1 /*
2 * CDDL HEADER START
3 *
4 * The contents of this file are subject to the terms of the
5 * Common Development and Distribution License (the "License").
6 * You may not use this file except in compliance with the License.
7 *
8 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
9 * or http://www.opensolaris.org/os/licensing.
10 * See the License for the specific language governing permissions
11 * and limitations under the License.
12 *
13 * When distributing Covered Code, include this CDDL HEADER in each
14 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
15 * If applicable, add the following below this CDDL HEADER, with the
16 * fields enclosed by brackets "[]" replaced with your own identifying
17 * information: Portions Copyright [yyyy] [name of copyright owner]
18 *
19 * CDDL HEADER END
20 */
21
22 /*
23 * Copyright 2009 Sun Microsystems, Inc. All rights reserved.
24 * Use is subject to license terms.
25 */
26
27 #include <stdio.h>
28 #include <dwarf.h>
29 #include <sys/types.h>
30 #include <sys/elf.h>
31
32 /*
33 * Little Endian Base 128 (LEB128) numbers.
34 * ----------------------------------------
35 *
36 * LEB128 is a scheme for encoding integers densely that exploits the
37 * assumption that most integers are small in magnitude. (This encoding
38 * is equally suitable whether the target machine architecture represents
39 * data in big-endian or little- endian
40 *
41 * Unsigned LEB128 numbers are encoded as follows: start at the low order
42 * end of an unsigned integer and chop it into 7-bit chunks. Place each
43 * chunk into the low order 7 bits of a byte. Typically, several of the
44 * high order bytes will be zero; discard them. Emit the remaining bytes in
45 * a stream, starting with the low order byte; set the high order bit on
46 * each byte except the last emitted byte. The high bit of zero on the last
47 * byte indicates to the decoder that it has encountered the last byte.
48 * The integer zero is a special case, consisting of a single zero byte.
49 *
50 * Signed, 2s complement LEB128 numbers are encoded in a similar except
51 * that the criterion for discarding high order bytes is not whether they
52 * are zero, but whether they consist entirely of sign extension bits.
53 * Consider the 32-bit integer -2. The three high level bytes of the number
54 * are sign extension, thus LEB128 would represent it as a single byte
55 * containing the low order 7 bits, with the high order bit cleared to
56 * indicate the end of the byte stream.
57 *
58 * Note that there is nothing within the LEB128 representation that
59 * indicates whether an encoded number is signed or unsigned. The decoder
60 * must know what type of number to expect.
61 *
62 * DWARF Exception Header Encoding
63 * -------------------------------
64 *
65 * The DWARF Exception Header Encoding is used to describe the type of data
66 * used in the .eh_frame_hdr section. The upper 4 bits indicate how the
67 * value is to be applied. The lower 4 bits indicate the format of the data.
68 *
69 * DWARF Exception Header value format
70 *
71 * Name Value Meaning
72 * DW_EH_PE_omit 0xff No value is present.
73 * DW_EH_PE_absptr 0x00 Value is a void*
74 * DW_EH_PE_uleb128 0x01 Unsigned value is encoded using the
75 * Little Endian Base 128 (LEB128)
76 * DW_EH_PE_udata2 0x02 A 2 bytes unsigned value.
77 * DW_EH_PE_udata4 0x03 A 4 bytes unsigned value.
78 * DW_EH_PE_udata8 0x04 An 8 bytes unsigned value.
79 * DW_EH_PE_signed 0x08 bit on for all signed encodings
80 * DW_EH_PE_sleb128 0x09 Signed value is encoded using the
81 * Little Endian Base 128 (LEB128)
82 * DW_EH_PE_sdata2 0x0A A 2 bytes signed value.
83 * DW_EH_PE_sdata4 0x0B A 4 bytes signed value.
84 * DW_EH_PE_sdata8 0x0C An 8 bytes signed value.
85 *
86 * DWARF Exception Header application
87 *
88 * Name Value Meaning
89 * DW_EH_PE_absptr 0x00 Value is used with no modification.
90 * DW_EH_PE_pcrel 0x10 Value is reletive to the location of itself
91 * DW_EH_PE_textrel 0x20
92 * DW_EH_PE_datarel 0x30 Value is reletive to the beginning of the
93 * eh_frame_hdr segment ( segment type
94 * PT_GNU_EH_FRAME )
95 * DW_EH_PE_funcrel 0x40
96 * DW_EH_PE_aligned 0x50 value is an aligned void*
97 * DW_EH_PE_indirect 0x80 bit to signal indirection after relocation
98 * DW_EH_PE_omit 0xff No value is present.
99 *
100 */
101
102 dwarf_error_t
103 uleb_extract(unsigned char *data, uint64_t *dotp, size_t len, uint64_t *ret)
104 {
105 uint64_t dot = *dotp;
106 uint64_t res = 0;
107 int more = 1;
108 int shift = 0;
109 int val;
110
111 data += dot;
112
113 while (more) {
114 if (dot > len)
115 return (DW_OVERFLOW);
116
117 /*
118 * Pull off lower 7 bits
119 */
120 val = (*data) & 0x7f;
121
122 /*
123 * Add prepend value to head of number.
124 */
125 res = res | (val << shift);
126
127 /*
128 * Increment shift & dot pointer
129 */
130 shift += 7;
131 dot++;
132
133 /*
134 * Check to see if hi bit is set - if not, this
135 * is the last byte.
136 */
137 more = ((*data++) & 0x80) >> 7;
138 }
139 *dotp = dot;
140 *ret = res;
141 return (DW_SUCCESS);
142 }
143
144 dwarf_error_t
145 sleb_extract(unsigned char *data, uint64_t *dotp, size_t len, int64_t *ret)
146 {
147 uint64_t dot = *dotp;
148 int64_t res = 0;
149 int more = 1;
150 int shift = 0;
151 int val;
152
153 data += dot;
154
155 while (more) {
156 if (dot > len)
157 return (DW_OVERFLOW);
158
159 /*
160 * Pull off lower 7 bits
161 */
162 val = (*data) & 0x7f;
163
164 /*
165 * Add prepend value to head of number.
166 */
167 res = res | (val << shift);
168
169 /*
170 * Increment shift & dot pointer
171 */
172 shift += 7;
173 dot++;
174
175 /*
176 * Check to see if hi bit is set - if not, this
177 * is the last byte.
178 */
179 more = ((*data++) & 0x80) >> 7;
180 }
181 *dotp = dot;
182
183 /*
184 * Make sure value is properly sign extended.
185 */
186 res = (res << (64 - shift)) >> (64 - shift);
187 *ret = res;
188 return (DW_SUCCESS);
189 }
190
191 /*
192 * Extract a DWARF encoded datum
193 *
194 * entry:
195 * data - Base of data buffer containing encoded bytes
196 * dotp - Address of variable containing index within data
197 * at which the desired datum starts.
198 * ehe_flags - DWARF encoding
199 * eident - ELF header e_ident[] array for object being processed
200 * frame_hdr - Boolean, true if we're extracting from .eh_frame_hdr
201 * sh_base - Base address of ELF section containing desired datum
202 * sh_offset - Offset relative to sh_base of desired datum.
203 * dbase - The base address to which DW_EH_PE_datarel is relative
204 * (if frame_hdr is false)
205 */
206 dwarf_error_t
207 dwarf_ehe_extract(unsigned char *data, size_t len, uint64_t *dotp,
208 uint64_t *ret, uint_t ehe_flags, unsigned char *eident,
209 boolean_t frame_hdr, uint64_t sh_base, uint64_t sh_offset,
210 uint64_t dbase)
211 {
212 uint64_t dot = *dotp;
213 uint_t lsb;
214 uint_t wordsize;
215 uint_t fsize;
216 uint64_t result;
217
218 if (eident[EI_DATA] == ELFDATA2LSB)
219 lsb = 1;
220 else
221 lsb = 0;
222
223 if (eident[EI_CLASS] == ELFCLASS64)
224 wordsize = 8;
225 else
226 wordsize = 4;
227
228 switch (ehe_flags & 0x0f) {
229 case DW_EH_PE_omit:
230 *ret = 0;
231 return (DW_SUCCESS);
232 case DW_EH_PE_absptr:
233 fsize = wordsize;
234 break;
235 case DW_EH_PE_udata8:
236 case DW_EH_PE_sdata8:
237 fsize = 8;
238 break;
239 case DW_EH_PE_udata4:
240 case DW_EH_PE_sdata4:
241 fsize = 4;
242 break;
243 case DW_EH_PE_udata2:
244 case DW_EH_PE_sdata2:
245 fsize = 2;
246 break;
247 case DW_EH_PE_uleb128:
248 return (uleb_extract(data, dotp, len, ret));
249 case DW_EH_PE_sleb128:
250 return (sleb_extract(data, dotp, len, (int64_t *)ret));
251 default:
252 *ret = 0;
253 return (DW_BAD_ENCODING);
254 }
255
256 if (lsb) {
257 /*
258 * Extract unaligned LSB formated data
259 */
260 uint_t cnt;
261
262 result = 0;
263 for (cnt = 0; cnt < fsize;
264 cnt++, dot++) {
265 uint64_t val;
266
267 if (dot > len)
268 return (DW_OVERFLOW);
269 val = data[dot];
270 result |= val << (cnt * 8);
271 }
272 } else {
273 /*
274 * Extract unaligned MSB formated data
275 */
276 uint_t cnt;
277 result = 0;
278 for (cnt = 0; cnt < fsize;
279 cnt++, dot++) {
280 uint64_t val;
281
282 if (dot > len)
283 return (DW_OVERFLOW);
284 val = data[dot];
285 result |= val << ((fsize - cnt - 1) * 8);
286 }
287 }
288 /*
289 * perform sign extension
290 */
291 if ((ehe_flags & DW_EH_PE_signed) &&
292 (fsize < sizeof (uint64_t))) {
293 int64_t sresult;
294 uint_t bitshift;
295 sresult = result;
296 bitshift = (sizeof (uint64_t) - fsize) * 8;
297 sresult = (sresult << bitshift) >> bitshift;
298 result = sresult;
299 }
300
301 /*
302 * If value is relative to a base address, adjust it
303 */
304 switch (ehe_flags & 0xf0) {
305 case DW_EH_PE_pcrel:
306 result += sh_base + sh_offset;
307 break;
308
309 /*
310 * datarel is relative to .eh_frame_hdr if within .eh_frame,
311 * but GOT if not.
312 */
313 case DW_EH_PE_datarel:
314 if (frame_hdr)
315 result += sh_base;
316 else
317 result += dbase;
318 break;
319 }
320
321 /* Truncate the result to its specified size */
322 result = (result << ((sizeof (uint64_t) - fsize) * 8)) >>
323 ((sizeof (uint64_t) - fsize) * 8);
324
325 *dotp = dot;
326 *ret = result;
327 return (DW_SUCCESS);
328 }