Fix for CAF retention when dynamically loading & unloading code

In a situaion where we have some statically-linked code and we want to
load and unload a series of objects, we need the CAFs in the
statically-linked code to be retained indefinitely, while the CAFs in
the dynamically-linked code should be GC'd as normal, so that we can
detect when the code is unloadable.  This was wrong before - we GC'd
CAFs in the static code, leading to a crash in the rare case where we
use a CAF, GC it, and then load a new object that uses it again.

I also did some tidy up: RtsConfig now has a field keep_cafs to
indicate whether we want CAFs to be retained in static code.

2 files changed, 7 insertions, 2 deletions

diff --git a/includes/RtsAPI.h b/includes/RtsAPI.h
index 3b6de0f10c..4748060dee 100644
--- a/includes/RtsAPI.h
+++ b/includes/RtsAPI.h
@@ -73,6 +73,9 @@ typedef struct {
     // True if GHC was not passed -no-hs-main
     HsBool rts_hs_main;
 
+    // Whether to retain CAFs (default: false)
+    HsBool keep_cafs;
+
     // Called before processing command-line flags, so that default
     // settings for RtsFlags can be provided.
     void (* defaultsHook) (void);
diff --git a/includes/rts/storage/GC.h b/includes/rts/storage/GC.h
index 444ef8871b..f7da838739 100644
--- a/includes/rts/storage/GC.h
+++ b/includes/rts/storage/GC.h
@@ -200,11 +200,13 @@ void performMajorGC(void);
    The CAF table - used to let us revert CAFs in GHCi
    -------------------------------------------------------------------------- */
 
-StgInd *newCAF    (StgRegTable *reg, StgIndStatic *caf);
-StgInd *newDynCAF (StgRegTable *reg, StgIndStatic *caf);
+StgInd *newCAF         (StgRegTable *reg, StgIndStatic *caf);
+StgInd *newRetainedCAF (StgRegTable *reg, StgIndStatic *caf);
+StgInd *newGCdCAF      (StgRegTable *reg, StgIndStatic *caf);
 void revertCAFs (void);
 
 // Request that all CAFs are retained indefinitely.
+// (preferably use RtsConfig.keep_cafs instead)
 void setKeepCAFs (void);
 
 /* -----------------------------------------------------------------------------