Module assertions: check for garbage collections

It's technically possible to write a user pointer finalizer that calls
into Emacs module functions.  This would be disastrous because it
would allow arbitrary Lisp code to run during garbage collection.
Therefore extend the module assertions to check for this case.

* src/emacs-module.c (module_assert_thread): Also check whether a
garbage collection is in progress.

* test/data/emacs-module/mod-test.c (invalid_finalizer)
(Fmod_test_invalid_finalizer): New test module functions.
(emacs_module_init): Register new test function.

* test/src/emacs-module-tests.el (module--test-assertion)
(module--with-temp-directory): New helper macros.
(module--test-assertions--load-non-live-object): Rename existing
unit test, use helper macros.
(module--test-assertions--call-emacs-from-gc): New unit test.

1 files changed, 4 insertions, 2 deletions

diff --git a/src/emacs-module.c b/src/emacs-module.c
index 7b1a402eeff..b80aa23abce 100644
--- a/src/emacs-module.c
+++ b/src/emacs-module.c
@@ -817,9 +817,11 @@ in_current_thread (void)
 static void
 module_assert_thread (void)
 {
-  if (! module_assertions || in_current_thread ())
+  if (! module_assertions || (in_current_thread () && ! gc_in_progress))
     return;
-  module_abort ("Module function called from outside the current Lisp thread");
+  module_abort (gc_in_progress ?
+                "Module function called during garbage collection" :
+                "Module function called from outside the current Lisp thread");
 }
 
 static void