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+// 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.