Re: [GOLD] Symbol target_flag for PowerPC64 localentry:0 tracking

[Alan Modra <amodra at gmail dot com>]

On Mon, Jul 31, 2017 at 11:21:55AM -0700, Cary Coutant wrote:
> > This patch provides a flag for target use in class Symbol, and
> > modifies Sized_target::resolve to return whether the symbol has been
> > resolved.  If not, normal processing continues.  I use this for
> > PowerPC64 ELFv2 to keep track of whether a symbol has any definition
> > with non-zero localentry, in order to disable --plt-localentry for
> > that symbol.
> >
> > I know the right way to add target specific symbol fields is via a
> > derived class and Sized_target::make_symbol, which would be easy to do
> > for powerpc, but there are lots of holes in Symbol available.  So I
> > thought I'd test the reaction to this patch before wasting another
> > word per symbol.
> >
> > OK?
> 
> I think I'd prefer it if we pretended that your new flag was not, in
> fact, target specific -- i.e., just name it something like
> has_localentry. You'd still need the target-specific resolve(), due to
> the way you have to check for the condition, but I can imagine another
> target maybe wanting that flag someday. As you say, it's a lot cheaper
> than deriving a new class.
> 
> (Ian was pretty prescient when he provided that target-specific
> resolve hook, heretofore never used! I've considered removing it on
> more than one occasion. (It's possible it was once used then removed,
> but I haven't done the archaeology to find out.))

OK, I'll call it non_zero_localentry and remove the ability to clear
the flag, which I don't need for PowerPC64.  Is this OK to commit?

	PR 21847
	* powerpc.cc (Target_powerpc::is_elfv2_localentry0): Test
	non_zero_localentry.
	(Target_powerpc::resolve): New function.
	(powerpc_info): Set has_resolve for 64-bit.
	* target.h (Sized_target::resolve): Return bool.
	* resolve.cc (Symbol_table::resolve): Continue with normal
	processing when target resolve returns false.
	* symtab.h (Symbol::non_zero_localentry, set_non_zero_localentry):
	New accessors.
	(Symbol::non_zero_localentry_): New flag bit.
	* symtab.cc (Symbol::init_fields): Init non_zero_localentry_.

diff --git a/gold/powerpc.cc b/gold/powerpc.cc
index 9a200ab..72b2d25 100644
--- a/gold/powerpc.cc
+++ b/gold/powerpc.cc
@@ -1026,7 +1026,8 @@ class Target_powerpc : public Sized_target<size, big_endian>
 	    && this->plt_localentry0()
 	    && gsym->type() == elfcpp::STT_FUNC
 	    && gsym->is_defined()
-	    && gsym->nonvis() >> 3 == 0);
+	    && gsym->nonvis() >> 3 == 0
+	    && !gsym->non_zero_localentry());
   }
 
   bool
@@ -1051,6 +1052,22 @@ class Target_powerpc : public Sized_target<size, big_endian>
     return false;
   }
 
+  // Remember any symbols seen with non-zero localentry, even those
+  // not providing a definition
+  bool
+  resolve(Symbol* to, const elfcpp::Sym<size, big_endian>& sym, Object*,
+	  const char*)
+  {
+    if (size == 64)
+      {
+	unsigned char st_other = sym.get_st_other();
+	if ((st_other & elfcpp::STO_PPC64_LOCAL_MASK) != 0)
+	  to->set_non_zero_localentry();
+      }
+    // We haven't resolved anything, continue normal processing.
+    return false;
+  }
+
   int
   abiversion() const
   { return this->processor_specific_flags() & elfcpp::EF_PPC64_ABI; }
@@ -1603,7 +1620,7 @@ Target::Target_info Target_powerpc<64, true>::powerpc_info =
   true,			// is_big_endian
   elfcpp::EM_PPC64,	// machine_code
   false,		// has_make_symbol
-  false,		// has_resolve
+  true,			// has_resolve
   false,		// has_code_fill
   true,			// is_default_stack_executable
   false,		// can_icf_inline_merge_sections
@@ -1631,7 +1648,7 @@ Target::Target_info Target_powerpc<64, false>::powerpc_info =
   false,		// is_big_endian
   elfcpp::EM_PPC64,	// machine_code
   false,		// has_make_symbol
-  false,		// has_resolve
+  true,			// has_resolve
   false,		// has_code_fill
   true,			// is_default_stack_executable
   false,		// can_icf_inline_merge_sections
diff --git a/gold/resolve.cc b/gold/resolve.cc
index 8f4d2e3..7c22606 100644
--- a/gold/resolve.cc
+++ b/gold/resolve.cc
@@ -266,8 +266,8 @@ Symbol_table::resolve(Sized_symbol<size>* to,
     {
       Sized_target<size, big_endian>* sized_target;
       sized_target = parameters->sized_target<size, big_endian>();
-      sized_target->resolve(to, sym, object, version);
-      return;
+      if (sized_target->resolve(to, sym, object, version))
+	return;
     }
 
   if (!object->is_dynamic())
diff --git a/gold/symtab.cc b/gold/symtab.cc
index 43909ff..7e0a3f8 100644
--- a/gold/symtab.cc
+++ b/gold/symtab.cc
@@ -81,6 +81,7 @@ Symbol::init_fields(const char* name, const char* version,
   this->undef_binding_weak_ = false;
   this->is_predefined_ = false;
   this->is_protected_ = false;
+  this->non_zero_localentry_ = false;
 }
 
 // Return the demangled version of the symbol's name, but only
diff --git a/gold/symtab.h b/gold/symtab.h
index 77552ae..c371731 100644
--- a/gold/symtab.h
+++ b/gold/symtab.h
@@ -883,6 +883,16 @@ class Symbol
   set_is_protected()
   { this->is_protected_ = true; }
 
+  // Return state of PowerPC64 ELFv2 specific flag.
+  bool
+  non_zero_localentry() const
+  { return this->non_zero_localentry_; }
+
+  // Set PowerPC64 ELFv2 specific flag.
+  void
+  set_non_zero_localentry()
+  { this->non_zero_localentry_ = true; }
+
  protected:
   // Instances of this class should always be created at a specific
   // size.
@@ -1084,6 +1094,8 @@ class Symbol
   // The visibility_ field will be STV_DEFAULT in this case because we
   // must treat it as such from outside the shared object.
   bool is_protected_  : 1;
+  // Used by PowerPC64 ELFv2 to track st_other localentry (bit 36).
+  bool non_zero_localentry_ : 1;
 };
 
 // The parts of a symbol which are size specific.  Using a template
diff --git a/gold/target.h b/gold/target.h
index 5ca8435..cf6d902 100644
--- a/gold/target.h
+++ b/gold/target.h
@@ -852,7 +852,7 @@ class Sized_target : public Target
   // pre-existing symbol.  SYM is the new symbol, seen in OBJECT.
   // VERSION is the version of SYM.  This will only be called if
   // has_resolve() returns true.
-  virtual void
+  virtual bool
   resolve(Symbol*, const elfcpp::Sym<size, big_endian>&, Object*,
 	  const char*)
   { gold_unreachable(); }


-- 
Alan Modra
Australia Development Lab, IBM