Always descend into output section statements in lang_do_assignments

See https://sourceware.org/ml/binutils/2016-07/msg00091.html
This patch stop --gc-sections elf_gc_sweep_symbol localizing symbols
that ought to remain global.

The difficulty with always descending into output section statements
is that symbols defined by the script in such statements don't have
a bfd section when lang_do_assignments runs early in the link process.
There are two approaches to curing this problem.  Either we can
create the bfd section early, or we can use a special section.  This
patch takes the latter approach and uses bfd_und_section.  (Creating
bfd sections early results in changed output section order, and thus
lots of testsuite failures.  You can't create all output sections
early to ensure proper ordering as KEEP then stops empty sections
from being stripped.)

The wrinkle with this approach is that some code that runs at
gc-sections time needs to be made aware of the odd defined symbols
using bfd_und_section.

bfd/
	* elf64-x86-64.c (elf_x86_64_convert_load_reloc): Handle symbols
	defined temporarily with bfd_und_section.
	* elflink.c (_bfd_elf_gc_keep): Don't set SEC_KEEP for bfd_und_section.
	* elfxx-mips.c (mips_elf_local_pic_function_p): Exclude defined
	symbols with bfd_und_section.
ld/
	* ldlang.c (lang_do_assignments_1): Descend into output section
	statements that do not yet have bfd sections.  Set symbol section
	temporarily for symbols defined in such statements to the undefined
	section.  Don't error on data or reloc statements until final phase.
	* ldexp.c (exp_fold_tree_1 <etree_assign>): Handle bfd_und_section
	in expld.section.
	* testsuite/ld-mmix/bpo-10.d: Adjust.
	* testsuite/ld-mmix/bpo-11.d: Adjust.

5 files changed, 39 insertions, 20 deletions

diff --git a/ld/ChangeLog b/ld/ChangeLog
index 4cfe874..1c71de1 100644
--- a/ld/ChangeLog
+++ b/ld/ChangeLog
@@ -1,3 +1,14 @@
+2016-10-11  Alan Modra  <amodra@gmail.com>
+
+	* ldlang.c (lang_do_assignments_1): Descend into output section
+	statements that do not yet have bfd sections.  Set symbol section
+	temporarily for symbols defined in such statements to the undefined
+	section.  Don't error on data or reloc statements until final phase.
+	* ldexp.c (exp_fold_tree_1 <etree_assign>): Handle bfd_und_section
+	in expld.section.
+	* testsuite/ld-mmix/bpo-10.d: Adjust.
+	* testsuite/ld-mmix/bpo-11.d: Adjust.
+
 2016-10-10  Andreas Krebbel  <krebbel@linux.vnet.ibm.com>
 
 	* emulparams/elf64_s390.sh: Move binary start to 16M.
diff --git a/ld/ldexp.c b/ld/ldexp.c
index b2c7620..cb5e093 100644
--- a/ld/ldexp.c
+++ b/ld/ldexp.c
@@ -1077,6 +1077,7 @@ exp_fold_tree_1 (etree_type *tree)
 		 before relaxation and so be stripped incorrectly.  */
 	      if (expld.phase == lang_mark_phase_enum
 		  && expld.section != bfd_abs_section_ptr
+		  && expld.section != bfd_und_section_ptr
 		  && !(expld.result.valid_p
 		       && expld.result.value == 0
 		       && (is_value (tree->assign.src, 0)
@@ -1085,7 +1086,8 @@ exp_fold_tree_1 (etree_type *tree)
 			   || is_align_conditional (tree->assign.src))))
 		expld.section->flags |= SEC_KEEP;
 
-	      if (!expld.result.valid_p)
+	      if (!expld.result.valid_p
+		  || expld.section == bfd_und_section_ptr)
 		{
 		  if (expld.phase != lang_mark_phase_enum)
 		    einfo (_("%F%S invalid assignment to"
diff --git a/ld/ldlang.c b/ld/ldlang.c
index fe0b844..af2ca99 100644
--- a/ld/ldlang.c
+++ b/ld/ldlang.c
@@ -5618,6 +5618,7 @@ lang_do_assignments_1 (lang_statement_union_type *s,
 	case lang_output_section_statement_enum:
 	  {
 	    lang_output_section_statement_type *os;
+	    bfd_vma newdot;
 
 	    os = &(s->output_section_statement);
 	    os->after_end = *found_end;
@@ -5629,18 +5630,24 @@ lang_do_assignments_1 (lang_statement_union_type *s,
 		    prefer_next_section = FALSE;
 		  }
 		dot = os->bfd_section->vma;
-
-		lang_do_assignments_1 (os->children.head,
-				       os, os->fill, dot, found_end);
-
-		/* .tbss sections effectively have zero size.  */
-		if (!IS_TBSS (os->bfd_section)
-		    || bfd_link_relocatable (&link_info))
-		  dot += TO_ADDR (os->bfd_section->size);
-
-		if (os->update_dot_tree != NULL)
-		  exp_fold_tree (os->update_dot_tree, bfd_abs_section_ptr,
-				 &dot);
+	      }
+	    newdot = lang_do_assignments_1 (os->children.head,
+					    os, os->fill, dot, found_end);
+	    if (!os->ignored)
+	      {
+		if (os->bfd_section != NULL)
+		  {
+		    /* .tbss sections effectively have zero size.  */
+		    if (!IS_TBSS (os->bfd_section)
+			|| bfd_link_relocatable (&link_info))
+		      dot += TO_ADDR (os->bfd_section->size);
+
+		    if (os->update_dot_tree != NULL)
+		      exp_fold_tree (os->update_dot_tree,
+				     bfd_abs_section_ptr, &dot);
+		  }
+		else
+		  dot = newdot;
 	      }
 	  }
 	  break;
@@ -5664,7 +5671,7 @@ lang_do_assignments_1 (lang_statement_union_type *s,
 	      if (expld.result.section != NULL)
 		s->data_statement.value += expld.result.section->vma;
 	    }
-	  else
+	  else if (expld.phase == lang_final_phase_enum)
 	    einfo (_("%F%P: invalid data statement\n"));
 	  {
 	    unsigned int size;
@@ -5697,7 +5704,7 @@ lang_do_assignments_1 (lang_statement_union_type *s,
 			 bfd_abs_section_ptr, &dot);
 	  if (expld.result.valid_p)
 	    s->reloc_statement.addend_value = expld.result.value;
-	  else
+	  else if (expld.phase == lang_final_phase_enum)
 	    einfo (_("%F%P: invalid reloc statement\n"));
 	  dot += TO_ADDR (bfd_get_reloc_size (s->reloc_statement.howto));
 	  break;
@@ -5733,7 +5740,8 @@ lang_do_assignments_1 (lang_statement_union_type *s,
 		*found_end = TRUE;
 	    }
 	  exp_fold_tree (s->assignment_statement.exp,
-			 current_os->bfd_section,
+			 (current_os->bfd_section != NULL
+			  ? current_os->bfd_section : bfd_und_section_ptr),
 			 &dot);
 	  break;
 
diff --git a/ld/testsuite/ld-mmix/bpo-10.d b/ld/testsuite/ld-mmix/bpo-10.d
index 1cb7d61..6f49287 100644
--- a/ld/testsuite/ld-mmix/bpo-10.d
+++ b/ld/testsuite/ld-mmix/bpo-10.d
@@ -14,11 +14,10 @@ SYMBOL TABLE:
 0+7f8 l +d  \.MMIX.reg_contents	0+ (|\.MMIX\.reg_contents)
 0+ l    df \*ABS\*	0+ .*
 0+ l       \.init	0+ _start
-0+ l    df \*ABS\*	0+ .*
-0+4 l       \.init	0+ _start\.
 2000000000000000 g       \.init	0+ __bss_start
 2000000000000000 g       \.init	0+ _edata
 2000000000000000 g       \.init	0+ _end
+0+4 g       \.init	0+ _start\.
 
 Contents of section \.init:
  0000 e37704a6                             .*
diff --git a/ld/testsuite/ld-mmix/bpo-11.d b/ld/testsuite/ld-mmix/bpo-11.d
index 9b38be8..1abf381 100644
--- a/ld/testsuite/ld-mmix/bpo-11.d
+++ b/ld/testsuite/ld-mmix/bpo-11.d
@@ -16,13 +16,12 @@ SYMBOL TABLE:
 0+7e8 l    d  \.MMIX\.reg_contents	0+ (|\.MMIX\.reg_contents)
 0+ l    df \*ABS\*	0+ .*
 0+ l       \.init	0+ _start
-0+ l    df \*ABS\*	0+ .*
-0+10 l       \.text	0+ _start\.
 0+14 g       \.text	0+ x
 0+10 g       \.text	0+ x2
 2000000000000000 g       \.text	0+ __bss_start
 2000000000000000 g       \.text	0+ _edata
 2000000000000000 g       \.text	0+ _end
+0+10 g       \.text	0+ _start\.
 
 Contents of section \.init:
  0000 00000000 0000003d 00000000 0000003a  .*