[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, 13 insertions, 0 deletions

diff --git a/gold/ehframe.h b/gold/ehframe.h
index 347ce46..f501634 100644
--- a/gold/ehframe.h
+++ b/gold/ehframe.h
@@ -217,6 +217,8 @@ class Fde
 	section_offset_type cie_offset, unsigned char fde_encoding,
 	Eh_frame_hdr* eh_frame_hdr);
 
+  bool operator==(const Fde&) const;
+
  private:
   // The object in which this FDE was seen.  This will be NULL for a
   // linker generated FDE.
@@ -298,6 +300,10 @@ class Cie
   add_fde(Fde* fde)
   { this->fdes_.push_back(fde); }
 
+  // Remove an FDE associated with this CIE.  Only the last FDE may be removed.
+  void
+  remove_fde(const Fde*);
+
   // Return the number of FDEs.
   unsigned int
   fde_count() const
@@ -405,6 +411,13 @@ class Eh_frame : public Output_section_data
 		      size_t cie_length, const unsigned char* fde_data,
 		      size_t fde_length);
 
+  // Remove unwind information for a PLT.  Only the last FDE added may
+  // be removed.
+  void
+  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);
+
   // Return the number of FDEs.
   unsigned int
   fde_count() const;