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 static int fd_map; /* File descriptor for file being modified. */ 37 static int mmap_failed; /* Boolean flag. */ 38 static void *ehdr_curr; /* current ElfXX_Ehdr * for resource cleanup */ 39 static char gpfx; /* prefix for global symbol name (sometimes '_') */ 40 static struct stat sb; /* Remember .st_size, etc. */ 41 static jmp_buf jmpenv; /* setjmp/longjmp per-file error escape */ 42 static const char *altmcount; /* alternate mcount symbol name */ 43 static int warn_on_notrace_sect; /* warn when section has mcount not being recorded */ 44 45 /* setjmp() return values */ 46 enum { 47 SJ_SETJMP = 0, /* hardwired first return */ 48 SJ_FAIL, 49 SJ_SUCCEED 50 }; 51 52 /* Per-file resource cleanup when multiple files. */ 53 static void 54 cleanup(void) 55 { 56 if (!mmap_failed) 57 munmap(ehdr_curr, sb.st_size); 58 else 59 free(ehdr_curr); 60 close(fd_map); 61 } 62 63 static void __attribute__((noreturn)) 64 fail_file(void) 65 { 66 cleanup(); 67 longjmp(jmpenv, SJ_FAIL); 68 } 69 70 static void __attribute__((noreturn)) 71 succeed_file(void) 72 { 73 cleanup(); 74 longjmp(jmpenv, SJ_SUCCEED); 75 } 76 77 /* ulseek, uread, ...: Check return value for errors. */ 78 79 static off_t 80 ulseek(int const fd, off_t const offset, int const whence) 81 { 82 off_t const w = lseek(fd, offset, whence); 83 if (w == (off_t)-1) { 84 perror("lseek"); 85 fail_file(); 86 } 87 return w; 88 } 89 90 static size_t 91 uread(int const fd, void *const buf, size_t const count) 92 { 93 size_t const n = read(fd, buf, count); 94 if (n != count) { 95 perror("read"); 96 fail_file(); 97 } 98 return n; 99 } 100 101 static size_t 102 uwrite(int const fd, void const *const buf, size_t const count) 103 { 104 size_t const n = write(fd, buf, count); 105 if (n != count) { 106 perror("write"); 107 fail_file(); 108 } 109 return n; 110 } 111 112 static void * 113 umalloc(size_t size) 114 { 115 void *const addr = malloc(size); 116 if (addr == 0) { 117 fprintf(stderr, "malloc failed: %zu bytes\n", size); 118 fail_file(); 119 } 120 return addr; 121 } 122 123 static unsigned char ideal_nop5_x86_64[5] = { 0x0f, 0x1f, 0x44, 0x00, 0x00 }; 124 static unsigned char ideal_nop5_x86_32[5] = { 0x3e, 0x8d, 0x74, 0x26, 0x00 }; 125 static unsigned char *ideal_nop; 126 127 static char rel_type_nop; 128 129 static int (*make_nop)(void *map, size_t const offset); 130 131 static int make_nop_x86(void *map, size_t const offset) 132 { 133 uint32_t *ptr; 134 unsigned char *op; 135 136 /* Confirm we have 0xe8 0x0 0x0 0x0 0x0 */ 137 ptr = map + offset; 138 if (*ptr != 0) 139 return -1; 140 141 op = map + offset - 1; 142 if (*op != 0xe8) 143 return -1; 144 145 /* convert to nop */ 146 ulseek(fd_map, offset - 1, SEEK_SET); 147 uwrite(fd_map, ideal_nop, 5); 148 return 0; 149 } 150 151 /* 152 * Get the whole file as a programming convenience in order to avoid 153 * malloc+lseek+read+free of many pieces. If successful, then mmap 154 * avoids copying unused pieces; else just read the whole file. 155 * Open for both read and write; new info will be appended to the file. 156 * Use MAP_PRIVATE so that a few changes to the in-memory ElfXX_Ehdr 157 * do not propagate to the file until an explicit overwrite at the last. 158 * This preserves most aspects of consistency (all except .st_size) 159 * for simultaneous readers of the file while we are appending to it. 160 * However, multiple writers still are bad. We choose not to use 161 * locking because it is expensive and the use case of kernel build 162 * makes multiple writers unlikely. 163 */ 164 static void *mmap_file(char const *fname) 165 { 166 void *addr; 167 168 fd_map = open(fname, O_RDWR); 169 if (fd_map < 0 || fstat(fd_map, &sb) < 0) { 170 perror(fname); 171 fail_file(); 172 } 173 if (!S_ISREG(sb.st_mode)) { 174 fprintf(stderr, "not a regular file: %s\n", fname); 175 fail_file(); 176 } 177 addr = mmap(0, sb.st_size, PROT_READ|PROT_WRITE, MAP_PRIVATE, 178 fd_map, 0); 179 mmap_failed = 0; 180 if (addr == MAP_FAILED) { 181 mmap_failed = 1; 182 addr = umalloc(sb.st_size); 183 uread(fd_map, addr, sb.st_size); 184 } 185 return addr; 186 } 187 188 /* w8rev, w8nat, ...: Handle endianness. */ 189 190 static uint64_t w8rev(uint64_t const x) 191 { 192 return ((0xff & (x >> (0 * 8))) << (7 * 8)) 193 | ((0xff & (x >> (1 * 8))) << (6 * 8)) 194 | ((0xff & (x >> (2 * 8))) << (5 * 8)) 195 | ((0xff & (x >> (3 * 8))) << (4 * 8)) 196 | ((0xff & (x >> (4 * 8))) << (3 * 8)) 197 | ((0xff & (x >> (5 * 8))) << (2 * 8)) 198 | ((0xff & (x >> (6 * 8))) << (1 * 8)) 199 | ((0xff & (x >> (7 * 8))) << (0 * 8)); 200 } 201 202 static uint32_t w4rev(uint32_t const x) 203 { 204 return ((0xff & (x >> (0 * 8))) << (3 * 8)) 205 | ((0xff & (x >> (1 * 8))) << (2 * 8)) 206 | ((0xff & (x >> (2 * 8))) << (1 * 8)) 207 | ((0xff & (x >> (3 * 8))) << (0 * 8)); 208 } 209 210 static uint32_t w2rev(uint16_t const x) 211 { 212 return ((0xff & (x >> (0 * 8))) << (1 * 8)) 213 | ((0xff & (x >> (1 * 8))) << (0 * 8)); 214 } 215 216 static uint64_t w8nat(uint64_t const x) 217 { 218 return x; 219 } 220 221 static uint32_t w4nat(uint32_t const x) 222 { 223 return x; 224 } 225 226 static uint32_t w2nat(uint16_t const x) 227 { 228 return x; 229 } 230 231 static uint64_t (*w8)(uint64_t); 232 static uint32_t (*w)(uint32_t); 233 static uint32_t (*w2)(uint16_t); 234 235 /* Names of the sections that could contain calls to mcount. */ 236 static int 237 is_mcounted_section_name(char const *const txtname) 238 { 239 return strcmp(".text", txtname) == 0 || 240 strcmp(".ref.text", txtname) == 0 || 241 strcmp(".sched.text", txtname) == 0 || 242 strcmp(".spinlock.text", txtname) == 0 || 243 strcmp(".irqentry.text", txtname) == 0 || 244 strcmp(".kprobes.text", txtname) == 0 || 245 strcmp(".text.unlikely", txtname) == 0; 246 } 247 248 /* 32 bit and 64 bit are very similar */ 249 #include "recordmcount.h" 250 #define RECORD_MCOUNT_64 251 #include "recordmcount.h" 252 253 /* 64-bit EM_MIPS has weird ELF64_Rela.r_info. 254 * http://techpubs.sgi.com/library/manuals/4000/007-4658-001/pdf/007-4658-001.pdf 255 * We interpret Table 29 Relocation Operation (Elf64_Rel, Elf64_Rela) [p.40] 256 * to imply the order of the members; the spec does not say so. 257 * typedef unsigned char Elf64_Byte; 258 * fails on MIPS64 because their <elf.h> already has it! 259 */ 260 261 typedef uint8_t myElf64_Byte; /* Type for a 8-bit quantity. */ 262 263 union mips_r_info { 264 Elf64_Xword r_info; 265 struct { 266 Elf64_Word r_sym; /* Symbol index. */ 267 myElf64_Byte r_ssym; /* Special symbol. */ 268 myElf64_Byte r_type3; /* Third relocation. */ 269 myElf64_Byte r_type2; /* Second relocation. */ 270 myElf64_Byte r_type; /* First relocation. */ 271 } r_mips; 272 }; 273 274 static uint64_t MIPS64_r_sym(Elf64_Rel const *rp) 275 { 276 return w(((union mips_r_info){ .r_info = rp->r_info }).r_mips.r_sym); 277 } 278 279 static void MIPS64_r_info(Elf64_Rel *const rp, unsigned sym, unsigned type) 280 { 281 rp->r_info = ((union mips_r_info){ 282 .r_mips = { .r_sym = w(sym), .r_type = type } 283 }).r_info; 284 } 285 286 static void 287 do_file(char const *const fname) 288 { 289 Elf32_Ehdr *const ehdr = mmap_file(fname); 290 unsigned int reltype = 0; 291 292 ehdr_curr = ehdr; 293 w = w4nat; 294 w2 = w2nat; 295 w8 = w8nat; 296 switch (ehdr->e_ident[EI_DATA]) { 297 static unsigned int const endian = 1; 298 default: 299 fprintf(stderr, "unrecognized ELF data encoding %d: %s\n", 300 ehdr->e_ident[EI_DATA], fname); 301 fail_file(); 302 break; 303 case ELFDATA2LSB: 304 if (*(unsigned char const *)&endian != 1) { 305 /* main() is big endian, file.o is little endian. */ 306 w = w4rev; 307 w2 = w2rev; 308 w8 = w8rev; 309 } 310 break; 311 case ELFDATA2MSB: 312 if (*(unsigned char const *)&endian != 0) { 313 /* main() is little endian, file.o is big endian. */ 314 w = w4rev; 315 w2 = w2rev; 316 w8 = w8rev; 317 } 318 break; 319 } /* end switch */ 320 if (memcmp(ELFMAG, ehdr->e_ident, SELFMAG) != 0 321 || w2(ehdr->e_type) != ET_REL 322 || ehdr->e_ident[EI_VERSION] != EV_CURRENT) { 323 fprintf(stderr, "unrecognized ET_REL file %s\n", fname); 324 fail_file(); 325 } 326 327 gpfx = 0; 328 switch (w2(ehdr->e_machine)) { 329 default: 330 fprintf(stderr, "unrecognized e_machine %d %s\n", 331 w2(ehdr->e_machine), fname); 332 fail_file(); 333 break; 334 case EM_386: 335 reltype = R_386_32; 336 make_nop = make_nop_x86; 337 ideal_nop = ideal_nop5_x86_32; 338 mcount_adjust_32 = -1; 339 break; 340 case EM_ARM: reltype = R_ARM_ABS32; 341 altmcount = "__gnu_mcount_nc"; 342 break; 343 case EM_IA_64: reltype = R_IA64_IMM64; gpfx = '_'; break; 344 case EM_MIPS: /* reltype: e_class */ gpfx = '_'; break; 345 case EM_PPC: reltype = R_PPC_ADDR32; gpfx = '_'; break; 346 case EM_PPC64: reltype = R_PPC64_ADDR64; gpfx = '_'; break; 347 case EM_S390: /* reltype: e_class */ gpfx = '_'; break; 348 case EM_SH: reltype = R_SH_DIR32; break; 349 case EM_SPARCV9: reltype = R_SPARC_64; gpfx = '_'; break; 350 case EM_X86_64: 351 make_nop = make_nop_x86; 352 ideal_nop = ideal_nop5_x86_64; 353 reltype = R_X86_64_64; 354 mcount_adjust_64 = -1; 355 break; 356 } /* end switch */ 357 358 switch (ehdr->e_ident[EI_CLASS]) { 359 default: 360 fprintf(stderr, "unrecognized ELF class %d %s\n", 361 ehdr->e_ident[EI_CLASS], fname); 362 fail_file(); 363 break; 364 case ELFCLASS32: 365 if (w2(ehdr->e_ehsize) != sizeof(Elf32_Ehdr) 366 || w2(ehdr->e_shentsize) != sizeof(Elf32_Shdr)) { 367 fprintf(stderr, 368 "unrecognized ET_REL file: %s\n", fname); 369 fail_file(); 370 } 371 if (w2(ehdr->e_machine) == EM_S390) { 372 reltype = R_390_32; 373 mcount_adjust_32 = -4; 374 } 375 if (w2(ehdr->e_machine) == EM_MIPS) { 376 reltype = R_MIPS_32; 377 is_fake_mcount32 = MIPS32_is_fake_mcount; 378 } 379 do32(ehdr, fname, reltype); 380 break; 381 case ELFCLASS64: { 382 Elf64_Ehdr *const ghdr = (Elf64_Ehdr *)ehdr; 383 if (w2(ghdr->e_ehsize) != sizeof(Elf64_Ehdr) 384 || w2(ghdr->e_shentsize) != sizeof(Elf64_Shdr)) { 385 fprintf(stderr, 386 "unrecognized ET_REL file: %s\n", fname); 387 fail_file(); 388 } 389 if (w2(ghdr->e_machine) == EM_S390) { 390 reltype = R_390_64; 391 mcount_adjust_64 = -8; 392 } 393 if (w2(ghdr->e_machine) == EM_MIPS) { 394 reltype = R_MIPS_64; 395 Elf64_r_sym = MIPS64_r_sym; 396 Elf64_r_info = MIPS64_r_info; 397 is_fake_mcount64 = MIPS64_is_fake_mcount; 398 } 399 do64(ghdr, fname, reltype); 400 break; 401 } 402 } /* end switch */ 403 404 cleanup(); 405 } 406 407 int 408 main(int argc, char *argv[]) 409 { 410 const char ftrace[] = "/ftrace.o"; 411 int ftrace_size = sizeof(ftrace) - 1; 412 int n_error = 0; /* gcc-4.3.0 false positive complaint */ 413 int c; 414 int i; 415 416 while ((c = getopt(argc, argv, "w")) >= 0) { 417 switch (c) { 418 case 'w': 419 warn_on_notrace_sect = 1; 420 break; 421 default: 422 fprintf(stderr, "usage: recordmcount [-w] file.o...\n"); 423 return 0; 424 } 425 } 426 427 if ((argc - optind) < 1) { 428 fprintf(stderr, "usage: recordmcount [-w] file.o...\n"); 429 return 0; 430 } 431 432 /* Process each file in turn, allowing deep failure. */ 433 for (i = optind; i < argc; i++) { 434 char *file = argv[i]; 435 int const sjval = setjmp(jmpenv); 436 int len; 437 438 /* 439 * The file kernel/trace/ftrace.o references the mcount 440 * function but does not call it. Since ftrace.o should 441 * not be traced anyway, we just skip it. 442 */ 443 len = strlen(file); 444 if (len >= ftrace_size && 445 strcmp(file + (len - ftrace_size), ftrace) == 0) 446 continue; 447 448 switch (sjval) { 449 default: 450 fprintf(stderr, "internal error: %s\n", file); 451 exit(1); 452 break; 453 case SJ_SETJMP: /* normal sequence */ 454 /* Avoid problems if early cleanup() */ 455 fd_map = -1; 456 ehdr_curr = NULL; 457 mmap_failed = 1; 458 do_file(file); 459 break; 460 case SJ_FAIL: /* error in do_file or below */ 461 ++n_error; 462 break; 463 case SJ_SUCCEED: /* premature success */ 464 /* do nothing */ 465 break; 466 } /* end switch */ 467 } 468 return !!n_error; 469 } 470 471 472