[RTS] Add getObjectLoadStatus

This adds a function to the RTS linker API which lets the
user check the status of dynamically linked objects.

It was initially proposed by @afarmer in D2068.
It's useful for testing the linker and also for detecting retention
problems in production.

It takes a path, because it's easier to use path as key instead of producing
some stable handle.

It returns an enum instead of bool, because I see no reason for destroying
information. All the complexity is already out in the open, so there's
nothing to save the users from.

Test Plan: ./validate

Reviewers: simonmar, Phyx, bgamari, austin, erikd

Reviewed By: Phyx, bgamari

Subscribers: rwbarton, afarmer, thomie

Differential Revision: https://phabricator.haskell.org/D3963

1 files changed, 14 insertions, 0 deletions

diff --git a/includes/rts/Linker.h b/includes/rts/Linker.h
index 793195b3ab..298dc6a366 100644
--- a/includes/rts/Linker.h
+++ b/includes/rts/Linker.h
@@ -47,6 +47,20 @@ HsInt insertSymbol(pathchar* obj_name, char* key, void* data);
 /* lookup a symbol in the hash table */
 void *lookupSymbol( char *lbl );
 
+/* See Linker.c Note [runtime-linker-phases] */
+typedef enum {
+    OBJECT_LOADED,
+    OBJECT_NEEDED,
+    OBJECT_RESOLVED,
+    OBJECT_UNLOADED,
+    OBJECT_DONT_RESOLVE,
+    OBJECT_NOT_LOADED     /* The object was either never loaded or has been
+                             fully unloaded */
+} OStatus;
+
+/* check object load status */
+OStatus getObjectLoadStatus( pathchar *path );
+
 /* delete an object from the pool */
 HsInt unloadObj( pathchar *path );