Fix linker_unload now that we are running constructors in the linker …

…(#8291)

See also #5435.

Now we have to remember the the StablePtrs that get created by the
module initializer so that we can free them again in unloadObj().

compiler/deSugar/DsForeign.lhs

@@ -676,7 +676,7 @@ foreignExportInitialiser hs_fn =
     [ text "static void stginit_export_" <> ppr hs_fn
          <> text "() __attribute__((constructor));"
     , text "static void stginit_export_" <> ppr hs_fn <> text "()"
-    , braces (text "getStablePtr"
+    , braces (text "foreignExportStablePtr"
        <> parens (text "(StgPtr) &" <> ppr hs_fn <> text "_closure")
        <> semi)
     ]

includes/rts/Linker.h

@@ -49,4 +49,7 @@ HsInt resolveObjs( void );
 /* load a dynamic library */
 const char *addDLL( pathchar* dll_name );
 
+/* called by the initialization code for a module, not a user API */
+StgStablePtr foreignExportStablePtr (StgPtr p);
+
 #endif /* RTS_LINKER_H */

rts/Linker.c

@@ -1116,6 +1116,7 @@ typedef struct _RtsSymbolVal {
       SymI_HasProto(getProgArgv)                                        \
       SymI_HasProto(getFullProgArgv)                                    \
       SymI_HasProto(getStablePtr)                                       \
+      SymI_HasProto(foreignExportStablePtr)                             \
       SymI_HasProto(hs_init)                                            \
       SymI_HasProto(hs_exit)                                            \
       SymI_HasProto(hs_set_argv)                                        \
@@ -1947,6 +1948,37 @@ lookupSymbol( char *lbl )
     }
 }
 
+/* -----------------------------------------------------------------------------
+   Create a StablePtr for a foeign export.  This is normally called by
+   a C function with __attribute__((constructor)), which is generated
+   by GHC and linked into the module.
+
+   If the object code is being loaded dynamically, then we remember
+   which StablePtrs were allocated by the constructors and free them
+   again in unloadObj().
+   -------------------------------------------------------------------------- */
+
+static ObjectCode *loading_obj = NULL;
+
+StgStablePtr foreignExportStablePtr (StgPtr p)
+{
+    ForeignExportStablePtr *fe_sptr;
+    StgStablePtr *sptr;
+
+    sptr = getStablePtr(p);
+
+    if (loading_obj != NULL) {
+        fe_sptr = stgMallocBytes(sizeof(ForeignExportStablePtr),
+                                 "foreignExportStablePtr");
+        fe_sptr->stable_ptr = sptr;
+        fe_sptr->next = loading_obj->stable_ptrs;
+        loading_obj->stable_ptrs = fe_sptr;
+    }
+
+    return sptr;
+}
+
+
 /* -----------------------------------------------------------------------------
  * Debugging aid: look in GHCi's object symbol tables for symbols
  * within DELTA bytes of the specified address, and show their names.
@@ -2143,6 +2175,7 @@ mkOc( pathchar *path, char *image, int imageSize,
    oc->symbols           = NULL;
    oc->sections          = NULL;
    oc->proddables        = NULL;
+   oc->stable_ptrs       = NULL;
 
 #ifndef USE_MMAP
 #ifdef darwin_HOST_OS
@@ -2786,6 +2819,8 @@ resolveObjs( void )
             if (!r) { return r; }
 
             // run init/init_array/ctors/mod_init_func
+
+            loading_obj = oc; // tells foreignExportStablePtr what to do
 #if defined(OBJFORMAT_ELF)
             r = ocRunInit_ELF ( oc );
 #elif defined(OBJFORMAT_PEi386)
@@ -2795,6 +2830,8 @@ resolveObjs( void )
 #else
             barf("resolveObjs: initializers not implemented on this platform");
 #endif
+            loading_obj = NULL;
+
             if (!r) { return r; }
 
             oc->status = OBJECT_RESOLVED;
@@ -2863,6 +2900,18 @@ unloadObj( pathchar *path )
 
             freeProddableBlocks(oc);
 
+            // Release any StablePtrs that were created when this
+            // object module was initialized.
+            {
+                ForeignExportStablePtr *fe_ptr, *next;
+
+                for (fe_ptr = oc->stable_ptrs; fe_ptr != NULL; fe_ptr = next) {
+                    next = fe_ptr->next;
+                    freeStablePtr(fe_ptr->stable_ptr);
+                    stgFree(fe_ptr);
+                }
+            }
+
             oc->status = OBJECT_UNLOADED;
 
             /* This could be a member of an archive so continue

rts/LinkerInternals.h

@@ -44,6 +44,17 @@ typedef
    }
    ProddableBlock;
 
+/*
+ * We must keep track of the StablePtrs that are created for foreign
+ * exports by constructor functions when the module is loaded, so that
+ * we can free them again when the module is unloaded.  If we don't do
+ * this, then the StablePtr will keep the module alive indefinitely.
+ */
+typedef struct ForeignExportStablePtr_ {
+    StgStablePtr stable_ptr;
+    struct ForeignExportStablePtr_ *next;
+} ForeignExportStablePtr;
+
 /* Jump Islands are sniplets of machine code required for relative
  * address relocations on the PowerPC, x86_64 and ARM.
  */
@@ -120,6 +131,8 @@ typedef struct _ObjectCode {
     unsigned long   n_symbol_extras;
 #endif
 
+    ForeignExportStablePtr *stable_ptrs;
+
 } ObjectCode;
 
 #define OC_INFORMATIVE_FILENAME(OC)             \