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