PowerPC PLT stub alignment fixes

Asking for ppc32 plt call stubs to be aligned at 32 byte boundaries
didn't quite work.  For ld.bfd they were spaced 32 bytes apart, but
only started on a 16 byte boundary.  ld.gold also didn't get it right.

Finding that bug made me check over the ppc64 plt stub alignment,
where I found that negative values for alignment (meaning align to
minimize boundary crossing) were not accepted.  Since no one has
complained about that, I guess I could have removed the feature from
ld.bfd documentation, but I've opted instead to correct the code.

I've also added an optional alignment paramenter for ppc32
--plt-align, for some consistency with gold and ppc64 ld.bfd.

bfd/
	* elf32-ppc.c (ppc_elf_create_glink): Correct alignment of .glink.
	* elf64-ppc.c (ppc64_elf_size_stubs): Handle negative plt_stub_align.
	(ppc64_elf_build_stubs): Likewise.
gold/
	* powerpc.cc (param_plt_align): New function supplying default
	--plt-align values.  Use it..
	(Stub_table::plt_call_align): ..here, and..
	(Output_data_glink::global_entry_align): ..here.
	(Stub_table::stub_align): Correct 32-bit minimum alignment.
ld/
	* emultempl/ppc32elf.em: Support optional --plt-align arg.
	* emultempl/ppc64elf.em: Support negative --plt-align arg.

3 files changed, 20 insertions, 8 deletions

diff --git a/bfd/ChangeLog b/bfd/ChangeLog
index f1c5c41..3c8fcf3 100644
--- a/bfd/ChangeLog
+++ b/bfd/ChangeLog
@@ -1,3 +1,9 @@
+2018-01-18  Alan Modra  <amodra@gmail.com>
+
+	* elf32-ppc.c (ppc_elf_create_glink): Correct alignment of .glink.
+	* elf64-ppc.c (ppc64_elf_size_stubs): Handle negative plt_stub_align.
+	(ppc64_elf_build_stubs): Likewise.
+
 2018-01-17  Nick Clifton  <nickc@redhat.com>
 
 	* po/ru.po: Updated Russian translation.
diff --git a/bfd/elf32-ppc.c b/bfd/elf32-ppc.c
index 73701d4..32104a1 100644
--- a/bfd/elf32-ppc.c
+++ b/bfd/elf32-ppc.c
@@ -3475,14 +3475,17 @@ ppc_elf_create_glink (bfd *abfd, struct bfd_link_info *info)
   struct ppc_elf_link_hash_table *htab = ppc_elf_hash_table (info);
   asection *s;
   flagword flags;
+  int p2align;
 
   flags = (SEC_ALLOC | SEC_LOAD | SEC_CODE | SEC_READONLY | SEC_HAS_CONTENTS
 	   | SEC_IN_MEMORY | SEC_LINKER_CREATED);
   s = bfd_make_section_anyway_with_flags (abfd, ".glink", flags);
   htab->glink = s;
+  p2align = htab->params->ppc476_workaround ? 6 : 4;
+  if (p2align < htab->params->plt_stub_align)
+    p2align = htab->params->plt_stub_align;
   if (s == NULL
-      || !bfd_set_section_alignment (abfd, s,
-				     htab->params->ppc476_workaround ? 6 : 4))
+      || !bfd_set_section_alignment (abfd, s, p2align))
     return FALSE;
 
   if (!info->no_ld_generated_unwind_info)
diff --git a/bfd/elf64-ppc.c b/bfd/elf64-ppc.c
index 65cf7fe..b2d288b 100644
--- a/bfd/elf64-ppc.c
+++ b/bfd/elf64-ppc.c
@@ -12743,9 +12743,11 @@ ppc64_elf_size_stubs (struct bfd_link_info *info)
       if (htab->params->plt_stub_align != 0)
 	for (group = htab->group; group != NULL; group = group->next)
 	  if (group->stub_sec != NULL)
-	    group->stub_sec->size = ((group->stub_sec->size
-				      + (1 << htab->params->plt_stub_align) - 1)
-				     & -(1 << htab->params->plt_stub_align));
+	    {
+	      int align = abs (htab->params->plt_stub_align);
+	      group->stub_sec->size
+		= (group->stub_sec->size + (1 << align) - 1) & -(1 << align);
+	    }
 
       for (group = htab->group; group != NULL; group = group->next)
 	if (group->stub_sec != NULL
@@ -13285,9 +13287,10 @@ ppc64_elf_build_stubs (struct bfd_link_info *info,
   if (htab->params->plt_stub_align != 0)
     for (group = htab->group; group != NULL; group = group->next)
       if ((stub_sec = group->stub_sec) != NULL)
-	stub_sec->size = ((stub_sec->size
-			   + (1 << htab->params->plt_stub_align) - 1)
-			  & -(1 << htab->params->plt_stub_align));
+	{
+	  int align = abs (htab->params->plt_stub_align);
+	  stub_sec->size = (stub_sec->size + (1 << align) - 1) & -(1 << align);
+	}
 
   for (group = htab->group; group != NULL; group = group->next)
     if ((stub_sec = group->stub_sec) != NULL)