Add pointer pinning to handle internal pointers. Use jl_active_task_stack. (#217)

This PR adds pinning that handles internal pointers. It also uses
`jl_active_task_stack` for stack scanning instead of `jl_task_stack_buffer`.

Author: qinsoon

mmtk/api/mmtk.h

@@ -49,7 +49,9 @@ extern int mmtk_object_is_managed_by_mmtk(void* addr);
 extern void mmtk_runtime_panic(void);
 extern void mmtk_unreachable(void);
 extern unsigned char mmtk_pin_object(void* obj);
-extern bool mmtk_is_pinned(void* obj);
+extern bool mmtk_is_object_pinned(void* obj);
+extern unsigned char mmtk_pin_pointer(void* ptr);
+extern bool mmtk_is_pointer_pinned(void* ptr);
 extern const char* get_mmtk_version(void);
 
 extern void mmtk_set_vm_space(void* addr, size_t size);

mmtk/src/api.rs

@@ -485,39 +485,131 @@ pub extern "C" fn mmtk_get_obj_size(obj: ObjectReference) -> usize {
     }
 }
 
+#[allow(unused_variables)]
+fn assert_is_object(object: ObjectReference) {
+    // The checks are quite expensive. Dont run it in normal builds.
+    const ASSERT_OBJECT: bool = false;
+    if ASSERT_OBJECT {
+        #[cfg(debug_assertions)]
+        {
+            use crate::object_model::{is_object_in_immixspace, is_object_in_los};
+            if !mmtk_object_is_managed_by_mmtk(object.to_raw_address().as_usize()) {
+                panic!("{} is not managed by MMTk", object);
+            }
+            if !is_object_in_immixspace(&object) && !is_object_in_los(&object) {
+                // We will use VO bit in the following check. But if the object is not in immix space or LOS, we cannot do the check.
+                return;
+            }
+            if !object
+                .to_raw_address()
+                .is_aligned_to(ObjectReference::ALIGNMENT)
+            {
+                panic!(
+                    "{} is not aligned, it cannot be an object reference",
+                    object
+                )
+            }
+            if memory_manager::is_mmtk_object(object.to_raw_address()).is_none() {
+                error!("{} is not an object", object);
+                if let Some(base_ref) = memory_manager::find_object_from_internal_pointer(
+                    object.to_raw_address(),
+                    usize::MAX,
+                ) {
+                    panic!("{} is an internal pointer of {}", object, base_ref);
+                } else {
+                    panic!(
+                        "{} is not recognised as an object reference, or an internal reference",
+                        object
+                    );
+                }
+            }
+        }
+    }
+}
 #[no_mangle]
 pub extern "C" fn mmtk_pin_object(object: ObjectReference) -> bool {
+    assert_is_object(object);
+    crate::early_return_for_non_moving_build!(false);
+    memory_manager::pin_object(object)
+}
+
+#[no_mangle]
+pub extern "C" fn mmtk_unpin_object(object: ObjectReference) -> bool {
+    assert_is_object(object);
+    crate::early_return_for_non_moving_build!(false);
+    memory_manager::unpin_object(object)
+}
+
+#[no_mangle]
+pub extern "C" fn mmtk_is_object_pinned(object: ObjectReference) -> bool {
+    assert_is_object(object);
     crate::early_return_for_non_moving_build!(false);
 
-    // We may in the future replace this with a check for the immix space (bound check), which should be much cheaper.
-    if mmtk_object_is_managed_by_mmtk(object.to_raw_address().as_usize()) {
-        memory_manager::pin_object(object)
+    memory_manager::is_pinned(object)
+}
+
+macro_rules! handle_potential_internal_pointer {
+    ($func: path, $addr: expr) => {{
+        if $addr.is_aligned_to(ObjectReference::ALIGNMENT) {
+            if let Some(obj) = memory_manager::is_mmtk_object($addr) {
+                return $func(obj);
+            }
+        }
+        let maybe_objref = memory_manager::find_object_from_internal_pointer($addr, usize::MAX);
+        if let Some(obj) = maybe_objref {
+            trace!(
+                "Attempt to pin {:?}, but it is an internal reference of {:?}",
+                $addr,
+                obj
+            );
+            $func(obj)
+        } else {
+            warn!(
+                "Attempt to pin {:?}, but it is not recognised as a object",
+                $addr
+            );
+            false
+        }
+    }};
+}
+
+#[no_mangle]
+pub extern "C" fn mmtk_pin_pointer(addr: Address) -> bool {
+    crate::early_return_for_non_moving_build!(false);
+
+    if crate::object_model::is_addr_in_immixspace(addr) {
+        handle_potential_internal_pointer!(memory_manager::pin_object, addr)
     } else {
-        debug!("Object is not managed by mmtk - (un)pinning it via this function isn't supported.");
+        debug!("Object is not in Immix space. MMTk will not move the object. No need to pin the object.");
         false
     }
 }
 
 #[no_mangle]
-pub extern "C" fn mmtk_unpin_object(object: ObjectReference) -> bool {
+pub extern "C" fn mmtk_unpin_pointer(addr: Address) -> bool {
     crate::early_return_for_non_moving_build!(false);
 
-    if mmtk_object_is_managed_by_mmtk(object.to_raw_address().as_usize()) {
-        memory_manager::unpin_object(object)
+    if crate::object_model::is_addr_in_immixspace(addr) {
+        handle_potential_internal_pointer!(memory_manager::unpin_object, addr)
     } else {
-        debug!("Object is not managed by mmtk - (un)pinning it via this function isn't supported.");
+        debug!("Object is not in Immix space. MMTk will not move the object. No need to unpin the object.");
         false
     }
 }
 
 #[no_mangle]
-pub extern "C" fn mmtk_is_pinned(object: ObjectReference) -> bool {
+pub extern "C" fn mmtk_is_pointer_pinned(addr: Address) -> bool {
     crate::early_return_for_non_moving_build!(false);
 
-    if mmtk_object_is_managed_by_mmtk(object.to_raw_address().as_usize()) {
-        memory_manager::is_pinned(object)
+    if crate::object_model::is_addr_in_immixspace(addr) {
+        handle_potential_internal_pointer!(memory_manager::is_pinned, addr)
+    } else if !mmtk_object_is_managed_by_mmtk(addr.as_usize()) {
+        debug!(
+            "Object is not in Immix space. MMTk will not move the object. We assume it is pinned."
+        );
+        true
     } else {
-        debug!("Object is not managed by mmtk - checking via this function isn't supported.");
+        debug!("Object is not managed by mmtk - checking pinning state via this function isn't supported.");
         false
     }
 }

mmtk/src/conservative.rs

@@ -1,4 +1,3 @@
-use crate::jl_task_stack_buffer;
 use crate::julia_types::*;
 use mmtk::memory_manager;
 use mmtk::util::constants::BYTES_IN_ADDRESS;
@@ -41,24 +40,38 @@ pub fn mmtk_conservative_scan_task_stack(ta: *const jl_task_t) {
     crate::early_return_for_non_moving_build!(());
     crate::early_return_for_current_gc!();
 
-    let mut size: u64 = 0;
-    let mut ptid: i32 = 0;
     log::debug!("mmtk_conservative_scan_native_stack begin ta = {:?}", ta);
-    let stk = unsafe { jl_task_stack_buffer(ta, &mut size as *mut _, &mut ptid as *mut _) };
+    let mut active_start = Address::ZERO;
+    let mut active_end = Address::ZERO;
+    let mut total_start = Address::ZERO;
+    let mut total_end = Address::ZERO;
+    unsafe {
+        crate::jl_active_task_stack(
+            ta,
+            &mut active_start as _,
+            &mut active_end as _,
+            &mut total_start as _,
+            &mut total_end as _,
+        )
+    };
     log::debug!(
-        "mmtk_conservative_scan_native_stack continue stk = {}, size = {}, ptid = {:x}",
-        stk,
-        size,
-        ptid
+        "mmtk_conservative_scan_native_stack continue, active = {},{}, total = {},{}",
+        active_start,
+        active_end,
+        total_start,
+        total_end,
     );
-    if !stk.is_zero() {
+
+    let size = active_end - active_start;
+
+    if !active_start.is_zero() {
         log::debug!("Conservatively scan the stack");
         // See jl_guard_size
         // TODO: Are we sure there are always guard pages we need to skip?
         const JL_GUARD_PAGE: usize = 4096 * 8;
-        let guard_page_start = stk + JL_GUARD_PAGE;
-        log::debug!("Skip guard page: {}, {}", stk, guard_page_start);
-        conservative_scan_range(guard_page_start, stk + size as usize);
+        let guard_page_start = active_start + JL_GUARD_PAGE;
+        log::debug!("Skip guard page: {}, {}", active_start, guard_page_start);
+        conservative_scan_range(guard_page_start, active_start + size);
     } else {
         log::warn!("Skip stack for {:?}", ta);
     }

mmtk/src/lib.rs

@@ -121,11 +121,13 @@ extern "C" {
     pub fn jl_gc_get_owner_address_to_mmtk(m: Address) -> Address;
     pub fn jl_gc_genericmemory_how(m: Address) -> usize;
     pub fn jl_gc_get_max_memory() -> usize;
-    pub fn jl_task_stack_buffer(
+    pub fn jl_active_task_stack(
         task: *const crate::julia_types::jl_task_t,
-        size: *mut u64,
-        ptid: *mut i32,
-    ) -> Address;
+        active_start: *mut Address,
+        active_end: *mut Address,
+        total_start: *mut Address,
+        total_end: *mut Address,
+    );
     pub static jl_true: *mut crate::julia_types::jl_value_t;
 }