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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.
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