[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, 3 insertions, 6 deletions

diff --git a/gold/layout.cc b/gold/layout.cc
index b83e8e6..fc7cdf8 100644
--- a/gold/layout.cc
+++ b/gold/layout.cc
@@ -1604,21 +1604,18 @@ Layout::add_eh_frame_for_plt(Output_data* plt, const unsigned char* cie_data,
     }
 }
 
-// Remove .eh_frame information for a PLT.  FDEs using the CIE must
-// be removed in reverse order to the order they were added.
+// Remove all post-map .eh_frame information for a PLT.
 
 void
 Layout::remove_eh_frame_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)
 {
   if (parameters->incremental())
     {
       // FIXME: Maybe this could work some day....
       return;
     }
-  this->eh_frame_data_->remove_ehframe_for_plt(plt, cie_data, cie_length,
-					       fde_data, fde_length);
+  this->eh_frame_data_->remove_ehframe_for_plt(plt, cie_data, cie_length);
 }
 
 // Scan a .debug_info or .debug_types section, and add summary