From 3151305a47fc17a35bc76cc50578b3e8f9b93d9d Mon Sep 17 00:00:00 2001
From: Ian Lance Taylor <iant@google.com>
Date: Wed, 26 Sep 2007 05:44:38 +0000
Subject: Add basic exception frame header, plus test.

---
 gold/ehframe.cc | 126 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 126 insertions(+)
 create mode 100644 gold/ehframe.cc

(limited to 'gold/ehframe.cc')

diff --git a/gold/ehframe.cc b/gold/ehframe.cc
new file mode 100644
index 0000000..1e0583a
--- /dev/null
+++ b/gold/ehframe.cc
@@ -0,0 +1,126 @@
+// ehframe.cc -- handle exception frame sections for gold
+
+// Copyright 2006, 2007 Free Software Foundation, Inc.
+// Written by Ian Lance Taylor <iant@google.com>.
+
+// This file is part of gold.
+
+// This program is free software; you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation; either version 3 of the License, or
+// (at your option) any later version.
+
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with this program; if not, write to the Free Software
+// Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,
+// MA 02110-1301, USA.
+
+#include "gold.h"
+
+#include "elfcpp.h"
+#include "dwarf.h"
+#include "ehframe.h"
+
+namespace gold
+{
+
+// This file handles generation of the exception frame header that
+// gcc's runtime support libraries use to find unwind information at
+// runtime.
+
+// The exception frame header starts with four bytes:
+
+// 0: The version number, currently 1.
+
+// 1: The encoding of the pointer to the exception frames.  This can
+//    be any DWARF unwind encoding (DW_EH_PE_*).  It is normally a 4
+//    byte PC relative offset (DW_EH_PE_pcrel | DW_EH_PE_sdata4).
+
+// 2: The encoding of the count of the number of FDE pointers in the
+//    lookup table.  This can be any DWARF unwind encoding, and in
+//    particular can be DW_EH_PE_omit if the count is omitted.  It is
+//    normally a 4 byte unsigned count (DW_EH_PE_udata4).
+
+// 3: The encoding of the lookup table entries.  Currently gcc's
+//    libraries will only support DW_EH_PE_datarel | DW_EH_PE_sdata4,
+//    which means that the values are 4 byte offsets from the start of
+//    the table.
+
+// The exception frame header is followed by a pointer to the contents
+// of the exception frame section (.eh_frame).  This pointer is
+// encoded as specified in the byte at offset 1 of the header (i.e.,
+// it is normally a 4 byte PC relative offset).
+
+// If there is a lookup table, this is followed by the count of the
+// number of FDE pointers, encoded as specified in the byte at offset
+// 2 of the header (i.e., normally a 4 byte unsigned integer).
+
+// This is followed by the table, which should start at an 4-byte
+// aligned address in memory.  Each entry in the table is 8 bytes.
+// Each entry represents an FDE.  The first four bytes of each entry
+// are an offset to the starting PC for the FDE.  The last four bytes
+// of each entry are an offset to the FDE data.  The offsets are from
+// the start of the exception frame header information.  The entries
+// are in sorted order by starting PC.
+
+// FIXME: We currently always generate an empty exception frame
+// header.
+
+const int eh_frame_hdr_size = 4;
+
+// Construct the exception frame header.
+
+Eh_frame_hdr::Eh_frame_hdr(const Target* target,
+			   Output_section* eh_frame_section)
+  : Output_section_data(4),
+    target_(target), eh_frame_section_(eh_frame_section)
+{
+}
+
+// Set the final address and size of the exception frame header.
+
+void
+Eh_frame_hdr::do_set_address(uint64_t, off_t)
+{
+  this->set_data_size(eh_frame_hdr_size + 4);
+}
+
+// Write the data to the flie.
+
+void
+Eh_frame_hdr::do_write(Output_file* of)
+{
+  const off_t off = this->offset();
+  const off_t oview_size = this->data_size();
+  unsigned char* const oview = of->get_output_view(off, oview_size);
+
+  // Version number.
+  oview[0] = 1;
+
+  // Write out a 4 byte PC relative offset to the address of the
+  // .eh_frame section.
+  oview[1] = elfcpp::DW_EH_PE_pcrel | elfcpp::DW_EH_PE_sdata4;
+  uint64_t eh_frame_address = this->eh_frame_section_->address();
+  uint64_t eh_frame_hdr_address = this->address();
+  uint64_t eh_frame_offset = (eh_frame_address -
+			      (eh_frame_hdr_address + 4));
+  if (this->target_->is_big_endian())
+    elfcpp::Swap<32, true>::writeval(oview + 4, eh_frame_offset);
+  else
+    elfcpp::Swap<32, false>::writeval(oview + 4, eh_frame_offset);
+
+  // We don't currently write out the sorted table.
+  oview[2] = elfcpp::DW_EH_PE_omit;
+  oview[3] = elfcpp::DW_EH_PE_omit;
+
+  gold_assert(oview_size == 8);
+
+  of->write_output_view(off, oview_size, oview);
+}
+
+} // End namespace gold.
-- 
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