently provides no
+ * declarations.  This makes any header that relies on C11 atomics
+ * (e.g. mimalloc) unparseable by bindgen.
+ *
+ * This file provides the standard C11 atomics API with non-atomic stubs.
+ * Bindgen only needs correct type layouts -- it never executes atomic
+ * operations -- so plain loads/stores are sufficient.
+ *
+ * The build script adds this directory via -isystem so it shadows a
+ * broken system header while remaining invisible when the real header
+ * works (libclang picks whichever it finds first on the include path).
+ */
+#ifndef _STDATOMIC_BINDGEN_FALLBACK_H
+#define _STDATOMIC_BINDGEN_FALLBACK_H
+
+/* Strip _Atomic qualifier -- bindgen cares about layout, not atomicity. */
+#define _Atomic(tp)  tp
+
+typedef enum {
+    memory_order_relaxed,
+    memory_order_consume,
+    memory_order_acquire,
+    memory_order_release,
+    memory_order_acq_rel,
+    memory_order_seq_cst
+} memory_order;
+
+#define ATOMIC_VAR_INIT(value)  (value)
+
+#define atomic_load_explicit(p, mo)                              (*(p))
+#define atomic_store_explicit(p, v, mo)                          ((void)(*(p) = (v)))
+#define atomic_fetch_add_explicit(p, v, mo)                      (*(p))
+#define atomic_fetch_sub_explicit(p, v, mo)                      (*(p))
+#define atomic_fetch_or_explicit(p, v, mo)                       (*(p))
+#define atomic_fetch_and_explicit(p, v, mo)                      (*(p))
+#define atomic_compare_exchange_weak_explicit(p, e, d, s, f)     1
+#define atomic_compare_exchange_strong_explicit(p, e, d, s, f)   1
+#define atomic_exchange_explicit(p, v, mo)                       (*(p))
+#define atomic_thread_fence(mo)                                  ((void)0)
+
+#endif /* _STDATOMIC_BINDGEN_FALLBACK_H */

Modules/cpython-sys/build.rs

@@ -150,6 +150,14 @@ fn generate_c_api_bindings(srcdir: &Path, builddir: Option<&str>, out_path: &Pat
     for dir in include_dirs {
         builder = builder.clang_arg(format!("-I{}", dir.display()));
     }
+
+    // Provide a fallback <stdatomic.h> for libclang versions that ship a
+    // broken one (e.g. libclang-18 on Ubuntu 24.04).  Using -isystem places
+    // it after -I paths but before the default system headers, so it only
+    // takes effect when the real <stdatomic.h> is unusable.
+    let fallback_dir = manifest_dir.join("bindgen-fallback");
+    builder = builder.clang_arg(format!("-isystem{}", fallback_dir.display()));
+
     builder = add_target_clang_args(builder, builddir);
 
     let bindings = builder