expose mmtk_get_base_pointer in the binding (#251)

We'll need this for the pinning profiler.

We want to track which object was pinned when we called `ptr_pin` on a
possibly internal pointer.

Author: d-netto

mmtk/api/mmtk.h

@@ -52,6 +52,7 @@ extern void mmtk_unreachable(void);
 extern unsigned char mmtk_pin_object(void* obj);
 extern unsigned char mmtk_unpin_object(void* obj);
 extern bool mmtk_is_object_pinned(void* obj);
+extern void* mmtk_get_base_pointer(void* ptr);
 extern unsigned char mmtk_pin_pointer(void* ptr);
 extern bool mmtk_is_pointer_pinned(void* ptr);
 extern const char* get_mmtk_version(void);

mmtk/src/api.rs

@@ -582,6 +582,14 @@ macro_rules! handle_potential_internal_pointer {
     }};
 }
 
+#[no_mangle]
+pub extern "C" fn mmtk_get_base_pointer(addr: Address) -> Address {
+    if let Some(obj) = memory_manager::find_object_from_internal_pointer(addr, usize::MAX) {
+        return obj.to_raw_address();
+    }
+    Address::ZERO
+}
+
 #[no_mangle]
 pub extern "C" fn mmtk_pin_pointer(addr: Address) -> bool {
     crate::early_return_for_non_moving_build!(false);