PowerPC PLT16 relocations

The PowerPC64 ELFv2 ABI and the PowerPC SysV ABI support a number of
relocations that can be used to create and access a PLT entry.
However, the relocs are not well defined.  The PLT16 family of relocs
talk about "the section offset or address of the procedure linkage
table entry".  It's plain that we do need a relative address when PIC
as otherwise we'd have dynamic text relocations, but "section offset"
doesn't specify which section.  The most obvious one, ".plt", isn't
that useful because there is no readily available way of addressing
the start of the ".plt" section.  Much more useful would be "the
GOT/TOC-pointer relative offset of the procedure linkage table entry",
and I suppose you could argue that is a "section offset" of sorts.
For PowerPC64 it is better to use the same TOC-pointer relative
addressing even when non-PIC, since ".plt" may be located outside the
range of a 32-bit address.  However, for ppc32 we do want an absolute
address when non-PIC as a GOT pointer may not be set up.  Also, for
ppc32 PIC we have a similar situation to R_PPC_PLTREL24 in that the
GOT pointer is set to a location in the .got2 section and we need to
specify the .got2 offset in the PLT16 reloc addend.

This patch supports PLT16 relocations using these semantics.  This is
not an ABI change for ppc32 since the relocations were not previously
supported by GNU ld, but is for ppc64 where some of the PLT16 relocs
were supported.  I'm not particularly concerned since the old ppc64
PLT16 reloc semantics made them almost completely useless.

bfd/
	* elf32-ppc.c (ppc_elf_check_relocs): Handle PLT16 relocs.
	(ppc_elf_relocate_section): Likewise.
	* elf64-ppc.c (ppc64_elf_check_relocs): Handle PLT16_LO_DS.
	(ppc64_elf_relocate_section): Likewise.  Correct PLT16
	resolution to plt entry relative to toc pointer.
gold/
	* powerpc.cc (Target_powerpc::plt_off): New functions.
	(is_plt16_reloc): New function.
	(Stub_table::plt_off): Use Target_powerpc::plt_off.
	(Stub_table::plt_call_size): Use plt_off.
	(Stub_table::do_write): Likewise.
	(Target_powerpc::Scan::get_reference_flags): Return RELATIVE_REF
	for PLT16 relocations.
	(Target_powerpc::Scan::reloc_needs_plt_for_ifunc): Return true
	for PLT16 relocations.
	(Target_powerpc::Scan::global): Make a PLT entry for PLT16 relocations.
	(Target_powerpc::Relocate::relocate): Support PLT16 relocations.
	(Powerpc_scan_relocatable_reloc::global_strategy): Return RELOC_SPECIAL
	for ppc32 plt16 relocs.

2 files changed, 151 insertions, 56 deletions

diff --git a/gold/ChangeLog b/gold/ChangeLog
index 1c92cf1..48c87e4 100644
--- a/gold/ChangeLog
+++ b/gold/ChangeLog
@@ -1,3 +1,19 @@
+2018-04-09  Alan Modra  <amodra@gmail.com>
+
+	* powerpc.cc (Target_powerpc::plt_off): New functions.
+	(is_plt16_reloc): New function.
+	(Stub_table::plt_off): Use Target_powerpc::plt_off.
+	(Stub_table::plt_call_size): Use plt_off.
+	(Stub_table::do_write): Likewise.
+	(Target_powerpc::Scan::get_reference_flags): Return RELATIVE_REF
+	for PLT16 relocations.
+	(Target_powerpc::Scan::reloc_needs_plt_for_ifunc): Return true
+	for PLT16 relocations.
+	(Target_powerpc::Scan::global): Make a PLT entry for PLT16 relocations.
+	(Target_powerpc::Relocate::relocate): Support PLT16 relocations.
+	(Powerpc_scan_relocatable_reloc::global_strategy): Return RELOC_SPECIAL
+	for ppc32 plt16 relocs.
+
 2018-04-06  Cary Coutant  <ccoutant@gmail.com>
 
 	* object.cc (Sized_relobj_file::include_section_group): Store
diff --git a/gold/powerpc.cc b/gold/powerpc.cc
index a2c9698..0975fee 100644
--- a/gold/powerpc.cc
+++ b/gold/powerpc.cc
@@ -860,6 +860,29 @@ class Target_powerpc : public Sized_target<size, big_endian>
     return this->iplt_;
   }
 
+  // Return the plt offset and section for the given global sym.
+  Address
+  plt_off(const Symbol* gsym,
+	  const Output_data_plt_powerpc<size, big_endian>** sec) const
+  {
+    if (gsym->type() == elfcpp::STT_GNU_IFUNC
+	&& gsym->can_use_relative_reloc(false))
+      *sec = this->iplt_section();
+    else
+      *sec = this->plt_section();
+    return gsym->plt_offset();
+  }
+
+  // Return the plt offset and section for the given local sym.
+  Address
+  plt_off(const Sized_relobj_file<size, big_endian>* relobj,
+	  unsigned int local_sym_index,
+	  const Output_data_plt_powerpc<size, big_endian>** sec) const
+  {
+    *sec = this->iplt_section();
+    return relobj->local_plt_offset(local_sym_index);
+  }
+
   // Get the .glink section.
   const Output_data_glink<size, big_endian>*
   glink_section() const
@@ -1730,6 +1753,17 @@ is_branch_reloc(unsigned int r_type)
 	  || r_type == elfcpp::R_POWERPC_ADDR14_BRNTAKEN);
 }
 
+// Reloc resolves to plt entry.
+template<int size>
+inline bool
+is_plt16_reloc(unsigned int r_type)
+{
+  return (r_type == elfcpp::R_POWERPC_PLT16_LO
+	  || r_type == elfcpp::R_POWERPC_PLT16_HI
+	  || r_type == elfcpp::R_POWERPC_PLT16_HA
+	  || (size == 64 && r_type == elfcpp::R_PPC64_PLT16_LO_DS));
+}
+
 // If INSN is an opcode that may be used with an @tls operand, return
 // the transformed insn for TLS optimisation, otherwise return 0.  If
 // REG is non-zero only match an insn with RB or RA equal to REG.
@@ -4408,21 +4442,17 @@ class Stub_table : public Output_relaxed_input_section
 
   // Return the plt offset for the given call stub.
   Address
-  plt_off(typename Plt_stub_entries::const_iterator p, bool* is_iplt) const
+  plt_off(typename Plt_stub_entries::const_iterator p,
+	  const Output_data_plt_powerpc<size, big_endian>** sec) const
   {
     const Symbol* gsym = p->first.sym_;
     if (gsym != NULL)
-      {
-	*is_iplt = (gsym->type() == elfcpp::STT_GNU_IFUNC
-		    && gsym->can_use_relative_reloc(false));
-	return gsym->plt_offset();
-      }
+      return this->targ_->plt_off(gsym, sec);
     else
       {
-	*is_iplt = true;
 	const Sized_relobj_file<size, big_endian>* relobj = p->first.object_;
 	unsigned int local_sym_index = p->first.locsym_;
-	return relobj->local_plt_offset(local_sym_index);
+	return this->targ_->plt_off(relobj, local_sym_index, sec);
       }
   }
 
@@ -4437,12 +4467,9 @@ class Stub_table : public Output_relaxed_input_section
 		+ (this->targ_->is_tls_get_addr_opt(gsym) ? 8 * 4 : 0));
       }
 
-    bool is_iplt;
-    Address plt_addr = this->plt_off(p, &is_iplt);
-    if (is_iplt)
-      plt_addr += this->targ_->iplt_section()->address();
-    else
-      plt_addr += this->targ_->plt_section()->address();
+    const Output_data_plt_powerpc<size, big_endian>* plt;
+    Address plt_addr = this->plt_off(p, &plt);
+    plt_addr += plt->address();
     Address got_addr = this->targ_->got_section()->output_section()->address();
     const Powerpc_relobj<size, big_endian>* ppcobj = static_cast
       <const Powerpc_relobj<size, big_endian>*>(p->first.object_);
@@ -5158,27 +5185,15 @@ Stub_table<size, big_endian>::do_write(Output_file* of)
 
       if (!this->plt_call_stubs_.empty())
 	{
-	  // The base address of the .plt section.
-	  Address plt_base = this->targ_->plt_section()->address();
-	  Address iplt_base = invalid_address;
-
 	  // Write out plt call stubs.
 	  typename Plt_stub_entries::const_iterator cs;
 	  for (cs = this->plt_call_stubs_.begin();
 	       cs != this->plt_call_stubs_.end();
 	       ++cs)
 	    {
-	      bool is_iplt;
-	      Address pltoff = this->plt_off(cs, &is_iplt);
-	      Address plt_addr = pltoff;
-	      if (is_iplt)
-		{
-		  if (iplt_base == invalid_address)
-		    iplt_base = this->targ_->iplt_section()->address();
-		  plt_addr += iplt_base;
-		}
-	      else
-		plt_addr += plt_base;
+	      const Output_data_plt_powerpc<size, big_endian>* plt;
+	      Address pltoff = this->plt_off(cs, &plt);
+	      Address plt_addr = pltoff + plt->address();
 	      const Powerpc_relobj<size, big_endian>* ppcobj = static_cast
 		<const Powerpc_relobj<size, big_endian>*>(cs->first.object_);
 	      Address got_addr = got_os_addr + ppcobj->toc_base_offset();
@@ -5397,9 +5412,6 @@ Stub_table<size, big_endian>::do_write(Output_file* of)
     {
       if (!this->plt_call_stubs_.empty())
 	{
-	  // The base address of the .plt section.
-	  Address plt_base = this->targ_->plt_section()->address();
-	  Address iplt_base = invalid_address;
 	  // The address of _GLOBAL_OFFSET_TABLE_.
 	  Address g_o_t = invalid_address;
 
@@ -5409,16 +5421,9 @@ Stub_table<size, big_endian>::do_write(Output_file* of)
 	       cs != this->plt_call_stubs_.end();
 	       ++cs)
 	    {
-	      bool is_iplt;
-	      Address plt_addr = this->plt_off(cs, &is_iplt);
-	      if (is_iplt)
-		{
-		  if (iplt_base == invalid_address)
-		    iplt_base = this->targ_->iplt_section()->address();
-		  plt_addr += iplt_base;
-		}
-	      else
-		plt_addr += plt_base;
+	      const Output_data_plt_powerpc<size, big_endian>* plt;
+	      Address plt_addr = this->plt_off(cs, &plt);
+	      plt_addr += plt->address();
 
 	      p = oview + cs->second.off_;
 	      const Symbol* gsym = cs->first.sym_;
@@ -6244,6 +6249,10 @@ Target_powerpc<size, big_endian>::Scan::get_reference_flags(
     case elfcpp::R_PPC64_TOC16_HA:
     case elfcpp::R_PPC64_TOC16_DS:
     case elfcpp::R_PPC64_TOC16_LO_DS:
+    case elfcpp::R_POWERPC_PLT16_LO:
+    case elfcpp::R_POWERPC_PLT16_HI:
+    case elfcpp::R_POWERPC_PLT16_HA:
+    case elfcpp::R_PPC64_PLT16_LO_DS:
       ref = Symbol::RELATIVE_REF;
       break;
 
@@ -6427,6 +6436,14 @@ Target_powerpc<size, big_endian>::Scan::reloc_needs_plt_for_ifunc(
     case elfcpp::R_PPC64_GOT16_LO_DS:
       return false;
 
+    // PLT relocs are OK and need a PLT entry.
+    case elfcpp::R_POWERPC_PLT16_LO:
+    case elfcpp::R_POWERPC_PLT16_HI:
+    case elfcpp::R_POWERPC_PLT16_HA:
+    case elfcpp::R_PPC64_PLT16_LO_DS:
+      return true;
+      break;
+
     // Function calls are good, and these do need a PLT entry.
     case elfcpp::R_POWERPC_ADDR24:
     case elfcpp::R_POWERPC_ADDR14:
@@ -7245,6 +7262,14 @@ Target_powerpc<size, big_endian>::Scan::global(
       }
       break;
 
+    case elfcpp::R_POWERPC_PLT16_LO:
+    case elfcpp::R_POWERPC_PLT16_HI:
+    case elfcpp::R_POWERPC_PLT16_HA:
+    case elfcpp::R_PPC64_PLT16_LO_DS:
+      if (!pushed_ifunc)
+	target->make_plt_entry(symtab, layout, gsym);
+      break;
+
     case elfcpp::R_PPC_PLTREL24:
     case elfcpp::R_POWERPC_REL24:
       if (!is_ifunc)
@@ -8366,9 +8391,12 @@ Target_powerpc<size, big_endian>::Relocate::relocate(
   bool has_stub_value = false;
   bool localentry0 = false;
   unsigned int r_sym = elfcpp::elf_r_sym<size>(rela.get_r_info());
-  if ((gsym != NULL
+  bool has_plt_offset
+    = (gsym != NULL
        ? gsym->use_plt_offset(Scan::get_reference_flags(r_type, target))
-       : object->local_has_plt_offset(r_sym))
+       : object->local_has_plt_offset(r_sym));
+  if (has_plt_offset
+      && !is_plt16_reloc<size>(r_type)
       && (!psymval->is_ifunc_symbol()
 	  || Scan::reloc_needs_plt_for_ifunc(target, object, r_type, false)))
     {
@@ -8440,12 +8468,38 @@ Target_powerpc<size, big_endian>::Relocate::relocate(
       gold_assert(has_stub_value || !(os->flags() & elfcpp::SHF_ALLOC));
     }
 
-  if (r_type == elfcpp::R_POWERPC_GOT16
-      || r_type == elfcpp::R_POWERPC_GOT16_LO
-      || r_type == elfcpp::R_POWERPC_GOT16_HI
-      || r_type == elfcpp::R_POWERPC_GOT16_HA
-      || r_type == elfcpp::R_PPC64_GOT16_DS
-      || r_type == elfcpp::R_PPC64_GOT16_LO_DS)
+  if (has_plt_offset && is_plt16_reloc<size>(r_type))
+    {
+      const Output_data_plt_powerpc<size, big_endian>* plt;
+      if (gsym)
+	value = target->plt_off(gsym, &plt);
+      else
+	value = target->plt_off(object, r_sym, &plt);
+      value += plt->address();
+
+      if (size == 64)
+	value -= (target->got_section()->output_section()->address()
+		  + object->toc_base_offset());
+      else if (parameters->options().output_is_position_independent())
+	{
+	  if (rela.get_r_addend() >= 32768)
+	    {
+	      unsigned int got2 = object->got2_shndx();
+	      value -= (object->get_output_section_offset(got2)
+			+ object->output_section(got2)->address()
+			+ rela.get_r_addend());
+	    }
+	  else
+	    value -= (target->got_section()->address()
+		      + target->got_section()->g_o_t());
+	}
+    }
+  else if (r_type == elfcpp::R_POWERPC_GOT16
+	   || r_type == elfcpp::R_POWERPC_GOT16_LO
+	   || r_type == elfcpp::R_POWERPC_GOT16_HI
+	   || r_type == elfcpp::R_POWERPC_GOT16_HA
+	   || r_type == elfcpp::R_PPC64_GOT16_DS
+	   || r_type == elfcpp::R_PPC64_GOT16_LO_DS)
     {
       if (gsym != NULL)
 	{
@@ -8777,7 +8831,11 @@ Target_powerpc<size, big_endian>::Relocate::relocate(
   else if (!has_stub_value)
     {
       Address addend = 0;
-      if (!(size == 32 && r_type == elfcpp::R_PPC_PLTREL24))
+      if (!(size == 32
+	    && (r_type == elfcpp::R_PPC_PLTREL24
+		|| r_type == elfcpp::R_POWERPC_PLT16_LO
+		|| r_type == elfcpp::R_POWERPC_PLT16_HI
+		|| r_type == elfcpp::R_POWERPC_PLT16_HA)))
 	addend = rela.get_r_addend();
       value = psymval->value(object, addend);
       if (size == 64 && is_branch_reloc(r_type))
@@ -8944,6 +9002,23 @@ Target_powerpc<size, big_endian>::Relocate::relocate(
       }
       break;
 
+    case elfcpp::R_POWERPC_PLT16_HA:
+      if (size == 32
+	  && !parameters->options().output_is_position_independent())
+	{
+	  Insn* iview = reinterpret_cast<Insn*>(view - d_offset);
+	  Insn insn = elfcpp::Swap<32, big_endian>::readval(iview);
+
+	  // Convert addis to lis.
+	  if ((insn & (0x3f << 26)) == 15u << 26
+	      && (insn & (0x1f << 16)) != 0)
+	    {
+	      insn &= ~(0x1f << 16);
+	      elfcpp::Swap<32, big_endian>::writeval(iview, insn);
+	    }
+	}
+      break;
+
     default:
       break;
     }
@@ -9345,6 +9420,7 @@ Target_powerpc<size, big_endian>::Relocate::relocate(
     case elfcpp::R_POWERPC_REL16_LO:
     case elfcpp::R_PPC64_TOC16_LO:
     case elfcpp::R_POWERPC_GOT16_LO:
+    case elfcpp::R_POWERPC_PLT16_LO:
     case elfcpp::R_POWERPC_SECTOFF_LO:
     case elfcpp::R_POWERPC_TPREL16_LO:
     case elfcpp::R_POWERPC_DTPREL16_LO:
@@ -9371,6 +9447,7 @@ Target_powerpc<size, big_endian>::Relocate::relocate(
     case elfcpp::R_POWERPC_REL16_HI:
     case elfcpp::R_PPC64_TOC16_HI:
     case elfcpp::R_POWERPC_GOT16_HI:
+    case elfcpp::R_POWERPC_PLT16_HI:
     case elfcpp::R_POWERPC_SECTOFF_HI:
     case elfcpp::R_POWERPC_TPREL16_HI:
     case elfcpp::R_POWERPC_DTPREL16_HI:
@@ -9392,6 +9469,7 @@ Target_powerpc<size, big_endian>::Relocate::relocate(
     case elfcpp::R_POWERPC_REL16_HA:
     case elfcpp::R_PPC64_TOC16_HA:
     case elfcpp::R_POWERPC_GOT16_HA:
+    case elfcpp::R_POWERPC_PLT16_HA:
     case elfcpp::R_POWERPC_SECTOFF_HA:
     case elfcpp::R_POWERPC_TPREL16_HA:
     case elfcpp::R_POWERPC_DTPREL16_HA:
@@ -9464,6 +9542,7 @@ Target_powerpc<size, big_endian>::Relocate::relocate(
     case elfcpp::R_PPC64_TOC16_LO_DS:
     case elfcpp::R_PPC64_GOT16_DS:
     case elfcpp::R_PPC64_GOT16_LO_DS:
+    case elfcpp::R_PPC64_PLT16_LO_DS:
     case elfcpp::R_PPC64_SECTOFF_DS:
     case elfcpp::R_PPC64_SECTOFF_LO_DS:
       maybe_dq_reloc = true;
@@ -9522,9 +9601,6 @@ Target_powerpc<size, big_endian>::Relocate::relocate(
 
     case elfcpp::R_POWERPC_PLT32:
     case elfcpp::R_POWERPC_PLTREL32:
-    case elfcpp::R_POWERPC_PLT16_LO:
-    case elfcpp::R_POWERPC_PLT16_HI:
-    case elfcpp::R_POWERPC_PLT16_HA:
     case elfcpp::R_PPC_SDAREL16:
     case elfcpp::R_POWERPC_ADDR30:
     case elfcpp::R_PPC64_PLT64:
@@ -9533,7 +9609,6 @@ Target_powerpc<size, big_endian>::Relocate::relocate(
     case elfcpp::R_PPC64_PLTGOT16_LO:
     case elfcpp::R_PPC64_PLTGOT16_HI:
     case elfcpp::R_PPC64_PLTGOT16_HA:
-    case elfcpp::R_PPC64_PLT16_LO_DS:
     case elfcpp::R_PPC64_PLTGOT16_DS:
     case elfcpp::R_PPC64_PLTGOT16_LO_DS:
     case elfcpp::R_PPC_EMB_RELSDA:
@@ -9660,7 +9735,11 @@ public:
   inline Relocatable_relocs::Reloc_strategy
   global_strategy(unsigned int r_type, Relobj*, unsigned int)
   {
-    if (r_type == elfcpp::R_PPC_PLTREL24)
+    if (size == 32
+	&& (r_type == elfcpp::R_PPC_PLTREL24
+	    || r_type == elfcpp::R_POWERPC_PLT16_LO
+	    || r_type == elfcpp::R_POWERPC_PLT16_HI
+	    || r_type == elfcpp::R_POWERPC_PLT16_HA))
       return Relocatable_relocs::RELOC_SPECIAL;
     return Relocatable_relocs::RELOC_COPY;
   }