Add rust_task::gc(size_t args) method that drops us back into the GC glue.

src/rt/rust_crate.cpp

@@ -26,6 +26,11 @@ rust_crate::get_unwind_glue() const {
   return ((uintptr_t)this + unwind_glue_off);
 }
 
+uintptr_t
+rust_crate::get_gc_glue() const {
+  return ((uintptr_t)this + gc_glue_off);
+}
+
 uintptr_t
 rust_crate::get_yield_glue() const {
   return ((uintptr_t)this + yield_glue_off);

src/rt/rust_internal.h

@@ -660,6 +660,9 @@ rust_task : public rc_base<rust_task>,
     // Fail self, assuming caller-on-stack is this task.
     void fail(size_t nargs);
 
+    // Run the gc glue on the task stack.
+    void gc(size_t nargs);
+
     // Notify tasks waiting for us that we are about to die.
     void notify_waiting_tasks();
 

src/rt/rust_task.cpp

@@ -345,6 +345,14 @@ rust_task::fail(size_t nargs) {
     }
 }
 
+void
+rust_task::gc(size_t nargs)
+{
+    dom->log(rust_log::TASK|rust_log::MEM,
+             "task 0x%" PRIxPTR " garbage collecting", this);
+    run_after_return(nargs, dom->root_crate->get_gc_glue());
+}
+
 void
 rust_task::notify_waiting_tasks()
 {