Ensure that vm_stack is cleared in `thread_cleanup_func_before_exec`.

If `vm_stack` is left dangling in a forked process, the gc attempts to scan
it, but it is invalid and will cause a segfault. Therefore, we clear it
before forking.

In order to simplify this, `rb_ec_clear_vm_stack` was introduced.

1 files changed, 4 insertions, 0 deletions

diff --git a/vm_core.h b/vm_core.h
index 99dee425ab..4993ef83ed 100644
--- a/vm_core.h
+++ b/vm_core.h
@@ -907,6 +907,10 @@ void rb_ec_set_vm_stack(rb_execution_context_t *ec, VALUE *stack, size_t size);
 // @param size the size of the stack, as in `VALUE stack[size]`.
 void rb_ec_initialize_vm_stack(rb_execution_context_t *ec, VALUE *stack, size_t size);
 
+// Clear (set to `NULL`) the vm_stack pointer.
+// @param ec the execution context to update.
+void rb_ec_clear_vm_stack(rb_execution_context_t *ec);
+
 typedef struct rb_thread_struct {
     struct list_node vmlt_node;
     VALUE self;