Always define referenced __start_SECNAME/__stop_SECNAME

Currently, linker will define __start_SECNAME and __stop_SECNAME symbols
only for orphaned sections.

However, during garbage collection, ELF linker marks all sections with
references to __start_SECNAME and __stop_SECNAME symbols as used even
when section SECNAME isn't an orphaned section and linker won't define
__start_SECNAME nor __stop_SECNAME.  And ELF linker stores the first
input section whose name matches __start_SECNAME or __stop_SECNAME in
u.undef.section for garbage collection.  If these symbols are provided
in linker script, u.undef.section is set to the section where they will
defined by linker script, which leads to the incorrect output.

This patch changes linker to always define referenced __start_SECNAME and
__stop_SECNAME if the input section name is the same as the output section
name, which is always true for orphaned sections, and SECNAME is a C
identifier.  Also __start_SECNAME and __stop_SECNAME symbols are marked
as hidden by ELF linker so that __start_SECNAME and __stop_SECNAME symbols
for section SECNAME in different modules are unique.  For garbage
collection, ELF linker stores the first matched input section in the
unused vtable field.

bfd/

	PR ld/20022
	PR ld/21557
	PR ld/21562
	PR ld/21571
	* elf-bfd.h (elf_link_hash_entry): Add start_stop.  Change the
	vtable field to a union.
	(_bfd_elf_is_start_stop): Removed.
	* elf32-i386.c (elf_i386_convert_load_reloc): Also check for
	__start_SECNAME and __stop_SECNAME symbols.
	* elf64-x86-64.c (elf_x86_64_convert_load_reloc): Likewise.
	* elflink.c (_bfd_elf_is_start_stop): Removed.
	(_bfd_elf_gc_mark_rsec): Check start_stop instead of calling
	_bfd_elf_is_start_stop.
	(elf_gc_propagate_vtable_entries_used): Skip __start_SECNAME and
	__stop_SECNAME symbols.  Updated.
	(elf_gc_smash_unused_vtentry_relocs): Likewise.
	(bfd_elf_gc_record_vtinherit): Likewise.
	(bfd_elf_gc_record_vtentry): Likewise.

ld/

	PR ld/20022
	PR ld/21557
	PR ld/21562
	PR ld/21571
	* ld.texinfo: Update __start_SECNAME/__stop_SECNAME symbols.
	* ldlang.c (lang_insert_orphan): Move handling of __start_SECNAME
	and __stop_SECNAME symbols to ...
	(lang_set_startof): Here.  Also define __start_SECNAME and
	__stop_SECNAME for -Ur.
	* emultempl/elf32.em (gld${EMULATION_NAME}_after_open): Mark
	referenced __start_SECNAME and __stop_SECNAME symbols as hidden
	and set start_stop for garbage collection.
	* testsuite/ld-elf/pr21562a.d: New file.
	* testsuite/ld-elf/pr21562a.s: Likewise.
	* testsuite/ld-elf/pr21562a.t: Likewise.
	* testsuite/ld-elf/pr21562b.d: Likewise.
	* testsuite/ld-elf/pr21562b.s: Likewise.
	* testsuite/ld-elf/pr21562b.t: Likewise.
	* testsuite/ld-elf/pr21562c.d: Likewise.
	* testsuite/ld-elf/pr21562c.t: Likewise.
	* testsuite/ld-elf/pr21562d.d: Likewise.
	* testsuite/ld-elf/pr21562d.t: Likewise.
	* testsuite/ld-elf/pr21562e.d: Likewise.
	* testsuite/ld-elf/pr21562f.d: Likewise.
	* testsuite/ld-elf/pr21562g.d: Likewise.
	* testsuite/ld-elf/pr21562h.d: Likewise.
	* testsuite/ld-elf/pr21562i.d: Likewise.
	* testsuite/ld-elf/pr21562j.d: Likewise.
	* testsuite/ld-elf/pr21562k.d: Likewise.
	* testsuite/ld-elf/pr21562l.d: Likewise.
	* testsuite/ld-elf/pr21562m.d: Likewise.
	* testsuite/ld-elf/pr21562n.d: Likewise.
	* testsuite/ld-gc/pr20022.d: Likewise.
	* testsuite/ld-gc/pr20022a.s: Likewise.
	* testsuite/ld-gc/pr20022b.s: Likewise.
	* testsuite/ld-gc/gc.exp: Run PR ld/20022 tests.
	* testsuite/ld-gc/pr19161.d: Also accept local __start_SECNAME
	symbol.
	* testsuite/ld-gc/start.d: Likewise.
	* testsuite/ld-x86-64/lea1a.d: Updated.
	* testsuite/ld-x86-64/lea1b.d: Updated.
	* testsuite/ld-x86-64/lea1d.d: Updated.
	* testsuite/ld-x86-64/lea1e.d: Likewise.

5 files changed, 92 insertions, 103 deletions

diff --git a/bfd/ChangeLog b/bfd/ChangeLog
index acddb3a..edff887 100644
--- a/bfd/ChangeLog
+++ b/bfd/ChangeLog
@@ -1,3 +1,24 @@
+2017-06-13  H.J. Lu  <hongjiu.lu@intel.com>
+
+	PR ld/20022
+	PR ld/21557
+	PR ld/21562
+	PR ld/21571
+	* elf-bfd.h (elf_link_hash_entry): Add start_stop.  Change the
+	vtable field to a union.
+	(_bfd_elf_is_start_stop): Removed.
+	* elf32-i386.c (elf_i386_convert_load_reloc): Also check for
+	__start_SECNAME and __stop_SECNAME symbols.
+	* elf64-x86-64.c (elf_x86_64_convert_load_reloc): Likewise.
+	* elflink.c (_bfd_elf_is_start_stop): Removed.
+	(_bfd_elf_gc_mark_rsec): Check start_stop instead of calling
+	_bfd_elf_is_start_stop.
+	(elf_gc_propagate_vtable_entries_used): Skip __start_SECNAME and
+	__stop_SECNAME symbols.  Updated.
+	(elf_gc_smash_unused_vtentry_relocs): Likewise.
+	(bfd_elf_gc_record_vtinherit): Likewise.
+	(bfd_elf_gc_record_vtentry): Likewise.
+
 2017-06-13  Nick Clifton  <nickc@redhat.com>
 
 	PR ld/21524
diff --git a/bfd/elf-bfd.h b/bfd/elf-bfd.h
index 567b63a..fe15b93 100644
--- a/bfd/elf-bfd.h
+++ b/bfd/elf-bfd.h
@@ -213,6 +213,9 @@ struct elf_link_hash_entry
   /* Symbol is defined by a shared library with non-default visibility
      in a read/write section.  */
   unsigned int protected_def : 1;
+  /* Symbol is __start_SECNAME or __stop_SECNAME to mark section
+     SECNAME.  */
+  unsigned int start_stop : 1;
 
   /* String table index in .dynstr if this is a dynamic symbol.  */
   unsigned long dynstr_index;
@@ -243,7 +246,15 @@ struct elf_link_hash_entry
     struct bfd_elf_version_tree *vertree;
   } verinfo;
 
-  struct elf_link_virtual_table_entry *vtable;
+  union
+  {
+    /* For __start_SECNAME and __stop_SECNAME symbols, record the first
+       input section whose section name is SECNAME.  */
+    asection *start_stop_section;
+
+    /* Vtable information. */
+    struct elf_link_virtual_table_entry *vtable;
+  } u2;
 };
 
 /* Will references to this symbol always reference the symbol
@@ -2445,9 +2456,6 @@ extern bfd_boolean bfd_elf_gc_common_finalize_got_offsets
 extern bfd_boolean bfd_elf_gc_common_final_link
   (bfd *, struct bfd_link_info *);
 
-extern asection *_bfd_elf_is_start_stop
-  (const struct bfd_link_info *, struct elf_link_hash_entry *);
-
 extern bfd_boolean bfd_elf_reloc_symbol_deleted_p
   (bfd_vma, void *);
 
diff --git a/bfd/elf32-i386.c b/bfd/elf32-i386.c
index f9142a9..6636551 100644
--- a/bfd/elf32-i386.c
+++ b/bfd/elf32-i386.c
@@ -1787,11 +1787,13 @@ convert_branch:
 	return TRUE;
 
       /* def_regular is set by an assignment in a linker script in
-	 bfd_elf_record_link_assignment.  */
-      if ((h->def_regular
-	   || h->root.type == bfd_link_hash_defined
-	   || h->root.type == bfd_link_hash_defweak)
-	  && SYMBOL_REFERENCES_LOCAL (link_info, h))
+	 bfd_elf_record_link_assignment.  start_stop is set on
+	 __start_SECNAME/__stop_SECNAME which mark section SECNAME.  */
+      if (h->start_stop
+	  || ((h->def_regular
+	       || h->root.type == bfd_link_hash_defined
+	       || h->root.type == bfd_link_hash_defweak)
+	      && SYMBOL_REFERENCES_LOCAL (link_info, h)))
 	{
 convert_load:
 	  if (opcode == 0x8b)
diff --git a/bfd/elf64-x86-64.c b/bfd/elf64-x86-64.c
index 5306019..ab6f068 100644
--- a/bfd/elf64-x86-64.c
+++ b/bfd/elf64-x86-64.c
@@ -1920,21 +1920,25 @@ elf_x86_64_convert_load_reloc (bfd *abfd, asection *sec,
 	}
       /* Avoid optimizing GOTPCREL relocations againt _DYNAMIC since
 	 ld.so may use its link-time address.  */
-      else if ((h->def_regular
-		|| h->root.type == bfd_link_hash_defined
-		|| h->root.type == bfd_link_hash_defweak)
-	       && h != htab->elf.hdynamic
-	       && SYMBOL_REFERENCES_LOCAL (link_info, h))
+      else if (h->start_stop
+	       || ((h->def_regular
+		    || h->root.type == bfd_link_hash_defined
+		    || h->root.type == bfd_link_hash_defweak)
+		   && h != htab->elf.hdynamic
+		   && SYMBOL_REFERENCES_LOCAL (link_info, h)))
 	{
 	  /* bfd_link_hash_new or bfd_link_hash_undefined is
 	     set by an assignment in a linker script in
-	     bfd_elf_record_link_assignment.   */
-	  if (h->def_regular
-	      && (h->root.type == bfd_link_hash_new
-		  || h->root.type == bfd_link_hash_undefined
-		  || ((h->root.type == bfd_link_hash_defined
-		       || h->root.type == bfd_link_hash_defweak)
-		      && h->root.u.def.section == bfd_und_section_ptr)))
+	     bfd_elf_record_link_assignment.  start_stop is set
+	     on __start_SECNAME/__stop_SECNAME which mark section
+	     SECNAME.  */
+	  if (h->start_stop
+	      || (h->def_regular
+		  && (h->root.type == bfd_link_hash_new
+		      || h->root.type == bfd_link_hash_undefined
+		      || ((h->root.type == bfd_link_hash_defined
+			   || h->root.type == bfd_link_hash_defweak)
+			  && h->root.u.def.section == bfd_und_section_ptr))))
 	    {
 	      /* Skip since R_X86_64_32/R_X86_64_32S may overflow.  */
 	      if (require_reloc_pc32)
diff --git a/bfd/elflink.c b/bfd/elflink.c
index f0ca33f..9b0f544 100644
--- a/bfd/elflink.c
+++ b/bfd/elflink.c
@@ -12698,55 +12698,6 @@ elf_gc_mark_debug_section (asection *sec ATTRIBUTE_UNUSED,
   return NULL;
 }
 
-/* For undefined __start_<name> and __stop_<name> symbols, return the
-   first input section matching <name>.  Return NULL otherwise.  */
-
-asection *
-_bfd_elf_is_start_stop (const struct bfd_link_info *info,
-			struct elf_link_hash_entry *h)
-{
-  asection *s;
-  const char *sec_name;
-
-  if (h->root.type != bfd_link_hash_undefined
-      && h->root.type != bfd_link_hash_undefweak)
-    return NULL;
-
-  s = h->root.u.undef.section;
-  if (s != NULL)
-    {
-      if (s == (asection *) 0 - 1)
-	return NULL;
-      return s;
-    }
-
-  sec_name = NULL;
-  if (strncmp (h->root.root.string, "__start_", 8) == 0)
-    sec_name = h->root.root.string + 8;
-  else if (strncmp (h->root.root.string, "__stop_", 7) == 0)
-    sec_name = h->root.root.string + 7;
-
-  if (sec_name != NULL && *sec_name != '\0')
-    {
-      bfd *i;
-
-      for (i = info->input_bfds; i != NULL; i = i->link.next)
-	{
-	  s = bfd_get_section_by_name (i, sec_name);
-	  if (s != NULL)
-	    {
-	      h->root.u.undef.section = s;
-	      break;
-	    }
-	}
-    }
-
-  if (s == NULL)
-    h->root.u.undef.section = (asection *) 0 - 1;
-
-  return s;
-}
-
 /* COOKIE->rel describes a relocation against section SEC, which is
    a section we've decided to keep.  Return the section that contains
    the relocation symbol, or NULL if no section contains it.  */
@@ -12792,10 +12743,9 @@ _bfd_elf_gc_mark_rsec (struct bfd_link_info *info, asection *sec,
 	     or __stop_XXX symbols.  The linker will later define such
 	     symbols for orphan input sections that have a name
 	     representable as a C identifier.  */
-	  asection *s = _bfd_elf_is_start_stop (info, h);
-
-	  if (s != NULL)
+	  if (h->start_stop)
 	    {
+	      asection *s = h->u2.start_stop_section;
 	      *start_stop = !s->gc_mark;
 	      return s;
 	    }
@@ -13136,26 +13086,28 @@ static bfd_boolean
 elf_gc_propagate_vtable_entries_used (struct elf_link_hash_entry *h, void *okp)
 {
   /* Those that are not vtables.  */
-  if (h->vtable == NULL || h->vtable->parent == NULL)
+  if (h->start_stop
+      || h->u2.vtable == NULL
+      || h->u2.vtable->parent == NULL)
     return TRUE;
 
   /* Those vtables that do not have parents, we cannot merge.  */
-  if (h->vtable->parent == (struct elf_link_hash_entry *) -1)
+  if (h->u2.vtable->parent == (struct elf_link_hash_entry *) -1)
     return TRUE;
 
   /* If we've already been done, exit.  */
-  if (h->vtable->used && h->vtable->used[-1])
+  if (h->u2.vtable->used && h->u2.vtable->used[-1])
     return TRUE;
 
   /* Make sure the parent's table is up to date.  */
-  elf_gc_propagate_vtable_entries_used (h->vtable->parent, okp);
+  elf_gc_propagate_vtable_entries_used (h->u2.vtable->parent, okp);
 
-  if (h->vtable->used == NULL)
+  if (h->u2.vtable->used == NULL)
     {
       /* None of this table's entries were referenced.  Re-use the
 	 parent's table.  */
-      h->vtable->used = h->vtable->parent->vtable->used;
-      h->vtable->size = h->vtable->parent->vtable->size;
+      h->u2.vtable->used = h->u2.vtable->parent->u2.vtable->used;
+      h->u2.vtable->size = h->u2.vtable->parent->u2.vtable->size;
     }
   else
     {
@@ -13163,9 +13115,9 @@ elf_gc_propagate_vtable_entries_used (struct elf_link_hash_entry *h, void *okp)
       bfd_boolean *cu, *pu;
 
       /* Or the parent's entries into ours.  */
-      cu = h->vtable->used;
+      cu = h->u2.vtable->used;
       cu[-1] = TRUE;
-      pu = h->vtable->parent->vtable->used;
+      pu = h->u2.vtable->parent->u2.vtable->used;
       if (pu != NULL)
 	{
 	  const struct elf_backend_data *bed;
@@ -13173,7 +13125,7 @@ elf_gc_propagate_vtable_entries_used (struct elf_link_hash_entry *h, void *okp)
 
 	  bed = get_elf_backend_data (h->root.u.def.section->owner);
 	  log_file_align = bed->s->log_file_align;
-	  n = h->vtable->parent->vtable->size >> log_file_align;
+	  n = h->u2.vtable->parent->u2.vtable->size >> log_file_align;
 	  while (n--)
 	    {
 	      if (*pu)
@@ -13198,7 +13150,9 @@ elf_gc_smash_unused_vtentry_relocs (struct elf_link_hash_entry *h, void *okp)
 
   /* Take care of both those symbols that do not describe vtables as
      well as those that are not loaded.  */
-  if (h->vtable == NULL || h->vtable->parent == NULL)
+  if (h->start_stop
+      || h->u2.vtable == NULL
+      || h->u2.vtable->parent == NULL)
     return TRUE;
 
   BFD_ASSERT (h->root.type == bfd_link_hash_defined
@@ -13220,11 +13174,11 @@ elf_gc_smash_unused_vtentry_relocs (struct elf_link_hash_entry *h, void *okp)
     if (rel->r_offset >= hstart && rel->r_offset < hend)
       {
 	/* If the entry is in use, do nothing.  */
-	if (h->vtable->used
-	    && (rel->r_offset - hstart) < h->vtable->size)
+	if (h->u2.vtable->used
+	    && (rel->r_offset - hstart) < h->u2.vtable->size)
 	  {
 	    bfd_vma entry = (rel->r_offset - hstart) >> log_file_align;
-	    if (h->vtable->used[entry])
+	    if (h->u2.vtable->used[entry])
 	      continue;
 	  }
 	/* Otherwise, kill it.  */
@@ -13448,11 +13402,11 @@ bfd_elf_gc_record_vtinherit (bfd *abfd,
   return FALSE;
 
  win:
-  if (!child->vtable)
+  if (!child->u2.vtable)
     {
-      child->vtable = ((struct elf_link_virtual_table_entry *)
-		       bfd_zalloc (abfd, sizeof (*child->vtable)));
-      if (!child->vtable)
+      child->u2.vtable = ((struct elf_link_virtual_table_entry *)
+			  bfd_zalloc (abfd, sizeof (*child->u2.vtable)));
+      if (!child->u2.vtable)
 	return FALSE;
     }
   if (!h)
@@ -13462,10 +13416,10 @@ bfd_elf_gc_record_vtinherit (bfd *abfd,
 	 would be bad.  It isn't worth paging in the local symbols to be
 	 sure though; that case should simply be handled by the assembler.  */
 
-      child->vtable->parent = (struct elf_link_hash_entry *) -1;
+      child->u2.vtable->parent = (struct elf_link_hash_entry *) -1;
     }
   else
-    child->vtable->parent = h;
+    child->u2.vtable->parent = h;
 
   return TRUE;
 }
@@ -13481,18 +13435,18 @@ bfd_elf_gc_record_vtentry (bfd *abfd ATTRIBUTE_UNUSED,
   const struct elf_backend_data *bed = get_elf_backend_data (abfd);
   unsigned int log_file_align = bed->s->log_file_align;
 
-  if (!h->vtable)
+  if (!h->u2.vtable)
     {
-      h->vtable = ((struct elf_link_virtual_table_entry *)
-		   bfd_zalloc (abfd, sizeof (*h->vtable)));
-      if (!h->vtable)
+      h->u2.vtable = ((struct elf_link_virtual_table_entry *)
+		      bfd_zalloc (abfd, sizeof (*h->u2.vtable)));
+      if (!h->u2.vtable)
 	return FALSE;
     }
 
-  if (addend >= h->vtable->size)
+  if (addend >= h->u2.vtable->size)
     {
       size_t size, bytes, file_align;
-      bfd_boolean *ptr = h->vtable->used;
+      bfd_boolean *ptr = h->u2.vtable->used;
 
       /* While the symbol is undefined, we have to be prepared to handle
 	 a zero size.  */
@@ -13523,7 +13477,7 @@ bfd_elf_gc_record_vtentry (bfd *abfd ATTRIBUTE_UNUSED,
 	    {
 	      size_t oldbytes;
 
-	      oldbytes = (((h->vtable->size >> log_file_align) + 1)
+	      oldbytes = (((h->u2.vtable->size >> log_file_align) + 1)
 			  * sizeof (bfd_boolean));
 	      memset (((char *) ptr) + oldbytes, 0, bytes - oldbytes);
 	    }
@@ -13535,11 +13489,11 @@ bfd_elf_gc_record_vtentry (bfd *abfd ATTRIBUTE_UNUSED,
 	return FALSE;
 
       /* And arrange for that done flag to be at index -1.  */
-      h->vtable->used = ptr + 1;
-      h->vtable->size = size;
+      h->u2.vtable->used = ptr + 1;
+      h->u2.vtable->size = size;
     }
 
-  h->vtable->used[addend >> log_file_align] = TRUE;
+  h->u2.vtable->used[addend >> log_file_align] = TRUE;
 
   return TRUE;
 }