Fix FirstDLOpenedLinkMap for case libgc not 1st dynamically linked (NetBSD)

Current GC_FirstDLOpenedLinkMap() for NetBSD calls dlinfo(RTLD_SELF,
RTLD_DI_LINKMAP, &lm) to find link_map. So it will find link_map of
libgc.  With guile's case, libgc is link to libguile and libguile is
linked to the guile command, so libgc is not the first one in the
link_map chain.  That is why, data section of libguile, where
scm_protects exists, is not added to GC root and GC_is_visible fails.

* dyn_load.c (GC_FirstDLOpenedLinkMap): Iterate over link_map
(provided by dlinfo(RTLD_SELF)) to return 2nd element instead of the
provided one which might not always belong to libgc (only for NETBSD
and defined RTLD_DI_LINKMAP).

1 files changed, 9 insertions, 2 deletions

diff --git a/dyn_load.c b/dyn_load.c
index 2c866cd2..3b907185 100644
--- a/dyn_load.c
+++ b/dyn_load.c
@@ -687,8 +687,15 @@ GC_FirstDLOpenedLinkMap(void)
     if( cachedResult == 0 ) {
 #     if defined(NETBSD) && defined(RTLD_DI_LINKMAP)
         struct link_map *lm = NULL;
-        if (!dlinfo(RTLD_SELF, RTLD_DI_LINKMAP, &lm))
-            cachedResult = lm;
+        if (!dlinfo(RTLD_SELF, RTLD_DI_LINKMAP, &lm) && lm != NULL) {
+            /* Now lm points link_map object of libgc.  Since it    */
+            /* might not be the first dynamically linked object,    */
+            /* try to find it (object next to the main object).     */
+            while (lm->l_prev != NULL) {
+                lm = lm->l_prev;
+            }
+            cachedResult = lm->l_next;
+        }
 #     else
         int tag;
         for( dp = _DYNAMIC; (tag = dp->d_tag) != 0; dp++ ) {