1 // SPDX-License-Identifier: GPL-2.0-only 2 /* 3 * recordmcount.c: construct a table of the locations of calls to 'mcount' 4 * so that ftrace can find them quickly. 5 * Copyright 2009 John F. Reiser <[email protected]>. All rights reserved. 6 * 7 * Restructured to fit Linux format, as well as other updates: 8 * Copyright 2010 Steven Rostedt <[email protected]>, Red Hat Inc. 9 */ 10 11 /* 12 * Strategy: alter the .o file in-place. 13 * 14 * Append a new STRTAB that has the new section names, followed by a new array 15 * ElfXX_Shdr[] that has the new section headers, followed by the section 16 * contents for __mcount_loc and its relocations. The old shstrtab strings, 17 * and the old ElfXX_Shdr[] array, remain as "garbage" (commonly, a couple 18 * kilobytes.) Subsequent processing by /bin/ld (or the kernel module loader) 19 * will ignore the garbage regions, because they are not designated by the 20 * new .e_shoff nor the new ElfXX_Shdr[]. [In order to remove the garbage, 21 * then use "ld -r" to create a new file that omits the garbage.] 22 */ 23 24 #include <sys/types.h> 25 #include <sys/mman.h> 26 #include <sys/stat.h> 27 #include <getopt.h> 28 #include <elf.h> 29 #include <fcntl.h> 30 #include <stdio.h> 31 #include <stdlib.h> 32 #include <string.h> 33 #include <unistd.h> 34 35 #ifndef EM_AARCH64 36 #define EM_AARCH64 183 37 #define R_AARCH64_NONE 0 38 #define R_AARCH64_ABS64 257 39 #endif 40 41 static int fd_map; /* File descriptor for file being modified. */ 42 static int mmap_failed; /* Boolean flag. */ 43 static char gpfx; /* prefix for global symbol name (sometimes '_') */ 44 static struct stat sb; /* Remember .st_size, etc. */ 45 static const char *altmcount; /* alternate mcount symbol name */ 46 static int warn_on_notrace_sect; /* warn when section has mcount not being recorded */ 47 static void *file_map; /* pointer of the mapped file */ 48 static void *file_end; /* pointer to the end of the mapped file */ 49 static int file_updated; /* flag to state file was changed */ 50 static void *file_ptr; /* current file pointer location */ 51 static void *file_append; /* added to the end of the file */ 52 static size_t file_append_size; /* how much is added to end of file */ 53 54 /* Per-file resource cleanup when multiple files. */ 55 static void cleanup(void) 56 { 57 if (!mmap_failed) 58 munmap(file_map, sb.st_size); 59 else 60 free(file_map); 61 file_map = NULL; 62 free(file_append); 63 file_append = NULL; 64 file_append_size = 0; 65 file_updated = 0; 66 } 67 68 /* ulseek, uwrite, ...: Check return value for errors. */ 69 70 static off_t ulseek(off_t const offset, int const whence) 71 { 72 switch (whence) { 73 case SEEK_SET: 74 file_ptr = file_map + offset; 75 break; 76 case SEEK_CUR: 77 file_ptr += offset; 78 break; 79 case SEEK_END: 80 file_ptr = file_map + (sb.st_size - offset); 81 break; 82 } 83 if (file_ptr < file_map) { 84 fprintf(stderr, "lseek: seek before file\n"); 85 return -1; 86 } 87 return file_ptr - file_map; 88 } 89 90 static ssize_t uwrite(void const *const buf, size_t const count) 91 { 92 size_t cnt = count; 93 off_t idx = 0; 94 95 file_updated = 1; 96 97 if (file_ptr + count >= file_end) { 98 off_t aoffset = (file_ptr + count) - file_end; 99 100 if (aoffset > file_append_size) { 101 file_append = realloc(file_append, aoffset); 102 file_append_size = aoffset; 103 } 104 if (!file_append) { 105 perror("write"); 106 cleanup(); 107 return -1; 108 } 109 if (file_ptr < file_end) { 110 cnt = file_end - file_ptr; 111 } else { 112 cnt = 0; 113 idx = aoffset - count; 114 } 115 } 116 117 if (cnt) 118 memcpy(file_ptr, buf, cnt); 119 120 if (cnt < count) 121 memcpy(file_append + idx, buf + cnt, count - cnt); 122 123 file_ptr += count; 124 return count; 125 } 126 127 static void * umalloc(size_t size) 128 { 129 void *const addr = malloc(size); 130 if (addr == 0) { 131 fprintf(stderr, "malloc failed: %zu bytes\n", size); 132 cleanup(); 133 return NULL; 134 } 135 return addr; 136 } 137 138 static unsigned char ideal_nop5_x86_64[5] = { 0x0f, 0x1f, 0x44, 0x00, 0x00 }; 139 static unsigned char ideal_nop5_x86_32[5] = { 0x3e, 0x8d, 0x74, 0x26, 0x00 }; 140 static unsigned char *ideal_nop; 141 142 static char rel_type_nop; 143 144 static int (*make_nop)(void *map, size_t const offset); 145 146 static int make_nop_x86(void *map, size_t const offset) 147 { 148 uint32_t *ptr; 149 unsigned char *op; 150 151 /* Confirm we have 0xe8 0x0 0x0 0x0 0x0 */ 152 ptr = map + offset; 153 if (*ptr != 0) 154 return -1; 155 156 op = map + offset - 1; 157 if (*op != 0xe8) 158 return -1; 159 160 /* convert to nop */ 161 if (ulseek(offset - 1, SEEK_SET) < 0) 162 return -1; 163 if (uwrite(ideal_nop, 5) < 0) 164 return -1; 165 return 0; 166 } 167 168 static unsigned char ideal_nop4_arm_le[4] = { 0x00, 0x00, 0xa0, 0xe1 }; /* mov r0, r0 */ 169 static unsigned char ideal_nop4_arm_be[4] = { 0xe1, 0xa0, 0x00, 0x00 }; /* mov r0, r0 */ 170 static unsigned char *ideal_nop4_arm; 171 172 static unsigned char bl_mcount_arm_le[4] = { 0xfe, 0xff, 0xff, 0xeb }; /* bl */ 173 static unsigned char bl_mcount_arm_be[4] = { 0xeb, 0xff, 0xff, 0xfe }; /* bl */ 174 static unsigned char *bl_mcount_arm; 175 176 static unsigned char push_arm_le[4] = { 0x04, 0xe0, 0x2d, 0xe5 }; /* push {lr} */ 177 static unsigned char push_arm_be[4] = { 0xe5, 0x2d, 0xe0, 0x04 }; /* push {lr} */ 178 static unsigned char *push_arm; 179 180 static unsigned char ideal_nop2_thumb_le[2] = { 0x00, 0xbf }; /* nop */ 181 static unsigned char ideal_nop2_thumb_be[2] = { 0xbf, 0x00 }; /* nop */ 182 static unsigned char *ideal_nop2_thumb; 183 184 static unsigned char push_bl_mcount_thumb_le[6] = { 0x00, 0xb5, 0xff, 0xf7, 0xfe, 0xff }; /* push {lr}, bl */ 185 static unsigned char push_bl_mcount_thumb_be[6] = { 0xb5, 0x00, 0xf7, 0xff, 0xff, 0xfe }; /* push {lr}, bl */ 186 static unsigned char *push_bl_mcount_thumb; 187 188 static int make_nop_arm(void *map, size_t const offset) 189 { 190 char *ptr; 191 int cnt = 1; 192 int nop_size; 193 size_t off = offset; 194 195 ptr = map + offset; 196 if (memcmp(ptr, bl_mcount_arm, 4) == 0) { 197 if (memcmp(ptr - 4, push_arm, 4) == 0) { 198 off -= 4; 199 cnt = 2; 200 } 201 ideal_nop = ideal_nop4_arm; 202 nop_size = 4; 203 } else if (memcmp(ptr - 2, push_bl_mcount_thumb, 6) == 0) { 204 cnt = 3; 205 nop_size = 2; 206 off -= 2; 207 ideal_nop = ideal_nop2_thumb; 208 } else 209 return -1; 210 211 /* Convert to nop */ 212 if (ulseek(off, SEEK_SET) < 0) 213 return -1; 214 215 do { 216 if (uwrite(ideal_nop, nop_size) < 0) 217 return -1; 218 } while (--cnt > 0); 219 220 return 0; 221 } 222 223 static unsigned char ideal_nop4_arm64[4] = {0x1f, 0x20, 0x03, 0xd5}; 224 static int make_nop_arm64(void *map, size_t const offset) 225 { 226 uint32_t *ptr; 227 228 ptr = map + offset; 229 /* bl <_mcount> is 0x94000000 before relocation */ 230 if (*ptr != 0x94000000) 231 return -1; 232 233 /* Convert to nop */ 234 if (ulseek(offset, SEEK_SET) < 0) 235 return -1; 236 if (uwrite(ideal_nop, 4) < 0) 237 return -1; 238 return 0; 239 } 240 241 /* 242 * Get the whole file as a programming convenience in order to avoid 243 * malloc+lseek+read+free of many pieces. If successful, then mmap 244 * avoids copying unused pieces; else just read the whole file. 245 * Open for both read and write; new info will be appended to the file. 246 * Use MAP_PRIVATE so that a few changes to the in-memory ElfXX_Ehdr 247 * do not propagate to the file until an explicit overwrite at the last. 248 * This preserves most aspects of consistency (all except .st_size) 249 * for simultaneous readers of the file while we are appending to it. 250 * However, multiple writers still are bad. We choose not to use 251 * locking because it is expensive and the use case of kernel build 252 * makes multiple writers unlikely. 253 */ 254 static void *mmap_file(char const *fname) 255 { 256 file_map = NULL; 257 sb.st_size = 0; 258 fd_map = open(fname, O_RDONLY); 259 if (fd_map < 0) { 260 perror(fname); 261 cleanup(); 262 return NULL; 263 } 264 if (fstat(fd_map, &sb) < 0) { 265 perror(fname); 266 cleanup(); 267 goto out; 268 } 269 if (!S_ISREG(sb.st_mode)) { 270 fprintf(stderr, "not a regular file: %s\n", fname); 271 cleanup(); 272 goto out; 273 } 274 file_map = mmap(0, sb.st_size, PROT_READ|PROT_WRITE, MAP_PRIVATE, 275 fd_map, 0); 276 mmap_failed = 0; 277 if (file_map == MAP_FAILED) { 278 mmap_failed = 1; 279 file_map = umalloc(sb.st_size); 280 if (!file_map) { 281 perror(fname); 282 goto out; 283 } 284 if (read(fd_map, file_map, sb.st_size) != sb.st_size) { 285 perror(fname); 286 free(file_map); 287 file_map = NULL; 288 goto out; 289 } 290 } 291 out: 292 close(fd_map); 293 294 file_end = file_map + sb.st_size; 295 296 return file_map; 297 } 298 299 static int write_file(const char *fname) 300 { 301 char tmp_file[strlen(fname) + 4]; 302 size_t n; 303 304 if (!file_updated) 305 return 0; 306 307 sprintf(tmp_file, "%s.rc", fname); 308 309 /* 310 * After reading the entire file into memory, delete it 311 * and write it back, to prevent weird side effects of modifying 312 * an object file in place. 313 */ 314 fd_map = open(tmp_file, O_WRONLY | O_TRUNC | O_CREAT, sb.st_mode); 315 if (fd_map < 0) { 316 perror(fname); 317 cleanup(); 318 return -1; 319 } 320 n = write(fd_map, file_map, sb.st_size); 321 if (n != sb.st_size) { 322 perror("write"); 323 cleanup(); 324 close(fd_map); 325 return -1; 326 } 327 if (file_append_size) { 328 n = write(fd_map, file_append, file_append_size); 329 if (n != file_append_size) { 330 perror("write"); 331 cleanup(); 332 close(fd_map); 333 return -1; 334 } 335 } 336 close(fd_map); 337 if (rename(tmp_file, fname) < 0) { 338 perror(fname); 339 cleanup(); 340 return -1; 341 } 342 return 0; 343 } 344 345 /* w8rev, w8nat, ...: Handle endianness. */ 346 347 static uint64_t w8rev(uint64_t const x) 348 { 349 return ((0xff & (x >> (0 * 8))) << (7 * 8)) 350 | ((0xff & (x >> (1 * 8))) << (6 * 8)) 351 | ((0xff & (x >> (2 * 8))) << (5 * 8)) 352 | ((0xff & (x >> (3 * 8))) << (4 * 8)) 353 | ((0xff & (x >> (4 * 8))) << (3 * 8)) 354 | ((0xff & (x >> (5 * 8))) << (2 * 8)) 355 | ((0xff & (x >> (6 * 8))) << (1 * 8)) 356 | ((0xff & (x >> (7 * 8))) << (0 * 8)); 357 } 358 359 static uint32_t w4rev(uint32_t const x) 360 { 361 return ((0xff & (x >> (0 * 8))) << (3 * 8)) 362 | ((0xff & (x >> (1 * 8))) << (2 * 8)) 363 | ((0xff & (x >> (2 * 8))) << (1 * 8)) 364 | ((0xff & (x >> (3 * 8))) << (0 * 8)); 365 } 366 367 static uint32_t w2rev(uint16_t const x) 368 { 369 return ((0xff & (x >> (0 * 8))) << (1 * 8)) 370 | ((0xff & (x >> (1 * 8))) << (0 * 8)); 371 } 372 373 static uint64_t w8nat(uint64_t const x) 374 { 375 return x; 376 } 377 378 static uint32_t w4nat(uint32_t const x) 379 { 380 return x; 381 } 382 383 static uint32_t w2nat(uint16_t const x) 384 { 385 return x; 386 } 387 388 static uint64_t (*w8)(uint64_t); 389 static uint32_t (*w)(uint32_t); 390 static uint32_t (*w2)(uint16_t); 391 392 /* Names of the sections that could contain calls to mcount. */ 393 static int is_mcounted_section_name(char const *const txtname) 394 { 395 return strncmp(".text", txtname, 5) == 0 || 396 strcmp(".init.text", txtname) == 0 || 397 strcmp(".ref.text", txtname) == 0 || 398 strcmp(".sched.text", txtname) == 0 || 399 strcmp(".spinlock.text", txtname) == 0 || 400 strcmp(".irqentry.text", txtname) == 0 || 401 strcmp(".softirqentry.text", txtname) == 0 || 402 strcmp(".kprobes.text", txtname) == 0 || 403 strcmp(".cpuidle.text", txtname) == 0; 404 } 405 406 static char const *already_has_rel_mcount = "success"; /* our work here is done! */ 407 408 /* 32 bit and 64 bit are very similar */ 409 #include "recordmcount.h" 410 #define RECORD_MCOUNT_64 411 #include "recordmcount.h" 412 413 /* 64-bit EM_MIPS has weird ELF64_Rela.r_info. 414 * http://techpubs.sgi.com/library/manuals/4000/007-4658-001/pdf/007-4658-001.pdf 415 * We interpret Table 29 Relocation Operation (Elf64_Rel, Elf64_Rela) [p.40] 416 * to imply the order of the members; the spec does not say so. 417 * typedef unsigned char Elf64_Byte; 418 * fails on MIPS64 because their <elf.h> already has it! 419 */ 420 421 typedef uint8_t myElf64_Byte; /* Type for a 8-bit quantity. */ 422 423 union mips_r_info { 424 Elf64_Xword r_info; 425 struct { 426 Elf64_Word r_sym; /* Symbol index. */ 427 myElf64_Byte r_ssym; /* Special symbol. */ 428 myElf64_Byte r_type3; /* Third relocation. */ 429 myElf64_Byte r_type2; /* Second relocation. */ 430 myElf64_Byte r_type; /* First relocation. */ 431 } r_mips; 432 }; 433 434 static uint64_t MIPS64_r_sym(Elf64_Rel const *rp) 435 { 436 return w(((union mips_r_info){ .r_info = rp->r_info }).r_mips.r_sym); 437 } 438 439 static void MIPS64_r_info(Elf64_Rel *const rp, unsigned sym, unsigned type) 440 { 441 rp->r_info = ((union mips_r_info){ 442 .r_mips = { .r_sym = w(sym), .r_type = type } 443 }).r_info; 444 } 445 446 static int do_file(char const *const fname) 447 { 448 Elf32_Ehdr *const ehdr = mmap_file(fname); 449 unsigned int reltype = 0; 450 int rc = -1; 451 452 if (!ehdr) 453 goto out; 454 455 w = w4nat; 456 w2 = w2nat; 457 w8 = w8nat; 458 switch (ehdr->e_ident[EI_DATA]) { 459 static unsigned int const endian = 1; 460 default: 461 fprintf(stderr, "unrecognized ELF data encoding %d: %s\n", 462 ehdr->e_ident[EI_DATA], fname); 463 cleanup(); 464 goto out; 465 case ELFDATA2LSB: 466 if (*(unsigned char const *)&endian != 1) { 467 /* main() is big endian, file.o is little endian. */ 468 w = w4rev; 469 w2 = w2rev; 470 w8 = w8rev; 471 } 472 ideal_nop4_arm = ideal_nop4_arm_le; 473 bl_mcount_arm = bl_mcount_arm_le; 474 push_arm = push_arm_le; 475 ideal_nop2_thumb = ideal_nop2_thumb_le; 476 push_bl_mcount_thumb = push_bl_mcount_thumb_le; 477 break; 478 case ELFDATA2MSB: 479 if (*(unsigned char const *)&endian != 0) { 480 /* main() is little endian, file.o is big endian. */ 481 w = w4rev; 482 w2 = w2rev; 483 w8 = w8rev; 484 } 485 ideal_nop4_arm = ideal_nop4_arm_be; 486 bl_mcount_arm = bl_mcount_arm_be; 487 push_arm = push_arm_be; 488 ideal_nop2_thumb = ideal_nop2_thumb_be; 489 push_bl_mcount_thumb = push_bl_mcount_thumb_be; 490 break; 491 } /* end switch */ 492 if (memcmp(ELFMAG, ehdr->e_ident, SELFMAG) != 0 || 493 w2(ehdr->e_type) != ET_REL || 494 ehdr->e_ident[EI_VERSION] != EV_CURRENT) { 495 fprintf(stderr, "unrecognized ET_REL file %s\n", fname); 496 cleanup(); 497 goto out; 498 } 499 500 gpfx = '_'; 501 switch (w2(ehdr->e_machine)) { 502 default: 503 fprintf(stderr, "unrecognized e_machine %u %s\n", 504 w2(ehdr->e_machine), fname); 505 cleanup(); 506 goto out; 507 case EM_386: 508 reltype = R_386_32; 509 rel_type_nop = R_386_NONE; 510 make_nop = make_nop_x86; 511 ideal_nop = ideal_nop5_x86_32; 512 mcount_adjust_32 = -1; 513 gpfx = 0; 514 break; 515 case EM_ARM: 516 reltype = R_ARM_ABS32; 517 altmcount = "__gnu_mcount_nc"; 518 make_nop = make_nop_arm; 519 rel_type_nop = R_ARM_NONE; 520 gpfx = 0; 521 break; 522 case EM_AARCH64: 523 reltype = R_AARCH64_ABS64; 524 make_nop = make_nop_arm64; 525 rel_type_nop = R_AARCH64_NONE; 526 ideal_nop = ideal_nop4_arm64; 527 break; 528 case EM_IA_64: reltype = R_IA64_IMM64; break; 529 case EM_MIPS: /* reltype: e_class */ break; 530 case EM_PPC: reltype = R_PPC_ADDR32; break; 531 case EM_PPC64: reltype = R_PPC64_ADDR64; break; 532 case EM_S390: /* reltype: e_class */ break; 533 case EM_SH: reltype = R_SH_DIR32; gpfx = 0; break; 534 case EM_SPARCV9: reltype = R_SPARC_64; break; 535 case EM_X86_64: 536 make_nop = make_nop_x86; 537 ideal_nop = ideal_nop5_x86_64; 538 reltype = R_X86_64_64; 539 rel_type_nop = R_X86_64_NONE; 540 mcount_adjust_64 = -1; 541 gpfx = 0; 542 break; 543 } /* end switch */ 544 545 switch (ehdr->e_ident[EI_CLASS]) { 546 default: 547 fprintf(stderr, "unrecognized ELF class %d %s\n", 548 ehdr->e_ident[EI_CLASS], fname); 549 cleanup(); 550 goto out; 551 case ELFCLASS32: 552 if (w2(ehdr->e_ehsize) != sizeof(Elf32_Ehdr) 553 || w2(ehdr->e_shentsize) != sizeof(Elf32_Shdr)) { 554 fprintf(stderr, 555 "unrecognized ET_REL file: %s\n", fname); 556 cleanup(); 557 goto out; 558 } 559 if (w2(ehdr->e_machine) == EM_MIPS) { 560 reltype = R_MIPS_32; 561 is_fake_mcount32 = MIPS32_is_fake_mcount; 562 } 563 if (do32(ehdr, fname, reltype) < 0) 564 goto out; 565 break; 566 case ELFCLASS64: { 567 Elf64_Ehdr *const ghdr = (Elf64_Ehdr *)ehdr; 568 if (w2(ghdr->e_ehsize) != sizeof(Elf64_Ehdr) 569 || w2(ghdr->e_shentsize) != sizeof(Elf64_Shdr)) { 570 fprintf(stderr, 571 "unrecognized ET_REL file: %s\n", fname); 572 cleanup(); 573 goto out; 574 } 575 if (w2(ghdr->e_machine) == EM_S390) { 576 reltype = R_390_64; 577 mcount_adjust_64 = -14; 578 } 579 if (w2(ghdr->e_machine) == EM_MIPS) { 580 reltype = R_MIPS_64; 581 Elf64_r_sym = MIPS64_r_sym; 582 Elf64_r_info = MIPS64_r_info; 583 is_fake_mcount64 = MIPS64_is_fake_mcount; 584 } 585 if (do64(ghdr, fname, reltype) < 0) 586 goto out; 587 break; 588 } 589 } /* end switch */ 590 591 rc = write_file(fname); 592 out: 593 cleanup(); 594 return rc; 595 } 596 597 int main(int argc, char *argv[]) 598 { 599 const char ftrace[] = "/ftrace.o"; 600 int ftrace_size = sizeof(ftrace) - 1; 601 int n_error = 0; /* gcc-4.3.0 false positive complaint */ 602 int c; 603 int i; 604 605 while ((c = getopt(argc, argv, "w")) >= 0) { 606 switch (c) { 607 case 'w': 608 warn_on_notrace_sect = 1; 609 break; 610 default: 611 fprintf(stderr, "usage: recordmcount [-w] file.o...\n"); 612 return 0; 613 } 614 } 615 616 if ((argc - optind) < 1) { 617 fprintf(stderr, "usage: recordmcount [-w] file.o...\n"); 618 return 0; 619 } 620 621 /* Process each file in turn, allowing deep failure. */ 622 for (i = optind; i < argc; i++) { 623 char *file = argv[i]; 624 int len; 625 626 /* 627 * The file kernel/trace/ftrace.o references the mcount 628 * function but does not call it. Since ftrace.o should 629 * not be traced anyway, we just skip it. 630 */ 631 len = strlen(file); 632 if (len >= ftrace_size && 633 strcmp(file + (len - ftrace_size), ftrace) == 0) 634 continue; 635 636 /* Avoid problems if early cleanup() */ 637 fd_map = -1; 638 mmap_failed = 1; 639 file_map = NULL; 640 file_ptr = NULL; 641 file_updated = 0; 642 if (do_file(file)) { 643 fprintf(stderr, "%s: failed\n", file); 644 ++n_error; 645 } 646 } 647 return !!n_error; 648 } 649