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 uint64_t 103 uleb_extract(unsigned char *data, uint64_t *dotp) 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 /* 115 * Pull off lower 7 bits 116 */ 117 val = (*data) & 0x7f; 118 119 /* 120 * Add prepend value to head of number. 121 */ 122 res = res | (val << shift); 123 124 /* 125 * Increment shift & dot pointer 126 */ 127 shift += 7; 128 dot++; 129 130 /* 131 * Check to see if hi bit is set - if not, this 132 * is the last byte. 133 */ 134 more = ((*data++) & 0x80) >> 7; 135 } 136 *dotp = dot; 137 return (res); 138 } 139 140 int64_t 141 sleb_extract(unsigned char *data, uint64_t *dotp) 142 { 143 uint64_t dot = *dotp; 144 int64_t res = 0; 145 int more = 1; 146 int shift = 0; 147 int val; 148 149 data += dot; 150 151 while (more) { 152 /* 153 * Pull off lower 7 bits 154 */ 155 val = (*data) & 0x7f; 156 157 /* 158 * Add prepend value to head of number. 159 */ 160 res = res | (val << shift); 161 162 /* 163 * Increment shift & dot pointer 164 */ 165 shift += 7; 166 dot++; 167 168 /* 169 * Check to see if hi bit is set - if not, this 170 * is the last byte. 171 */ 172 more = ((*data++) & 0x80) >> 7; 173 } 174 *dotp = dot; 175 176 /* 177 * Make sure value is properly sign extended. 178 */ 179 res = (res << (64 - shift)) >> (64 - shift); 180 181 return (res); 182 } 183 184 /* 185 * Extract a DWARF encoded datum 186 * 187 * entry: 188 * data - Base of data buffer containing encoded bytes 189 * dotp - Address of variable containing index within data 190 * at which the desired datum starts. 191 * ehe_flags - DWARF encoding 192 * eident - ELF header e_ident[] array for object being processed 193 * frame_hdr - Boolean, true if we're extracting from .eh_frame_hdr 194 * sh_base - Base address of ELF section containing desired datum 195 * sh_offset - Offset relative to sh_base of desired datum. 196 * dbase - The base address to which DW_EH_PE_datarel is relative 197 * (if frame_hdr is false) 198 */ 199 uint64_t 200 dwarf_ehe_extract(unsigned char *data, uint64_t *dotp, uint_t ehe_flags, 201 unsigned char *eident, boolean_t frame_hdr, uint64_t sh_base, 202 uint64_t sh_offset, uint64_t dbase) 203 { 204 uint64_t dot = *dotp; 205 uint_t lsb; 206 uint_t wordsize; 207 uint_t fsize; 208 uint64_t result; 209 210 if (eident[EI_DATA] == ELFDATA2LSB) 211 lsb = 1; 212 else 213 lsb = 0; 214 215 if (eident[EI_CLASS] == ELFCLASS64) 216 wordsize = 8; 217 else 218 wordsize = 4; 219 220 switch (ehe_flags & 0x0f) { 221 case DW_EH_PE_omit: 222 return (0); 223 case DW_EH_PE_absptr: 224 fsize = wordsize; 225 break; 226 case DW_EH_PE_udata8: 227 case DW_EH_PE_sdata8: 228 fsize = 8; 229 break; 230 case DW_EH_PE_udata4: 231 case DW_EH_PE_sdata4: 232 fsize = 4; 233 break; 234 case DW_EH_PE_udata2: 235 case DW_EH_PE_sdata2: 236 fsize = 2; 237 break; 238 case DW_EH_PE_uleb128: 239 return (uleb_extract(data, dotp)); 240 case DW_EH_PE_sleb128: 241 return ((uint64_t)sleb_extract(data, dotp)); 242 default: 243 return (0); 244 } 245 246 if (lsb) { 247 /* 248 * Extract unaligned LSB formated data 249 */ 250 uint_t cnt; 251 252 result = 0; 253 for (cnt = 0; cnt < fsize; 254 cnt++, dot++) { 255 uint64_t val; 256 val = data[dot]; 257 result |= val << (cnt * 8); 258 } 259 } else { 260 /* 261 * Extract unaligned MSB formated data 262 */ 263 uint_t cnt; 264 result = 0; 265 for (cnt = 0; cnt < fsize; 266 cnt++, dot++) { 267 uint64_t val; 268 val = data[dot]; 269 result |= val << ((fsize - cnt - 1) * 8); 270 } 271 } 272 /* 273 * perform sign extension 274 */ 275 if ((ehe_flags & DW_EH_PE_signed) && 276 (fsize < sizeof (uint64_t))) { 277 int64_t sresult; 278 uint_t bitshift; 279 sresult = result; 280 bitshift = (sizeof (uint64_t) - fsize) * 8; 281 sresult = (sresult << bitshift) >> bitshift; 282 result = sresult; 283 } 284 285 /* 286 * If value is relative to a base address, adjust it 287 */ 288 switch (ehe_flags & 0xf0) { 289 case DW_EH_PE_pcrel: 290 result += sh_base + sh_offset; 291 break; 292 293 /* 294 * datarel is relative to .eh_frame_hdr if within .eh_frame, 295 * but GOT if not. 296 */ 297 case DW_EH_PE_datarel: 298 if (frame_hdr) 299 result += sh_base; 300 else 301 result += dbase; 302 break; 303 } 304 305 /* Truncate the result to its specified size */ 306 result = (result << ((sizeof (uint64_t) - fsize) * 8)) >> 307 ((sizeof (uint64_t) - fsize) * 8); 308 309 *dotp = dot; 310 return (result); 311 } 312