Re: PATCH: PR 797: Alignment in empty section changes the output layout

["H. J. Lu" <hjl at lucon dot org>]

On Wed, Mar 23, 2005 at 04:36:53PM -0800, H. J. Lu wrote:
> This patch tries to undo the damange caused by the unused output
> sections in linker script by removing them and resizing the remaining
> sections.
> 
> 
> H.J.
> ----
> 2005-03-23  H.J. Lu  <hongjiu.lu@intel.com>
> 
> 	PR 797
> 	* emultempl/elf32.em (gld${EMULATION_NAME}_finish): Remove
> 	the unused output sections without input sections and the empty
> 	unused output sections created by linker, if they don't have
> 	any contents. Resize sections.
> 
> 	* ldlang.c (lang_output_section_statement_lookup_1): Set the
> 	ignored field to FALSE.
> 	(lang_size_sections_1): Skip an output section if it should
> 	be ignored.
> 
> 	* ldlang.h (lang_output_section_statement_type): Add ignored.
> 

I missed one place in lang_do_assignments_1. We need to skip the
ignored output section when we assign values to symbols. Otherwise,
their values will be incorrect.


H.J.
----
2005-03-24  H.J. Lu  <hongjiu.lu@intel.com>

	PR 797
	* emultempl/elf32.em (gld${EMULATION_NAME}_finish): Remove
	the unused output sections without input sections and the empty
	unused output sections created by linker, if they don't have
	any contents. Resize sections.

	* ldlang.c (lang_output_section_statement_lookup_1): Set the
	ignored field to FALSE.
	(lang_size_sections_1): Skip an output section if it should
	be ignored.
	(lang_do_assignments_1): Likewise.

	* ldlang.h (lang_output_section_statement_type): Add ignored.

--- ld/emultempl/elf32.em.empty	2005-03-23 11:05:04.000000000 -0800
+++ ld/emultempl/elf32.em	2005-03-24 08:58:05.000000000 -0800
@@ -1472,20 +1472,76 @@ gld${EMULATION_NAME}_finish (void)
   if (!link_info.relocatable)
     {
       lang_output_section_statement_type *os;
+      asection *s, **p;
+      bfd_boolean resize = FALSE;
+
+      /* We want to remove unused output sections and resize the
+	 remaining sections so that any alignment changes caused by
+	 those removed output sections are reverted. Possible unused
+	 output sections are those without input sections or empty.
+	 We can't remove all unused output sections without input
+	 sections since they may be created by linker scripts. We can't
+	 remove all empty unused output sections since they may have
+	 empty input sections whose alignments may affect the memory
+	 layout of output sections which we don't want to change.
+	 
+	 So we remove the unused output sections without input sections
+	 and the empty unused output sections created by linker, if
+	 they don't have any contents.  */
 
       for (os = &lang_output_section_statement.head->output_section_statement;
 	   os != NULL;
 	   os = os->next)
 	{
-	  asection *s;
+	  if (os == abs_output_section || os->constraint == -1)
+	    continue;
+	  s = os->bfd_section;
+	  if (s != NULL
+	      && (s->linker_has_input == 0
+		  || (s->size == 0
+		      && (s->flags & SEC_LINKER_CREATED) != 0))
+	      && (s->flags & (SEC_KEEP | SEC_HAS_CONTENTS)) == 0)
+	    {
+	      os->ignored = TRUE;
+	      resize = TRUE;
+
+	      for (p = &output_bfd->sections; *p; p = &(*p)->next)
+		if (*p == s)
+		  {
+		    bfd_section_list_remove (output_bfd, p);
+		    output_bfd->section_count--;
+		    break;
+		  }
+	    }
+	}
+
+      /* Resize to revert the changes from those removed sections.  */
+      if (resize)
+	{
+	  lang_reset_memory_regions ();
+
+	  /* Resize the sections.  */
+	  lang_size_sections (stat_ptr->head, abs_output_section,
+			      &stat_ptr->head, 0, (bfd_vma) 0,
+			      NULL, TRUE);
+
+	  /* Redo special stuff.  */
+	  ldemul_after_allocation ();
+
+	  /* Do the assignments again.  */
+	  lang_do_assignments (stat_ptr->head, abs_output_section,
+			       (fill_type *) 0, (bfd_vma) 0);
+	}
 
+      for (os = &lang_output_section_statement.head->output_section_statement;
+	   os != NULL;
+	   os = os->next)
+	{
 	  if (os == abs_output_section || os->constraint == -1)
 	    continue;
 	  s = os->bfd_section;
 	  if (s != NULL && s->size == 0 && (s->flags & SEC_KEEP) == 0)
 	    {
-	      asection **p;
-
 	      for (p = &output_bfd->sections; *p; p = &(*p)->next)
 		if (*p == s)
 		  {
--- ld/ldlang.c.empty	2005-03-24 11:13:06.000000000 -0800
+++ ld/ldlang.c	2005-03-24 12:37:30.431168331 -0800
@@ -637,6 +637,7 @@ lang_output_section_statement_lookup_1 (
       lookup->bfd_section = NULL;
       lookup->processed = 0;
       lookup->constraint = constraint;
+      lookup->ignored = FALSE;
       lookup->sectype = normal_section;
       lookup->addr_tree = NULL;
       lang_list_init (&lookup->children);
@@ -3418,8 +3419,8 @@ lang_size_sections_1
 	    lang_output_section_statement_type *os;
 
 	    os = &s->output_section_statement;
-	    if (os->bfd_section == NULL)
-	      /* This section was never actually created.  */
+	    if (os->bfd_section == NULL || os->ignored)
+	      /* This section was removed or never actually created.  */
 	      break;
 
 	    /* If this is a COFF shared library section, use the size and
@@ -3914,7 +3915,7 @@ lang_do_assignments_1
 	    lang_output_section_statement_type *os;
 
 	    os = &(s->output_section_statement);
-	    if (os->bfd_section != NULL)
+	    if (os->bfd_section != NULL && !os->ignored)
 	      {
 		dot = os->bfd_section->vma;
 		lang_do_assignments_1 (os->children.head, os, os->fill, dot);
@@ -3928,7 +3929,7 @@ lang_do_assignments_1
 	      {
 		/* If nothing has been placed into the output section then
 		   it won't have a bfd_section.  */
-		if (os->bfd_section)
+		if (os->bfd_section && !os->ignored)
 		  {
 		    os->bfd_section->lma
 		      = exp_get_abs_int (os->load_base, 0, "load base",
--- ld/ldlang.h.empty	2005-03-03 08:56:33.000000000 -0800
+++ ld/ldlang.h	2005-03-24 08:58:05.000000000 -0800
@@ -148,6 +148,7 @@ typedef struct lang_output_section_state
   int section_alignment;	/* Alignment of start of section.  */
   int constraint;
   bfd_boolean all_input_readonly;
+  bfd_boolean ignored; 
 
   union etree_union *load_base;