PowerPC64 PLT vs. mixed objects

PowerPC64 PLT vs. mixed objects

[Alan Modra]

We were generating duplicate PLT entries when the linker was fed a mix
of dot-sym and no-dot-sym objects.  Fixed as follows.

	* elf64-ppc.c (move_plt_plist): New function, extracted from..
	(ppc64_elf_copy_indirect_symbol): ..here.
	(func_desc_adjust): Use move_plt_plist.

Index: bfd/elf64-ppc.c
===================================================================
RCS file: /cvs/src/src/bfd/elf64-ppc.c,v
retrieving revision 1.189
diff -u -p -r1.189 elf64-ppc.c
--- bfd/elf64-ppc.c	6 Feb 2005 10:29:39 -0000	1.189
+++ bfd/elf64-ppc.c	11 Feb 2005 03:32:22 -0000
@@ -3766,6 +3766,41 @@ ppc64_elf_create_dynamic_sections (bfd *
   return TRUE;
 }
 
+/* Move PLT info on FROM and merge with that on TO.  */
+
+static void
+move_plt_plist (struct ppc_link_hash_entry *from,
+		struct ppc_link_hash_entry *to)
+{
+  if (from->elf.plt.plist != NULL)
+    {
+      if (to->elf.plt.plist != NULL)
+	{
+	  struct plt_entry **entp;
+	  struct plt_entry *ent;
+
+	  for (entp = &from->elf.plt.plist; (ent = *entp) != NULL; )
+	    {
+	      struct plt_entry *dent;
+
+	      for (dent = to->elf.plt.plist; dent != NULL; dent = dent->next)
+		if (dent->addend == ent->addend)
+		  {
+		    dent->plt.refcount += ent->plt.refcount;
+		    *entp = ent->next;
+		    break;
+		  }
+	      if (dent == NULL)
+		entp = &ent->next;
+	    }
+	  *entp = to->elf.plt.plist;
+	}
+
+      to->elf.plt.plist = from->elf.plt.plist;
+      from->elf.plt.plist = NULL;
+    }
+}
+
 /* Copy the extra info we tack onto an elf_link_hash_entry.  */
 
 static void
@@ -3868,33 +3903,7 @@ ppc64_elf_copy_indirect_symbol
     }
 
   /* And plt entries.  */
-  if (eind->elf.plt.plist != NULL)
-    {
-      if (edir->elf.plt.plist != NULL)
-	{
-	  struct plt_entry **entp;
-	  struct plt_entry *ent;
-
-	  for (entp = &eind->elf.plt.plist; (ent = *entp) != NULL; )
-	    {
-	      struct plt_entry *dent;
-
-	      for (dent = edir->elf.plt.plist; dent != NULL; dent = dent->next)
-		if (dent->addend == ent->addend)
-		  {
-		    dent->plt.refcount += ent->plt.refcount;
-		    *entp = ent->next;
-		    break;
-		  }
-	      if (dent == NULL)
-		entp = &ent->next;
-	    }
-	  *entp = edir->elf.plt.plist;
-	}
-
-      edir->elf.plt.plist = eind->elf.plt.plist;
-      eind->elf.plt.plist = NULL;
-    }
+  move_plt_plist (eind, edir);
 
   if (edir->elf.dynindx == -1)
     {
@@ -5462,11 +5471,7 @@ func_desc_adjust (struct elf_link_hash_e
       fdh->elf.non_got_ref |= fh->elf.non_got_ref;
       if (ELF_ST_VISIBILITY (fh->elf.other) == STV_DEFAULT)
 	{
-	  struct plt_entry **ep = &fdh->elf.plt.plist;
-	  while (*ep != NULL)
-	    ep = &(*ep)->next;
-	  *ep = fh->elf.plt.plist;
-	  fh->elf.plt.plist = NULL;
+	  move_plt_plist (fh, fdh);
 	  fdh->elf.needs_plt = 1;
 	}
       fdh->is_func_descriptor = 1;

-- 
Alan Modra
IBM OzLabs - Linux Technology Centre

Re: PowerPC64 PLT vs. mixed objects

[Alan Modra]

On Fri, Feb 11, 2005 at 02:16:28PM +1030, Alan Modra wrote:
> We were generating duplicate PLT entries when the linker was fed a mix
> of dot-sym and no-dot-sym objects.

Sigh.  Yet another problem with mixtures of dot-sym and no-dot-sym
object files.  This time it was a bad decision regarding the need for
toc adjusting stubs on calls into a section of an old-style object.
The old-style object in question made plt calls, so needed r2 to be
correct, but the code checking for plt calls ignored all undefined
syms.  With an old-style object making calls to a new-style dynamic lib,
the symbol on the branch reloc will stay undefined.  A bad r2 value
results in a wild call which usually segfaults.

	* elf64-ppc.c (toc_adjusting_stub_needed): Return true for
	old-style branches to undefined dot-symbols which will be
	satisfied by a plt call.

Index: bfd/elf64-ppc.c
===================================================================
RCS file: /cvs/src/src/bfd/elf64-ppc.c,v
retrieving revision 1.190
diff -u -p -r1.190 elf64-ppc.c
--- bfd/elf64-ppc.c	11 Feb 2005 03:47:40 -0000	1.190
+++ bfd/elf64-ppc.c	11 Feb 2005 14:10:16 -0000
@@ -8361,13 +8361,27 @@ toc_adjusting_stub_needed (struct bfd_li
 	  break;
 	}
 
-      /* Ignore branches to undefined syms.  */
+      /* Calls to dynamic lib functions go through a plt call stub
+	 that uses r2.  Branches to undefined symbols might be a call
+	 using old-style dot symbols that can be satisfied by a plt
+	 call into a new-style dynamic library.  */
       if (sym_sec == NULL)
-	continue;
+	{
+	  struct ppc_link_hash_entry *eh = (struct ppc_link_hash_entry *) h;
+	  if (eh != NULL
+	      && eh->oh != NULL
+	      && eh->oh->elf.plt.plist != NULL)
+	    {
+	      ret = 1;
+	      break;
+	    }
 
-      /* Calls to dynamic lib functions go through a plt call stub
-	 that uses r2.  Assume branches to other sections not included
-	 in the link need stubs too, to cover -R and absolute syms.  */
+	  /* Ignore other undefined symbols.  */
+	  continue;
+	}
+
+      /* Assume branches to other sections not included in the link need
+	 stubs too, to cover -R and absolute syms.  */
       if (sym_sec->output_section == NULL)
 	{
 	  ret = 1;
@@ -8389,7 +8403,6 @@ toc_adjusting_stub_needed (struct bfd_li
       opd_adjust = get_opd_info (sym_sec);
       if (opd_adjust != NULL)
 	{
-
 	  if (h == NULL)
 	    {
 	      long adjust;

-- 
Alan Modra
IBM OzLabs - Linux Technology Centre