rts: Refactor foreign export tracking

This avoids calling `libc` in the initializers which are responsible for
registering foreign exports. We believe this should avoid the corruption
observed in #18548.

See Note [Tracking foreign exports] in rts/ForeignExports.c for an
overview of the new scheme.

2 files changed, 39 insertions, 0 deletions

diff --git a/includes/Rts.h b/includes/Rts.h
index 989394b590..589ef8b82c 100644
--- a/includes/Rts.h
+++ b/includes/Rts.h
@@ -212,6 +212,9 @@ void _assertFail(const char *filename, unsigned int linenum)
 #include "rts/storage/GC.h"
 #include "rts/NonMoving.h"
 
+/* Foreign exports */
+#include "rts/ForeignExports.h"
+
 /* Other RTS external APIs */
 #include "rts/Parallel.h"
 #include "rts/Signals.h"
diff --git a/includes/rts/ForeignExports.h b/includes/rts/ForeignExports.h
new file mode 100644
index 0000000000..f8828e59d4
--- /dev/null
+++ b/includes/rts/ForeignExports.h
@@ -0,0 +1,36 @@
+/* -----------------------------------------------------------------------------
+ *
+ * (c) The GHC Team, 1995-2009
+ *
+ * Interface to the RTS's foreign export tracking code.
+ *
+ * Do not #include this file directly: #include "Rts.h" instead.
+ *
+ * To understand the structure of the RTS headers, see the wiki:
+ *   https://gitlab.haskell.org/ghc/ghc/wikis/commentary/source-tree/includes
+ *
+ * ---------------------------------------------------------------------------*/
+
+#pragma once
+
+struct _ObjectCode;
+
+/* N.B. See Note [Tracking foreign exports] in
+ * rts/ForeignExports.c. */
+struct ForeignExportsList {
+      /* a link field for linking these together into lists.
+       */
+    struct ForeignExportsList *next;
+      /* the length of ->exports */
+    int n_entries;
+      /* if the RTS linker loaded the module,
+       * to which ObjectCode these exports belong. */
+    struct _ObjectCode *oc;
+      /* if the RTS linker loaded the module,
+       * this points to an array of length ->n_entries
+       * recording the StablePtr for each export. */
+    StgPtr exports[];
+};
+
+void registerForeignExports(struct ForeignExportsList *exports);
+