gold patch committed: Calls to __i686.get_pc_thunk.bx don't split stack

[Ian Lance Taylor <iant at google dot com>]

When gold was changing functions to force a stack split for the i386
target, it considered a call to the function __i686.get_pc_thunk.bx to
force a stack split.  That is pointless since that function, created
by gcc, does not use any stack space.  Calls to that function appear
in any -fPIC code which refers to a global variable, so they are
fairly common.  Committed to mainline.

Ian


2010-03-10  Ian Lance Taylor  <iant@google.com>

	* reloc.cc (Sized_relobj::split_stack_adjust_reltype): Call the
	target to ask whether a reference to a symbol requires a stack
	split.
	* target.h (Target::is_call_to_non_split): New function.
	(Target::do_is_call_to_non_split): Declare virtual function.
	* target.cc: Include "symtab.h".
	(Target::do_is_call_to_non_split): New function.
	* i386.cc (Target_i386::do_is_call_to_non_split): New function.


Index: i386.cc
===================================================================
RCS file: /cvs/src/src/gold/i386.cc,v
retrieving revision 1.115
diff -p -u -r1.115 i386.cc
--- i386.cc	4 Mar 2010 01:33:22 -0000	1.115
+++ i386.cc	11 Mar 2010 01:03:23 -0000
@@ -171,6 +171,10 @@ class Target_i386 : public Target_freebs
     return Target::do_is_local_label_name(name);
   }
 
+  // Return whether SYM is call to a non-split function.
+  bool
+  do_is_call_to_non_split(const Symbol* sym, unsigned int) const;
+
   // Adjust -fstack-split code which calls non-stack-split code.
   void
   do_calls_non_split(Relobj* object, unsigned int shndx,
@@ -2776,6 +2780,17 @@ Target_i386::do_code_fill(section_size_t
   return std::string(nops[length], length);
 }
 
+// Return whether SYM should be treated as a call to a non-split
+// function.  We don't want that to be true of a call to a
+// get_pc_thunk function.
+
+bool
+Target_i386::do_is_call_to_non_split(const Symbol* sym, unsigned int) const
+{
+  return (sym->type() == elfcpp::STT_FUNC
+	  && !is_prefix_of("__i686.get_pc_thunk.", sym->name()));
+}
+
 // FNOFFSET in section SHNDX in OBJECT is the start of a function
 // compiled with -fstack-split.  The function calls non-stack-split
 // code.  We have to change the function so that it always ensures
Index: reloc.cc
===================================================================
RCS file: /cvs/src/src/gold/reloc.cc,v
retrieving revision 1.55
diff -p -u -r1.55 reloc.cc
--- reloc.cc	10 Mar 2010 17:37:11 -0000	1.55
+++ reloc.cc	11 Mar 2010 01:03:33 -0000
@@ -1106,14 +1106,17 @@ Sized_relobj<size, big_endian>::split_st
       // cases we will ask for a large stack unnecessarily, but this
       // is not fatal.  FIXME: Some targets have symbols which are
       // functions but are not type STT_FUNC, e.g., STT_ARM_TFUNC.
-      if (gsym->type() == elfcpp::STT_FUNC
-	  && !gsym->is_undefined()
+      if (!gsym->is_undefined()
 	  && gsym->source() == Symbol::FROM_OBJECT
 	  && !gsym->object()->uses_split_stack())
 	{
-	  section_offset_type offset =
-	    convert_to_section_size_type(reloc.get_r_offset());
-	  non_split_refs.push_back(offset);
+	  unsigned int r_type = elfcpp::elf_r_type<size>(reloc.get_r_info());
+	  if (parameters->target().is_call_to_non_split(gsym, r_type))
+	    {
+	      section_offset_type offset =
+		convert_to_section_size_type(reloc.get_r_offset());
+	      non_split_refs.push_back(offset);
+	    }
 	}
     }
 
Index: target.cc
===================================================================
RCS file: /cvs/src/src/gold/target.cc,v
retrieving revision 1.5
diff -p -u -r1.5 target.cc
--- target.cc	9 Oct 2009 23:18:19 -0000	1.5
+++ target.cc	11 Mar 2010 01:03:33 -0000
@@ -21,10 +21,11 @@
 // MA 02110-1301, USA.
 
 #include "gold.h"
-#include "target.h"
+#include "elfcpp.h"
 #include "dynobj.h"
+#include "symtab.h"
 #include "output.h"
-#include "elfcpp.h"
+#include "target.h"
 
 namespace gold
 {
@@ -144,6 +145,15 @@ Target::do_make_output_section(const cha
   return new Output_section(name, type, flags);
 }
 
+// Default for whether a reloc is a call to a non-split function is
+// whether the symbol is a function.
+
+bool
+Target::do_is_call_to_non_split(const Symbol* sym, unsigned int) const
+{
+  return sym->type() == elfcpp::STT_FUNC;
+}
+
 // Default conversion for -fsplit-stack is to give an error.
 
 void
Index: target.h
===================================================================
RCS file: /cvs/src/src/gold/target.h,v
retrieving revision 1.45
diff -p -u -r1.45 target.h
--- target.h	13 Feb 2010 02:04:21 -0000	1.45
+++ target.h	11 Mar 2010 01:03:34 -0000
@@ -247,6 +247,14 @@ class Target
   reloc_addend(void* arg, unsigned int type, uint64_t addend) const
   { return this->do_reloc_addend(arg, type, addend); }
 
+  // Return true if a reference to SYM from a reloc of type R_TYPE
+  // means that the current function may call an object compiled
+  // without -fsplit-stack.  SYM is known to be defined in an object
+  // compiled without -fsplit-stack.
+  bool
+  is_call_to_non_split(const Symbol* sym, unsigned int r_type) const
+  { return this->do_is_call_to_non_split(sym, r_type); }
+
   // A function starts at OFFSET in section SHNDX in OBJECT.  That
   // function was compiled with -fsplit-stack, but it refers to a
   // function which was compiled without -fsplit-stack.  VIEW is a
@@ -440,6 +448,12 @@ class Target
   do_reloc_addend(void*, unsigned int, uint64_t) const
   { gold_unreachable(); }
 
+  // Virtual function which may be overridden by the child class.  The
+  // default implementation is that any function not defined by the
+  // ABI is a call to a non-split function.
+  virtual bool
+  do_is_call_to_non_split(const Symbol* sym, unsigned int) const;
+
   // Virtual function which may be overridden by the child class.
   virtual void
   do_calls_non_split(Relobj* object, unsigned int, section_offset_type,