Re: PATCH: PR ld/14323: Linker fails to handle weak alias with __start_SECNAME symbol

[Alan Modra <amodra at gmail dot com>]

Since a binary search may return a match on any of a series of
matching entries, I think we've always had a problem matching up
symbol aliases.  Given a weak and global alias, with the weak symbol
already strongly defined, we'd get both symbols in sorted_sym_hash.
Then fail to find the global if it was first in the qsort output and
the binary search happened to land on the second of the two symbols.

This patch cures that problem and pr14323 too.  I've made a few other
tweaks that might make the code a little faster.

HJ, please commit the modified version of your testcase that fails
without this patch.

	PR ld/14323
	* elflink.c (elf_sort_symbol): Sort by size too.
	(elf_link_add_object_symbols <weakdefs>): Simplify binary search.
	Do not depend on ordering of symbol aliases.  Match largest size.

Index: bfd/elflink.c
===================================================================
RCS file: /cvs/src/src/bfd/elflink.c,v
retrieving revision 1.449
diff -u -p -r1.449 elflink.c
--- bfd/elflink.c	3 Jul 2012 14:44:34 -0000	1.449
+++ bfd/elflink.c	9 Jul 2012 07:21:45 -0000
@@ -3145,7 +3145,7 @@ on_needed_list (const char *soname, stru
   return FALSE;
 }
 
-/* Sort symbol by value and section.  */
+/* Sort symbol by value, section, and size.  */
 static int
 elf_sort_symbol (const void *arg1, const void *arg2)
 {
@@ -3164,7 +3164,8 @@ elf_sort_symbol (const void *arg1, const
       if (sdiff != 0)
 	return sdiff > 0 ? 1 : -1;
     }
-  return 0;
+  vdiff = h1->size - h2->size;
+  return vdiff == 0 ? 0 : vdiff > 0 ? 1 : -1;
 }
 
 /* This function is used to adjust offsets into .dynstr for
@@ -4726,7 +4727,6 @@ error_free_dyn:
 	  struct elf_link_hash_entry *hlook;
 	  asection *slook;
 	  bfd_vma vlook;
-	  long ilook;
 	  size_t i, j, idx;
 
 	  hlook = weaks;
@@ -4740,14 +4740,13 @@ error_free_dyn:
 	  slook = hlook->root.u.def.section;
 	  vlook = hlook->root.u.def.value;
 
-	  ilook = -1;
 	  i = 0;
 	  j = sym_count;
-	  while (i < j)
+	  while (i != j)
 	    {
 	      bfd_signed_vma vdiff;
 	      idx = (i + j) / 2;
-	      h = sorted_sym_hash [idx];
+	      h = sorted_sym_hash[idx];
 	      vdiff = vlook - h->root.u.def.value;
 	      if (vdiff < 0)
 		j = idx;
@@ -4761,24 +4760,36 @@ error_free_dyn:
 		  else if (sdiff > 0)
 		    i = idx + 1;
 		  else
-		    {
-		      ilook = idx;
-		      break;
-		    }
+		    break;
 		}
 	    }
 
 	  /* We didn't find a value/section match.  */
-	  if (ilook == -1)
+	  if (i == j)
 	    continue;
 
-	  for (i = ilook; i < sym_count; i++)
+	  /* With multiple aliases, or when the weak symbol is already
+	     strongly defined, we have multiple matching symbols and
+	     the binary search above may land on any of them.  Step
+	     one past the matching symbol(s).  */
+	  while (++idx != j)
+	    {
+	      h = sorted_sym_hash[idx];
+	      if (h->root.u.def.section != slook
+		  || h->root.u.def.value != vlook)
+		break;
+	    }
+
+	  /* Now look back over the aliases.  Since we sorted by size
+	     as well as value and section, we'll choose the one with
+	     the largest size.  */
+	  while (idx-- != i)
 	    {
-	      h = sorted_sym_hash [i];
+	      h = sorted_sym_hash[idx];
 
 	      /* Stop if value or section doesn't match.  */
-	      if (h->root.u.def.value != vlook
-		  || h->root.u.def.section != slook)
+	      if (h->root.u.def.section != slook
+		  || h->root.u.def.value != vlook)
 		break;
 	      else if (h != hlook)
 		{

-- 
Alan Modra
Australia Development Lab, IBM