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