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_ABS64 257 46 #endif 47 48 static int fd_map; /* File descriptor for file being modified. */ 49 static int mmap_failed; /* Boolean flag. */ 50 static void *ehdr_curr; /* current ElfXX_Ehdr * for resource cleanup */ 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 57 /* setjmp() return values */ 58 enum { 59 SJ_SETJMP = 0, /* hardwired first return */ 60 SJ_FAIL, 61 SJ_SUCCEED 62 }; 63 64 /* Per-file resource cleanup when multiple files. */ 65 static void 66 cleanup(void) 67 { 68 if (!mmap_failed) 69 munmap(ehdr_curr, sb.st_size); 70 else 71 free(ehdr_curr); 72 close(fd_map); 73 } 74 75 static void __attribute__((noreturn)) 76 fail_file(void) 77 { 78 cleanup(); 79 longjmp(jmpenv, SJ_FAIL); 80 } 81 82 static void __attribute__((noreturn)) 83 succeed_file(void) 84 { 85 cleanup(); 86 longjmp(jmpenv, SJ_SUCCEED); 87 } 88 89 /* ulseek, uread, ...: Check return value for errors. */ 90 91 static off_t 92 ulseek(int const fd, off_t const offset, int const whence) 93 { 94 off_t const w = lseek(fd, offset, whence); 95 if (w == (off_t)-1) { 96 perror("lseek"); 97 fail_file(); 98 } 99 return w; 100 } 101 102 static size_t 103 uread(int const fd, void *const buf, size_t const count) 104 { 105 size_t const n = read(fd, buf, count); 106 if (n != count) { 107 perror("read"); 108 fail_file(); 109 } 110 return n; 111 } 112 113 static size_t 114 uwrite(int const fd, void const *const buf, size_t const count) 115 { 116 size_t const n = write(fd, buf, count); 117 if (n != count) { 118 perror("write"); 119 fail_file(); 120 } 121 return n; 122 } 123 124 static void * 125 umalloc(size_t size) 126 { 127 void *const addr = malloc(size); 128 if (addr == 0) { 129 fprintf(stderr, "malloc failed: %zu bytes\n", size); 130 fail_file(); 131 } 132 return addr; 133 } 134 135 static unsigned char ideal_nop5_x86_64[5] = { 0x0f, 0x1f, 0x44, 0x00, 0x00 }; 136 static unsigned char ideal_nop5_x86_32[5] = { 0x3e, 0x8d, 0x74, 0x26, 0x00 }; 137 static unsigned char *ideal_nop; 138 139 static char rel_type_nop; 140 141 static int (*make_nop)(void *map, size_t const offset); 142 143 static int make_nop_x86(void *map, size_t const offset) 144 { 145 uint32_t *ptr; 146 unsigned char *op; 147 148 /* Confirm we have 0xe8 0x0 0x0 0x0 0x0 */ 149 ptr = map + offset; 150 if (*ptr != 0) 151 return -1; 152 153 op = map + offset - 1; 154 if (*op != 0xe8) 155 return -1; 156 157 /* convert to nop */ 158 ulseek(fd_map, offset - 1, SEEK_SET); 159 uwrite(fd_map, ideal_nop, 5); 160 return 0; 161 } 162 163 /* 164 * Get the whole file as a programming convenience in order to avoid 165 * malloc+lseek+read+free of many pieces. If successful, then mmap 166 * avoids copying unused pieces; else just read the whole file. 167 * Open for both read and write; new info will be appended to the file. 168 * Use MAP_PRIVATE so that a few changes to the in-memory ElfXX_Ehdr 169 * do not propagate to the file until an explicit overwrite at the last. 170 * This preserves most aspects of consistency (all except .st_size) 171 * for simultaneous readers of the file while we are appending to it. 172 * However, multiple writers still are bad. We choose not to use 173 * locking because it is expensive and the use case of kernel build 174 * makes multiple writers unlikely. 175 */ 176 static void *mmap_file(char const *fname) 177 { 178 void *addr; 179 180 fd_map = open(fname, O_RDWR); 181 if (fd_map < 0 || fstat(fd_map, &sb) < 0) { 182 perror(fname); 183 fail_file(); 184 } 185 if (!S_ISREG(sb.st_mode)) { 186 fprintf(stderr, "not a regular file: %s\n", fname); 187 fail_file(); 188 } 189 addr = mmap(0, sb.st_size, PROT_READ|PROT_WRITE, MAP_PRIVATE, 190 fd_map, 0); 191 mmap_failed = 0; 192 if (addr == MAP_FAILED) { 193 mmap_failed = 1; 194 addr = umalloc(sb.st_size); 195 uread(fd_map, addr, sb.st_size); 196 } 197 return addr; 198 } 199 200 /* w8rev, w8nat, ...: Handle endianness. */ 201 202 static uint64_t w8rev(uint64_t const x) 203 { 204 return ((0xff & (x >> (0 * 8))) << (7 * 8)) 205 | ((0xff & (x >> (1 * 8))) << (6 * 8)) 206 | ((0xff & (x >> (2 * 8))) << (5 * 8)) 207 | ((0xff & (x >> (3 * 8))) << (4 * 8)) 208 | ((0xff & (x >> (4 * 8))) << (3 * 8)) 209 | ((0xff & (x >> (5 * 8))) << (2 * 8)) 210 | ((0xff & (x >> (6 * 8))) << (1 * 8)) 211 | ((0xff & (x >> (7 * 8))) << (0 * 8)); 212 } 213 214 static uint32_t w4rev(uint32_t const x) 215 { 216 return ((0xff & (x >> (0 * 8))) << (3 * 8)) 217 | ((0xff & (x >> (1 * 8))) << (2 * 8)) 218 | ((0xff & (x >> (2 * 8))) << (1 * 8)) 219 | ((0xff & (x >> (3 * 8))) << (0 * 8)); 220 } 221 222 static uint32_t w2rev(uint16_t const x) 223 { 224 return ((0xff & (x >> (0 * 8))) << (1 * 8)) 225 | ((0xff & (x >> (1 * 8))) << (0 * 8)); 226 } 227 228 static uint64_t w8nat(uint64_t const x) 229 { 230 return x; 231 } 232 233 static uint32_t w4nat(uint32_t const x) 234 { 235 return x; 236 } 237 238 static uint32_t w2nat(uint16_t const x) 239 { 240 return x; 241 } 242 243 static uint64_t (*w8)(uint64_t); 244 static uint32_t (*w)(uint32_t); 245 static uint32_t (*w2)(uint16_t); 246 247 /* Names of the sections that could contain calls to mcount. */ 248 static int 249 is_mcounted_section_name(char const *const txtname) 250 { 251 return strcmp(".text", txtname) == 0 || 252 strcmp(".ref.text", txtname) == 0 || 253 strcmp(".sched.text", txtname) == 0 || 254 strcmp(".spinlock.text", txtname) == 0 || 255 strcmp(".irqentry.text", txtname) == 0 || 256 strcmp(".kprobes.text", txtname) == 0 || 257 strcmp(".text.unlikely", txtname) == 0; 258 } 259 260 /* 32 bit and 64 bit are very similar */ 261 #include "recordmcount.h" 262 #define RECORD_MCOUNT_64 263 #include "recordmcount.h" 264 265 /* 64-bit EM_MIPS has weird ELF64_Rela.r_info. 266 * http://techpubs.sgi.com/library/manuals/4000/007-4658-001/pdf/007-4658-001.pdf 267 * We interpret Table 29 Relocation Operation (Elf64_Rel, Elf64_Rela) [p.40] 268 * to imply the order of the members; the spec does not say so. 269 * typedef unsigned char Elf64_Byte; 270 * fails on MIPS64 because their <elf.h> already has it! 271 */ 272 273 typedef uint8_t myElf64_Byte; /* Type for a 8-bit quantity. */ 274 275 union mips_r_info { 276 Elf64_Xword r_info; 277 struct { 278 Elf64_Word r_sym; /* Symbol index. */ 279 myElf64_Byte r_ssym; /* Special symbol. */ 280 myElf64_Byte r_type3; /* Third relocation. */ 281 myElf64_Byte r_type2; /* Second relocation. */ 282 myElf64_Byte r_type; /* First relocation. */ 283 } r_mips; 284 }; 285 286 static uint64_t MIPS64_r_sym(Elf64_Rel const *rp) 287 { 288 return w(((union mips_r_info){ .r_info = rp->r_info }).r_mips.r_sym); 289 } 290 291 static void MIPS64_r_info(Elf64_Rel *const rp, unsigned sym, unsigned type) 292 { 293 rp->r_info = ((union mips_r_info){ 294 .r_mips = { .r_sym = w(sym), .r_type = type } 295 }).r_info; 296 } 297 298 static void 299 do_file(char const *const fname) 300 { 301 Elf32_Ehdr *const ehdr = mmap_file(fname); 302 unsigned int reltype = 0; 303 304 ehdr_curr = ehdr; 305 w = w4nat; 306 w2 = w2nat; 307 w8 = w8nat; 308 switch (ehdr->e_ident[EI_DATA]) { 309 static unsigned int const endian = 1; 310 default: 311 fprintf(stderr, "unrecognized ELF data encoding %d: %s\n", 312 ehdr->e_ident[EI_DATA], fname); 313 fail_file(); 314 break; 315 case ELFDATA2LSB: 316 if (*(unsigned char const *)&endian != 1) { 317 /* main() is big endian, file.o is little endian. */ 318 w = w4rev; 319 w2 = w2rev; 320 w8 = w8rev; 321 } 322 break; 323 case ELFDATA2MSB: 324 if (*(unsigned char const *)&endian != 0) { 325 /* main() is little endian, file.o is big endian. */ 326 w = w4rev; 327 w2 = w2rev; 328 w8 = w8rev; 329 } 330 break; 331 } /* end switch */ 332 if (memcmp(ELFMAG, ehdr->e_ident, SELFMAG) != 0 333 || w2(ehdr->e_type) != ET_REL 334 || ehdr->e_ident[EI_VERSION] != EV_CURRENT) { 335 fprintf(stderr, "unrecognized ET_REL file %s\n", fname); 336 fail_file(); 337 } 338 339 gpfx = 0; 340 switch (w2(ehdr->e_machine)) { 341 default: 342 fprintf(stderr, "unrecognized e_machine %d %s\n", 343 w2(ehdr->e_machine), fname); 344 fail_file(); 345 break; 346 case EM_386: 347 reltype = R_386_32; 348 make_nop = make_nop_x86; 349 ideal_nop = ideal_nop5_x86_32; 350 mcount_adjust_32 = -1; 351 break; 352 case EM_ARM: reltype = R_ARM_ABS32; 353 altmcount = "__gnu_mcount_nc"; 354 break; 355 case EM_AARCH64: 356 reltype = R_AARCH64_ABS64; gpfx = '_'; break; 357 case EM_IA_64: reltype = R_IA64_IMM64; gpfx = '_'; break; 358 case EM_METAG: reltype = R_METAG_ADDR32; 359 altmcount = "_mcount_wrapper"; 360 rel_type_nop = R_METAG_NONE; 361 /* We happen to have the same requirement as MIPS */ 362 is_fake_mcount32 = MIPS32_is_fake_mcount; 363 break; 364 case EM_MIPS: /* reltype: e_class */ gpfx = '_'; break; 365 case EM_PPC: reltype = R_PPC_ADDR32; gpfx = '_'; break; 366 case EM_PPC64: reltype = R_PPC64_ADDR64; gpfx = '_'; break; 367 case EM_S390: /* reltype: e_class */ gpfx = '_'; break; 368 case EM_SH: reltype = R_SH_DIR32; break; 369 case EM_SPARCV9: reltype = R_SPARC_64; gpfx = '_'; break; 370 case EM_X86_64: 371 make_nop = make_nop_x86; 372 ideal_nop = ideal_nop5_x86_64; 373 reltype = R_X86_64_64; 374 mcount_adjust_64 = -1; 375 break; 376 } /* end switch */ 377 378 switch (ehdr->e_ident[EI_CLASS]) { 379 default: 380 fprintf(stderr, "unrecognized ELF class %d %s\n", 381 ehdr->e_ident[EI_CLASS], fname); 382 fail_file(); 383 break; 384 case ELFCLASS32: 385 if (w2(ehdr->e_ehsize) != sizeof(Elf32_Ehdr) 386 || w2(ehdr->e_shentsize) != sizeof(Elf32_Shdr)) { 387 fprintf(stderr, 388 "unrecognized ET_REL file: %s\n", fname); 389 fail_file(); 390 } 391 if (w2(ehdr->e_machine) == EM_MIPS) { 392 reltype = R_MIPS_32; 393 is_fake_mcount32 = MIPS32_is_fake_mcount; 394 } 395 do32(ehdr, fname, reltype); 396 break; 397 case ELFCLASS64: { 398 Elf64_Ehdr *const ghdr = (Elf64_Ehdr *)ehdr; 399 if (w2(ghdr->e_ehsize) != sizeof(Elf64_Ehdr) 400 || w2(ghdr->e_shentsize) != sizeof(Elf64_Shdr)) { 401 fprintf(stderr, 402 "unrecognized ET_REL file: %s\n", fname); 403 fail_file(); 404 } 405 if (w2(ghdr->e_machine) == EM_S390) { 406 reltype = R_390_64; 407 mcount_adjust_64 = -14; 408 } 409 if (w2(ghdr->e_machine) == EM_MIPS) { 410 reltype = R_MIPS_64; 411 Elf64_r_sym = MIPS64_r_sym; 412 Elf64_r_info = MIPS64_r_info; 413 is_fake_mcount64 = MIPS64_is_fake_mcount; 414 } 415 do64(ghdr, fname, reltype); 416 break; 417 } 418 } /* end switch */ 419 420 cleanup(); 421 } 422 423 int 424 main(int argc, char *argv[]) 425 { 426 const char ftrace[] = "/ftrace.o"; 427 int ftrace_size = sizeof(ftrace) - 1; 428 int n_error = 0; /* gcc-4.3.0 false positive complaint */ 429 int c; 430 int i; 431 432 while ((c = getopt(argc, argv, "w")) >= 0) { 433 switch (c) { 434 case 'w': 435 warn_on_notrace_sect = 1; 436 break; 437 default: 438 fprintf(stderr, "usage: recordmcount [-w] file.o...\n"); 439 return 0; 440 } 441 } 442 443 if ((argc - optind) < 1) { 444 fprintf(stderr, "usage: recordmcount [-w] file.o...\n"); 445 return 0; 446 } 447 448 /* Process each file in turn, allowing deep failure. */ 449 for (i = optind; i < argc; i++) { 450 char *file = argv[i]; 451 int const sjval = setjmp(jmpenv); 452 int len; 453 454 /* 455 * The file kernel/trace/ftrace.o references the mcount 456 * function but does not call it. Since ftrace.o should 457 * not be traced anyway, we just skip it. 458 */ 459 len = strlen(file); 460 if (len >= ftrace_size && 461 strcmp(file + (len - ftrace_size), ftrace) == 0) 462 continue; 463 464 switch (sjval) { 465 default: 466 fprintf(stderr, "internal error: %s\n", file); 467 exit(1); 468 break; 469 case SJ_SETJMP: /* normal sequence */ 470 /* Avoid problems if early cleanup() */ 471 fd_map = -1; 472 ehdr_curr = NULL; 473 mmap_failed = 1; 474 do_file(file); 475 break; 476 case SJ_FAIL: /* error in do_file or below */ 477 ++n_error; 478 break; 479 case SJ_SUCCEED: /* premature success */ 480 /* do nothing */ 481 break; 482 } /* end switch */ 483 } 484 return !!n_error; 485 } 486