Elf sample code: elf_obj

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ELF : libelf examples

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file: elf_obj_loc.c

1 /* 2 * Copyright (C) 2007 Emmanuel AZENCOT All Rights Reserved. * 3 * 4 * This program is free software; you can redistribute it and/or modify it 5 * under the terms of version 2 of the GNU General Public License as 6 * published by the Free Software Foundation. 7 * 8 * The address of the Free Software Foundation is 9 * Free Software Foundation, Inc., 51 Franklin St, Fifth Floor, 10 * Boston, MA 02110-1301, USA. 11 */ 12 13 /* 14 * Prepare an elf relocatable object for disassemby (objdump) 15 * 16 * 2007-11-14 16:11:49 Emmanuel AZENCOT 17 * Creation 18 * 2008-01-21 15:44:08 19 * Fix resolution for data 20 * Sun Nov 22 20:33:20 CET 2009 21 * bug fix in error message \%s\" 22 * 23 * build : gcc -Wall -g -o elf_obj_loc -lelf elf_obj_loc.c 24 * TODO : 25 * clean output, have a verbose mode 26 * use info file to retreive .rel corresponding section (instead of name) 27 * test big endian object 28 * test 64 bits object 29 * test other processors 30 * deal with other ABI 31 */ 32 #include <string.h> 33 #include <stdio.h> 34 #include <stdlib.h> 35 #include <sysexits.h> 36 #include <unistd.h> 37 #include <fcntl.h> 38 #include <errno.h> 39 40 #include <err.h> 41 #include <gelf.h> 42 43 #include </usr/include/asm/byteorder.h> 44 45 #define /*X*/ endian_to_target(tgt_is_be, value) ( (sizeof(value) == 4)?\ 46 ((tgt_is_be)?__cpu_to_be32(value):__cpu_to_le32(value)): \ 47 ((tgt_is_be)?__cpu_to_be64(value):__cpu_to_le64(value)) ) 48 49 50 #define /*X*/ errx(code, fmt, args...) { \ 51 fprintf(stderr,#code ": error in file %s at line %d in function %s:", __FILE__,__LINE__,__FUNCTION__); \ 52 fprintf(stderr,fmt "\n", ##args); \ 53 exit(1); \ 54 } 55 #define /*X*/ merrx(code, fmt, args...) { \ 56 fprintf(stderr,#code ": error in file %s at line %d in function %s:", __FILE__,__LINE__,__FUNCTION__); \ 57 fprintf(stderr,fmt "\n", ##args); \ 58 return -1; \ 59 } 60 /** 61 * @memo Find a section given its name 62 * @doc 63 * Look in evry secttion until it find a section name "scn_name" 64 * @param __elf Elf Handle to search in 65 * @param scn_name section name 66 * @return -1 error, 0 not found, section index 67 */ 68 int /*X*/ melf_scn_by_name(Elf *__elf, char *scn_name) { 69 size_t shstrndx; 70 size_t scn_ndx = 0; 71 Elf_Scn *scn; 72 GElf_Shdr shdr; 73 char *name; 74 75 if (elf_getshstrndx(__elf, &shstrndx) != 0) 76 merrx(EX_SOFTWARE, "getshstrndx() failed: %s.", elf_errmsg(-1)); 77 78 while ((scn = elf_getscn(__elf, scn_ndx)) != NULL) { 79 80 if (gelf_getshdr(scn, &shdr) != &shdr) 81 merrx(EX_SOFTWARE, "gelf_getshdr() failed: %s.", elf_errmsg(-1)); 82 83 if ((name = elf_strptr(__elf, shstrndx, shdr.sh_name)) == NULL) 84 merrx(EX_SOFTWARE, "elf_strptr() failed: %s.", elf_errmsg(-1)); 85 if ( !strcmp(scn_name, name) ) 86 return scn_ndx; 87 scn_ndx++; 88 } 89 return 0; 90 } 91 /** 92 * @memo Symbol table section adtatation 93 * @doc 94 * As symbol table contains section indexes, there must be changed according to new elf 95 * section layout 96 * @param __elf a valid input/output elf handle 97 * @param conv_tbl a section table conversion (see melf_rel_scn_layout) 98 * @param len conv_tbl number of entries 99 * @return -1 error, symbol table section index 100 */ 101 int /*X*/ melf_scn_sym_shconv(Elf *__elf, ssize_t *conv_tbl, size_t len) { 102 ssize_t scn_ndx_sym; 103 Elf_Scn *scn_sym; 104 Elf_Data *data_sym; 105 size_t ndx_sym; 106 GElf_Sym sym; 107 108 if ( (scn_ndx_sym = melf_scn_by_name(__elf, ".symtab")) <= 0) 109 merrx(EX_SOFTWARE, "melf_scn_by_name() failed to find section .symtab."); 110 111 if ( (scn_sym = elf_getscn(__elf, scn_ndx_sym)) == NULL) 112 merrx(EX_SOFTWARE, "getscn() failed: %s.", elf_errmsg(-1)); 113 114 if ( (data_sym = elf_getdata(scn_sym, 0)) == NULL ) 115 merrx(EX_SOFTWARE, "elf_getdata() failed: %s.", elf_errmsg(-1)); 116 117 ndx_sym = 0; 118 while ( gelf_getsym (data_sym, ndx_sym, &sym) == &sym ) { 119 // if ( sym.st_shndx > SHN_LORESERVE && ++ndx_sym) continue; 120 if ( 0 < (ssize_t) sym.st_shndx && (ssize_t) sym.st_shndx < len) { 121 if ( conv_tbl[sym.st_shndx] == -1 ) 122 merrx(EX_SOFTWARE, "Can't convert section (0x%x) for symbol index %d", sym.st_shndx, ndx_sym); 123 sym.st_shndx = conv_tbl[sym.st_shndx]; 124 if ( gelf_update_sym (data_sym, ndx_sym, &sym) == 0) 125 merrx(EX_SOFTWARE, "gelf_update_sym() failed: %s.", elf_errmsg(-1)); 126 } 127 ++ndx_sym; 128 } 129 if ( elf_flagdata (data_sym, ELF_C_SET, ELF_F_DIRTY) == 0) 130 merrx(EX_SOFTWARE, "elf_flagdata() failed: %s.", elf_errmsg(-1)); 131 132 return scn_ndx_sym; 133 } 134 /** 135 * @memo Section content Hexa dump 136 * @ doc 137 * Output section content in hexadecimal format. 138 * Section can be given by handle or by name. 139 * @param __elf a valid input elf handle 140 * @param scn a valid scn handle or 0 141 * @param scn_name a section name or 0 142 * @return -1 error, 0 okay 143 */ 144 int /*X*/ melf_scn_dump(Elf *__elf, Elf_Scn *scn, char *scn_name) { 145 GElf_Shdr shdr; 146 Elf_Data *data; 147 size_t shstrndx; 148 char *p; int i; 149 150 if ( !scn ) { 151 size_t scn_ndx; 152 if ( !scn_name ) 153 merrx(EX_SOFTWARE, "Both name and scn handle are nul"); 154 if ( (scn_ndx = melf_scn_by_name(__elf, scn_name)) <= 0) 155 merrx(EX_SOFTWARE, "melf_scn_by_name() failed to find section %s.", scn_name); 156 if ( (scn = elf_getscn(__elf, scn_ndx)) == NULL) 157 merrx(EX_SOFTWARE, "getscn() failed: %s.", elf_errmsg(-1)); 158 159 } 160 if (elf_getshstrndx(__elf, &shstrndx) != 0) 161 merrx(EX_SOFTWARE, "getshstrndx() failed: %s.", elf_errmsg(-1)); 162 163 if (gelf_getshdr(scn, &shdr) != &shdr) 164 merrx(EX_SOFTWARE, "getshdr(shstrndx) failed: %s.", elf_errmsg(-1)); 165 if ((scn_name = elf_strptr(__elf, shstrndx, shdr.sh_name)) == NULL) 166 merrx(EX_SOFTWARE, "elf_strptr() failed: %s.", elf_errmsg(-1)); 167 if ( (data = elf_getdata(scn, 0)) == NULL ) 168 merrx(EX_SOFTWARE, "elf_getdata() failed: %s.", elf_errmsg(-1)); 169 170 printf("Dump section %s: size=%jd\n", scn_name, (uintmax_t) shdr.sh_size); 171 172 p = (char *) data->d_buf; 173 for ( i = 0; i < data->d_size; i++ ) { 174 printf("%02hhx ", *p++); 175 if ( !((i + 17) %16) ) printf("\n"); 176 } 177 printf("\n"); 178 return 0; 179 } 180 /** 181 * @memo Symbol table listing 182 * @doc 183 * print the symbol table. Symbol strings are taken from the section named 184 * ".strtab". (Usualy, the strings and taken from section index pointed by 185 * sh_link field of section header). 186 * @param __elf valid input elf handle 187 * @return -1 error, symbol table section index 188 */ 189 int /*X*/ melf_scn_sym_list(Elf *__elf) { 190 ssize_t scn_ndx_sym, scn_ndx_str; 191 Elf_Scn *scn_sym; 192 Elf_Data *data_sym; 193 GElf_Sym sym; 194 size_t ndx_sym; 195 196 if ( (scn_ndx_sym = melf_scn_by_name(__elf, ".symtab")) <= 0) 197 merrx(EX_SOFTWARE, "melf_scn_by_name() failed to find section .symtab."); 198 /* should use shdr_sym.sh_link ? */ 199 if ( (scn_ndx_str = melf_scn_by_name(__elf, ".strtab")) <= 0) 200 merrx(EX_SOFTWARE, "melf_scn_by_name() failed to find section .symtab."); 201 202 if ( (scn_sym = elf_getscn(__elf, scn_ndx_sym)) == NULL) 203 merrx(EX_SOFTWARE, "getscn() failed: %s.", elf_errmsg(-1)); 204 205 if ( (data_sym = elf_getdata(scn_sym, 0)) == NULL ) 206 merrx(EX_SOFTWARE, "elf_getdata() failed: %s.", elf_errmsg(-1)); 207 208 /* walk throught symbols table */ 209 printf("name value size info other shndx\n"); 210 ndx_sym = 0; 211 while ( gelf_getsym (data_sym, ndx_sym, &sym) == &sym ) { 212 char *name; 213 if ((name = elf_strptr(__elf, scn_ndx_str, sym.st_name)) == NULL) 214 merrx(EX_SOFTWARE, "elf_strptr() failed: %s.", elf_errmsg(-1)); 215 216 printf("%05x %08llx %04llx %08x %05x %04x %s\n", 217 sym.st_name, sym.st_value, sym.st_size, sym.st_info, sym.st_other, sym.st_shndx, name); 218 ++ndx_sym; 219 } 220 221 return scn_ndx_sym; 222 } 223 224 /** 225 * @memo Symbol table locatioon adtatation 226 * @doc 227 * Produce a trivial memory mapping for the alloc sections. Change sections adresses 228 * according to it. 229 * Give all UNDEF symbol a recognisable location and change value in symbol table. 230 * @param __elf a valid input/output elf handle 231 * @return -1 error, symbol table section index 232 */ 233 int /*X*/ melf_scn_sym_lnk(Elf *__elf) { 234 ssize_t scn_ndx_sym, scn_ndx; 235 Elf_Scn *scn_sym, *scn; 236 GElf_Shdr shdr; 237 Elf_Data *data_sym; 238 Elf64_Addr PC = 0x08048000; 239 size_t ndx_sym; 240 GElf_Sym sym; 241 242 243 if ( (scn_ndx_sym = melf_scn_by_name(__elf, ".symtab")) <= 0) 244 merrx(EX_SOFTWARE, "melf_scn_by_name() failed to find section .symtab."); 245 if ( (scn_sym = elf_getscn(__elf, scn_ndx_sym)) == NULL) 246 merrx(EX_SOFTWARE, "getscn() failed: %s.", elf_errmsg(-1)); 247 248 if ( (data_sym = elf_getdata(scn_sym, 0)) == NULL ) 249 merrx(EX_SOFTWARE, "elf_getdata() failed: %s.", elf_errmsg(-1)); 250 251 /* Map alloc sectionq in memory */ 252 for ( scn = 0; (scn = elf_nextscn(__elf, scn)) != NULL; ) { 253 scn_ndx = elf_ndxscn (scn); 254 255 if (gelf_getshdr(scn, &shdr) != &shdr) 256 merrx(EX_SOFTWARE, "gelf_getshdr() failed: %s.", elf_errmsg(-1)); 257 if ( !(shdr.sh_flags & SHF_ALLOC) && ++scn_ndx ) 258 continue; 259 260 shdr.sh_addr = PC; 261 if ( shdr.sh_addralign ) 262 PC += ((shdr.sh_size + shdr.sh_addralign-1)/shdr.sh_addralign)*shdr.sh_addralign; 263 else 264 PC += shdr.sh_size; 265 if ( elf_flagshdr (scn, ELF_C_SET, ELF_F_DIRTY) == 0) 266 merrx(EX_SOFTWARE, "elf_flagshdr() failed: %s.", elf_errmsg(-1)); 267 if ( gelf_update_shdr (scn, &shdr) == 0) 268 merrx(EX_SOFTWARE, "gelf_update_shdr() failed: %s.", elf_errmsg(-1)); 269 } 270 /* give UNDEF a decent location */ 271 PC = 0x02500000; 272 ndx_sym = 0; 273 while ( gelf_getsym (data_sym, ndx_sym, &sym) == &sym ) { 274 if ( sym.st_shndx != 0 && ++ndx_sym) continue; 275 sym.st_value = PC; 276 sym.st_shndx = SHN_ABS; 277 PC += 0x10; 278 if ( gelf_update_sym (data_sym, ndx_sym, &sym) == 0) 279 merrx(EX_SOFTWARE, "gelf_update_sym() failed: %s.", elf_errmsg(-1)); 280 281 ++ndx_sym; 282 } 283 if ( elf_flagdata (data_sym, ELF_C_SET, ELF_F_DIRTY) == 0) 284 merrx(EX_SOFTWARE, "elf_flagdata() failed: %s.", elf_errmsg(-1)); 285 286 return scn_ndx_sym; 287 } 288 /** 289 * @memo target data encoding 290 * 0 little endian 291 * 1 big endian 292 */ 293 int /*X*/ target_is_big_endian; 294 /** 295 * @memo Relocate section 296 * @doc 297 * Apply the relocations contained in .rel section to a section. 298 * Note : Symbole table section .symtab must have adapted prior. 299 * @param elf Elf handler for section beeing relocated 300 * @param scn_ndx_out Section index to relocate 301 * @param scn_ndx_rel Reloc section index 302 * @param scn_ndx_sym Symbol table section 303 * @return -1 on error, 0 else 304 */ 305 int /*X*/ melf_scn_rel(Elf *elf_out, size_t scn_ndx_out, 306 Elf *elf_rel, size_t scn_ndx_rel, 307 Elf *elf_sym, size_t scn_ndx_sym) { 308 Elf_Scn *scn_out, *scn_rel, *scn_sym; 309 GElf_Shdr shdr_out, shdr_rel, shdr_sym; 310 Elf_Data *data_out, *data_rel, *data_sym; 311 int rel_i; 312 313 printf("index out : %d, rel : %d, sym : %d", scn_ndx_out, scn_ndx_rel, scn_ndx_sym); 314 315 if ( (scn_rel = elf_getscn(elf_rel, scn_ndx_rel)) == NULL) 316 merrx(EX_SOFTWARE, "getscn() failed: %s.", elf_errmsg(-1)); 317 if ( (scn_out = elf_getscn(elf_out, scn_ndx_out)) == NULL) 318 merrx(EX_SOFTWARE, "getscn() failed: %s.", elf_errmsg(-1)); 319 if ( (scn_sym = elf_getscn(elf_sym, scn_ndx_sym)) == NULL) 320 merrx(EX_SOFTWARE, "getscn() failed: %s.", elf_errmsg(-1)); 321 322 if (gelf_getshdr(scn_rel, &shdr_rel) != &shdr_rel) 323 merrx(EX_SOFTWARE, "getshdr() failed: %s.", elf_errmsg(-1)); 324 if (gelf_getshdr(scn_out, &shdr_out) != &shdr_out) 325 merrx(EX_SOFTWARE, "getshdr() failed: %s.", elf_errmsg(-1)); 326 if (gelf_getshdr(scn_sym, &shdr_sym) != &shdr_sym) 327 merrx(EX_SOFTWARE, "getshdr() failed: %s.", elf_errmsg(-1)); 328 329 if ( (data_out = elf_getdata(scn_out, 0)) == NULL) 330 merrx(EX_SOFTWARE, "getdata() failed: %s.", elf_errmsg(-1)); 331 if ( shdr_out.sh_size != data_out->d_size ) 332 fprintf(stderr, "warning tgt data containt more than one chunk\n"); 333 334 if ( (data_rel = elf_getdata(scn_rel, 0)) == NULL) 335 merrx(EX_SOFTWARE, "getdata() failed: %s.", elf_errmsg(-1)); 336 if ( shdr_rel.sh_size != data_rel->d_size ) 337 fprintf(stderr, "warning rel data is in more than one chunk\n"); 338 339 if ( (data_sym = elf_getdata(scn_sym, 0)) == NULL) 340 merrx(EX_SOFTWARE, "getdata() failed: %s.", elf_errmsg(-1)); 341 if ( shdr_sym.sh_size != data_sym->d_size ) 342 fprintf(stderr, "warning tgt data containt more than one chunk\n"); 343 344 for (rel_i = 0; ; rel_i++ ) { 345 GElf_Rel rel; 346 GElf_Sym sym; 347 Elf_Scn *scn_dst; 348 GElf_Shdr shdr_dst; 349 Elf64_Addr shaddr = 0; 350 351 if ( gelf_getrel (data_rel, rel_i, &rel) != &rel ) 352 break; 353 354 if ( gelf_getsym (data_sym, GELF_R_SYM(rel.r_info), &sym) != &sym ) 355 merrx(EX_SOFTWARE, "gelf_getsym() failed: %s. Symbol %lld not found", elf_errmsg(-1), GELF_R_SYM(rel.r_info)); 356 357 if ( sym.st_shndx < SHN_LORESERVE ) { 358 if ( (scn_dst = elf_getscn(elf_out, sym.st_shndx)) == NULL) 359 merrx(EX_SOFTWARE, "getscn() failed: %s.", elf_errmsg(-1)); 360 if (gelf_getshdr(scn_dst, &shdr_dst) != &shdr_dst) 361 merrx(EX_SOFTWARE, "getshdr() failed: %s.", elf_errmsg(-1)); 362 shaddr = shdr_dst.sh_addr; 363 } 364 switch (GELF_R_TYPE(rel.r_info)) { 365 case R_386_32: 366 *((uint32_t *)(((char *)data_out->d_buf) + rel.r_offset)) += 367 endian_to_target(target_is_big_endian,(uint32_t)(sym.st_value + shaddr)); 368 break; 369 case R_386_PC32: { 370 371 *((uint32_t *)(((char *)data_out->d_buf) + rel.r_offset)) = 372 endian_to_target(target_is_big_endian,(uint32_t)(sym.st_value + shaddr - (shdr_out.sh_addr + rel.r_offset) - 4)); 373 break; 374 } 375 default: 376 merrx(EX_SOFTWARE, "Can you help me to about this type of reloc (%lld) ? Oh I would do much you tacke care of this ... please ...\n", GELF_R_TYPE(rel.r_info)); 377 } 378 } 379 if ( elf_flagdata (data_out, ELF_C_SET, ELF_F_DIRTY) == 0) 380 merrx(EX_SOFTWARE, "elf_flagdata() failed: %s.", elf_errmsg(-1)); 381 382 if ( gelf_update_shdr (scn_out, &shdr_out) == 0) 383 errx(EX_SOFTWARE, "gelf_update_shdr() failed: %s.", elf_errmsg(-1)); 384 // printf("@%d ELF error %s\n", __LINE__, elf_errmsg(-1)); 385 return 0; 386 } 387 /** 388 * @memo Build output section table 389 * @doc 390 * The table is indexed by input section indexes. For each of them, the value 391 * can be (-1) not used or the output section. 392 * @param __elf valid input elf handle 393 * @param conv_tbl an array of at least the number of section in __elf 394 * @return -1 on error, number of sections in output. 395 */ 396 int /*X*/ melf_rel_scn_layout(Elf *__elf, ssize_t *conv_tbl) { 397 GElf_Ehdr ehdr; 398 GElf_Shdr shdr; 399 Elf_Scn *scn; 400 size_t ndx_out = 1; 401 402 if (gelf_getehdr(__elf, &ehdr) != &ehdr) 403 errx(EX_SOFTWARE, "gelf_getehdr() failed: %s.", elf_errmsg(-1)); 404 405 conv_tbl[0] = 0; 406 /* set allocable sections first */ 407 for ( scn = 0; (scn = elf_nextscn(__elf, scn)) != NULL; ) { 408 conv_tbl[elf_ndxscn (scn)] = -1; 409 if (gelf_getshdr(scn, &shdr) != &shdr) 410 merrx(EX_SOFTWARE, "getshdr() failed: %s.", elf_errmsg(-1)); 411 if ( shdr.sh_type == SHT_REL || shdr.sh_type == SHT_RELA) continue; 412 if ( !(shdr.sh_flags & SHF_ALLOC) ) continue; 413 conv_tbl[elf_ndxscn (scn)] = ndx_out++; 414 } 415 for ( scn = 0; (scn = elf_nextscn(__elf, scn)) != NULL; ) { 416 if (gelf_getshdr(scn, &shdr) != &shdr) 417 merrx(EX_SOFTWARE, "getshdr() failed: %s.", elf_errmsg(-1)); 418 if ( shdr.sh_type == SHT_REL || shdr.sh_type == SHT_RELA) continue; 419 if ( (shdr.sh_flags & SHF_ALLOC) ) continue; 420 conv_tbl[elf_ndxscn (scn)] = ndx_out++; 421 } 422 for ( scn = 0; (scn = elf_nextscn(__elf, scn)) != NULL; ) { 423 printf ( "section transfert table[%2d] = %2d\n", elf_ndxscn (scn), conv_tbl[elf_ndxscn (scn)]); 424 } 425 return ndx_out; 426 } 427 /** 428 * @memo Find .rel section correspondind to a section 429 * @doc 430 * Get peer section .rel that correspond to a section. The criteria to find peer is 431 * done througth the section name. 432 * Should use sh_link and sh_info instead. 433 * @param elf Elf handler 434 * @param scn_ndx Section index 435 * @return -1 on error, 0 not find, or scn index 436 */ 437 int /*X*/ melf_find_rel_section(Elf *__elf, size_t scn_ndx) { 438 size_t shstrndx; 439 Elf_Scn *scn, *scn_r; 440 GElf_Shdr shdr, shdr_r; 441 char *scn_name, *scn_name_r; 442 443 if (elf_getshstrndx(__elf, &shstrndx) != 0) 444 merrx(EX_SOFTWARE, "getshstrndx() failed: %s.", elf_errmsg(-1)); 445 if ( (scn = elf_getscn(__elf, scn_ndx)) == NULL) 446 merrx(EX_SOFTWARE, "getscn() failed: %s.", elf_errmsg(-1)); 447 if (gelf_getshdr(scn, &shdr) != &shdr) 448 merrx(EX_SOFTWARE, "getshdr() failed: %s.", elf_errmsg(-1)); 449 if ((scn_name = elf_strptr(__elf, shstrndx, shdr.sh_name)) == NULL) 450 merrx(EX_SOFTWARE, "elf_strptr() failed: %s.", elf_errmsg(-1)); 451 452 for ( scn_r = 0; (scn_r = elf_nextscn(__elf, scn_r)) != NULL; ) { 453 454 if ( gelf_getshdr(scn_r, &shdr_r) != &shdr_r) 455 merrx(EX_SOFTWARE, "getshdr() failed: %s.", elf_errmsg(-1)); 456 457 if ( shdr_r.sh_type != SHT_REL && shdr_r.sh_type != SHT_RELA) continue; 458 459 if ((scn_name_r = elf_strptr(__elf, shstrndx, shdr_r.sh_name)) == NULL) 460 merrx(EX_SOFTWARE, "elf_strptr() failed: %s.", elf_errmsg(-1)); 461 if ( memcmp(scn_name_r, ".rel", 4) ) continue; 462 if ( strcmp(scn_name_r + 4, scn_name) ) continue; 463 return elf_ndxscn (scn_r); 464 } 465 466 return 0; 467 } 468 int /*X*/ melf_is_scn_reloc(Elf_Scn *scn) { 469 GElf_Shdr shdr; 470 471 if (gelf_getshdr(scn, &shdr) != &shdr) 472 errx(EX_SOFTWARE, "gelf_getshdr() failed: %s.", elf_errmsg(-1)); 473 474 if ( shdr.sh_type == SHT_REL || shdr.sh_type == SHT_RELA) { 475 return 1; 476 } else { 477 return 0; 478 } 479 return -1; 480 } 481 /** 482 * @memo Prepare an elf from relocatable object for disassemble 483 * @doc 484 * binutils objdump disassemble does not give a correct output for relocatable 485 * object, mainly because it does not apply relocation section indications to 486 * the corresponding section. 487 * This tool handle this relocation. 488 */ 489 int /*X*/ main(int argc, char *argv[]) { 490 int fd_in = -1, fd_out = -1; 491 Elf *elf_in = 0, *elf_out = 0; 492 493 Elf_Scn *scn_in, *scn_out; 494 Elf_Data *data_in, *data_out; 495 GElf_Ehdr ehdr_in, ehdr_out; 496 497 GElf_Shdr shdr_in, shdr_out; 498 size_t n, shstrndx; 499 500 ssize_t *v_scn_in_2_out; 501 char **sh_names; 502 503 int scn_ndx_sym, scn_ndx_out = 0, scn_ndx_in; 504 505 if (argc != 3) 506 errx(EX_USAGE, "USAGE: %s in-file-name out-file-name", argv[0]); 507 508 if (elf_version(EV_CURRENT) == EV_NONE) 509 errx(EX_SOFTWARE, "ELF library initialization failed: %s", elf_errmsg(-1)); 510 511 /* Elf input setup */ 512 if ((fd_in = open(argv[1], O_RDONLY, 0)) < 0) 513 err(EX_NOINPUT, "open \"%s\" failed", argv[1]); 514 515 if ((elf_in = elf_begin(fd_in, ELF_C_READ, NULL)) == NULL) 516 errx(EX_SOFTWARE, "elf_begin() failed: %s.", elf_errmsg(-1)); 517 518 if (gelf_getehdr(elf_in, &ehdr_in) != &ehdr_in) 519 errx(EX_SOFTWARE, "gelf_getehdr() failed: %s.", elf_errmsg(-1)); 520 521 /* Checks and warns */ 522 if ( elf_kind(elf_in) != ELF_K_ELF || ehdr_in.e_type != ET_REL) { 523 fprintf(stderr, "%s : %s must be an elf relocatable object\n", argv[0], argv[1]); 524 exit(1); 525 } 526 if ( ehdr_in.e_ident[EI_OSABI] != ELFOSABI_LINUX ) { 527 fprintf(stderr, "%s warning : target OS not implemented\n", argv[0]); 528 } 529 switch ( ehdr_in.e_ident[EI_DATA] ) { 530 case ELFDATA2LSB: 531 target_is_big_endian = 0; 532 break; 533 case ELFDATA2MSB: 534 fprintf(stderr, "%s warning : big endian data encoding is not tested\n", argv[0]); 535 target_is_big_endian = 1; 536 break; 537 default : 538 fprintf(stderr, "%s : unsupported data type (%d)\n", argv[0], ehdr_in.e_ident[EI_DATA]); 539 break; 540 } 541 if ( ehdr_in.e_machine != EM_386 ) { 542 fprintf(stderr, "%s warning : machine not implemented\n", argv[0]); 543 } 544 545 printf("ELF %s contains %d sections\n", argv[1], ehdr_in.e_shnum); 546 547 if (!(sh_names = (char **)malloc(ehdr_in.e_shnum*sizeof(char *)))) 548 errx(EX_SOFTWARE, "malloc \"%s\" failed", strerror(errno)); 549 550 if (elf_getshstrndx(elf_in, &shstrndx) != 0) 551 errx(EX_SOFTWARE, "getshstrndx() failed: %s, %d.", elf_errmsg(-1), shstrndx); 552 553 for ( scn_ndx_in = 0; scn_ndx_in < ehdr_in.e_shnum; scn_ndx_in++ ) { 554 if ((scn_in = elf_getscn(elf_in, scn_ndx_in)) == NULL) 555 errx(EX_SOFTWARE, "getscn() failed: %s.", elf_errmsg(-1)); 556 557 if (gelf_getshdr(scn_in, &shdr_in) != &shdr_in) 558 errx(EX_SOFTWARE, "getshdr() failed: %s.", elf_errmsg(-1)); 559 560 if ((sh_names[scn_ndx_in] = elf_strptr(elf_in, shstrndx, shdr_in.sh_name)) == NULL) 561 errx(EX_SOFTWARE, "elf_strptr() failed: %s.", elf_errmsg(-1)); 562 } 563 564 // if ((fd_out = open(argv[2], O_WRONLY|O_CREAT, 0777)) < 0) 565 if ((fd_out = open(argv[2], O_RDWR|O_CREAT, 0777)) < 0) 566 errx(EX_OSERR, "open \"%s\" failed", argv[2]); 567 568 if ((elf_out = elf_begin(fd_out, ELF_C_WRITE, NULL)) == NULL) 569 // if ((elf_out = elf_begin(fd_out, ELF_C_RDWR, NULL)) == NULL) 570 errx(EX_SOFTWARE, "elf_begin() failed: %s.", elf_errmsg(-1)); 571 572 /* Create and set new Elf header */ 573 if ( gelf_newehdr(elf_out, ehdr_in.e_ident[EI_CLASS]) == 0) 574 errx(EX_SOFTWARE, "gelf_newehdr() failed: %s.", elf_errmsg(-1)); 575 576 if ( gelf_getehdr(elf_out, &ehdr_out) != &ehdr_out) 577 errx(EX_SOFTWARE, "gelf_getehdr() failed: %s.", elf_errmsg(-1)); 578 ehdr_out = ehdr_in; 579 if ( gelf_update_ehdr (elf_out, &ehdr_out) == 0) 580 errx(EX_SOFTWARE, "gelf_update_ehdr() failed: %s.", elf_errmsg(-1)); 581 582 /* Build section layout table */ 583 if (!(v_scn_in_2_out = (ssize_t *)malloc(ehdr_in.e_shnum * sizeof(ssize_t)))) 584 errx(EX_SOFTWARE, "malloc \"%s\" failed", strerror(errno)); 585 v_scn_in_2_out[0] = 0; 586 if ( (ssize_t)(scn_ndx_out = melf_rel_scn_layout(elf_in, v_scn_in_2_out)) < 0 ) 587 errx(EX_SOFTWARE, "melf_rel_scn_layout() failed."); 588 ehdr_out.e_shnum = scn_ndx_out; 589 590 /* copy all sections to new elf execpt rel.section followin v_scn_in2_out layout */ 591 printf("Copy section to new elf : "); 592 for ( scn_ndx_out = 1; scn_ndx_out < ehdr_out.e_shnum; scn_ndx_out++ ) { 593 594 /* get source section corresponding to scn_ndx_out in layout */ 595 for ( scn_ndx_in = 0; scn_ndx_in < ehdr_in.e_shnum; scn_ndx_in++) { 596 if ( scn_ndx_out == v_scn_in_2_out[scn_ndx_in] ) goto found_scn_source; 597 } 598 continue; 599 found_scn_source: 600 601 /* Recognize and set section names string table index */ 602 if ( shstrndx == scn_ndx_in ) ehdr_out.e_shstrndx = scn_ndx_out; 603 604 if ((scn_in = elf_getscn(elf_in, scn_ndx_in)) == NULL) 605 errx(EX_SOFTWARE, "getscn() failed: %s.", elf_errmsg(-1)); 606 607 /* copy section to new elf */ 608 if (gelf_getshdr(scn_in, &shdr_in) != &shdr_in) 609 errx(EX_SOFTWARE, "gelf_getshdr() failed: %s.", elf_errmsg(-1)); 610 611 if ((scn_out = elf_newscn(elf_out)) == NULL) 612 errx(EX_SOFTWARE, "elf_newscn() failed: %s.", elf_errmsg(-1)); 613 data_in = NULL; n = 0; 614 while (n < shdr_in.sh_size && (data_in = elf_getdata(scn_in, data_in)) != NULL) { 615 if ((data_out = elf_newdata(scn_out)) == NULL) 616 errx(EX_SOFTWARE, "elf_newdata() failed: %s.", elf_errmsg(-1)); 617 *data_out = *data_in; 618 n += data_in->d_size; 619 } 620 621 if ( gelf_getshdr(scn_out, &shdr_out) != &shdr_out) 622 errx(EX_SOFTWARE, "gelf_getshdr() failed: %s.", elf_errmsg(-1)); 623 624 shdr_out = shdr_in; 625 /* convert link to new section numbering */ 626 if ( shdr_in.sh_link ) 627 shdr_out.sh_link = v_scn_in_2_out[shdr_in.sh_link]; 628 629 if ( gelf_update_shdr (scn_out, &shdr_out) == 0) 630 errx(EX_SOFTWARE, "gelf_update_shdr() failed: %s.", elf_errmsg(-1)); 631 632 printf("%d<%d ", scn_ndx_out, scn_ndx_in); 633 } 634 printf("done\n"); 635 636 /* update ehdr to record e_shstrndx */ 637 if ( gelf_update_ehdr (elf_out, &ehdr_out) == 0) 638 errx(EX_SOFTWARE, "gelf_update_ehdr() failed: %s.", elf_errmsg(-1)); 639 640 if (elf_update(elf_out, ELF_C_WRITE) < 0) 641 errx(EX_SOFTWARE, "elf_update() failed: %s.", elf_errmsg(-1)); 642 643 elf_end(elf_out); 644 /* 645 * I did not found an other way to modify section in out elf 646 * other than to reopen it in read/write mode 647 */ 648 if ((elf_out = elf_begin(fd_out, ELF_C_RDWR, NULL)) == NULL) 649 errx(EX_SOFTWARE, "elf_begin() failed: %s.", elf_errmsg(-1)); 650 651 if ( melf_scn_sym_shconv(elf_out, v_scn_in_2_out, ehdr_in.e_shnum) < 0) 652 errx(EX_SOFTWARE, "melf_scn_sym_shconv failled"); 653 if (elf_update(elf_out, ELF_C_NULL) < 0) 654 errx(EX_SOFTWARE, "elf_update() failed: %s.", elf_errmsg(-1)); 655 656 /* Adapt symbol table */ 657 if ( (scn_ndx_sym = melf_scn_sym_lnk(elf_out)) < 0) 658 errx(EX_SOFTWARE, "melf_scn_sym_lnk() failed"); 659 if (elf_update(elf_out, ELF_C_NULL) < 0) 660 errx(EX_SOFTWARE, "elf_update() failed: %s.", elf_errmsg(-1)); 661 662 // if (melf_scn_sym_list(elf_out) < 0 ) exit(1); 663 // if (melf_scn_dump(elf_out, 0, ".symtab") <0 ) exit(1); 664 // if (melf_scn_dump(elf_out, 0, ".shstrtab") <0 ) exit(1); 665 666 /* peer section and rel.section */ 667 for ( scn_ndx_out = 1; scn_ndx_out < ehdr_out.e_shnum; scn_ndx_out++ ) { 668 ssize_t scn_rel_i; 669 /* skip .rel<.sections> */ 670 for ( scn_ndx_in = 0; scn_ndx_in < ehdr_in.e_shnum; scn_ndx_in++) { 671 if ( scn_ndx_out == v_scn_in_2_out[scn_ndx_in] ) goto found_scn_source_2; 672 } 673 continue; 674 found_scn_source_2: 675 676 /* track section count for section names string table index */ 677 printf("[%d] : %s", scn_ndx_in, sh_names[scn_ndx_in]); 678 switch ( (scn_rel_i = melf_find_rel_section(elf_in, scn_ndx_in)) ) { 679 case -1: errx(EX_SOFTWARE, "melf_find_rel_section() failed"); break; 680 case 0: break; 681 default : 682 /* Locate section if there is a .rel for it */ 683 printf(" linked with section : [%d]", scn_rel_i); 684 if ( melf_scn_rel(elf_out, scn_ndx_out, elf_in, scn_rel_i, elf_out, scn_ndx_sym) < 0 ) 685 errx(EX_SOFTWARE, "melf_scn_reloc() failed"); 686 } 687 printf("\n"); 688 } 689 690 /* 691 if (elf_update(elf_out, ELF_C_NULL) < 0) 692 errx(EX_SOFTWARE, "elf_update(NULL) failed: %s.", elf_errmsg(-1)); 693 */ 694 if (elf_update(elf_out, ELF_C_WRITE) < 0) 695 errx(EX_SOFTWARE, "elf_update() failed: %s.", elf_errmsg(-1)); 696 697 if ( elf_out ) elf_end(elf_out); 698 if ( fd_out >= 0 ) close(fd_out); 699 if ( elf_in ) elf_end(elf_in); 700 if ( fd_in >= 0 ) close(fd_in); 701 702 703 exit(EX_OK); 704 } 705