[GOLD] PowerPC recreate eh_frame for stubs on each relax pass

There is a very small but non-zero probability that a stub group
contains stubs on one relax pass, but does not on the next.  In that
case we would get an FDE covering a zero length address range.
(Actually, it's even worse.  Alignment padding for stubs can mean the
address for the non-existent stubs is past the end of the original
section to which stubs are attached, and due to the way
do_plt_fde_location calculates the length we can get a negative
length.)  Fixing this properly requires removing the FDE.

Also, I have been implementing the __tls_get_addr_opt support for
gold, and that stub needs something other than the default FDE.  The
necessary FDE will depend on the offset to the __tls_get_addr_opt
stub, which of course can change during relaxation.  That means at the
very least, rewriting the FDE on each pass, possibly changing the FDE
size.  I think that is better done by completely recreating PLT
eh_frame FDEs.

	* ehframe.cc (Fde::operator==): New.
	(Cie::remove_fde, Eh_frame::remove_ehframe_for_plt): New.
	* ehframe.h (Fde::operator==): Declare.
	(Cie::remove_fde, Eh_frame::remove_ehframe_for_plt): Likewise.
	* layout.cc (Layout::remove_eh_frame_for_plt): New.
	* layout.h (Layout::remove_eh_frame_for_plt): Declare.
	* powerpc.cc (Target_powerpc::do_relax): Remove old eh_frame FDEs.
	(Stub_table::add_eh_frame): Delete eh_frame_added_ condition.
	Don't add eh_frame for empty stub section.
	(Stub_table::remove_eh_frame): New.

1 files changed, 46 insertions, 0 deletions

diff --git a/gold/ehframe.cc b/gold/ehframe.cc
index fd72a4f..61b5193 100644
--- a/gold/ehframe.cc
+++ b/gold/ehframe.cc
@@ -325,6 +325,21 @@ Eh_frame_hdr::get_fde_addresses(Output_file* of,
 
 // Class Fde.
 
+bool
+Fde::operator==(const Fde& that) const
+{
+  if (this->object_ != that.object_
+      || this->contents_ != that.contents_)
+    return false;
+  if (this->object_ == NULL)
+    return (this->u_.from_linker.plt == that.u_.from_linker.plt
+	    && this->u_.from_linker.post_map == that.u_.from_linker.post_map);
+  else
+    return (this->u_.from_object.shndx == that.u_.from_object.shndx
+	    && (this->u_.from_object.input_offset
+		== that.u_.from_object.input_offset));
+}
+
 // Write the FDE to OVIEW starting at OFFSET.  CIE_OFFSET is the
 // offset of the CIE in OVIEW.  OUTPUT_OFFSET is the offset of the
 // Eh_frame section within the output section.  FDE_ENCODING is the
@@ -443,6 +458,15 @@ Cie::set_output_offset(section_offset_type output_offset,
   return output_offset + length;
 }
 
+// Remove FDE.  Only the last FDE using this CIE may be removed.
+
+void
+Cie::remove_fde(const Fde* fde)
+{
+  gold_assert(*fde == *this->fdes_.back());
+  this->fdes_.pop_back();
+}
+
 // Write the CIE to OVIEW starting at OFFSET.  OUTPUT_OFFSET is the
 // offset of the Eh_frame section within the output section.  Round up
 // the bytes to ADDRALIGN.  ADDRESS is the virtual address of OVIEW.
@@ -1143,6 +1167,28 @@ Eh_frame::add_ehframe_for_plt(Output_data* plt, const unsigned char* cie_data,
     this->final_data_size_ += align_address(fde_length + 8, this->addralign());
 }
 
+// Remove unwind information for a PLT.  Only the last FDE added may be removed.
+
+void
+Eh_frame::remove_ehframe_for_plt(Output_data* plt,
+				 const unsigned char* cie_data,
+				 size_t cie_length,
+				 const unsigned char* fde_data,
+				 size_t fde_length)
+{
+  Cie cie(NULL, 0, 0, elfcpp::DW_EH_PE_pcrel | elfcpp::DW_EH_PE_sdata4, "",
+	  cie_data, cie_length);
+  Cie_offsets::iterator find_cie = this->cie_offsets_.find(&cie);
+  gold_assert (find_cie != this->cie_offsets_.end());
+  Cie* pcie = *find_cie;
+
+  Fde* fde = new Fde(plt, fde_data, fde_length, this->mappings_are_done_);
+  pcie->remove_fde(fde);
+
+  if (this->mappings_are_done_)
+    this->final_data_size_ -= align_address(fde_length + 8, this->addralign());
+}
+
 // Return the number of FDEs.
 
 unsigned int