rt: Stop logging on the Rust stack. Closes #1478

Author: brson

src/rt/rust_log.cpp

@@ -106,6 +106,10 @@ rust_log::trace_ln(char *prefix, char *message) {
 void
 rust_log::trace_ln(rust_task *task, uint32_t level, char *message) {
 
+    if (task) {
+        // There is not enough room to be logging on the rust stack
+        assert(!task->on_rust_stack() && "logging on rust stack");
+    }
 
     // FIXME: The scheduler and task names used to have meaning,
     // but they are always equal to 'main' currently

src/rt/rust_task.cpp

@@ -196,7 +196,6 @@ void task_start_wrapper(spawn_args *a)
     if(env) {
         // free the environment (which should be a unique closure).
         const type_desc *td = env->td;
-        LOG(task, task, "Freeing env %p with td %p", env, td);
         td->drop_glue(NULL, NULL, td->first_param, box_body(env));
         upcall_free_shared_type_desc(env->td);
         upcall_shared_free(env);
@@ -720,6 +719,11 @@ Returns true if we're currently running on the Rust stack
  */
 bool
 rust_task::on_rust_stack() {
+    if (stk == NULL) {
+        // This only happens during construction
+        return false;
+    }
+
     uintptr_t sp = get_sp();
     bool in_first_segment = sp_in_stk_seg(sp, stk);
     if (in_first_segment) {