linker issue on ppc64el?

[Alan Modra]

On Wed, Mar 14, 2018 at 09:27:18AM +0100, Matthias Klose wrote:
> Hi Alan,
> 
> would it be possible to have a look at
> https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=886264
> 
> The bug report has an analysis, but no easy reproducer. The binutils 2.30 branch
> is used.

I think I see the problem.

This calculation in relocate_section

	      if (stub_entry->stub_type == ppc_stub_save_res)
		relocation += (stub_sec->output_offset
			       + stub_sec->output_section->vma
			       + stub_sec->size - htab->sfpr->size
			       - htab->sfpr->output_offset
			       - htab->sfpr->output_section->vma);

to adjust from the original out-of-line save/restore function address
in sfpr to a copy at the end of stub_sec goes wrong when stub_sec is
padded, because the copy is no longer at the end of stub_sec.  The
solution is to pad before copying sfpr, so the copy is always at the
end of stub_sec.

	* elf64-ppc.c (sfpr_define): Adjust for stub_sec size having
	sfpr size added before defining alias symbols.
	(ppc64_elf_build_stubs): Add stub section padding before
	copying sfpr contents and defining save/restore alias symbols.

The bug has been lurking since git commit a4b6fadd50, 2015-09-01, but
likely only became evident since git commit 2420fff633, 2017-09-09,
when plt stub alignment was enabled by default.

diff --git a/bfd/elf64-ppc.c b/bfd/elf64-ppc.c
index 44237bc..889bdb0 100644
--- a/bfd/elf64-ppc.c
+++ b/bfd/elf64-ppc.c
@@ -6660,7 +6660,7 @@ sfpr_define (struct bfd_link_info *info,
 		{
 		  s->root.type = bfd_link_hash_defined;
 		  s->root.u.def.section = stub_sec;
-		  s->root.u.def.value = (stub_sec->size
+		  s->root.u.def.value = (stub_sec->size - htab->sfpr->size
 					 + h->elf.root.u.def.value);
 		  s->ref_regular = 1;
 		  s->def_regular = 1;
@@ -13247,20 +13247,7 @@ ppc64_elf_build_stubs (struct bfd_link_info *info,
 
   for (group = htab->group; group != NULL; group = group->next)
     if (group->needs_save_res)
-      {
-	stub_sec = group->stub_sec;
-	memcpy (stub_sec->contents + stub_sec->size, htab->sfpr->contents,
-		htab->sfpr->size);
-	if (htab->params->emit_stub_syms)
-	  {
-	    unsigned int i;
-
-	    for (i = 0; i < ARRAY_SIZE (save_res_funcs); i++)
-	      if (!sfpr_define (info, &save_res_funcs[i], stub_sec))
-		return FALSE;
-	  }
-	stub_sec->size += htab->sfpr->size;
-      }
+      group->stub_sec->size += htab->sfpr->size;
 
   if (htab->relbrlt != NULL)
     htab->relbrlt->reloc_count = 0;
@@ -13274,6 +13261,22 @@ ppc64_elf_build_stubs (struct bfd_link_info *info,
 	}
 
   for (group = htab->group; group != NULL; group = group->next)
+    if (group->needs_save_res)
+      {
+	stub_sec = group->stub_sec;
+	memcpy (stub_sec->contents + stub_sec->size - htab->sfpr->size,
+		htab->sfpr->contents, htab->sfpr->size);
+	if (htab->params->emit_stub_syms)
+	  {
+	    unsigned int i;
+
+	    for (i = 0; i < ARRAY_SIZE (save_res_funcs); i++)
+	      if (!sfpr_define (info, &save_res_funcs[i], stub_sec))
+		return FALSE;
+	  }
+      }
+
+  for (group = htab->group; group != NULL; group = group->next)
     if ((stub_sec = group->stub_sec) != NULL)
       {
 	stub_sec_count += 1;


-- 
Alan Modra
Australia Development Lab, IBM