[GOLD] PowerPC notoc eh_frame

When generating notoc call and branch stubs without the benefit of
pc-relative insns, the stubs need to use LR to access the run time PC.
All LR changes must be described in .eh_frame if we're to support
unwinding through asynchronous exceptions.  That's what this patch
does.

The patch has gone through way too many iterations.  At first I
attempted to add multiple FDEs, one for each stub.  That ran into
difficulties with do_plt_fde_location which is only capable of setting
the address of a single FDE per Output_data section, and with removing
any FDEs added on a previous do_relax pass.  Removing FDEs (git commit
be897fb774) went overboard in matching the FDE contents.  That means
either stashing the contents created for add_eh_frame_for_plt to use
when calling remove_eh_frame_for_plt, or recreating contents on the
fly (*) just to remove FDEs.  In fact, FDE content matching is quite
unnecesary.  FDEs added by a previous do_relax pass are those with
u_.from_linker.post_map set.  So they can easily be recognised just by
looking at that flag.  This patch keeps that part of the multiple FDE
changes.

In the end I went for just one FDE per stub group to describe the call
stubs.  That's reasonably efficient for the common case of only
needing to describe the __tls_get_addr_opt call stub.  We don't expect
to be making many calls using notoc stubs without pc-relative insns.

*) Which has it's own set of problems.  The contents must be recreated
using the old stub layout, but .eh_frame size can affect stub
requirements so you need to temporarily keep the old .eh_frame size
when creating new stubs, then reset .eh_frame size before adding new
FDEs.

	* ehframe.cc (Fde::operator==): Delete.
	(Cie::remove_fde): Delete.
	(Eh_frame::remove_ehframe_for_plt): Delete fde_data and fde_length
	parameters.  Remove all post-map plt FDEs.
	* ehframe.h (Fde:post_map): Make const, add variant to compare plt.
	(Fde::operator==): Delete.
	(Cie::remove_fde): Implement here.
	(Cie::last_fde): New accessor.
	(Eh_frame::remove_ehframe_for_plt): Update prototype.
	* layout.cc (Layout::remove_eh_frame_for_plt): Delete fde_data and
	fde_length parameters.
	* layout.h (Layout::remove_eh_frame_for_plt): Update prototype.
	* powerpc.cc (Stub_table::tls_get_addr_opt_bctrl_): Delete.
	(Stub_table::plt_fde_len_, plt_fde_, init_plt_fde): Delete.
	(Stub_table::add_plt_call_entry): Don't set tls_get_addr_opt_bctrl_.
	(eh_advance): New function.
	(stub_sort): New function.
	(Stub_table::add_eh_frame): Emit eh_frame for notoc plt calls and
	branches as well as __tls_get_addr_opt plt call stub.
	(Stub_table::remove_eh_frame): Update to suit.

1 files changed, 16 insertions, 9 deletions

diff --git a/gold/ehframe.h b/gold/ehframe.h
index ba65083..4fd8f3e 100644
--- a/gold/ehframe.h
+++ b/gold/ehframe.h
@@ -203,9 +203,14 @@ class Fde
 
   // Return whether this FDE was added after merge mapping.
   bool
-  post_map()
+  post_map() const
   { return this->object_ == NULL && this->u_.from_linker.post_map; }
 
+  // Return whether this FDE was added for the PLT after merge mapping.
+  bool
+  post_map(const Output_data* plt) const
+  { return this->post_map() && this->u_.from_linker.plt == plt; }
+
   // Write the FDE to OVIEW starting at OFFSET.  FDE_ENCODING is the
   // encoding, from the CIE.  Round up the bytes to ADDRALIGN if
   // necessary.  ADDRESS is the virtual address of OVIEW.  Record the
@@ -217,8 +222,6 @@ 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.
@@ -300,9 +303,15 @@ 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.
+  // Remove the last FDE associated with this CIE.
   void
-  remove_fde(const Fde*);
+  remove_fde()
+  { this->fdes_.pop_back(); }
+
+  // Access the last FDE associated with this CIE.
+  const Fde*
+  last_fde() const
+  { return this->fdes_.back(); }
 
   // Return the number of FDEs.
   unsigned int
@@ -411,12 +420,10 @@ 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.
+  // Remove all post-map unwind information for a PLT.
   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);
+			 size_t cie_length);
 
   // Return the number of FDEs.
   unsigned int