[GOLD] powerpc64le-linux fails to link large Linux kernel

Gold attaches stubs to an existing section in contrast to ld.bfd which
inserts a new section for stubs.  If we want stubs before branches,
then the stubs must be added to the previous section.  Adding to the
previous section is a disaster if there is a large gap between the
previous section and the group.

	PR gold/20878
	* powerpc.cc (Stub_control): Replace stubs_always_before_branch_
	with stubs_always_after_branch_, group_end_addr_ with
	group_start_addr_.
	(Stub_control::can_add_to_stub_group): Rewrite to suit scanning
	sections by increasing address.
	(Target_powerpc::group_sections): Scan that way.  Delete corner
	case.
	* options.h (--stub-group-size): Update help string.

3 files changed, 64 insertions, 79 deletions

diff --git a/gold/ChangeLog b/gold/ChangeLog
index 30d53d9250e..d45bb48b71c 100644
--- a/gold/ChangeLog
+++ b/gold/ChangeLog
@@ -2,6 +2,17 @@
 
 	Apply from master
 	2016-12-07  Alan Modra  <amodra@gmail.com>
+	PR gold/20878
+	* powerpc.cc (Stub_control): Replace stubs_always_before_branch_
+	with stubs_always_after_branch_, group_end_addr_ with
+	group_start_addr_.
+	(Stub_control::can_add_to_stub_group): Rewrite to suit scanning
+	sections by increasing address.
+	(Target_powerpc::group_sections): Scan that way.  Delete corner
+	case.
+	* options.h (--stub-group-size): Update help string.
+
+	2016-12-07  Alan Modra  <amodra@gmail.com>
 	* powerpc.cc (Stub_table_owner): Provide constructor.
 	(Powerpc_relobj::set_stub_table): Resize fill with -1.
 	(Target_powerpc::Branch_info::make_stub): Provide target debug
diff --git a/gold/options.h b/gold/options.h
index 4c5b2aea122..f63758ba976 100644
--- a/gold/options.h
+++ b/gold/options.h
@@ -1097,9 +1097,8 @@ class General_options
 
   DEFINE_int(stub_group_size, options::TWO_DASHES , '\0', 1,
 	     N_("(ARM, PowerPC only) The maximum distance from instructions "
-		"in a group of sections to their stubs.  Negative values mean "
-		"stubs are always after (PowerPC before) the group.  1 means "
-		"use default size.\n"),
+		"in a group of sections to their stubs. Negative values mean "
+		"stubs are always after the group. 1 means use default size"),
 	     N_("SIZE"));
 
   DEFINE_bool(no_keep_memory, options::TWO_DASHES, '\0', false,
diff --git a/gold/powerpc.cc b/gold/powerpc.cc
index d8d332a95e1..931f177901c 100644
--- a/gold/powerpc.cc
+++ b/gold/powerpc.cc
@@ -2439,13 +2439,13 @@ class Stub_control
  public:
   // Determine the stub group size.  The group size is the absolute
   // value of the parameter --stub-group-size.  If --stub-group-size
-  // is passed a negative value, we restrict stubs to be always before
+  // is passed a negative value, we restrict stubs to be always after
   // the stubbed branches.
   Stub_control(int32_t size, bool no_size_errors)
     : state_(NO_GROUP), stub_group_size_(abs(size)),
-      stubs_always_before_branch_(size < 0),
+      stubs_always_after_branch_(size < 0),
       suppress_size_errors_(no_size_errors), group_size_(0),
-      group_end_addr_(0), owner_(NULL), output_section_(NULL)
+      group_start_addr_(0), owner_(NULL), output_section_(NULL)
   {
   }
 
@@ -2482,13 +2482,13 @@ class Stub_control
 
   State state_;
   uint32_t stub_group_size_;
-  bool stubs_always_before_branch_;
+  bool stubs_always_after_branch_;
   bool suppress_size_errors_;
   // Current max size of group.  Starts at stub_group_size_ but is
   // reduced to stub_group_size_/1024 on seeing a section with
   // external conditional branches.
   uint32_t group_size_;
-  uint64_t group_end_addr_;
+  uint64_t group_start_addr_;
   // owner_ and output_section_ specify the section to which stubs are
   // attached.  The stubs are placed at the end of this section.
   const Output_section::Input_section* owner_;
@@ -2496,8 +2496,8 @@ class Stub_control
 };
 
 // Return true iff input section can be handled by current stub
-// group.  Sections are presented to this function in reverse order,
-// so the first section is the tail of the group.
+// group.  Sections are presented to this function in order,
+// so the first section is the head of the group.
 
 bool
 Stub_control::can_add_to_stub_group(Output_section* o,
@@ -2518,6 +2518,7 @@ Stub_control::can_add_to_stub_group(Output_section* o,
       this_size = i->data_size();
     }
 
+  uint64_t end_addr = start_addr + this_size;
   uint32_t group_size = this->stub_group_size_;
   if (has14)
     this->group_size_ = group_size = group_size >> 10;
@@ -2532,64 +2533,56 @@ Stub_control::can_add_to_stub_group(Output_section* o,
 	     i->relobj()->name().c_str(),
 	     i->relobj()->section_name(i->shndx()).c_str(),
 	     (long long) this_size,
-	     (long long) this->group_end_addr_ - start_addr);
+	     (this->state_ == NO_GROUP
+	      ? this_size
+	      : (long long) end_addr - this->group_start_addr_));
 
-  uint64_t end_addr = start_addr + this_size;
   if (this->state_ == HAS_STUB_SECTION)
     {
-      // Can we add this section, which is before the stubs, to the
+      // Can we add this section, which is after the stubs, to the
       // group?
-      if (this->group_end_addr_ - start_addr <= this->group_size_)
+      if (end_addr - this->group_start_addr_ <= this->group_size_)
 	return true;
     }
-  else
+  else if (this->state_ == FINDING_STUB_SECTION)
     {
-      // Stubs are added at the end of "owner_".
-      // The current section can always be the stub owner, except when
-      // whole_sec is true and the current section isn't the last of
-      // the pasted sections.  (This restriction for the whole_sec
-      // case is just to simplify the corner case mentioned in
-      // group_sections.)
-      // Note that "owner_" itself is not necessarily part of the
-      // group of sections served by these stubs!
-      if (!whole_sec || this->output_section_ != o)
+      if ((whole_sec && this->output_section_ == o)
+	  || end_addr - this->group_start_addr_ <= this->group_size_)
 	{
+	  // Stubs are added at the end of "owner_".
 	  this->owner_ = i;
 	  this->output_section_ = o;
+	  return true;
 	}
-
-      if (this->state_ == FINDING_STUB_SECTION)
-	{
-	  if (this->group_end_addr_ - start_addr <= this->group_size_)
-	    return true;
-	  // The group after the stubs has reached maximum size.
-	  // Now see about adding sections before the stubs to the
-	  // group.  If the current section has a 14-bit branch and
-	  // the group after the stubs exceeds group_size_ (because
-	  // they didn't have 14-bit branches), don't add sections
-	  // before the stubs:  The size of stubs for such a large
-	  // group may exceed the reach of a 14-bit branch.
-	  if (!this->stubs_always_before_branch_
-	      && this_size <= this->group_size_
-	      && this->group_end_addr_ - end_addr <= this->group_size_)
-	    {
-	      gold_debug(DEBUG_TARGET, "adding before stubs");
-	      this->state_ = HAS_STUB_SECTION;
-	      this->group_end_addr_ = end_addr;
-	      return true;
-	    }
-	}
-      else if (this->state_ == NO_GROUP)
+      // The group before the stubs has reached maximum size.
+      // Now see about adding sections after the stubs to the
+      // group.  If the current section has a 14-bit branch and
+      // the group before the stubs exceeds group_size_ (because
+      // they didn't have 14-bit branches), don't add sections
+      // after the stubs:  The size of stubs for such a large
+      // group may exceed the reach of a 14-bit branch.
+      if (!this->stubs_always_after_branch_
+	  && this_size <= this->group_size_
+	  && start_addr - this->group_start_addr_ <= this->group_size_)
 	{
-	  // Only here on very first use of Stub_control
-	  this->state_ = FINDING_STUB_SECTION;
-	  this->group_size_ = group_size;
-	  this->group_end_addr_ = end_addr;
+	  gold_debug(DEBUG_TARGET, "adding after stubs");
+	  this->state_ = HAS_STUB_SECTION;
+	  this->group_start_addr_ = start_addr;
 	  return true;
 	}
-      else
-	gold_unreachable();
     }
+  else if (this->state_ == NO_GROUP)
+    {
+      // Only here on very first use of Stub_control
+      this->owner_ = i;
+      this->output_section_ = o;
+      this->state_ = FINDING_STUB_SECTION;
+      this->group_size_ = group_size;
+      this->group_start_addr_ = start_addr;
+      return true;
+    }
+  else
+    gold_unreachable();
 
   gold_debug(DEBUG_TARGET, "nope, didn't fit\n");
 
@@ -2599,7 +2592,7 @@ Stub_control::can_add_to_stub_group(Output_section* o,
   // group.
   this->state_ = FINDING_STUB_SECTION;
   this->group_size_ = group_size;
-  this->group_end_addr_ = end_addr;
+  this->group_start_addr_ = start_addr;
   return false;
 }
 
@@ -2619,14 +2612,14 @@ Target_powerpc<size, big_endian>::group_sections(Layout* layout,
   Layout::Section_list section_list;
   layout->get_executable_sections(&section_list);
   std::stable_sort(section_list.begin(), section_list.end(), Sort_sections());
-  for (Layout::Section_list::reverse_iterator o = section_list.rbegin();
-       o != section_list.rend();
+  for (Layout::Section_list::iterator o = section_list.begin();
+       o != section_list.end();
        ++o)
     {
       typedef Output_section::Input_section_list Input_section_list;
-      for (Input_section_list::const_reverse_iterator i
-	     = (*o)->input_sections().rbegin();
-	   i != (*o)->input_sections().rend();
+      for (Input_section_list::const_iterator i
+	     = (*o)->input_sections().begin();
+	   i != (*o)->input_sections().end();
 	   ++i)
 	{
 	  if (i->is_input_section()
@@ -2653,26 +2646,8 @@ Target_powerpc<size, big_endian>::group_sections(Layout* layout,
     }
   if (table_owner != NULL)
     {
-      const Output_section::Input_section* i = stub_control.owner();
-
-      if (tables.size() >= 2 && tables[tables.size() - 2]->owner == i)
-	{
-	  // Corner case.  A new stub group was made for the first
-	  // section (last one looked at here) for some reason, but
-	  // the first section is already being used as the owner for
-	  // a stub table for following sections.  Force it into that
-	  // stub group.
-	  tables.pop_back();
-	  delete table_owner;
-	  Powerpc_relobj<size, big_endian>* ppcobj = static_cast
-	    <Powerpc_relobj<size, big_endian>*>(i->relobj());
-	  ppcobj->set_stub_table(i->shndx(), tables.size() - 1);
-	}
-      else
-	{
-	  table_owner->output_section = stub_control.output_section();
-	  table_owner->owner = i;
-	}
+      table_owner->output_section = stub_control.output_section();
+      table_owner->owner = stub_control.owner();;
     }
   for (typename std::vector<Stub_table_owner*>::iterator t = tables.begin();
        t != tables.end();