From b6a27c3a28839bd5ef549a087baa1beb02149d8e Mon Sep 17 00:00:00 2001
From: Alasdair Allan <alasdair.allan@gmail.com>
Date: Thu, 7 May 2026 14:37:24 +0100
Subject: [PATCH] Fix BaseException escape from host callback trampoline (#336)

The host-callback trampoline in `wasmtime/_func.py` caught `Exception`,
which let `BaseException` subclasses (`KeyboardInterrupt`, `SystemExit`,
custom `BaseException` subclasses) escape into the Rust array_call
trampoline with an undefined `c_void_p` return value, causing a libmalloc
SIGABRT inside `HostFunc::array_call_trampoline`.

Broadens the catch to `BaseException`. The existing `LAST_EXCEPTION` /
`Trap("python exception")` machinery handles propagation back to the
Python caller unchanged.

Adds regression tests for `KeyboardInterrupt`, `SystemExit`, and a
custom `BaseException` subclass raised from host callbacks.

Fixes #336
---
 tests/test_func.py | 33 +++++++++++++++++++++++++++++++++
 wasmtime/_func.py  |  2 +-
 2 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/tests/test_func.py b/tests/test_func.py
index 00be6c3f..ef7ddb8e 100644
--- a/tests/test_func.py
+++ b/tests/test_func.py
@@ -85,6 +85,39 @@ def do_raise():
         with self.assertRaises(Exception, msg="hello"):
             func(store)
 
+    def test_host_base_exception(self):
+        # Regression test for #336: a BaseException subclass raised from a
+        # host callback (KeyboardInterrupt, SystemExit, custom BaseException
+        # subclasses) used to escape the trampoline's `except Exception`
+        # handler and abort the process inside Rust's array_call_trampoline
+        # with a libmalloc SIGABRT. It must propagate cleanly to the caller.
+        store = Store()
+        ty = FuncType([], [])
+
+        def raise_keyboard_interrupt():
+            raise KeyboardInterrupt
+
+        func = Func(store, ty, raise_keyboard_interrupt)
+        with self.assertRaises(KeyboardInterrupt):
+            func(store)
+
+        def raise_system_exit():
+            raise SystemExit(0)
+
+        func = Func(store, ty, raise_system_exit)
+        with self.assertRaises(SystemExit):
+            func(store)
+
+        class CustomBaseException(BaseException):
+            pass
+
+        def raise_custom():
+            raise CustomBaseException("custom")
+
+        func = Func(store, ty, raise_custom)
+        with self.assertRaises(CustomBaseException):
+            func(store)
+
     def test_type(self):
         store = Store()
         i32 = ValType.i32()
diff --git a/wasmtime/_func.py b/wasmtime/_func.py
index ccfdbf3c..64623aa4 100644
--- a/wasmtime/_func.py
+++ b/wasmtime/_func.py
@@ -209,7 +209,7 @@ def trampoline(idx, caller, params, nparams, results, nresults):  # type: ignore
             for i, result in enumerate(pyresults):
                 results[i] = Val._convert_to_raw(caller, result_tys[i], result)
         return 0
-    except Exception as e:
+    except BaseException as e:
         global LAST_EXCEPTION
         LAST_EXCEPTION = e
         trap = Trap("python exception")._consume()