| 1 | // ehframe.cc -- handle exception frame sections for gold |
| 2 | |
| 3 | // Copyright 2006, 2007 Free Software Foundation, Inc. |
| 4 | // Written by Ian Lance Taylor <iant@google.com>. |
| 5 | |
| 6 | // This file is part of gold. |
| 7 | |
| 8 | // This program is free software; you can redistribute it and/or modify |
| 9 | // it under the terms of the GNU General Public License as published by |
| 10 | // the Free Software Foundation; either version 3 of the License, or |
| 11 | // (at your option) any later version. |
| 12 | |
| 13 | // This program is distributed in the hope that it will be useful, |
| 14 | // but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 15 | // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 16 | // GNU General Public License for more details. |
| 17 | |
| 18 | // You should have received a copy of the GNU General Public License |
| 19 | // along with this program; if not, write to the Free Software |
| 20 | // Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston, |
| 21 | // MA 02110-1301, USA. |
| 22 | |
| 23 | #include "gold.h" |
| 24 | |
| 25 | #include "elfcpp.h" |
| 26 | #include "dwarf.h" |
| 27 | #include "ehframe.h" |
| 28 | |
| 29 | namespace gold |
| 30 | { |
| 31 | |
| 32 | // This file handles generation of the exception frame header that |
| 33 | // gcc's runtime support libraries use to find unwind information at |
| 34 | // runtime. |
| 35 | |
| 36 | // The exception frame header starts with four bytes: |
| 37 | |
| 38 | // 0: The version number, currently 1. |
| 39 | |
| 40 | // 1: The encoding of the pointer to the exception frames. This can |
| 41 | // be any DWARF unwind encoding (DW_EH_PE_*). It is normally a 4 |
| 42 | // byte PC relative offset (DW_EH_PE_pcrel | DW_EH_PE_sdata4). |
| 43 | |
| 44 | // 2: The encoding of the count of the number of FDE pointers in the |
| 45 | // lookup table. This can be any DWARF unwind encoding, and in |
| 46 | // particular can be DW_EH_PE_omit if the count is omitted. It is |
| 47 | // normally a 4 byte unsigned count (DW_EH_PE_udata4). |
| 48 | |
| 49 | // 3: The encoding of the lookup table entries. Currently gcc's |
| 50 | // libraries will only support DW_EH_PE_datarel | DW_EH_PE_sdata4, |
| 51 | // which means that the values are 4 byte offsets from the start of |
| 52 | // the table. |
| 53 | |
| 54 | // The exception frame header is followed by a pointer to the contents |
| 55 | // of the exception frame section (.eh_frame). This pointer is |
| 56 | // encoded as specified in the byte at offset 1 of the header (i.e., |
| 57 | // it is normally a 4 byte PC relative offset). |
| 58 | |
| 59 | // If there is a lookup table, this is followed by the count of the |
| 60 | // number of FDE pointers, encoded as specified in the byte at offset |
| 61 | // 2 of the header (i.e., normally a 4 byte unsigned integer). |
| 62 | |
| 63 | // This is followed by the table, which should start at an 4-byte |
| 64 | // aligned address in memory. Each entry in the table is 8 bytes. |
| 65 | // Each entry represents an FDE. The first four bytes of each entry |
| 66 | // are an offset to the starting PC for the FDE. The last four bytes |
| 67 | // of each entry are an offset to the FDE data. The offsets are from |
| 68 | // the start of the exception frame header information. The entries |
| 69 | // are in sorted order by starting PC. |
| 70 | |
| 71 | // FIXME: We currently always generate an empty exception frame |
| 72 | // header. |
| 73 | |
| 74 | const int eh_frame_hdr_size = 4; |
| 75 | |
| 76 | // Construct the exception frame header. |
| 77 | |
| 78 | Eh_frame_hdr::Eh_frame_hdr(Output_section* eh_frame_section) |
| 79 | : Output_section_data(4), |
| 80 | eh_frame_section_(eh_frame_section) |
| 81 | { |
| 82 | } |
| 83 | |
| 84 | // Set the final address and size of the exception frame header. |
| 85 | |
| 86 | void |
| 87 | Eh_frame_hdr::do_set_address(uint64_t, off_t) |
| 88 | { |
| 89 | this->set_data_size(eh_frame_hdr_size + 4); |
| 90 | } |
| 91 | |
| 92 | // Write the data to the flie. |
| 93 | |
| 94 | void |
| 95 | Eh_frame_hdr::do_write(Output_file* of) |
| 96 | { |
| 97 | const off_t off = this->offset(); |
| 98 | const off_t oview_size = this->data_size(); |
| 99 | unsigned char* const oview = of->get_output_view(off, oview_size); |
| 100 | |
| 101 | // Version number. |
| 102 | oview[0] = 1; |
| 103 | |
| 104 | // Write out a 4 byte PC relative offset to the address of the |
| 105 | // .eh_frame section. |
| 106 | oview[1] = elfcpp::DW_EH_PE_pcrel | elfcpp::DW_EH_PE_sdata4; |
| 107 | uint64_t eh_frame_address = this->eh_frame_section_->address(); |
| 108 | uint64_t eh_frame_hdr_address = this->address(); |
| 109 | uint64_t eh_frame_offset = (eh_frame_address - |
| 110 | (eh_frame_hdr_address + 4)); |
| 111 | if (parameters->is_big_endian()) |
| 112 | elfcpp::Swap<32, true>::writeval(oview + 4, eh_frame_offset); |
| 113 | else |
| 114 | elfcpp::Swap<32, false>::writeval(oview + 4, eh_frame_offset); |
| 115 | |
| 116 | // We don't currently write out the sorted table. |
| 117 | oview[2] = elfcpp::DW_EH_PE_omit; |
| 118 | oview[3] = elfcpp::DW_EH_PE_omit; |
| 119 | |
| 120 | gold_assert(oview_size == 8); |
| 121 | |
| 122 | of->write_output_view(off, oview_size, oview); |
| 123 | } |
| 124 | |
| 125 | } // End namespace gold. |