1 /* 2 * recordmcount.c: construct a table of the locations of calls to 'mcount' 3 * so that ftrace can find them quickly. 4 * Copyright 2009 John F. Reiser <jreiser@BitWagon.com>. All rights reserved. 5 * Licensed under the GNU General Public License, version 2 (GPLv2). 6 * 7 * Restructured to fit Linux format, as well as other updates: 8 * Copyright 2010 Steven Rostedt <srostedt@redhat.com>, 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 <setjmp.h> 31 #include <stdio.h> 32 #include <stdlib.h> 33 #include <string.h> 34 #include <unistd.h> 35 36 /* 37 * glibc synced up and added the metag number but didn't add the relocations. 38 * Work around this in a crude manner for now. 39 */ 40 #ifndef EM_METAG 41 #define EM_METAG 174 42 #endif 43 #ifndef R_METAG_ADDR32 44 #define R_METAG_ADDR32 2 45 #endif 46 #ifndef R_METAG_NONE 47 #define R_METAG_NONE 3 48 #endif 49 50 #ifndef EM_AARCH64 51 #define EM_AARCH64 183 52 #define R_AARCH64_NONE 0 53 #define R_AARCH64_ABS64 257 54 #endif 55 56 static int fd_map; /* File descriptor for file being modified. */ 57 static int mmap_failed; /* Boolean flag. */ 58 static char gpfx; /* prefix for global symbol name (sometimes '_') */ 59 static struct stat sb; /* Remember .st_size, etc. */ 60 static jmp_buf jmpenv; /* setjmp/longjmp per-file error escape */ 61 static const char *altmcount; /* alternate mcount symbol name */ 62 static int warn_on_notrace_sect; /* warn when section has mcount not being recorded */ 63 static void *file_map; /* pointer of the mapped file */ 64 static void *file_end; /* pointer to the end of the mapped file */ 65 static int file_updated; /* flag to state file was changed */ 66 static void *file_ptr; /* current file pointer location */ 67 static void *file_append; /* added to the end of the file */ 68 static size_t file_append_size; /* how much is added to end of file */ 69 70 /* setjmp() return values */ 71 enum { 72 SJ_SETJMP = 0, /* hardwired first return */ 73 SJ_FAIL, 74 SJ_SUCCEED 75 }; 76 77 /* Per-file resource cleanup when multiple files. */ 78 static void 79 cleanup(void) 80 { 81 if (!mmap_failed) 82 munmap(file_map, sb.st_size); 83 else 84 free(file_map); 85 file_map = NULL; 86 free(file_append); 87 file_append = NULL; 88 file_append_size = 0; 89 file_updated = 0; 90 } 91 92 static void __attribute__((noreturn)) 93 fail_file(void) 94 { 95 cleanup(); 96 longjmp(jmpenv, SJ_FAIL); 97 } 98 99 static void __attribute__((noreturn)) 100 succeed_file(void) 101 { 102 cleanup(); 103 longjmp(jmpenv, SJ_SUCCEED); 104 } 105 106 /* ulseek, uread, ...: Check return value for errors. */ 107 108 static off_t 109 ulseek(int const fd, off_t const offset, int const whence) 110 { 111 switch (whence) { 112 case SEEK_SET: 113 file_ptr = file_map + offset; 114 break; 115 case SEEK_CUR: 116 file_ptr += offset; 117 break; 118 case SEEK_END: 119 file_ptr = file_map + (sb.st_size - offset); 120 break; 121 } 122 if (file_ptr < file_map) { 123 fprintf(stderr, "lseek: seek before file\n"); 124 fail_file(); 125 } 126 return file_ptr - file_map; 127 } 128 129 static size_t 130 uread(int const fd, void *const buf, size_t const count) 131 { 132 size_t const n = read(fd, buf, count); 133 if (n != count) { 134 perror("read"); 135 fail_file(); 136 } 137 return n; 138 } 139 140 static size_t 141 uwrite(int const fd, void const *const buf, size_t const count) 142 { 143 size_t cnt = count; 144 off_t idx = 0; 145 146 file_updated = 1; 147 148 if (file_ptr + count >= file_end) { 149 off_t aoffset = (file_ptr + count) - file_end; 150 151 if (aoffset > file_append_size) { 152 file_append = realloc(file_append, aoffset); 153 file_append_size = aoffset; 154 } 155 if (!file_append) { 156 perror("write"); 157 fail_file(); 158 } 159 if (file_ptr < file_end) { 160 cnt = file_end - file_ptr; 161 } else { 162 cnt = 0; 163 idx = aoffset - count; 164 } 165 } 166 167 if (cnt) 168 memcpy(file_ptr, buf, cnt); 169 170 if (cnt < count) 171 memcpy(file_append + idx, buf + cnt, count - cnt); 172 173 file_ptr += count; 174 return count; 175 } 176 177 static void * 178 umalloc(size_t size) 179 { 180 void *const addr = malloc(size); 181 if (addr == 0) { 182 fprintf(stderr, "malloc failed: %zu bytes\n", size); 183 fail_file(); 184 } 185 return addr; 186 } 187 188 static unsigned char ideal_nop5_x86_64[5] = { 0x0f, 0x1f, 0x44, 0x00, 0x00 }; 189 static unsigned char ideal_nop5_x86_32[5] = { 0x3e, 0x8d, 0x74, 0x26, 0x00 }; 190 static unsigned char *ideal_nop; 191 192 static char rel_type_nop; 193 194 static int (*make_nop)(void *map, size_t const offset); 195 196 static int make_nop_x86(void *map, size_t const offset) 197 { 198 uint32_t *ptr; 199 unsigned char *op; 200 201 /* Confirm we have 0xe8 0x0 0x0 0x0 0x0 */ 202 ptr = map + offset; 203 if (*ptr != 0) 204 return -1; 205 206 op = map + offset - 1; 207 if (*op != 0xe8) 208 return -1; 209 210 /* convert to nop */ 211 ulseek(fd_map, offset - 1, SEEK_SET); 212 uwrite(fd_map, ideal_nop, 5); 213 return 0; 214 } 215 216 static unsigned char ideal_nop4_arm64[4] = {0x1f, 0x20, 0x03, 0xd5}; 217 static int make_nop_arm64(void *map, size_t const offset) 218 { 219 uint32_t *ptr; 220 221 ptr = map + offset; 222 /* bl <_mcount> is 0x94000000 before relocation */ 223 if (*ptr != 0x94000000) 224 return -1; 225 226 /* Convert to nop */ 227 ulseek(fd_map, offset, SEEK_SET); 228 uwrite(fd_map, ideal_nop, 4); 229 return 0; 230 } 231 232 /* 233 * Get the whole file as a programming convenience in order to avoid 234 * malloc+lseek+read+free of many pieces. If successful, then mmap 235 * avoids copying unused pieces; else just read the whole file. 236 * Open for both read and write; new info will be appended to the file. 237 * Use MAP_PRIVATE so that a few changes to the in-memory ElfXX_Ehdr 238 * do not propagate to the file until an explicit overwrite at the last. 239 * This preserves most aspects of consistency (all except .st_size) 240 * for simultaneous readers of the file while we are appending to it. 241 * However, multiple writers still are bad. We choose not to use 242 * locking because it is expensive and the use case of kernel build 243 * makes multiple writers unlikely. 244 */ 245 static void *mmap_file(char const *fname) 246 { 247 fd_map = open(fname, O_RDONLY); 248 if (fd_map < 0 || fstat(fd_map, &sb) < 0) { 249 perror(fname); 250 fail_file(); 251 } 252 if (!S_ISREG(sb.st_mode)) { 253 fprintf(stderr, "not a regular file: %s\n", fname); 254 fail_file(); 255 } 256 file_map = mmap(0, sb.st_size, PROT_READ|PROT_WRITE, MAP_PRIVATE, 257 fd_map, 0); 258 mmap_failed = 0; 259 if (file_map == MAP_FAILED) { 260 mmap_failed = 1; 261 file_map = umalloc(sb.st_size); 262 uread(fd_map, file_map, sb.st_size); 263 } 264 close(fd_map); 265 266 file_end = file_map + sb.st_size; 267 268 return file_map; 269 } 270 271 static void write_file(const char *fname) 272 { 273 char tmp_file[strlen(fname) + 4]; 274 size_t n; 275 276 if (!file_updated) 277 return; 278 279 sprintf(tmp_file, "%s.rc", fname); 280 281 /* 282 * After reading the entire file into memory, delete it 283 * and write it back, to prevent weird side effects of modifying 284 * an object file in place. 285 */ 286 fd_map = open(tmp_file, O_WRONLY | O_TRUNC | O_CREAT, sb.st_mode); 287 if (fd_map < 0) { 288 perror(fname); 289 fail_file(); 290 } 291 n = write(fd_map, file_map, sb.st_size); 292 if (n != sb.st_size) { 293 perror("write"); 294 fail_file(); 295 } 296 if (file_append_size) { 297 n = write(fd_map, file_append, file_append_size); 298 if (n != file_append_size) { 299 perror("write"); 300 fail_file(); 301 } 302 } 303 close(fd_map); 304 if (rename(tmp_file, fname) < 0) { 305 perror(fname); 306 fail_file(); 307 } 308 } 309 310 /* w8rev, w8nat, ...: Handle endianness. */ 311 312 static uint64_t w8rev(uint64_t const x) 313 { 314 return ((0xff & (x >> (0 * 8))) << (7 * 8)) 315 | ((0xff & (x >> (1 * 8))) << (6 * 8)) 316 | ((0xff & (x >> (2 * 8))) << (5 * 8)) 317 | ((0xff & (x >> (3 * 8))) << (4 * 8)) 318 | ((0xff & (x >> (4 * 8))) << (3 * 8)) 319 | ((0xff & (x >> (5 * 8))) << (2 * 8)) 320 | ((0xff & (x >> (6 * 8))) << (1 * 8)) 321 | ((0xff & (x >> (7 * 8))) << (0 * 8)); 322 } 323 324 static uint32_t w4rev(uint32_t const x) 325 { 326 return ((0xff & (x >> (0 * 8))) << (3 * 8)) 327 | ((0xff & (x >> (1 * 8))) << (2 * 8)) 328 | ((0xff & (x >> (2 * 8))) << (1 * 8)) 329 | ((0xff & (x >> (3 * 8))) << (0 * 8)); 330 } 331 332 static uint32_t w2rev(uint16_t const x) 333 { 334 return ((0xff & (x >> (0 * 8))) << (1 * 8)) 335 | ((0xff & (x >> (1 * 8))) << (0 * 8)); 336 } 337 338 static uint64_t w8nat(uint64_t const x) 339 { 340 return x; 341 } 342 343 static uint32_t w4nat(uint32_t const x) 344 { 345 return x; 346 } 347 348 static uint32_t w2nat(uint16_t const x) 349 { 350 return x; 351 } 352 353 static uint64_t (*w8)(uint64_t); 354 static uint32_t (*w)(uint32_t); 355 static uint32_t (*w2)(uint16_t); 356 357 /* Names of the sections that could contain calls to mcount. */ 358 static int 359 is_mcounted_section_name(char const *const txtname) 360 { 361 return strcmp(".text", txtname) == 0 || 362 strcmp(".ref.text", txtname) == 0 || 363 strcmp(".sched.text", txtname) == 0 || 364 strcmp(".spinlock.text", txtname) == 0 || 365 strcmp(".irqentry.text", txtname) == 0 || 366 strcmp(".kprobes.text", txtname) == 0 || 367 strcmp(".text.unlikely", txtname) == 0; 368 } 369 370 /* 32 bit and 64 bit are very similar */ 371 #include "recordmcount.h" 372 #define RECORD_MCOUNT_64 373 #include "recordmcount.h" 374 375 /* 64-bit EM_MIPS has weird ELF64_Rela.r_info. 376 * http://techpubs.sgi.com/library/manuals/4000/007-4658-001/pdf/007-4658-001.pdf 377 * We interpret Table 29 Relocation Operation (Elf64_Rel, Elf64_Rela) [p.40] 378 * to imply the order of the members; the spec does not say so. 379 * typedef unsigned char Elf64_Byte; 380 * fails on MIPS64 because their <elf.h> already has it! 381 */ 382 383 typedef uint8_t myElf64_Byte; /* Type for a 8-bit quantity. */ 384 385 union mips_r_info { 386 Elf64_Xword r_info; 387 struct { 388 Elf64_Word r_sym; /* Symbol index. */ 389 myElf64_Byte r_ssym; /* Special symbol. */ 390 myElf64_Byte r_type3; /* Third relocation. */ 391 myElf64_Byte r_type2; /* Second relocation. */ 392 myElf64_Byte r_type; /* First relocation. */ 393 } r_mips; 394 }; 395 396 static uint64_t MIPS64_r_sym(Elf64_Rel const *rp) 397 { 398 return w(((union mips_r_info){ .r_info = rp->r_info }).r_mips.r_sym); 399 } 400 401 static void MIPS64_r_info(Elf64_Rel *const rp, unsigned sym, unsigned type) 402 { 403 rp->r_info = ((union mips_r_info){ 404 .r_mips = { .r_sym = w(sym), .r_type = type } 405 }).r_info; 406 } 407 408 static void 409 do_file(char const *const fname) 410 { 411 Elf32_Ehdr *const ehdr = mmap_file(fname); 412 unsigned int reltype = 0; 413 414 w = w4nat; 415 w2 = w2nat; 416 w8 = w8nat; 417 switch (ehdr->e_ident[EI_DATA]) { 418 static unsigned int const endian = 1; 419 default: 420 fprintf(stderr, "unrecognized ELF data encoding %d: %s\n", 421 ehdr->e_ident[EI_DATA], fname); 422 fail_file(); 423 break; 424 case ELFDATA2LSB: 425 if (*(unsigned char const *)&endian != 1) { 426 /* main() is big endian, file.o is little endian. */ 427 w = w4rev; 428 w2 = w2rev; 429 w8 = w8rev; 430 } 431 break; 432 case ELFDATA2MSB: 433 if (*(unsigned char const *)&endian != 0) { 434 /* main() is little endian, file.o is big endian. */ 435 w = w4rev; 436 w2 = w2rev; 437 w8 = w8rev; 438 } 439 break; 440 } /* end switch */ 441 if (memcmp(ELFMAG, ehdr->e_ident, SELFMAG) != 0 442 || w2(ehdr->e_type) != ET_REL 443 || ehdr->e_ident[EI_VERSION] != EV_CURRENT) { 444 fprintf(stderr, "unrecognized ET_REL file %s\n", fname); 445 fail_file(); 446 } 447 448 gpfx = 0; 449 switch (w2(ehdr->e_machine)) { 450 default: 451 fprintf(stderr, "unrecognized e_machine %d %s\n", 452 w2(ehdr->e_machine), fname); 453 fail_file(); 454 break; 455 case EM_386: 456 reltype = R_386_32; 457 rel_type_nop = R_386_NONE; 458 make_nop = make_nop_x86; 459 ideal_nop = ideal_nop5_x86_32; 460 mcount_adjust_32 = -1; 461 break; 462 case EM_ARM: reltype = R_ARM_ABS32; 463 altmcount = "__gnu_mcount_nc"; 464 break; 465 case EM_AARCH64: 466 reltype = R_AARCH64_ABS64; 467 make_nop = make_nop_arm64; 468 rel_type_nop = R_AARCH64_NONE; 469 ideal_nop = ideal_nop4_arm64; 470 gpfx = '_'; 471 break; 472 case EM_IA_64: reltype = R_IA64_IMM64; gpfx = '_'; break; 473 case EM_METAG: reltype = R_METAG_ADDR32; 474 altmcount = "_mcount_wrapper"; 475 rel_type_nop = R_METAG_NONE; 476 /* We happen to have the same requirement as MIPS */ 477 is_fake_mcount32 = MIPS32_is_fake_mcount; 478 break; 479 case EM_MIPS: /* reltype: e_class */ gpfx = '_'; break; 480 case EM_PPC: reltype = R_PPC_ADDR32; gpfx = '_'; break; 481 case EM_PPC64: reltype = R_PPC64_ADDR64; gpfx = '_'; break; 482 case EM_S390: /* reltype: e_class */ gpfx = '_'; break; 483 case EM_SH: reltype = R_SH_DIR32; break; 484 case EM_SPARCV9: reltype = R_SPARC_64; gpfx = '_'; break; 485 case EM_X86_64: 486 make_nop = make_nop_x86; 487 ideal_nop = ideal_nop5_x86_64; 488 reltype = R_X86_64_64; 489 rel_type_nop = R_X86_64_NONE; 490 mcount_adjust_64 = -1; 491 break; 492 } /* end switch */ 493 494 switch (ehdr->e_ident[EI_CLASS]) { 495 default: 496 fprintf(stderr, "unrecognized ELF class %d %s\n", 497 ehdr->e_ident[EI_CLASS], fname); 498 fail_file(); 499 break; 500 case ELFCLASS32: 501 if (w2(ehdr->e_ehsize) != sizeof(Elf32_Ehdr) 502 || w2(ehdr->e_shentsize) != sizeof(Elf32_Shdr)) { 503 fprintf(stderr, 504 "unrecognized ET_REL file: %s\n", fname); 505 fail_file(); 506 } 507 if (w2(ehdr->e_machine) == EM_MIPS) { 508 reltype = R_MIPS_32; 509 is_fake_mcount32 = MIPS32_is_fake_mcount; 510 } 511 do32(ehdr, fname, reltype); 512 break; 513 case ELFCLASS64: { 514 Elf64_Ehdr *const ghdr = (Elf64_Ehdr *)ehdr; 515 if (w2(ghdr->e_ehsize) != sizeof(Elf64_Ehdr) 516 || w2(ghdr->e_shentsize) != sizeof(Elf64_Shdr)) { 517 fprintf(stderr, 518 "unrecognized ET_REL file: %s\n", fname); 519 fail_file(); 520 } 521 if (w2(ghdr->e_machine) == EM_S390) { 522 reltype = R_390_64; 523 mcount_adjust_64 = -14; 524 } 525 if (w2(ghdr->e_machine) == EM_MIPS) { 526 reltype = R_MIPS_64; 527 Elf64_r_sym = MIPS64_r_sym; 528 Elf64_r_info = MIPS64_r_info; 529 is_fake_mcount64 = MIPS64_is_fake_mcount; 530 } 531 do64(ghdr, fname, reltype); 532 break; 533 } 534 } /* end switch */ 535 536 write_file(fname); 537 cleanup(); 538 } 539 540 int 541 main(int argc, char *argv[]) 542 { 543 const char ftrace[] = "/ftrace.o"; 544 int ftrace_size = sizeof(ftrace) - 1; 545 int n_error = 0; /* gcc-4.3.0 false positive complaint */ 546 int c; 547 int i; 548 549 while ((c = getopt(argc, argv, "w")) >= 0) { 550 switch (c) { 551 case 'w': 552 warn_on_notrace_sect = 1; 553 break; 554 default: 555 fprintf(stderr, "usage: recordmcount [-w] file.o...\n"); 556 return 0; 557 } 558 } 559 560 if ((argc - optind) < 1) { 561 fprintf(stderr, "usage: recordmcount [-w] file.o...\n"); 562 return 0; 563 } 564 565 /* Process each file in turn, allowing deep failure. */ 566 for (i = optind; i < argc; i++) { 567 char *file = argv[i]; 568 int const sjval = setjmp(jmpenv); 569 int len; 570 571 /* 572 * The file kernel/trace/ftrace.o references the mcount 573 * function but does not call it. Since ftrace.o should 574 * not be traced anyway, we just skip it. 575 */ 576 len = strlen(file); 577 if (len >= ftrace_size && 578 strcmp(file + (len - ftrace_size), ftrace) == 0) 579 continue; 580 581 switch (sjval) { 582 default: 583 fprintf(stderr, "internal error: %s\n", file); 584 exit(1); 585 break; 586 case SJ_SETJMP: /* normal sequence */ 587 /* Avoid problems if early cleanup() */ 588 fd_map = -1; 589 mmap_failed = 1; 590 file_map = NULL; 591 file_ptr = NULL; 592 file_updated = 0; 593 do_file(file); 594 break; 595 case SJ_FAIL: /* error in do_file or below */ 596 fprintf(stderr, "%s: failed\n", file); 597 ++n_error; 598 break; 599 case SJ_SUCCEED: /* premature success */ 600 /* do nothing */ 601 break; 602 } /* end switch */ 603 } 604 return !!n_error; 605 } 606