When looking for lua shared objects, dynamically adjust the pathnames to
include "64/", when running a 64-bit lua executable.

For example:
  /usr/lib/lua/5.3/gv.so
becomes:
  /usr/lib/lua/5.3/64/gv.so

The lua maintainers are not interested in this patch.

--- lua-5.3.2/src/loadlib.c.~1~	2017-03-10 20:14:16.979286128 +0300
+++ lua-5.3.2/src/loadlib.c	2017-03-10 20:20:03.100208291 +0300
@@ -393,25 +393,92 @@
 }
 
 
+/*
+** Return 1 if template is a shared object (has an extension of ".so"),
+** otherwise 0.
+*/
+static int
+issharedobj(const char *template) {
+  const char *ext;
+  if (strlen(template) < 3)
+    return 0;
+  ext = template + strlen(template) - 3;
+  return strcmp(ext, ".so") == 0;
+}
+
+/*
+** Return 1 if this is a 64-bit executable, otherwise 0.
+*/
+static int is64bit() {
+  return sizeof(void *) == 8;
+}
+
 static const char *searchpath (lua_State *L, const char *name,
                                              const char *path,
                                              const char *sep,
                                              const char *dirsep) {
   luaL_Buffer msg;  /* to build error message */
+  char *name64;
   luaL_buffinit(L, &msg);
   if (*sep != '\0')  /* non-empty separator? */
     name = luaL_gsub(L, name, sep, dirsep);  /* replace it by 'dirsep' */
+  if (is64bit()) {
+    name64 = calloc(strlen(name) + 4, 1);
+    strcpy(name64, "64/");
+    strcat(name64, name);
+  } else
+    name64 = strdup(name);
   while ((path = pushnexttemplate(L, path)) != NULL) {
-    const char *filename = luaL_gsub(L, lua_tostring(L, -1),
-                                     LUA_PATH_MARK, name);
+    char *filename;
+    const char *item = lua_tostring(L, -1);
+
+    if (is64bit() && issharedobj(item)) {
+      name = name64;
+      if (strstr(item, LUA_PATH_MARK))
+        filename = (char *)luaL_gsub(L, item, LUA_PATH_MARK, name);
+      else {
+        /*
+         * There's nothing to substitute, so we have to go digging through the
+         * path to find where to put the 64-bit directory.  Search for "/" in
+         * the template element until we can't find any more, replace that with
+         * "?", and replace that with "/64/".
+         */
+        char *p1, *p2;
+        char *s = strdup(item);
+        for (p1 = s; p1; p1 = strstr(p1 + 1, "/"))
+          p2 = p1;
+        if (p2 != s)
+          *p2 = '?';
+        else {
+          /*
+           * We didn't find any slashes; that either means there aren't any, or
+           * item is in the root directory.
+           */
+          free(s);
+          s = calloc(strlen(item) + 3, 1);
+          if (item[0] == '/')
+            strcpy(s, "/64");
+          else
+            strcpy(s, "64/");
+          strcat(s, item);
+        }
+        filename = (char *)luaL_gsub(L, s, LUA_PATH_MARK, "/64/");
+        free(s);
+      }
+    } else
+      filename = (char *)luaL_gsub(L, item, LUA_PATH_MARK, name);
+
     lua_remove(L, -2);  /* remove path template */
-    if (readable(filename))  /* does file exist and is readable? */
+    if (readable(filename)) {  /* does file exist and is readable? */
+      free(name64);
       return filename;  /* return that file name */
+    }
     lua_pushfstring(L, "\n\tno file '%s'", filename);
     lua_remove(L, -2);  /* remove file name */
     luaL_addvalue(&msg);  /* concatenate error msg. entry */
   }
   luaL_pushresult(&msg);  /* create error message */
+  free(name64);
   return NULL;  /* not found */
 }