Copying symbol type in ld script assignments

There is a call to update_definedness between code that evaluates an
assignment expression value and code that transfers symbol
attributes.  When script assignment expressions contain DEFINED, that
can mean the wrong symbol type is copied.  This patch tracks symbols
read during expression evaluation, rather than examining the
expression and re-evaluating conditionals.  Not only does this
simplify the code, it also means ld can now copy symbol types in more
complex expressions.

An unfortunate side effect of copying symbol type for more complex
expressions affects mmix, which uses
 PROVIDE (Main = DEFINED (Main) ? Main : (DEFINED (_start) ? _start : _start.));
in a default script.  So now _start or _start. symbol type may be
copied, losing the function type specially set up for Main.  This can
be avoided by making bfd_copy_link_hash_symbol_type do nothing for
mmix.

bfd/
	* elf64-mmix.c (bfd_elf64_bfd_copy_link_hash_symbol_type): Define.
ld/
	* ldexp.h (struct ldexp_control): Add "assign_src".
	* ldexp.c (fold_trinary): Save and restore assign_src around
	condition evaluation.
	(fold_name <NAME>): Set expld.assign_src.
	(try_copy_symbol_type): Delete.
	(exp_fold_tree_1): Set symbol type using expld.assign_src.

bfd/ChangeLog

@@ -1,3 +1,7 @@
+2017-11-28  Alan Modra  <amodra@gmail.com>
+
+	* elf64-mmix.c (bfd_elf64_bfd_copy_link_hash_symbol_type): Define.
+
 2017-11-28  H.J. Lu  <hongjiu.lu@intel.com>
 
 	PR ld/22502

bfd/elf64-mmix.c

@@ -2908,6 +2908,9 @@ mmix_elf_relax_section (bfd *abfd,
 #define elf_backend_omit_section_dynsym \
   ((bfd_boolean (*) (bfd *, struct bfd_link_info *, asection *)) bfd_true)
 
+#define bfd_elf64_bfd_copy_link_hash_symbol_type \
+  _bfd_generic_copy_link_hash_symbol_type
+
 #define bfd_elf64_bfd_is_local_label_name \
 	mmix_elf_is_local_label_name
 

ld/ChangeLog

@@ -1,3 +1,12 @@
+2017-11-28  Alan Modra  <amodra@gmail.com>
+
+	* ldexp.h (struct ldexp_control): Add "assign_src".
+	* ldexp.c (fold_trinary): Save and restore assign_src around
+	condition evaluation.
+	(fold_name <NAME>): Set expld.assign_src.
+	(try_copy_symbol_type): Delete.
+	(exp_fold_tree_1): Set symbol type using expld.assign_src.
+
 2017-11-28  H.J. Lu  <hongjiu.lu@intel.com>
 
 	PR ld/22502

ld/ldexp.c

@@ -673,7 +673,10 @@ fold_binary (etree_type *tree)
 static void
 fold_trinary (etree_type *tree)
 {
+  struct bfd_link_hash_entry *save = expld.assign_src;
+
   exp_fold_tree_1 (tree->trinary.cond);
+  expld.assign_src = save;
   if (expld.result.valid_p)
     exp_fold_tree_1 (expld.result.value
 		     ? tree->trinary.lhs
@@ -790,6 +793,10 @@ fold_name (etree_type *tree)
 	      if (h->u.undef.next == NULL && h != link_info.hash->undefs_tail)
 		bfd_link_add_undef (link_info.hash, h);
 	    }
+	  if (expld.assign_src == NULL)
+	    expld.assign_src = h;
+	  else
+	    expld.assign_src = (struct bfd_link_hash_entry *) 0 - 1;
 	}
       break;
 
@@ -1001,19 +1008,6 @@ is_align_conditional (const etree_type *tree)
   return FALSE;
 }
 
-/* Subroutine of exp_fold_tree_1 for copying a symbol type.  */
-
-static void
-try_copy_symbol_type (struct bfd_link_hash_entry *h, etree_type *src)
-{
-  struct bfd_link_hash_entry *hsrc;
-
-  hsrc = bfd_link_hash_lookup (link_info.hash, src->name.name,
-			       FALSE, FALSE, TRUE);
-  if (hsrc != NULL)
-    bfd_copy_link_hash_symbol_type (link_info.output_bfd, h, hsrc);
-}
-
 static void
 exp_fold_tree_1 (etree_type *tree)
 {
@@ -1162,6 +1156,7 @@ exp_fold_tree_1 (etree_type *tree)
 	    }
 
 	  expld.assign_name = tree->assign.dst;
+	  expld.assign_src = NULL;
 	  exp_fold_tree_1 (tree->assign.src);
 	  /* expld.assign_name remaining equal to tree->assign.dst
 	     below indicates the evaluation of tree->assign.src did
@@ -1209,27 +1204,15 @@ exp_fold_tree_1 (etree_type *tree)
 	      if (tree->type.node_class == etree_provide)
 		tree->type.node_class = etree_provided;
 
-	      /* Copy the symbol type if this is a simple assignment of
-		 one symbol to another.  Also, handle the case of a foldable
-		 ternary conditional with names on either side.  */
-	      if (tree->assign.src->type.node_class == etree_name)
-		try_copy_symbol_type (h, tree->assign.src);
-	      else if (tree->assign.src->type.node_class == etree_trinary)
-		{
-		  exp_fold_tree_1 (tree->assign.src->trinary.cond);
-		  if (expld.result.valid_p)
-		    {
-		      if (expld.result.value
-			  && tree->assign.src->trinary.lhs->type.node_class
-			     == etree_name)
-			try_copy_symbol_type (h, tree->assign.src->trinary.lhs);
-
-		      if (!expld.result.value
-			  && tree->assign.src->trinary.rhs->type.node_class
-			     == etree_name)
-			try_copy_symbol_type (h, tree->assign.src->trinary.rhs);
-		    }
-		}
+	      /* Copy the symbol type if this is an expression only
+		 referencing a single symbol.  (If the expression
+		 contains ternary conditions, ignoring symbols on
+		 false branches.)  */
+	      if (expld.result.valid_p
+		  && expld.assign_src != NULL
+		  && expld.assign_src != (struct bfd_link_hash_entry *) 0 - 1)
+		bfd_copy_link_hash_symbol_type (link_info.output_bfd, h,
+						expld.assign_src);
 	    }
 	  else if (expld.phase == lang_final_phase_enum)
 	    {

ld/ldexp.h

@@ -163,6 +163,11 @@ struct ldexp_control {
      does the false branch of a trinary expression.  */
   const char *assign_name;
 
+  /* If evaluating an assignment, the source if it is an expression
+     referencing single etree_name NAME, or a trinary expression where
+     the true branch references a single etree_name NAME.  */
+  struct bfd_link_hash_entry *assign_src;
+
   /* Working results.  */
   etree_value_type result;
   bfd_vma dot;