1 /* Advance to next CFI entry.
2 Copyright (C) 2009-2010, 2014 Red Hat, Inc.
3 This file is part of elfutils.
4
5 This file is free software; you can redistribute it and/or modify
6 it under the terms of either
7
8 * the GNU Lesser General Public License as published by the Free
9 Software Foundation; either version 3 of the License, or (at
10 your option) any later version
11
12 or
13
14 * the GNU General Public License as published by the Free
15 Software Foundation; either version 2 of the License, or (at
16 your option) any later version
17
18 or both in parallel, as here.
19
20 elfutils is distributed in the hope that it will be useful, but
21 WITHOUT ANY WARRANTY; without even the implied warranty of
22 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
23 General Public License for more details.
24
25 You should have received copies of the GNU General Public License and
26 the GNU Lesser General Public License along with this program. If
27 not, see <http://www.gnu.org/licenses/>. */
28
29 #ifdef HAVE_CONFIG_H
30 # include <config.h>
31 #endif
32
33 #include "cfi.h"
34 #include "encoded-value.h"
35
36 #include <string.h>
37
38
39 int
dwarf_next_cfi(const unsigned char e_ident[],Elf_Data * data,bool eh_frame_p,Dwarf_Off off,Dwarf_Off * next_off,Dwarf_CFI_Entry * entry)40 dwarf_next_cfi (const unsigned char e_ident[],
41 Elf_Data *data,
42 bool eh_frame_p,
43 Dwarf_Off off,
44 Dwarf_Off *next_off,
45 Dwarf_CFI_Entry *entry)
46 {
47 /* Dummy struct for memory-access.h macros. */
48 BYTE_ORDER_DUMMY (dw, e_ident);
49
50 /* If we reached the end before don't do anything. */
51 if (off == (Dwarf_Off) -1l
52 /* Make sure there is enough space in the .debug_frame section
53 for at least the initial word. We cannot test the rest since
54 we don't know yet whether this is a 64-bit object or not. */
55 || unlikely (off + 4 >= data->d_size))
56 {
57 done:
58 *next_off = (Dwarf_Off) -1l;
59 return 1;
60 }
61
62 /* This points into the .debug_frame section at the start of the entry. */
63 const uint8_t *bytes = data->d_buf + off;
64 const uint8_t *limit = data->d_buf + data->d_size;
65
66 /* The format of a CFI entry is described in DWARF3 6.4.1:
67 */
68
69 uint64_t length = read_4ubyte_unaligned_inc (&dw, bytes);
70 size_t offset_size = 4;
71 if (length == DWARF3_LENGTH_64_BIT)
72 {
73 /* This is the 64-bit DWARF format. */
74 offset_size = 8;
75 if (unlikely (limit - bytes < 8))
76 {
77 invalid:
78 __libdw_seterrno (DWARF_E_INVALID_DWARF);
79 return -1;
80 }
81 length = read_8ubyte_unaligned_inc (&dw, bytes);
82 }
83
84 /* Not explicitly in the DWARF spec, but mentioned in the LSB exception
85 frames (.eh_frame) spec. If Length contains the value 0, then this
86 CIE shall be considered a terminator and processing shall end. */
87 if (length == 0)
88 goto done;
89
90 if (unlikely ((uint64_t) (limit - bytes) < length)
91 || unlikely (length < offset_size + 1))
92 goto invalid;
93
94 /* Now we know how large the entry is. Note the trick in the
95 computation. If the offset_size is 4 the '- 4' term undoes the
96 '2 *'. If offset_size is 8 this term computes the size of the
97 escape value plus the 8 byte offset. */
98 *next_off = off + (2 * offset_size - 4) + length;
99
100 limit = bytes + length;
101
102 const uint8_t *const cie_pointer_start = bytes;
103 if (offset_size == 8)
104 entry->cie.CIE_id = read_8ubyte_unaligned_inc (&dw, bytes);
105 else
106 {
107 entry->cie.CIE_id = read_4ubyte_unaligned_inc (&dw, bytes);
108 /* Canonicalize the 32-bit CIE_ID value to 64 bits. */
109 if (!eh_frame_p && entry->cie.CIE_id == DW_CIE_ID_32)
110 entry->cie.CIE_id = DW_CIE_ID_64;
111 }
112 if (eh_frame_p)
113 {
114 /* Canonicalize the .eh_frame CIE pointer to .debug_frame format. */
115 if (entry->cie.CIE_id == 0)
116 entry->cie.CIE_id = DW_CIE_ID_64;
117 else
118 {
119 /* In .eh_frame format, a CIE pointer is the distance from where
120 it appears back to the beginning of the CIE. */
121 ptrdiff_t pos = cie_pointer_start - (const uint8_t *) data->d_buf;
122 if (unlikely (entry->cie.CIE_id > (Dwarf_Off) pos)
123 || unlikely (pos <= (ptrdiff_t) offset_size))
124 goto invalid;
125 entry->cie.CIE_id = pos - entry->cie.CIE_id;
126 }
127 }
128
129 if (entry->cie.CIE_id == DW_CIE_ID_64)
130 {
131 /* Read the version stamp. Always an 8-bit value. */
132 uint8_t version = *bytes++;
133
134 if (version != 1 && (unlikely (version < 3) || unlikely (version > 4)))
135 goto invalid;
136
137 entry->cie.augmentation = (const char *) bytes;
138
139 bytes = memchr (bytes, '\0', limit - bytes);
140 if (unlikely (bytes == NULL))
141 goto invalid;
142 ++bytes;
143
144 /* The address size for CFI is implicit in the ELF class. */
145 uint_fast8_t address_size = e_ident[EI_CLASS] == ELFCLASS32 ? 4 : 8;
146 uint_fast8_t segment_size = 0;
147 if (version >= 4)
148 {
149 if (unlikely (limit - bytes < 5))
150 goto invalid;
151 /* XXX We don't actually support address_size not matching the class.
152 To do so, we'd have to return it here so that intern_new_cie
153 could use it choose a specific fde_encoding. */
154 if (unlikely (*bytes != address_size))
155 {
156 __libdw_seterrno (DWARF_E_VERSION);
157 return -1;
158 }
159 address_size = *bytes++;
160 segment_size = *bytes++;
161 /* We don't actually support segment selectors. We'd have to
162 roll this into the fde_encoding bits or something. */
163 if (unlikely (segment_size != 0))
164 {
165 __libdw_seterrno (DWARF_E_VERSION);
166 return -1;
167 }
168 }
169
170 const char *ap = entry->cie.augmentation;
171
172 /* g++ v2 "eh" has pointer immediately following augmentation string,
173 so it must be handled first. */
174 if (unlikely (ap[0] == 'e' && ap[1] == 'h'))
175 {
176 ap += 2;
177 bytes += address_size;
178 }
179
180 if (bytes >= limit)
181 goto invalid;
182 get_uleb128 (entry->cie.code_alignment_factor, bytes, limit);
183
184 if (bytes >= limit)
185 goto invalid;
186 get_sleb128 (entry->cie.data_alignment_factor, bytes, limit);
187
188 if (bytes >= limit)
189 goto invalid;
190
191 if (version >= 3) /* DWARF 3+ */
192 get_uleb128 (entry->cie.return_address_register, bytes, limit);
193 else /* DWARF 2 */
194 entry->cie.return_address_register = *bytes++;
195
196 /* If we have sized augmentation data,
197 we don't need to grok it all. */
198 entry->cie.fde_augmentation_data_size = 0;
199 bool sized_augmentation = *ap == 'z';
200 if (sized_augmentation)
201 {
202 if (bytes >= limit)
203 goto invalid;
204 get_uleb128 (entry->cie.augmentation_data_size, bytes, limit);
205 if ((Dwarf_Word) (limit - bytes) < entry->cie.augmentation_data_size)
206 goto invalid;
207 entry->cie.augmentation_data = bytes;
208 bytes += entry->cie.augmentation_data_size;
209 }
210 else
211 {
212 entry->cie.augmentation_data = bytes;
213
214 for (; *ap != '\0'; ++ap)
215 {
216 uint8_t encoding;
217 switch (*ap)
218 {
219 case 'L': /* Skip LSDA pointer encoding byte. */
220 case 'R': /* Skip FDE address encoding byte. */
221 encoding = *bytes++;
222 entry->cie.fde_augmentation_data_size
223 += encoded_value_size (data, e_ident, encoding, NULL);
224 continue;
225 case 'P': /* Skip encoded personality routine pointer. */
226 encoding = *bytes++;
227 bytes += encoded_value_size (data, e_ident, encoding, bytes);
228 continue;
229 case 'S': /* Skip signal-frame flag. */
230 continue;
231 default:
232 /* Unknown augmentation string. initial_instructions might
233 actually start with some augmentation data. */
234 break;
235 }
236 break;
237 }
238 entry->cie.augmentation_data_size
239 = bytes - entry->cie.augmentation_data;
240 }
241
242 entry->cie.initial_instructions = bytes;
243 entry->cie.initial_instructions_end = limit;
244 }
245 else
246 {
247 entry->fde.start = bytes;
248 entry->fde.end = limit;
249 }
250
251 return 0;
252 }
253 INTDEF (dwarf_next_cfi)
254