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Diffstat (limited to 'gold/ehframe.cc')
-rw-r--r-- | gold/ehframe.cc | 126 |
1 files changed, 126 insertions, 0 deletions
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. |