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3151305a ILT |
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 | ||
9025d29d | 78 | Eh_frame_hdr::Eh_frame_hdr(Output_section* eh_frame_section) |
3151305a | 79 | : Output_section_data(4), |
9025d29d | 80 | eh_frame_section_(eh_frame_section) |
3151305a ILT |
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)); | |
9025d29d | 111 | if (parameters->is_big_endian()) |
3151305a ILT |
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. |