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