[GOLD] PowerPC --stub-group-multi

Adds a new option, defaulting to off, that allows a group of stubs to
serve multiple output sections.  Prior to this patch powerpc gold
allowed this unconditionally, which is a little unsafe with clever
code that discards/reuses sections at runtime.

	* options.h (--stub-group-multi): New PowerPC option.
	* powerpc.cc (Stub_control): Add multi_os_ var and param
	to constructor.  Sort start_ var later.  Comment State.
	(Stub_control::can_add_to_stub_group): Heed multi_os_.
	(Target_powerpc::group_sections): Update.

3 files changed, 42 insertions, 19 deletions

diff --git a/gold/ChangeLog b/gold/ChangeLog
index 367cb02..2fcd80e 100644
--- a/gold/ChangeLog
+++ b/gold/ChangeLog
@@ -1,5 +1,13 @@
 2016-12-07  Alan Modra  <amodra@gmail.com>
 
+	* options.h (--stub-group-multi): New PowerPC option.
+	* powerpc.cc (Stub_control): Add multi_os_ var and param
+	to constructor.  Sort start_ var later.  Comment State.
+	(Stub_control::can_add_to_stub_group): Heed multi_os_.
+	(Target_powerpc::group_sections): Update.
+
+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
diff --git a/gold/options.h b/gold/options.h
index 90ccc80..6722667 100644
--- a/gold/options.h
+++ b/gold/options.h
@@ -1219,6 +1219,10 @@ class General_options
 		"stubs are always after the group. 1 means use default size"),
 	     N_("SIZE"));
 
+  DEFINE_bool(stub_group_multi, options::TWO_DASHES, '\0', false,
+	      N_("(PowerpC only) Allow a group of stubs to serve multiple "
+		 "output sections"), NULL);
+
   DEFINE_uint(split_stack_adjust_size, options::TWO_DASHES, '\0', 0x4000,
 	      N_("Stack size when -fsplit-stack function calls non-split"),
 	      N_("SIZE"));
diff --git a/gold/powerpc.cc b/gold/powerpc.cc
index f763618..068f5ca 100644
--- a/gold/powerpc.cc
+++ b/gold/powerpc.cc
@@ -2441,11 +2441,11 @@ class Stub_control
   // value of the parameter --stub-group-size.  If --stub-group-size
   // 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_after_branch_(size < 0),
-      suppress_size_errors_(no_size_errors), group_size_(0),
-      group_start_addr_(0), owner_(NULL), output_section_(NULL)
+  Stub_control(int32_t size, bool no_size_errors, bool multi_os)
+    : stub_group_size_(abs(size)), stubs_always_after_branch_(size < 0),
+      suppress_size_errors_(no_size_errors), multi_os_(multi_os),
+      state_(NO_GROUP), group_size_(0), group_start_addr_(0),
+      owner_(NULL), output_section_(NULL)
   {
   }
 
@@ -2475,15 +2475,20 @@ class Stub_control
  private:
   typedef enum
   {
+    // Initial state.
     NO_GROUP,
+    // Adding group sections before the stubs.
     FINDING_STUB_SECTION,
+    // Adding group sections after the stubs.
     HAS_STUB_SECTION
   } State;
 
-  State state_;
   uint32_t stub_group_size_;
   bool stubs_always_after_branch_;
   bool suppress_size_errors_;
+  // True if a stub group can serve multiple output sections.
+  bool multi_os_;
+  State state_;
   // 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.
@@ -2537,7 +2542,19 @@ Stub_control::can_add_to_stub_group(Output_section* o,
 	      ? this_size
 	      : (long long) end_addr - this->group_start_addr_));
 
-  if (this->state_ == HAS_STUB_SECTION)
+  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 if (!this->multi_os_ && this->output_section_ != o)
+    ;
+  else if (this->state_ == HAS_STUB_SECTION)
     {
       // Can we add this section, which is after the stubs, to the
       // group?
@@ -2571,20 +2588,13 @@ Stub_control::can_add_to_stub_group(Output_section* o,
 	  return true;
 	}
     }
-  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");
+  gold_debug(DEBUG_TARGET,
+	     !this->multi_os_ && this->output_section_ != o
+	     ? "nope, new output section\n"
+	     : "nope, didn't fit\n");
 
   // The section fails to fit in the current group.  Set up a few
   // things for the next group.  owner_ and output_section_ will be
@@ -2604,7 +2614,8 @@ Target_powerpc<size, big_endian>::group_sections(Layout* layout,
 						 const Task*,
 						 bool no_size_errors)
 {
-  Stub_control stub_control(this->stub_group_size_, no_size_errors);
+  Stub_control stub_control(this->stub_group_size_, no_size_errors,
+			    parameters->options().stub_group_multi());
 
   // Group input sections and insert stub table
   Stub_table_owner* table_owner = NULL;