elfheaders.c
1 /* elf header parsing */ 2 /* SPDX-License-Identifier: GPL-2.0-only */ 3 4 #include <stdio.h> 5 #include <stdlib.h> 6 #include <string.h> 7 8 #include "elfparsing.h" 9 #include "common.h" 10 #include "cbfs.h" 11 12 /* 13 * Short form: this is complicated, but we've tried making it simple 14 * and we keep hitting problems with our ELF parsing. 15 * 16 * The ELF parsing situation has always been a bit tricky. In fact, 17 * we (and most others) have been getting it wrong in small ways for 18 * years. Recently this has caused real trouble for the ARM V8 build. 19 * In this file we attempt to finally get it right for all variations 20 * of endian-ness and word size and target architectures and 21 * architectures we might get run on. Phew!. To do this we borrow a 22 * page from the FreeBSD NFS xdr model (see elf_ehdr and elf_phdr), 23 * the Plan 9 endianness functions (see xdr.c), and Go interfaces (see 24 * how we use buffer structs in this file). This ends up being a bit 25 * wordy at the lowest level, but greatly simplifies the elf parsing 26 * code and removes a common source of bugs, namely, forgetting to 27 * flip type endianness when referencing a struct member. 28 * 29 * ELF files can have four combinations of data layout: 32/64, and 30 * big/little endian. Further, to add to the fun, depending on the 31 * word size, the size of the ELF structs varies. The coreboot SELF 32 * format is simpler in theory: it's supposed to be always BE, and the 33 * various struct members allow room for growth: the entry point is 34 * always 64 bits, for example, so the size of a SELF struct is 35 * constant, regardless of target architecture word size. Hence, we 36 * need to do some transformation of the ELF files. 37 * 38 * A given architecture, realistically, only supports one of the four 39 * combinations at a time as the 'native' format. Hence, our code has 40 * been sprinkled with every variation of [nh]to[hn][sll] over the 41 * years. We've never quite gotten it all right, however, and a quick 42 * pass over this code revealed another bug. It's all worked because, 43 * until now, all the working platforms that had CBFS were 32 LE. Even then, 44 * however, bugs crept in: we recently realized that we're not 45 * transforming the entry point to big format when we store into the 46 * SELF image. 47 * 48 * The problem is essentially an XDR operation: 49 * we have something in a foreign format and need to transform it. 50 * It's most like XDR because: 51 * 1) the byte order can be wrong 52 * 2) the word size can be wrong 53 * 3) the size of elements in the stream depends on the value 54 * of other elements in the stream 55 * it's not like XDR because: 56 * 1) the byte order can be right 57 * 2) the word size can be right 58 * 3) the struct members are all on a natural alignment 59 * 60 * Hence, this new approach. To cover word size issues, we *always* 61 * transform the two structs we care about, the file header and 62 * program header, into a native struct in the 64 bit format: 63 * 64 * [32,little] -> [Elf64_Ehdr, Elf64_Phdr] 65 * [64,little] -> [Elf64_Ehdr, Elf64_Phdr] 66 * [32,big] -> [Elf64_Ehdr, Elf64_Phdr] 67 * [64,big] -> [Elf64_Ehdr, Elf64_Phdr] 68 * Then we just use those structs, and all the need for inline ntoh* goes away, 69 * as well as all the chances for error. 70 * This works because all the SELF structs have fields large enough for 71 * the largest ELF 64 struct members, and all the Elf64 struct members 72 * are at least large enough for all ELF 32 struct members. 73 * We end up with one function to do all our ELF parsing, and two functions 74 * to transform the headers. For the put case, we also have 75 * XDR functions, and hopefully we'll never again spend 5 years with the 76 * wrong endian-ness on an output value :-) 77 * This should work for all word sizes and endianness we hope to target. 78 * I *really* don't want to be here for 128 bit addresses. 79 * 80 * The parse functions are called with a pointer to an input buffer 81 * struct. One might ask: are there enough bytes in the input buffer? 82 * We know there need to be at *least* sizeof(Elf32_Ehdr) + 83 * sizeof(Elf32_Phdr) bytes. Realistically, there has to be some data 84 * too. If we start to worry, though we have not in the past, we 85 * might apply the simple test: the input buffer needs to be at least 86 * sizeof(Elf64_Ehdr) + sizeof(Elf64_Phdr) bytes because, even if it's 87 * ELF 32, there's got to be *some* data! This is not theoretically 88 * accurate but it is actually good enough in practice. It allows the 89 * header transformation code to ignore the possibility of underrun. 90 * 91 * We also must accommodate different ELF files, and hence formats, 92 * in the same cbfs invocation. We might load a 64-bit payload 93 * on a 32-bit machine; we might even have a mixed armv7/armv8 94 * SOC or even a system with an x86/ARM! 95 * 96 * A possibly problematic (though unlikely to be so) assumption 97 * is that we expect the BIOS to remain in the lowest 32 bits 98 * of the physical address space. Since ARMV8 has standardized 99 * on that, and x86_64 also has, this seems a safe assumption. 100 * 101 * To repeat, ELF structs are different sizes because ELF struct 102 * members are different sizes, depending on values in the ELF file 103 * header. For this we use the functions defined in xdr.c, which 104 * consume bytes, convert the endianness, and advance the data pointer 105 * in the buffer struct. 106 */ 107 108 109 static int iself(const void *input) 110 { 111 const Elf32_Ehdr *ehdr = input; 112 return !memcmp(ehdr->e_ident, ELFMAG, 4); 113 } 114 115 /* Get the ident array, so we can figure out 116 * endian-ness, word size, and in future other useful 117 * parameters 118 */ 119 static void 120 elf_eident(struct buffer *input, Elf64_Ehdr *ehdr) 121 { 122 bgets(input, ehdr->e_ident, sizeof(ehdr->e_ident)); 123 } 124 125 126 static int 127 check_size(const struct buffer *b, size_t offset, size_t size, const char *desc) 128 { 129 if (size == 0) 130 return 0; 131 132 if (offset >= buffer_size(b) || (offset + size) > buffer_size(b)) { 133 ERROR("The file is not large enough for the '%s'. " 134 "%zu bytes @ offset %zu, input %zu bytes.\n", 135 desc, size, offset, buffer_size(b)); 136 return -1; 137 } 138 return 0; 139 } 140 141 static void 142 elf_ehdr(struct buffer *input, Elf64_Ehdr *ehdr, struct xdr *xdr, int bit64) 143 { 144 ehdr->e_type = xdr->get16(input); 145 ehdr->e_machine = xdr->get16(input); 146 ehdr->e_version = xdr->get32(input); 147 if (bit64){ 148 ehdr->e_entry = xdr->get64(input); 149 ehdr->e_phoff = xdr->get64(input); 150 ehdr->e_shoff = xdr->get64(input); 151 } else { 152 ehdr->e_entry = xdr->get32(input); 153 ehdr->e_phoff = xdr->get32(input); 154 ehdr->e_shoff = xdr->get32(input); 155 } 156 ehdr->e_flags = xdr->get32(input); 157 ehdr->e_ehsize = xdr->get16(input); 158 ehdr->e_phentsize = xdr->get16(input); 159 ehdr->e_phnum = xdr->get16(input); 160 ehdr->e_shentsize = xdr->get16(input); 161 ehdr->e_shnum = xdr->get16(input); 162 ehdr->e_shstrndx = xdr->get16(input); 163 } 164 165 static void 166 elf_phdr(struct buffer *pinput, Elf64_Phdr *phdr, 167 int entsize, struct xdr *xdr, int bit64) 168 { 169 /* 170 * The entsize need not be sizeof(*phdr). 171 * Hence, it is easier to keep a copy of the input, 172 * as the xdr functions may not advance the input 173 * pointer the full entsize; rather than get tricky 174 * we just advance it below. 175 */ 176 struct buffer input; 177 buffer_clone(&input, pinput); 178 if (bit64){ 179 phdr->p_type = xdr->get32(&input); 180 phdr->p_flags = xdr->get32(&input); 181 phdr->p_offset = xdr->get64(&input); 182 phdr->p_vaddr = xdr->get64(&input); 183 phdr->p_paddr = xdr->get64(&input); 184 phdr->p_filesz = xdr->get64(&input); 185 phdr->p_memsz = xdr->get64(&input); 186 phdr->p_align = xdr->get64(&input); 187 } else { 188 phdr->p_type = xdr->get32(&input); 189 phdr->p_offset = xdr->get32(&input); 190 phdr->p_vaddr = xdr->get32(&input); 191 phdr->p_paddr = xdr->get32(&input); 192 phdr->p_filesz = xdr->get32(&input); 193 phdr->p_memsz = xdr->get32(&input); 194 phdr->p_flags = xdr->get32(&input); 195 phdr->p_align = xdr->get32(&input); 196 } 197 buffer_seek(pinput, entsize); 198 } 199 200 static void 201 elf_shdr(struct buffer *pinput, Elf64_Shdr *shdr, 202 int entsize, struct xdr *xdr, int bit64) 203 { 204 /* 205 * The entsize need not be sizeof(*shdr). 206 * Hence, it is easier to keep a copy of the input, 207 * as the xdr functions may not advance the input 208 * pointer the full entsize; rather than get tricky 209 * we just advance it below. 210 */ 211 struct buffer input = *pinput; 212 if (bit64){ 213 shdr->sh_name = xdr->get32(&input); 214 shdr->sh_type = xdr->get32(&input); 215 shdr->sh_flags = xdr->get64(&input); 216 shdr->sh_addr = xdr->get64(&input); 217 shdr->sh_offset = xdr->get64(&input); 218 shdr->sh_size= xdr->get64(&input); 219 shdr->sh_link = xdr->get32(&input); 220 shdr->sh_info = xdr->get32(&input); 221 shdr->sh_addralign = xdr->get64(&input); 222 shdr->sh_entsize = xdr->get64(&input); 223 } else { 224 shdr->sh_name = xdr->get32(&input); 225 shdr->sh_type = xdr->get32(&input); 226 shdr->sh_flags = xdr->get32(&input); 227 shdr->sh_addr = xdr->get32(&input); 228 shdr->sh_offset = xdr->get32(&input); 229 shdr->sh_size = xdr->get32(&input); 230 shdr->sh_link = xdr->get32(&input); 231 shdr->sh_info = xdr->get32(&input); 232 shdr->sh_addralign = xdr->get32(&input); 233 shdr->sh_entsize = xdr->get32(&input); 234 } 235 buffer_seek(pinput, entsize); 236 } 237 238 static int 239 phdr_read(const struct buffer *in, struct parsed_elf *pelf, 240 struct xdr *xdr, int bit64) 241 { 242 struct buffer b; 243 Elf64_Phdr *phdr; 244 Elf64_Ehdr *ehdr; 245 int i; 246 247 ehdr = &pelf->ehdr; 248 /* cons up an input buffer for the headers. 249 * Note that the program headers can be anywhere, 250 * per the ELF spec, You'd be surprised how many ELF 251 * readers miss this little detail. 252 */ 253 buffer_splice(&b, in, ehdr->e_phoff, 254 (uint32_t)ehdr->e_phentsize * ehdr->e_phnum); 255 if (check_size(in, ehdr->e_phoff, buffer_size(&b), "program headers")) 256 return -1; 257 258 /* gather up all the phdrs. 259 * We do them all at once because there is more 260 * than one loop over all the phdrs. 261 */ 262 phdr = calloc(ehdr->e_phnum, sizeof(*phdr)); 263 for (i = 0; i < ehdr->e_phnum; i++) { 264 DEBUG("Parsing segment %d\n", i); 265 elf_phdr(&b, &phdr[i], ehdr->e_phentsize, xdr, bit64); 266 267 /* Ensure the contents are valid within the elf file. */ 268 if (check_size(in, phdr[i].p_offset, phdr[i].p_filesz, 269 "segment contents")) { 270 free(phdr); 271 return -1; 272 } 273 } 274 275 pelf->phdr = phdr; 276 277 return 0; 278 } 279 280 static int 281 shdr_read(const struct buffer *in, struct parsed_elf *pelf, 282 struct xdr *xdr, int bit64) 283 { 284 struct buffer b; 285 Elf64_Shdr *shdr; 286 Elf64_Ehdr *ehdr; 287 int i; 288 289 ehdr = &pelf->ehdr; 290 291 /* cons up an input buffer for the section headers. 292 * Note that the section headers can be anywhere, 293 * per the ELF spec, You'd be surprised how many ELF 294 * readers miss this little detail. 295 */ 296 buffer_splice(&b, in, ehdr->e_shoff, 297 (uint32_t)ehdr->e_shentsize * ehdr->e_shnum); 298 if (check_size(in, ehdr->e_shoff, buffer_size(&b), "section headers")) 299 return -1; 300 301 /* gather up all the shdrs. */ 302 shdr = calloc(ehdr->e_shnum, sizeof(*shdr)); 303 for (i = 0; i < ehdr->e_shnum; i++) { 304 DEBUG("Parsing section %d\n", i); 305 elf_shdr(&b, &shdr[i], ehdr->e_shentsize, xdr, bit64); 306 } 307 308 pelf->shdr = shdr; 309 310 return 0; 311 } 312 313 static int 314 reloc_read(const struct buffer *in, struct parsed_elf *pelf, 315 struct xdr *xdr, int bit64) 316 { 317 struct buffer b; 318 Elf64_Word i; 319 Elf64_Ehdr *ehdr; 320 321 ehdr = &pelf->ehdr; 322 pelf->relocs = calloc(ehdr->e_shnum, sizeof(Elf64_Rela *)); 323 324 /* Allocate array for each section that contains relocation entries. */ 325 for (i = 0; i < ehdr->e_shnum; i++) { 326 Elf64_Shdr *shdr; 327 Elf64_Rela *rela; 328 Elf64_Xword j; 329 Elf64_Xword nrelocs; 330 int is_rela; 331 332 shdr = &pelf->shdr[i]; 333 334 /* Only process REL and RELA sections. */ 335 if (shdr->sh_type != SHT_REL && shdr->sh_type != SHT_RELA) 336 continue; 337 338 DEBUG("Checking relocation section %u\n", i); 339 340 /* Ensure the section that relocations apply is a valid. */ 341 if (shdr->sh_info >= ehdr->e_shnum || 342 shdr->sh_info == SHN_UNDEF) { 343 ERROR("Relocations apply to an invalid section: %u\n", 344 shdr[i].sh_info); 345 return -1; 346 } 347 348 is_rela = shdr->sh_type == SHT_RELA; 349 350 /* Determine the number relocations in this section. */ 351 nrelocs = shdr->sh_size / shdr->sh_entsize; 352 353 pelf->relocs[i] = calloc(nrelocs, sizeof(Elf64_Rela)); 354 355 buffer_splice(&b, in, shdr->sh_offset, shdr->sh_size); 356 if (check_size(in, shdr->sh_offset, buffer_size(&b), 357 "relocation section")) { 358 ERROR("Relocation section %u failed.\n", i); 359 return -1; 360 } 361 362 rela = pelf->relocs[i]; 363 for (j = 0; j < nrelocs; j++) { 364 if (bit64) { 365 rela->r_offset = xdr->get64(&b); 366 rela->r_info = xdr->get64(&b); 367 if (is_rela) 368 rela->r_addend = xdr->get64(&b); 369 } else { 370 uint32_t r_info; 371 372 rela->r_offset = xdr->get32(&b); 373 r_info = xdr->get32(&b); 374 rela->r_info = ELF64_R_INFO(ELF32_R_SYM(r_info), 375 ELF32_R_TYPE(r_info)); 376 if (is_rela) 377 rela->r_addend = xdr->get32(&b); 378 } 379 rela++; 380 } 381 } 382 383 return 0; 384 } 385 386 static int strtab_read(const struct buffer *in, struct parsed_elf *pelf) 387 { 388 Elf64_Ehdr *ehdr; 389 Elf64_Word i; 390 391 ehdr = &pelf->ehdr; 392 393 if (ehdr->e_shstrndx >= ehdr->e_shnum) { 394 ERROR("Section header string table index out of range: %d\n", 395 ehdr->e_shstrndx); 396 return -1; 397 } 398 399 /* For each section of type SHT_STRTAB create a symtab buffer. */ 400 pelf->strtabs = calloc(ehdr->e_shnum, sizeof(struct buffer *)); 401 402 for (i = 0; i < ehdr->e_shnum; i++) { 403 struct buffer *b; 404 Elf64_Shdr *shdr = &pelf->shdr[i]; 405 406 if (shdr->sh_type != SHT_STRTAB) 407 continue; 408 409 b = calloc(1, sizeof(*b)); 410 buffer_splice(b, in, shdr->sh_offset, shdr->sh_size); 411 if (check_size(in, shdr->sh_offset, buffer_size(b), "strtab")) { 412 ERROR("STRTAB section not within bounds: %d\n", i); 413 free(b); 414 return -1; 415 } 416 pelf->strtabs[i] = b; 417 } 418 419 return 0; 420 } 421 422 static int 423 symtab_read(const struct buffer *in, struct parsed_elf *pelf, 424 struct xdr *xdr, int bit64) 425 { 426 Elf64_Ehdr *ehdr; 427 Elf64_Shdr *shdr; 428 Elf64_Half shnum; 429 Elf64_Xword i; 430 Elf64_Xword nsyms; 431 Elf64_Sym *sym; 432 struct buffer b; 433 434 ehdr = &pelf->ehdr; 435 436 shdr = NULL; 437 for (shnum = 0; shnum < ehdr->e_shnum; shnum++) { 438 if (pelf->shdr[shnum].sh_type != SHT_SYMTAB) 439 continue; 440 441 if (shdr != NULL) { 442 ERROR("Multiple symbol sections found. %u and %u\n", 443 (unsigned int)(shdr - pelf->shdr), shnum); 444 return -1; 445 } 446 447 shdr = &pelf->shdr[shnum]; 448 } 449 450 if (shdr == NULL) { 451 ERROR("No symbol table found.\n"); 452 return -1; 453 } 454 455 buffer_splice(&b, in, shdr->sh_offset, shdr->sh_size); 456 if (check_size(in, shdr->sh_offset, buffer_size(&b), "symtab")) 457 return -1; 458 459 nsyms = shdr->sh_size / shdr->sh_entsize; 460 461 pelf->syms = calloc(nsyms, sizeof(Elf64_Sym)); 462 463 for (i = 0; i < nsyms; i++) { 464 sym = &pelf->syms[i]; 465 466 if (bit64) { 467 sym->st_name = xdr->get32(&b); 468 sym->st_info = xdr->get8(&b); 469 sym->st_other = xdr->get8(&b); 470 sym->st_shndx = xdr->get16(&b); 471 sym->st_value = xdr->get64(&b); 472 sym->st_size = xdr->get64(&b); 473 } else { 474 sym->st_name = xdr->get32(&b); 475 sym->st_value = xdr->get32(&b); 476 sym->st_size = xdr->get32(&b); 477 sym->st_info = xdr->get8(&b); 478 sym->st_other = xdr->get8(&b); 479 sym->st_shndx = xdr->get16(&b); 480 } 481 } 482 483 return 0; 484 } 485 486 int parse_elf(const struct buffer *pinput, struct parsed_elf *pelf, int flags) 487 { 488 struct xdr *xdr = &xdr_le; 489 int bit64 = 0; 490 struct buffer input; 491 Elf64_Ehdr *ehdr; 492 493 /* Zero out the parsed elf structure. */ 494 memset(pelf, 0, sizeof(*pelf)); 495 496 if (!iself(buffer_get(pinput))) { 497 DEBUG("The stage file is not in ELF format!\n"); 498 return -1; 499 } 500 501 buffer_clone(&input, pinput); 502 ehdr = &pelf->ehdr; 503 elf_eident(&input, ehdr); 504 bit64 = ehdr->e_ident[EI_CLASS] == ELFCLASS64; 505 /* Assume LE unless we are sure otherwise. 506 * We're not going to take on the task of 507 * fully validating the ELF file. That way 508 * lies madness. 509 */ 510 if (ehdr->e_ident[EI_DATA] == ELFDATA2MSB) 511 xdr = &xdr_be; 512 513 elf_ehdr(&input, ehdr, xdr, bit64); 514 515 /* Relocation processing requires section header parsing. */ 516 if (flags & ELF_PARSE_RELOC) 517 flags |= ELF_PARSE_SHDR; 518 519 /* String table processing requires section header parsing. */ 520 if (flags & ELF_PARSE_STRTAB) 521 flags |= ELF_PARSE_SHDR; 522 523 /* Symbole table processing requires section header parsing. */ 524 if (flags & ELF_PARSE_SYMTAB) 525 flags |= ELF_PARSE_SHDR; 526 527 if ((flags & ELF_PARSE_PHDR) && phdr_read(pinput, pelf, xdr, bit64)) 528 goto fail; 529 530 if ((flags & ELF_PARSE_SHDR) && shdr_read(pinput, pelf, xdr, bit64)) 531 goto fail; 532 533 if ((flags & ELF_PARSE_RELOC) && reloc_read(pinput, pelf, xdr, bit64)) 534 goto fail; 535 536 if ((flags & ELF_PARSE_STRTAB) && strtab_read(pinput, pelf)) 537 goto fail; 538 539 if ((flags & ELF_PARSE_SYMTAB) && symtab_read(pinput, pelf, xdr, bit64)) 540 goto fail; 541 542 return 0; 543 544 fail: 545 parsed_elf_destroy(pelf); 546 return -1; 547 } 548 549 void parsed_elf_destroy(struct parsed_elf *pelf) 550 { 551 Elf64_Half i; 552 553 free(pelf->phdr); 554 free(pelf->shdr); 555 if (pelf->relocs != NULL) { 556 for (i = 0; i < pelf->ehdr.e_shnum; i++) 557 free(pelf->relocs[i]); 558 } 559 free(pelf->relocs); 560 561 if (pelf->strtabs != NULL) { 562 for (i = 0; i < pelf->ehdr.e_shnum; i++) 563 free(pelf->strtabs[i]); 564 } 565 free(pelf->strtabs); 566 free(pelf->syms); 567 } 568 569 /* Get the headers from the buffer. 570 * Return -1 in the event of an error. 571 * The section headers are optional; if NULL 572 * is passed in for pshdr they won't be parsed. 573 * We don't (yet) make payload parsing optional 574 * because we've never seen a use case. 575 */ 576 int 577 elf_headers(const struct buffer *pinput, 578 Elf64_Ehdr *ehdr, 579 Elf64_Phdr **pphdr, 580 Elf64_Shdr **pshdr) 581 { 582 struct parsed_elf pelf; 583 int flags; 584 585 flags = ELF_PARSE_PHDR; 586 587 if (pshdr != NULL) 588 flags |= ELF_PARSE_SHDR; 589 590 if (parse_elf(pinput, &pelf, flags)) 591 return -1; 592 593 /* Copy out the parsed elf header. */ 594 memcpy(ehdr, &pelf.ehdr, sizeof(*ehdr)); 595 596 *pphdr = calloc(ehdr->e_phnum, sizeof(Elf64_Phdr)); 597 memcpy(*pphdr, pelf.phdr, ehdr->e_phnum * sizeof(Elf64_Phdr)); 598 599 if (pshdr != NULL) { 600 *pshdr = calloc(ehdr->e_shnum, sizeof(Elf64_Shdr)); 601 memcpy(*pshdr, pelf.shdr, ehdr->e_shnum * sizeof(Elf64_Shdr)); 602 } 603 604 parsed_elf_destroy(&pelf); 605 606 return 0; 607 } 608 609 /* ELF Writing Support 610 * 611 * The ELF file is written according to the following layout: 612 * +------------------+ 613 * | ELF Header | 614 * +------------------+ 615 * | Section Headers | 616 * +------------------+ 617 * | Program Headers | 618 * +------------------+ 619 * | String table | 620 * +------------------+ <- 4KiB Aligned 621 * | Code/Data | 622 * +------------------+ 623 */ 624 625 void elf_init_eheader(Elf64_Ehdr *ehdr, int machine, int nbits, int endian) 626 { 627 memset(ehdr, 0, sizeof(*ehdr)); 628 ehdr->e_ident[EI_MAG0] = ELFMAG0; 629 ehdr->e_ident[EI_MAG1] = ELFMAG1; 630 ehdr->e_ident[EI_MAG2] = ELFMAG2; 631 ehdr->e_ident[EI_MAG3] = ELFMAG3; 632 ehdr->e_ident[EI_CLASS] = nbits; 633 ehdr->e_ident[EI_DATA] = endian; 634 ehdr->e_ident[EI_VERSION] = EV_CURRENT; 635 ehdr->e_type = ET_EXEC; 636 ehdr->e_machine = machine; 637 ehdr->e_version = EV_CURRENT; 638 if (nbits == ELFCLASS64) { 639 ehdr->e_ehsize = sizeof(Elf64_Ehdr); 640 ehdr->e_phentsize = sizeof(Elf64_Phdr); 641 ehdr->e_shentsize = sizeof(Elf64_Shdr); 642 } else { 643 ehdr->e_ehsize = sizeof(Elf32_Ehdr); 644 ehdr->e_phentsize = sizeof(Elf32_Phdr); 645 ehdr->e_shentsize = sizeof(Elf32_Shdr); 646 } 647 } 648 649 /* Arbitrary maximum number of sections. */ 650 #define MAX_SECTIONS 16 651 struct elf_writer_section { 652 Elf64_Shdr shdr; 653 struct buffer content; 654 const char *name; 655 }; 656 657 struct elf_writer_string_table { 658 size_t next_offset; 659 size_t max_size; 660 char *buffer; 661 }; 662 663 struct elf_writer_sym_table { 664 size_t max_entries; 665 size_t num_entries; 666 Elf64_Sym *syms; 667 }; 668 669 #define MAX_REL_NAME 32 670 struct elf_writer_rel { 671 size_t num_entries; 672 size_t max_entries; 673 Elf64_Rel *rels; 674 struct elf_writer_section *sec; 675 char name[MAX_REL_NAME]; 676 }; 677 678 struct elf_writer 679 { 680 Elf64_Ehdr ehdr; 681 struct xdr *xdr; 682 size_t num_secs; 683 struct elf_writer_section sections[MAX_SECTIONS]; 684 struct elf_writer_rel rel_sections[MAX_SECTIONS]; 685 Elf64_Phdr *phdrs; 686 struct elf_writer_section *shstrtab_sec; 687 struct elf_writer_section *strtab_sec; 688 struct elf_writer_section *symtab_sec; 689 struct elf_writer_string_table strtab; 690 struct elf_writer_sym_table symtab; 691 int bit64; 692 }; 693 694 static size_t section_index(struct elf_writer *ew, 695 struct elf_writer_section *sec) 696 { 697 return sec - &ew->sections[0]; 698 } 699 700 static struct elf_writer_section *last_section(struct elf_writer *ew) 701 { 702 return &ew->sections[ew->num_secs - 1]; 703 } 704 705 static void strtab_init(struct elf_writer *ew, size_t size) 706 { 707 struct buffer b; 708 Elf64_Shdr shdr; 709 710 /* Start adding strings after the initial NUL entry. */ 711 ew->strtab.next_offset = 1; 712 ew->strtab.max_size = size; 713 ew->strtab.buffer = calloc(1, ew->strtab.max_size); 714 715 buffer_init(&b, NULL, ew->strtab.buffer, ew->strtab.max_size); 716 memset(&shdr, 0, sizeof(shdr)); 717 shdr.sh_type = SHT_STRTAB; 718 shdr.sh_addralign = 1; 719 shdr.sh_size = ew->strtab.max_size; 720 elf_writer_add_section(ew, &shdr, &b, ".strtab"); 721 ew->strtab_sec = last_section(ew); 722 } 723 724 static void symtab_init(struct elf_writer *ew, size_t max_entries) 725 { 726 struct buffer b; 727 Elf64_Shdr shdr; 728 729 memset(&shdr, 0, sizeof(shdr)); 730 shdr.sh_type = SHT_SYMTAB; 731 732 if (ew->bit64) { 733 shdr.sh_entsize = sizeof(Elf64_Sym); 734 shdr.sh_addralign = sizeof(Elf64_Addr); 735 } else { 736 shdr.sh_entsize = sizeof(Elf32_Sym); 737 shdr.sh_addralign = sizeof(Elf32_Addr); 738 } 739 740 shdr.sh_size = shdr.sh_entsize * max_entries; 741 742 ew->symtab.syms = calloc(max_entries, sizeof(Elf64_Sym)); 743 ew->symtab.num_entries = 1; 744 ew->symtab.max_entries = max_entries; 745 746 buffer_init(&b, NULL, ew->symtab.syms, shdr.sh_size); 747 748 elf_writer_add_section(ew, &shdr, &b, ".symtab"); 749 ew->symtab_sec = last_section(ew); 750 } 751 752 struct elf_writer *elf_writer_init(const Elf64_Ehdr *ehdr) 753 { 754 struct elf_writer *ew; 755 Elf64_Shdr shdr; 756 struct buffer empty_buffer; 757 758 if (!iself(ehdr)) 759 return NULL; 760 761 ew = calloc(1, sizeof(*ew)); 762 763 memcpy(&ew->ehdr, ehdr, sizeof(ew->ehdr)); 764 765 ew->bit64 = ew->ehdr.e_ident[EI_CLASS] == ELFCLASS64; 766 767 /* Set the endinan ops. */ 768 if (ew->ehdr.e_ident[EI_DATA] == ELFDATA2MSB) 769 ew->xdr = &xdr_be; 770 else 771 ew->xdr = &xdr_le; 772 773 /* Reset count and offsets */ 774 ew->ehdr.e_phoff = 0; 775 ew->ehdr.e_shoff = 0; 776 ew->ehdr.e_shnum = 0; 777 ew->ehdr.e_phnum = 0; 778 779 memset(&empty_buffer, 0, sizeof(empty_buffer)); 780 memset(&shdr, 0, sizeof(shdr)); 781 782 /* Add SHT_NULL section header. */ 783 shdr.sh_type = SHT_NULL; 784 elf_writer_add_section(ew, &shdr, &empty_buffer, NULL); 785 786 /* Add section header string table and maintain reference to it. */ 787 shdr.sh_type = SHT_STRTAB; 788 elf_writer_add_section(ew, &shdr, &empty_buffer, ".shstrtab"); 789 ew->shstrtab_sec = last_section(ew); 790 ew->ehdr.e_shstrndx = section_index(ew, ew->shstrtab_sec); 791 792 /* Add a small string table and symbol table. */ 793 strtab_init(ew, 4096); 794 symtab_init(ew, 100); 795 796 return ew; 797 } 798 799 /* 800 * Clean up any internal state represented by ew. Aftewards the elf_writer 801 * is invalid. 802 * It is safe to call elf_writer_destroy with ew as NULL. It returns without 803 * performing any action. 804 */ 805 void elf_writer_destroy(struct elf_writer *ew) 806 { 807 int i; 808 if (ew == NULL) 809 return; 810 if (ew->phdrs != NULL) 811 free(ew->phdrs); 812 free(ew->strtab.buffer); 813 free(ew->symtab.syms); 814 for (i = 0; i < MAX_SECTIONS; i++) 815 free(ew->rel_sections[i].rels); 816 free(ew); 817 } 818 819 /* 820 * Add a section to the ELF file. Section type, flags, and memsize are 821 * maintained from the passed in Elf64_Shdr. The buffer represents the 822 * content of the section while the name is the name of section itself. 823 * Returns < 0 on error, 0 on success. 824 */ 825 int elf_writer_add_section(struct elf_writer *ew, const Elf64_Shdr *shdr, 826 struct buffer *contents, const char *name) 827 { 828 struct elf_writer_section *newsh; 829 830 if (ew->num_secs == MAX_SECTIONS) 831 return -1; 832 833 newsh = &ew->sections[ew->num_secs]; 834 ew->num_secs++; 835 836 memcpy(&newsh->shdr, shdr, sizeof(newsh->shdr)); 837 newsh->shdr.sh_offset = 0; 838 839 newsh->name = name; 840 if (contents != NULL) 841 buffer_clone(&newsh->content, contents); 842 843 return 0; 844 } 845 846 static void ehdr_write(struct elf_writer *ew, struct buffer *m) 847 { 848 int i; 849 850 for (i = 0; i < EI_NIDENT; i++) 851 ew->xdr->put8(m, ew->ehdr.e_ident[i]); 852 ew->xdr->put16(m, ew->ehdr.e_type); 853 ew->xdr->put16(m, ew->ehdr.e_machine); 854 ew->xdr->put32(m, ew->ehdr.e_version); 855 if (ew->bit64) { 856 ew->xdr->put64(m, ew->ehdr.e_entry); 857 ew->xdr->put64(m, ew->ehdr.e_phoff); 858 ew->xdr->put64(m, ew->ehdr.e_shoff); 859 } else { 860 ew->xdr->put32(m, ew->ehdr.e_entry); 861 ew->xdr->put32(m, ew->ehdr.e_phoff); 862 ew->xdr->put32(m, ew->ehdr.e_shoff); 863 } 864 ew->xdr->put32(m, ew->ehdr.e_flags); 865 ew->xdr->put16(m, ew->ehdr.e_ehsize); 866 ew->xdr->put16(m, ew->ehdr.e_phentsize); 867 ew->xdr->put16(m, ew->ehdr.e_phnum); 868 ew->xdr->put16(m, ew->ehdr.e_shentsize); 869 ew->xdr->put16(m, ew->ehdr.e_shnum); 870 ew->xdr->put16(m, ew->ehdr.e_shstrndx); 871 } 872 873 static void shdr_write(struct elf_writer *ew, size_t n, struct buffer *m) 874 { 875 struct xdr *xdr = ew->xdr; 876 int bit64 = ew->bit64; 877 struct elf_writer_section *sec = &ew->sections[n]; 878 Elf64_Shdr *shdr = &sec->shdr; 879 880 xdr->put32(m, shdr->sh_name); 881 xdr->put32(m, shdr->sh_type); 882 if (bit64) { 883 xdr->put64(m, shdr->sh_flags); 884 xdr->put64(m, shdr->sh_addr); 885 xdr->put64(m, shdr->sh_offset); 886 xdr->put64(m, shdr->sh_size); 887 xdr->put32(m, shdr->sh_link); 888 xdr->put32(m, shdr->sh_info); 889 xdr->put64(m, shdr->sh_addralign); 890 xdr->put64(m, shdr->sh_entsize); 891 } else { 892 xdr->put32(m, shdr->sh_flags); 893 xdr->put32(m, shdr->sh_addr); 894 xdr->put32(m, shdr->sh_offset); 895 xdr->put32(m, shdr->sh_size); 896 xdr->put32(m, shdr->sh_link); 897 xdr->put32(m, shdr->sh_info); 898 xdr->put32(m, shdr->sh_addralign); 899 xdr->put32(m, shdr->sh_entsize); 900 } 901 } 902 903 static void 904 phdr_write(struct elf_writer *ew, struct buffer *m, Elf64_Phdr *phdr) 905 { 906 if (ew->bit64) { 907 ew->xdr->put32(m, phdr->p_type); 908 ew->xdr->put32(m, phdr->p_flags); 909 ew->xdr->put64(m, phdr->p_offset); 910 ew->xdr->put64(m, phdr->p_vaddr); 911 ew->xdr->put64(m, phdr->p_paddr); 912 ew->xdr->put64(m, phdr->p_filesz); 913 ew->xdr->put64(m, phdr->p_memsz); 914 ew->xdr->put64(m, phdr->p_align); 915 } else { 916 ew->xdr->put32(m, phdr->p_type); 917 ew->xdr->put32(m, phdr->p_offset); 918 ew->xdr->put32(m, phdr->p_vaddr); 919 ew->xdr->put32(m, phdr->p_paddr); 920 ew->xdr->put32(m, phdr->p_filesz); 921 ew->xdr->put32(m, phdr->p_memsz); 922 ew->xdr->put32(m, phdr->p_flags); 923 ew->xdr->put32(m, phdr->p_align); 924 } 925 926 } 927 928 static int section_consecutive(struct elf_writer *ew, Elf64_Half secidx) 929 { 930 Elf64_Half i; 931 struct elf_writer_section *prev_alloc = NULL; 932 933 if (secidx == 0) 934 return 0; 935 936 for (i = 0; i < secidx; i++) { 937 if (ew->sections[i].shdr.sh_flags & SHF_ALLOC) 938 prev_alloc = &ew->sections[i]; 939 } 940 941 if (prev_alloc == NULL) 942 return 0; 943 944 if (prev_alloc->shdr.sh_addr + prev_alloc->shdr.sh_size == 945 ew->sections[secidx].shdr.sh_addr) 946 return 1; 947 948 return 0; 949 } 950 951 static void write_phdrs(struct elf_writer *ew, struct buffer *phdrs) 952 { 953 Elf64_Half i; 954 Elf64_Phdr phdr; 955 size_t num_written = 0; 956 size_t num_needs_write = 0; 957 958 for (i = 0; i < ew->num_secs; i++) { 959 struct elf_writer_section *sec = &ew->sections[i]; 960 961 if (!(sec->shdr.sh_flags & SHF_ALLOC)) 962 continue; 963 964 if (!section_consecutive(ew, i)) { 965 /* Write out previously set phdr. */ 966 if (num_needs_write != num_written) { 967 phdr_write(ew, phdrs, &phdr); 968 num_written++; 969 } 970 phdr.p_type = PT_LOAD; 971 phdr.p_offset = sec->shdr.sh_offset; 972 phdr.p_vaddr = sec->shdr.sh_addr; 973 phdr.p_paddr = sec->shdr.sh_addr; 974 phdr.p_filesz = buffer_size(&sec->content); 975 phdr.p_memsz = sec->shdr.sh_size; 976 phdr.p_flags = 0; 977 if (sec->shdr.sh_flags & SHF_EXECINSTR) 978 phdr.p_flags |= PF_X | PF_R; 979 if (sec->shdr.sh_flags & SHF_WRITE) 980 phdr.p_flags |= PF_W; 981 phdr.p_align = sec->shdr.sh_addralign; 982 num_needs_write++; 983 984 } else { 985 /* Accumulate file size and memsize. The assumption 986 * is that each section is either NOBITS or full 987 * (sh_size == file size). This is standard in that 988 * an ELF section doesn't have a file size component. */ 989 if (sec->shdr.sh_flags & SHF_EXECINSTR) 990 phdr.p_flags |= PF_X | PF_R; 991 if (sec->shdr.sh_flags & SHF_WRITE) 992 phdr.p_flags |= PF_W; 993 phdr.p_filesz += buffer_size(&sec->content); 994 phdr.p_memsz += sec->shdr.sh_size; 995 } 996 } 997 998 /* Write out the last phdr. */ 999 if (num_needs_write != num_written) { 1000 phdr_write(ew, phdrs, &phdr); 1001 num_written++; 1002 } 1003 assert(num_written == ew->ehdr.e_phnum); 1004 } 1005 1006 static void fixup_symbol_table(struct elf_writer *ew) 1007 { 1008 struct elf_writer_section *sec = ew->symtab_sec; 1009 1010 /* If there is only the NULL section, mark section as inactive. */ 1011 if (ew->symtab.num_entries == 1) { 1012 sec->shdr.sh_type = SHT_NULL; 1013 sec->shdr.sh_size = 0; 1014 } else { 1015 size_t i; 1016 struct buffer wr; 1017 1018 buffer_clone(&wr, &sec->content); 1019 /* To appease xdr. */ 1020 buffer_set_size(&wr, 0); 1021 for (i = 0; i < ew->symtab.num_entries; i++) { 1022 /* Create local copy as were over-writing backing 1023 * store of the symbol. */ 1024 Elf64_Sym sym = ew->symtab.syms[i]; 1025 if (ew->bit64) { 1026 ew->xdr->put32(&wr, sym.st_name); 1027 ew->xdr->put8(&wr, sym.st_info); 1028 ew->xdr->put8(&wr, sym.st_other); 1029 ew->xdr->put16(&wr, sym.st_shndx); 1030 ew->xdr->put64(&wr, sym.st_value); 1031 ew->xdr->put64(&wr, sym.st_size); 1032 } else { 1033 ew->xdr->put32(&wr, sym.st_name); 1034 ew->xdr->put32(&wr, sym.st_value); 1035 ew->xdr->put32(&wr, sym.st_size); 1036 ew->xdr->put8(&wr, sym.st_info); 1037 ew->xdr->put8(&wr, sym.st_other); 1038 ew->xdr->put16(&wr, sym.st_shndx); 1039 } 1040 } 1041 1042 /* Update section size. */ 1043 sec->shdr.sh_size = sec->shdr.sh_entsize; 1044 sec->shdr.sh_size *= ew->symtab.num_entries; 1045 1046 /* Fix up sh_link to point to string table. */ 1047 sec->shdr.sh_link = section_index(ew, ew->strtab_sec); 1048 /* sh_info is supposed to be 1 greater than symbol table 1049 * index of last local binding. Just use max symbols. */ 1050 sec->shdr.sh_info = ew->symtab.num_entries; 1051 } 1052 1053 buffer_set_size(&sec->content, sec->shdr.sh_size); 1054 } 1055 1056 static void fixup_relocations(struct elf_writer *ew) 1057 { 1058 int i; 1059 Elf64_Xword type; 1060 1061 switch (ew->ehdr.e_machine) { 1062 case EM_386: 1063 type = R_386_32; 1064 break; 1065 case EM_X86_64: 1066 type = R_AMD64_64; 1067 break; 1068 case EM_ARM: 1069 type = R_ARM_ABS32; 1070 break; 1071 case EM_AARCH64: 1072 type = R_AARCH64_ABS64; 1073 break; 1074 case EM_MIPS: 1075 type = R_MIPS_32; 1076 break; 1077 case EM_RISCV: 1078 type = R_RISCV_32; 1079 break; 1080 case EM_PPC64: 1081 type = R_PPC64_ADDR32; 1082 break; 1083 default: 1084 ERROR("Unable to handle relocations for e_machine %x\n", 1085 ew->ehdr.e_machine); 1086 return; 1087 } 1088 1089 for (i = 0; i < MAX_SECTIONS; i++) { 1090 struct elf_writer_rel *rel_sec = &ew->rel_sections[i]; 1091 struct elf_writer_section *sec = rel_sec->sec; 1092 struct buffer writer; 1093 size_t j; 1094 1095 if (sec == NULL) 1096 continue; 1097 1098 /* Update section header size as well as content size. */ 1099 buffer_init(&sec->content, sec->content.name, rel_sec->rels, 1100 rel_sec->num_entries * sec->shdr.sh_entsize); 1101 sec->shdr.sh_size = buffer_size(&sec->content); 1102 buffer_clone(&writer, &sec->content); 1103 /* To make xdr happy. */ 1104 buffer_set_size(&writer, 0); 1105 1106 for (j = 0; j < ew->rel_sections[i].num_entries; j++) { 1107 /* Make copy as we're overwriting backing store. */ 1108 Elf64_Rel rel = rel_sec->rels[j]; 1109 rel.r_info = ELF64_R_INFO(ELF64_R_SYM(rel.r_info), 1110 ELF64_R_TYPE(type)); 1111 1112 if (ew->bit64) { 1113 ew->xdr->put64(&writer, rel.r_offset); 1114 ew->xdr->put64(&writer, rel.r_info); 1115 } else { 1116 Elf32_Rel rel32; 1117 rel32.r_offset = rel.r_offset; 1118 rel32.r_info = 1119 ELF32_R_INFO(ELF64_R_SYM(rel.r_info), 1120 ELF64_R_TYPE(rel.r_info)); 1121 ew->xdr->put32(&writer, rel32.r_offset); 1122 ew->xdr->put32(&writer, rel32.r_info); 1123 } 1124 } 1125 } 1126 } 1127 1128 /* 1129 * Serialize the ELF file to the output buffer. Return < 0 on error, 1130 * 0 on success. 1131 */ 1132 int elf_writer_serialize(struct elf_writer *ew, struct buffer *out) 1133 { 1134 Elf64_Half i; 1135 Elf64_Xword metadata_size; 1136 Elf64_Xword program_size; 1137 Elf64_Off shstroffset; 1138 size_t shstrlen; 1139 struct buffer metadata; 1140 struct buffer phdrs; 1141 struct buffer data; 1142 struct buffer *strtab; 1143 1144 INFO("Writing %zu sections.\n", ew->num_secs); 1145 1146 /* Perform any necessary work for special sections. */ 1147 fixup_symbol_table(ew); 1148 fixup_relocations(ew); 1149 1150 /* Determine size of sections to be written. */ 1151 program_size = 0; 1152 /* Start with 1 byte for first byte of section header string table. */ 1153 shstrlen = 1; 1154 for (i = 0; i < ew->num_secs; i++) { 1155 struct elf_writer_section *sec = &ew->sections[i]; 1156 1157 if (sec->shdr.sh_flags & SHF_ALLOC) { 1158 if (!section_consecutive(ew, i)) 1159 ew->ehdr.e_phnum++; 1160 } 1161 1162 program_size += buffer_size(&sec->content); 1163 1164 /* Keep track of the length sections' names. */ 1165 if (sec->name != NULL) { 1166 sec->shdr.sh_name = shstrlen; 1167 shstrlen += strlen(sec->name) + 1; 1168 } 1169 } 1170 ew->ehdr.e_shnum = ew->num_secs; 1171 metadata_size = 0; 1172 metadata_size += ew->ehdr.e_ehsize; 1173 metadata_size += (Elf64_Xword)ew->ehdr.e_shnum * ew->ehdr.e_shentsize; 1174 metadata_size += (Elf64_Xword)ew->ehdr.e_phnum * ew->ehdr.e_phentsize; 1175 shstroffset = metadata_size; 1176 /* Align up section header string size and metadata size to 4KiB */ 1177 metadata_size = ALIGN_UP(metadata_size + shstrlen, 4096); 1178 1179 if (buffer_create(out, metadata_size + program_size, "elfout")) { 1180 ERROR("Could not create output buffer for ELF.\n"); 1181 return -1; 1182 } 1183 1184 INFO("Created %zu output buffer for ELF file.\n", buffer_size(out)); 1185 1186 /* 1187 * Write out ELF header. Section headers come right after ELF header 1188 * followed by the program headers. Buffers need to be created first 1189 * to do the writing. 1190 */ 1191 ew->ehdr.e_shoff = ew->ehdr.e_ehsize; 1192 ew->ehdr.e_phoff = ew->ehdr.e_shoff + 1193 (Elf64_Off)ew->ehdr.e_shnum * ew->ehdr.e_shentsize; 1194 1195 buffer_splice(&metadata, out, 0, metadata_size); 1196 buffer_splice(&phdrs, out, ew->ehdr.e_phoff, 1197 (uint32_t)ew->ehdr.e_phnum * ew->ehdr.e_phentsize); 1198 buffer_splice(&data, out, metadata_size, program_size); 1199 /* Set up the section header string table contents. */ 1200 strtab = &ew->shstrtab_sec->content; 1201 buffer_splice(strtab, out, shstroffset, shstrlen); 1202 ew->shstrtab_sec->shdr.sh_size = shstrlen; 1203 1204 /* Reset current locations. */ 1205 buffer_set_size(&metadata, 0); 1206 buffer_set_size(&data, 0); 1207 buffer_set_size(&phdrs, 0); 1208 buffer_set_size(strtab, 0); 1209 1210 /* ELF Header */ 1211 ehdr_write(ew, &metadata); 1212 1213 /* Write out section headers, section strings, section content, and 1214 * program headers. */ 1215 ew->xdr->put8(strtab, 0); 1216 for (i = 0; i < ew->num_secs; i++) { 1217 struct elf_writer_section *sec = &ew->sections[i]; 1218 1219 /* Update section offsets. Be sure to not update SHN_UNDEF. */ 1220 if (sec == ew->shstrtab_sec) 1221 sec->shdr.sh_offset = shstroffset; 1222 else if (i != SHN_UNDEF) 1223 sec->shdr.sh_offset = buffer_size(&data) + 1224 metadata_size; 1225 1226 shdr_write(ew, i, &metadata); 1227 1228 /* Add section name to string table. */ 1229 if (sec->name != NULL) 1230 bputs(strtab, sec->name, strlen(sec->name) + 1); 1231 1232 /* Output section data for all sections but SHN_UNDEF and 1233 * section header string table. */ 1234 if (i != SHN_UNDEF && sec != ew->shstrtab_sec) 1235 bputs(&data, buffer_get(&sec->content), 1236 buffer_size(&sec->content)); 1237 } 1238 1239 write_phdrs(ew, &phdrs); 1240 1241 return 0; 1242 } 1243 1244 /* Add a string to the string table returning index on success, < 0 on error. */ 1245 static int elf_writer_add_string(struct elf_writer *ew, const char *new) 1246 { 1247 size_t current_offset; 1248 size_t new_len; 1249 1250 for (current_offset = 0; current_offset < ew->strtab.next_offset; ) { 1251 const char *str = ew->strtab.buffer + current_offset; 1252 size_t len = strlen(str) + 1; 1253 1254 if (!strcmp(str, new)) 1255 return current_offset; 1256 current_offset += len; 1257 } 1258 1259 new_len = strlen(new) + 1; 1260 1261 if (current_offset + new_len > ew->strtab.max_size) { 1262 ERROR("No space for string in .strtab.\n"); 1263 return -1; 1264 } 1265 1266 memcpy(ew->strtab.buffer + current_offset, new, new_len); 1267 ew->strtab.next_offset = current_offset + new_len; 1268 1269 return current_offset; 1270 } 1271 1272 static int elf_writer_section_index(struct elf_writer *ew, const char *name) 1273 { 1274 size_t i; 1275 1276 for (i = 0; i < ew->num_secs; i++) { 1277 if (ew->sections[i].name == NULL) 1278 continue; 1279 if (!strcmp(ew->sections[i].name, name)) 1280 return i; 1281 } 1282 1283 ERROR("ELF Section not found: %s\n", name); 1284 1285 return -1; 1286 } 1287 1288 int elf_writer_add_symbol(struct elf_writer *ew, const char *name, 1289 const char *section_name, 1290 Elf64_Addr value, Elf64_Word size, 1291 int binding, int type) 1292 { 1293 int i; 1294 Elf64_Sym sym = { 1295 .st_value = value, 1296 .st_size = size, 1297 .st_info = ELF64_ST_INFO(binding, type), 1298 }; 1299 1300 if (ew->symtab.max_entries == ew->symtab.num_entries) { 1301 ERROR("No more symbol entries left.\n"); 1302 return -1; 1303 } 1304 1305 i = elf_writer_add_string(ew, name); 1306 if (i < 0) 1307 return -1; 1308 sym.st_name = i; 1309 1310 i = elf_writer_section_index(ew, section_name); 1311 if (i < 0) 1312 return -1; 1313 sym.st_shndx = i; 1314 1315 ew->symtab.syms[ew->symtab.num_entries++] = sym; 1316 1317 return 0; 1318 } 1319 1320 static int elf_sym_index(struct elf_writer *ew, const char *sym) 1321 { 1322 int j; 1323 size_t i; 1324 Elf64_Word st_name; 1325 1326 /* Determine index of symbol in the string table. */ 1327 j = elf_writer_add_string(ew, sym); 1328 if (j < 0) 1329 return -1; 1330 1331 st_name = j; 1332 1333 for (i = 0; i < ew->symtab.num_entries; i++) 1334 if (ew->symtab.syms[i].st_name == st_name) 1335 return i; 1336 1337 return -1; 1338 } 1339 1340 static struct elf_writer_rel *rel_section(struct elf_writer *ew, 1341 const Elf64_Rel *r) 1342 { 1343 Elf64_Sym *sym; 1344 struct elf_writer_rel *rel; 1345 Elf64_Shdr shdr; 1346 struct buffer b; 1347 1348 sym = &ew->symtab.syms[ELF64_R_SYM(r->r_info)]; 1349 1350 /* Determine if section has been initialized yet. */ 1351 rel = &ew->rel_sections[sym->st_shndx]; 1352 if (rel->sec != NULL) 1353 return rel; 1354 1355 memset(&shdr, 0, sizeof(shdr)); 1356 shdr.sh_type = SHT_REL; 1357 shdr.sh_link = section_index(ew, ew->symtab_sec); 1358 shdr.sh_info = sym->st_shndx; 1359 1360 if (ew->bit64) { 1361 shdr.sh_addralign = sizeof(Elf64_Addr); 1362 shdr.sh_entsize = sizeof(Elf64_Rel); 1363 } else { 1364 shdr.sh_addralign = sizeof(Elf32_Addr); 1365 shdr.sh_entsize = sizeof(Elf32_Rel); 1366 } 1367 1368 if ((strlen(".rel") + strlen(ew->sections[sym->st_shndx].name) + 1) > 1369 MAX_REL_NAME) { 1370 ERROR("Rel Section name won't fit\n"); 1371 return NULL; 1372 } 1373 1374 strcat(rel->name, ".rel"); 1375 strcat(rel->name, ew->sections[sym->st_shndx].name); 1376 buffer_init(&b, rel->name, NULL, 0); 1377 1378 elf_writer_add_section(ew, &shdr, &b, rel->name); 1379 rel->sec = last_section(ew); 1380 1381 return rel; 1382 } 1383 1384 static int add_rel(struct elf_writer_rel *rel_sec, const Elf64_Rel *rel) 1385 { 1386 if (rel_sec->num_entries == rel_sec->max_entries) { 1387 size_t num = rel_sec->max_entries * 2; 1388 Elf64_Rel *old_rels; 1389 1390 if (num == 0) 1391 num = 128; 1392 1393 old_rels = rel_sec->rels; 1394 rel_sec->rels = calloc(num, sizeof(Elf64_Rel)); 1395 1396 memcpy(rel_sec->rels, old_rels, 1397 rel_sec->num_entries * sizeof(Elf64_Rel)); 1398 free(old_rels); 1399 1400 rel_sec->max_entries = num; 1401 } 1402 1403 rel_sec->rels[rel_sec->num_entries] = *rel; 1404 rel_sec->num_entries++; 1405 1406 return 0; 1407 } 1408 1409 int elf_writer_add_rel(struct elf_writer *ew, const char *sym, Elf64_Addr addr) 1410 { 1411 Elf64_Rel rel; 1412 Elf64_Xword sym_info; 1413 int sym_index; 1414 struct elf_writer_rel *rel_sec; 1415 1416 sym_index = elf_sym_index(ew, sym); 1417 1418 if (sym_index < 0) { 1419 ERROR("Unable to locate symbol: %s\n", sym); 1420 return -1; 1421 } 1422 1423 sym_info = sym_index; 1424 1425 /* The relocation type will get fixed prior to serialization. */ 1426 rel.r_offset = addr; 1427 rel.r_info = ELF64_R_INFO(sym_info, 0); 1428 1429 rel_sec = rel_section(ew, &rel); 1430 1431 if (rel_sec == NULL) 1432 return -1; 1433 1434 return add_rel(rel_sec, &rel); 1435 } 1436 1437 int elf_program_file_size_align(const struct buffer *input, size_t *file_size, size_t *align) 1438 { 1439 Elf64_Ehdr ehdr; 1440 Elf64_Phdr *phdr; 1441 int i; 1442 size_t loadable_file_size = 0; 1443 size_t align_size = 0; 1444 1445 if (elf_headers(input, &ehdr, &phdr, NULL)) 1446 return -1; 1447 1448 for (i = 0; i < ehdr.e_phnum; i++) { 1449 if (phdr[i].p_type != PT_LOAD) 1450 continue; 1451 loadable_file_size += phdr[i].p_filesz; 1452 align_size = MAX(align_size, phdr[i].p_align); 1453 } 1454 1455 *file_size = loadable_file_size; 1456 *align = align_size; 1457 1458 free(phdr); 1459 1460 return 0; 1461 }