cpukit/libdl: Fix loading symbols from an object file at runtime

- Assume a relocation record with a symbol name with a length of
  0 is resolved. ARM seems to create a symbol with no name for
  R_ARM_V4BX relocation records.

- Move the addition of the rtems_rtl_base_sym_global_add symbol
  to the global symbol table to the weak
  rtems_rtl_base_global_syms_init call. If symbols are
  embedded the support for runtime loading symbols is over
  loaded. This change is required so the base object has a
  valid global symbol table attached to track dependencies.

Fixes #5234

cpukit/include/rtems/rtl/rtl-obj.h

@@ -374,7 +374,7 @@ static inline size_t rtems_rtl_obj_align (size_t   offset,
 }
 
 /**
- * Is the symbol in this object's files globa symbol table?
+ * Is the symbol in this object's files global symbol table?
  *
  * @param obj The object file's descriptor to search.
  * @param sym The symbol to check.

cpukit/include/rtems/rtl/rtl-sym.h

@@ -97,6 +97,15 @@ bool rtems_rtl_symbol_table_open (rtems_rtl_symbols* symbols,
  */
 void rtems_rtl_symbol_table_close (rtems_rtl_symbols* symbols);
 
+/**
+ * Insert a symbol into a symbol table.
+ *
+ * @param symbols Symbol table
+ * @param symbols Symbol to add
+ */
+void rtems_rtl_symbol_global_insert (rtems_rtl_symbols* symbols,
+                                     rtems_rtl_obj_sym* symbol);
+
 /**
  * Add a table of exported symbols to the symbol table.
  *

cpukit/libdl/rtl-elf.c

@@ -557,6 +557,8 @@ rtems_rtl_elf_relocate_worker (rtems_rtl_obj*              obj,
       resolved = rtems_rtl_elf_find_symbol (obj,
                                             &sym, symname,
                                             &symbol, &symvalue);
+    if (symname != NULL && strlen(symname) == 0)
+      resolved = true;
 
     if (!handler (obj,
                   is_rela, relbuf, targetsect,

cpukit/libdl/rtl-sym.c

@@ -48,16 +48,6 @@
 #include <rtems/rtl/rtl-sym.h>
 #include <rtems/rtl/rtl-trace.h>
 
-/**
- * The single symbol forced into the global symbol table that is used to load a
- * symbol table from an object file.
- */
-static rtems_rtl_obj_sym global_sym_add =
-{
-  .name  = "rtems_rtl_base_sym_global_add",
-  .value = (void*) rtems_rtl_base_sym_global_add
-};
-
 static uint_fast32_t
 rtems_rtl_symbol_hash (const char *s)
 {
@@ -68,15 +58,6 @@ rtems_rtl_symbol_hash (const char *s)
   return h & 0xffffffff;
 }
 
-static void
-rtems_rtl_symbol_global_insert (rtems_rtl_symbols* symbols,
-                                rtems_rtl_obj_sym* symbol)
-{
-  uint_fast32_t hash = rtems_rtl_symbol_hash (symbol->name);
-  rtems_chain_append (&symbols->buckets[hash % symbols->nbuckets],
-                      &symbol->node);
-}
-
 static const rtems_rtl_tls_offset*
 rtems_rtl_symbol_find_tls_offset (size_t                      index,
                                   const rtems_rtl_tls_offset* tls_offsets,
@@ -108,7 +89,6 @@ rtems_rtl_symbol_table_open (rtems_rtl_symbols* symbols,
   symbols->nbuckets = buckets;
   for (buckets = 0; buckets < symbols->nbuckets; ++buckets)
     rtems_chain_initialize_empty (&symbols->buckets[buckets]);
-  rtems_rtl_symbol_global_insert (symbols, &global_sym_add);
   return true;
 }
 
@@ -118,6 +98,15 @@ rtems_rtl_symbol_table_close (rtems_rtl_symbols* symbols)
   rtems_rtl_alloc_del (RTEMS_RTL_ALLOC_SYMBOL, symbols->buckets);
 }
 
+void
+rtems_rtl_symbol_global_insert (rtems_rtl_symbols* symbols,
+                                rtems_rtl_obj_sym* symbol)
+{
+  uint_fast32_t hash = rtems_rtl_symbol_hash (symbol->name);
+  rtems_chain_append (&symbols->buckets[hash % symbols->nbuckets],
+                      &symbol->node);
+}
+
 bool
 rtems_rtl_symbol_global_add (rtems_rtl_obj*              obj,
                              const unsigned char*        esyms,

cpukit/libdl/rtl-unresolved.c

@@ -562,10 +562,18 @@ rtems_rtl_unresolved_add (rtems_rtl_obj*        obj,
   rtems_rtl_unresolv_block* block;
   rtems_rtl_unresolv_rec*   rec;
   int                       name_index;
+  const int                 name_len = (int) strlen(name);
 
   if (rtems_rtl_trace (RTEMS_RTL_TRACE_UNRESOLVED))
-    printf ("rtl: unresolv: add: %s(s:%d) -> %s\n",
-            rtems_rtl_obj_oname (obj), sect, name);
+    printf ("rtl: unresolv: add: %s(s:%d) -> '%s' (len: %i)\n",
+            rtems_rtl_obj_oname (obj), sect, name, name_len);
+
+  /*
+   * No name or an empty name is not able to resolved?
+   */
+  if (name_len == 0) {
+    return false;
+  }
 
   unresolved = rtems_rtl_unresolved_unprotected ();
   if (!unresolved)

cpukit/libdl/rtl.c

@@ -78,17 +78,47 @@
 static rtems_rtl_data* rtl;
 static bool            rtl_data_init;
 
+/**
+ * The single symbol forced into the global symbol table that is used to load a
+ * symbol table from an object file.
+ */
+static rtems_rtl_obj_sym default_global_syms =
+{
+  .name  = "rtems_rtl_base_sym_global_add",
+  .value = (void*) rtems_rtl_base_sym_global_add
+};
+
 /**
  * Define a default base global symbol loader function that is weak
  * so a real table can be linked in when the user wants one.
+ *
+ * The default init handler add the one symbol used when loading
+ * symbols with an object file. It is an unresolved external in that
+ * object file.
  */
 void rtems_rtl_base_global_syms_init (void) __attribute__ ((weak));
 void
 rtems_rtl_base_global_syms_init (void)
 {
-  /*
-   * Do nothing.
-   */
+  rtems_rtl_symbols* symbols;
+
+  if (rtems_rtl_trace (RTEMS_RTL_TRACE_GLOBAL_SYM))
+    printf ("rtl: adding default global symbol\n");
+
+  if (!rtems_rtl_lock ())
+  {
+    rtems_rtl_set_error (EINVAL, "global add cannot lock rtl");
+    return;
+  }
+
+  symbols = rtems_rtl_global_symbols ();
+
+  rtl->base->global_table = &default_global_syms;
+  rtl->base->global_syms = 1;
+
+  rtems_rtl_symbol_global_insert (symbols, &default_global_syms);
+
+  rtems_rtl_unlock ();
 }
 
 static bool