scripts/recordmcount.c

   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 #define R_ARM_PC24              1
  57 #define R_ARM_THM_CALL          10
  58 #define R_ARM_CALL              28
  59
  60 static int fd_map;      /* File descriptor for file being modified. */
  61 static int mmap_failed; /* Boolean flag. */
  62 static char gpfx;       /* prefix for global symbol name (sometimes '_') */
  63 static struct stat sb;  /* Remember .st_size, etc. */
  64 static jmp_buf jmpenv;  /* setjmp/longjmp per-file error escape */
  65 static const char *altmcount;   /* alternate mcount symbol name */
  66 static int warn_on_notrace_sect; /* warn when section has mcount not being recorded */
  67 static void *file_map;  /* pointer of the mapped file */
  68 static void *file_end;  /* pointer to the end of the mapped file */
  69 static int file_updated; /* flag to state file was changed */
  70 static void *file_ptr;  /* current file pointer location */
  71 static void *file_append; /* added to the end of the file */
  72 static size_t file_append_size; /* how much is added to end of file */
  73
  74 /* setjmp() return values */
  75 enum {
  76         SJ_SETJMP = 0,  /* hardwired first return */
  77         SJ_FAIL,
  78         SJ_SUCCEED
  79 };
  80
  81 /* Per-file resource cleanup when multiple files. */
  82 static void
  83 cleanup(void)
  84 {
  85         if (!mmap_failed)
  86                 munmap(file_map, sb.st_size);
  87         else
  88                 free(file_map);
  89         file_map = NULL;
  90         free(file_append);
  91         file_append = NULL;
  92         file_append_size = 0;
  93         file_updated = 0;
  94 }
  95
  96 static void __attribute__((noreturn))
  97 fail_file(void)
  98 {
  99         cleanup();
 100         longjmp(jmpenv, SJ_FAIL);
 101 }
 102
 103 static void __attribute__((noreturn))
 104 succeed_file(void)
 105 {
 106         cleanup();
 107         longjmp(jmpenv, SJ_SUCCEED);
 108 }
 109
 110 /* ulseek, uread, ...:  Check return value for errors. */
 111
 112 static off_t
 113 ulseek(int const fd, off_t const offset, int const whence)
 114 {
 115         switch (whence) {
 116         case SEEK_SET:
 117                 file_ptr = file_map + offset;
 118                 break;
 119         case SEEK_CUR:
 120                 file_ptr += offset;
 121                 break;
 122         case SEEK_END:
 123                 file_ptr = file_map + (sb.st_size - offset);
 124                 break;
 125         }
 126         if (file_ptr < file_map) {
 127                 fprintf(stderr, "lseek: seek before file\n");
 128                 fail_file();
 129         }
 130         return file_ptr - file_map;
 131 }
 132
 133 static size_t
 134 uread(int const fd, void *const buf, size_t const count)
 135 {
 136         size_t const n = read(fd, buf, count);
 137         if (n != count) {
 138                 perror("read");
 139                 fail_file();
 140         }
 141         return n;
 142 }
 143
 144 static size_t
 145 uwrite(int const fd, void const *const buf, size_t const count)
 146 {
 147         size_t cnt = count;
 148         off_t idx = 0;
 149
 150         file_updated = 1;
 151
 152         if (file_ptr + count >= file_end) {
 153                 off_t aoffset = (file_ptr + count) - file_end;
 154
 155                 if (aoffset > file_append_size) {
 156                         file_append = realloc(file_append, aoffset);
 157                         file_append_size = aoffset;
 158                 }
 159                 if (!file_append) {
 160                         perror("write");
 161                         fail_file();
 162                 }
 163                 if (file_ptr < file_end) {
 164                         cnt = file_end - file_ptr;
 165                 } else {
 166                         cnt = 0;
 167                         idx = aoffset - count;
 168                 }
 169         }
 170
 171         if (cnt)
 172                 memcpy(file_ptr, buf, cnt);
 173
 174         if (cnt < count)
 175                 memcpy(file_append + idx, buf + cnt, count - cnt);
 176
 177         file_ptr += count;
 178         return count;
 179 }
 180
 181 static void *
 182 umalloc(size_t size)
 183 {
 184         void *const addr = malloc(size);
 185         if (addr == 0) {
 186                 fprintf(stderr, "malloc failed: %zu bytes\n", size);
 187                 fail_file();
 188         }
 189         return addr;
 190 }
 191
 192 static unsigned char ideal_nop5_x86_64[5] = { 0x0f, 0x1f, 0x44, 0x00, 0x00 };
 193 static unsigned char ideal_nop5_x86_32[5] = { 0x3e, 0x8d, 0x74, 0x26, 0x00 };
 194 static unsigned char *ideal_nop;
 195
 196 static char rel_type_nop;
 197
 198 static int (*make_nop)(void *map, size_t const offset);
 199
 200 static int make_nop_x86(void *map, size_t const offset)
 201 {
 202         uint32_t *ptr;
 203         unsigned char *op;
 204
 205         /* Confirm we have 0xe8 0x0 0x0 0x0 0x0 */
 206         ptr = map + offset;
 207         if (*ptr != 0)
 208                 return -1;
 209
 210         op = map + offset - 1;
 211         if (*op != 0xe8)
 212                 return -1;
 213
 214         /* convert to nop */
 215         ulseek(fd_map, offset - 1, SEEK_SET);
 216         uwrite(fd_map, ideal_nop, 5);
 217         return 0;
 218 }
 219
 220 static unsigned char ideal_nop4_arm64[4] = {0x1f, 0x20, 0x03, 0xd5};
 221 static int make_nop_arm64(void *map, size_t const offset)
 222 {
 223         uint32_t *ptr;
 224
 225         ptr = map + offset;
 226         /* bl <_mcount> is 0x94000000 before relocation */
 227         if (*ptr != 0x94000000)
 228                 return -1;
 229
 230         /* Convert to nop */
 231         ulseek(fd_map, offset, SEEK_SET);
 232         uwrite(fd_map, ideal_nop, 4);
 233         return 0;
 234 }
 235
 236 /*
 237  * Get the whole file as a programming convenience in order to avoid
 238  * malloc+lseek+read+free of many pieces.  If successful, then mmap
 239  * avoids copying unused pieces; else just read the whole file.
 240  * Open for both read and write; new info will be appended to the file.
 241  * Use MAP_PRIVATE so that a few changes to the in-memory ElfXX_Ehdr
 242  * do not propagate to the file until an explicit overwrite at the last.
 243  * This preserves most aspects of consistency (all except .st_size)
 244  * for simultaneous readers of the file while we are appending to it.
 245  * However, multiple writers still are bad.  We choose not to use
 246  * locking because it is expensive and the use case of kernel build
 247  * makes multiple writers unlikely.
 248  */
 249 static void *mmap_file(char const *fname)
 250 {
 251         fd_map = open(fname, O_RDONLY);
 252         if (fd_map < 0 || fstat(fd_map, &sb) < 0) {
 253                 perror(fname);
 254                 fail_file();
 255         }
 256         if (!S_ISREG(sb.st_mode)) {
 257                 fprintf(stderr, "not a regular file: %s\n", fname);
 258                 fail_file();
 259         }
 260         file_map = mmap(0, sb.st_size, PROT_READ|PROT_WRITE, MAP_PRIVATE,
 261                         fd_map, 0);
 262         mmap_failed = 0;
 263         if (file_map == MAP_FAILED) {
 264                 mmap_failed = 1;
 265                 file_map = umalloc(sb.st_size);
 266                 uread(fd_map, file_map, sb.st_size);
 267         }
 268         close(fd_map);
 269
 270         file_end = file_map + sb.st_size;
 271
 272         return file_map;
 273 }
 274
 275 static void write_file(const char *fname)
 276 {
 277         char tmp_file[strlen(fname) + 4];
 278         size_t n;
 279
 280         if (!file_updated)
 281                 return;
 282
 283         sprintf(tmp_file, "%s.rc", fname);
 284
 285         /*
 286          * After reading the entire file into memory, delete it
 287          * and write it back, to prevent weird side effects of modifying
 288          * an object file in place.
 289          */
 290         fd_map = open(tmp_file, O_WRONLY | O_TRUNC | O_CREAT, sb.st_mode);
 291         if (fd_map < 0) {
 292                 perror(fname);
 293                 fail_file();
 294         }
 295         n = write(fd_map, file_map, sb.st_size);
 296         if (n != sb.st_size) {
 297                 perror("write");
 298                 fail_file();
 299         }
 300         if (file_append_size) {
 301                 n = write(fd_map, file_append, file_append_size);
 302                 if (n != file_append_size) {
 303                         perror("write");
 304                         fail_file();
 305                 }
 306         }
 307         close(fd_map);
 308         if (rename(tmp_file, fname) < 0) {
 309                 perror(fname);
 310                 fail_file();
 311         }
 312 }
 313
 314 /* w8rev, w8nat, ...: Handle endianness. */
 315
 316 static uint64_t w8rev(uint64_t const x)
 317 {
 318         return   ((0xff & (x >> (0 * 8))) << (7 * 8))
 319                | ((0xff & (x >> (1 * 8))) << (6 * 8))
 320                | ((0xff & (x >> (2 * 8))) << (5 * 8))
 321                | ((0xff & (x >> (3 * 8))) << (4 * 8))
 322                | ((0xff & (x >> (4 * 8))) << (3 * 8))
 323                | ((0xff & (x >> (5 * 8))) << (2 * 8))
 324                | ((0xff & (x >> (6 * 8))) << (1 * 8))
 325                | ((0xff & (x >> (7 * 8))) << (0 * 8));
 326 }
 327
 328 static uint32_t w4rev(uint32_t const x)
 329 {
 330         return   ((0xff & (x >> (0 * 8))) << (3 * 8))
 331                | ((0xff & (x >> (1 * 8))) << (2 * 8))
 332                | ((0xff & (x >> (2 * 8))) << (1 * 8))
 333                | ((0xff & (x >> (3 * 8))) << (0 * 8));
 334 }
 335
 336 static uint32_t w2rev(uint16_t const x)
 337 {
 338         return   ((0xff & (x >> (0 * 8))) << (1 * 8))
 339                | ((0xff & (x >> (1 * 8))) << (0 * 8));
 340 }
 341
 342 static uint64_t w8nat(uint64_t const x)
 343 {
 344         return x;
 345 }
 346
 347 static uint32_t w4nat(uint32_t const x)
 348 {
 349         return x;
 350 }
 351
 352 static uint32_t w2nat(uint16_t const x)
 353 {
 354         return x;
 355 }
 356
 357 static uint64_t (*w8)(uint64_t);
 358 static uint32_t (*w)(uint32_t);
 359 static uint32_t (*w2)(uint16_t);
 360
 361 /* Names of the sections that could contain calls to mcount. */
 362 static int
 363 is_mcounted_section_name(char const *const txtname)
 364 {
 365         return strcmp(".text",           txtname) == 0 ||
 366                 strcmp(".ref.text",      txtname) == 0 ||
 367                 strcmp(".sched.text",    txtname) == 0 ||
 368                 strcmp(".spinlock.text", txtname) == 0 ||
 369                 strcmp(".irqentry.text", txtname) == 0 ||
 370                 strcmp(".softirqentry.text", txtname) == 0 ||
 371                 strcmp(".kprobes.text", txtname) == 0 ||
 372                 strcmp(".cpuidle.text", txtname) == 0 ||
 373                 strcmp(".text.unlikely", txtname) == 0;
 374 }
 375
 376 /* 32 bit and 64 bit are very similar */
 377 #include "recordmcount.h"
 378 #define RECORD_MCOUNT_64
 379 #include "recordmcount.h"
 380
 381 static int arm_is_fake_mcount(Elf32_Rel const *rp)
 382 {
 383         switch (ELF32_R_TYPE(w(rp->r_info))) {
 384         case R_ARM_THM_CALL:
 385         case R_ARM_CALL:
 386         case R_ARM_PC24:
 387                 return 0;
 388         }
 389
 390         return 1;
 391 }
 392
 393 /* 64-bit EM_MIPS has weird ELF64_Rela.r_info.
 394  * http://techpubs.sgi.com/library/manuals/4000/007-4658-001/pdf/007-4658-001.pdf
 395  * We interpret Table 29 Relocation Operation (Elf64_Rel, Elf64_Rela) [p.40]
 396  * to imply the order of the members; the spec does not say so.
 397  *      typedef unsigned char Elf64_Byte;
 398  * fails on MIPS64 because their <elf.h> already has it!
 399  */
 400
 401 typedef uint8_t myElf64_Byte;           /* Type for a 8-bit quantity.  */
 402
 403 union mips_r_info {
 404         Elf64_Xword r_info;
 405         struct {
 406                 Elf64_Word r_sym;               /* Symbol index.  */
 407                 myElf64_Byte r_ssym;            /* Special symbol.  */
 408                 myElf64_Byte r_type3;           /* Third relocation.  */
 409                 myElf64_Byte r_type2;           /* Second relocation.  */
 410                 myElf64_Byte r_type;            /* First relocation.  */
 411         } r_mips;
 412 };
 413
 414 static uint64_t MIPS64_r_sym(Elf64_Rel const *rp)
 415 {
 416         return w(((union mips_r_info){ .r_info = rp->r_info }).r_mips.r_sym);
 417 }
 418
 419 static void MIPS64_r_info(Elf64_Rel *const rp, unsigned sym, unsigned type)
 420 {
 421         rp->r_info = ((union mips_r_info){
 422                 .r_mips = { .r_sym = w(sym), .r_type = type }
 423         }).r_info;
 424 }
 425
 426 static void
 427 do_file(char const *const fname)
 428 {
 429         Elf32_Ehdr *const ehdr = mmap_file(fname);
 430         unsigned int reltype = 0;
 431
 432         w = w4nat;
 433         w2 = w2nat;
 434         w8 = w8nat;
 435         switch (ehdr->e_ident[EI_DATA]) {
 436                 static unsigned int const endian = 1;
 437         default:
 438                 fprintf(stderr, "unrecognized ELF data encoding %d: %s\n",
 439                         ehdr->e_ident[EI_DATA], fname);
 440                 fail_file();
 441                 break;
 442         case ELFDATA2LSB:
 443                 if (*(unsigned char const *)&endian != 1) {
 444                         /* main() is big endian, file.o is little endian. */
 445                         w = w4rev;
 446                         w2 = w2rev;
 447                         w8 = w8rev;
 448                 }
 449                 break;
 450         case ELFDATA2MSB:
 451                 if (*(unsigned char const *)&endian != 0) {
 452                         /* main() is little endian, file.o is big endian. */
 453                         w = w4rev;
 454                         w2 = w2rev;
 455                         w8 = w8rev;
 456                 }
 457                 break;
 458         }  /* end switch */
 459         if (memcmp(ELFMAG, ehdr->e_ident, SELFMAG) != 0
 460         ||  w2(ehdr->e_type) != ET_REL
 461         ||  ehdr->e_ident[EI_VERSION] != EV_CURRENT) {
 462                 fprintf(stderr, "unrecognized ET_REL file %s\n", fname);
 463                 fail_file();
 464         }
 465
 466         gpfx = 0;
 467         switch (w2(ehdr->e_machine)) {
 468         default:
 469                 fprintf(stderr, "unrecognized e_machine %d %s\n",
 470                         w2(ehdr->e_machine), fname);
 471                 fail_file();
 472                 break;
 473         case EM_386:
 474                 reltype = R_386_32;
 475                 rel_type_nop = R_386_NONE;
 476                 make_nop = make_nop_x86;
 477                 ideal_nop = ideal_nop5_x86_32;
 478                 mcount_adjust_32 = -1;
 479                 break;
 480         case EM_ARM:     reltype = R_ARM_ABS32;
 481                          altmcount = "__gnu_mcount_nc";
 482                          is_fake_mcount32 = arm_is_fake_mcount;
 483                          break;
 484         case EM_AARCH64:
 485                         reltype = R_AARCH64_ABS64;
 486                         make_nop = make_nop_arm64;
 487                         rel_type_nop = R_AARCH64_NONE;
 488                         ideal_nop = ideal_nop4_arm64;
 489                         gpfx = '_';
 490                         break;
 491         case EM_IA_64:   reltype = R_IA64_IMM64;   gpfx = '_'; break;
 492         case EM_METAG:   reltype = R_METAG_ADDR32;
 493                          altmcount = "_mcount_wrapper";
 494                          rel_type_nop = R_METAG_NONE;
 495                          /* We happen to have the same requirement as MIPS */
 496                          is_fake_mcount32 = MIPS32_is_fake_mcount;
 497                          break;
 498         case EM_MIPS:    /* reltype: e_class    */ gpfx = '_'; break;
 499         case EM_PPC:     reltype = R_PPC_ADDR32;   gpfx = '_'; break;
 500         case EM_PPC64:   reltype = R_PPC64_ADDR64; gpfx = '_'; break;
 501         case EM_S390:    /* reltype: e_class    */ gpfx = '_'; break;
 502         case EM_SH:      reltype = R_SH_DIR32;                 break;
 503         case EM_SPARCV9: reltype = R_SPARC_64;     gpfx = '_'; break;
 504         case EM_X86_64:
 505                 make_nop = make_nop_x86;
 506                 ideal_nop = ideal_nop5_x86_64;
 507                 reltype = R_X86_64_64;
 508                 rel_type_nop = R_X86_64_NONE;
 509                 mcount_adjust_64 = -1;
 510                 break;
 511         }  /* end switch */
 512
 513         switch (ehdr->e_ident[EI_CLASS]) {
 514         default:
 515                 fprintf(stderr, "unrecognized ELF class %d %s\n",
 516                         ehdr->e_ident[EI_CLASS], fname);
 517                 fail_file();
 518                 break;
 519         case ELFCLASS32:
 520                 if (w2(ehdr->e_ehsize) != sizeof(Elf32_Ehdr)
 521                 ||  w2(ehdr->e_shentsize) != sizeof(Elf32_Shdr)) {
 522                         fprintf(stderr,
 523                                 "unrecognized ET_REL file: %s\n", fname);
 524                         fail_file();
 525                 }
 526                 if (w2(ehdr->e_machine) == EM_MIPS) {
 527                         reltype = R_MIPS_32;
 528                         is_fake_mcount32 = MIPS32_is_fake_mcount;
 529                 }
 530                 do32(ehdr, fname, reltype);
 531                 break;
 532         case ELFCLASS64: {
 533                 Elf64_Ehdr *const ghdr = (Elf64_Ehdr *)ehdr;
 534                 if (w2(ghdr->e_ehsize) != sizeof(Elf64_Ehdr)
 535                 ||  w2(ghdr->e_shentsize) != sizeof(Elf64_Shdr)) {
 536                         fprintf(stderr,
 537                                 "unrecognized ET_REL file: %s\n", fname);
 538                         fail_file();
 539                 }
 540                 if (w2(ghdr->e_machine) == EM_S390) {
 541                         reltype = R_390_64;
 542                         mcount_adjust_64 = -14;
 543                 }
 544                 if (w2(ghdr->e_machine) == EM_MIPS) {
 545                         reltype = R_MIPS_64;
 546                         Elf64_r_sym = MIPS64_r_sym;
 547                         Elf64_r_info = MIPS64_r_info;
 548                         is_fake_mcount64 = MIPS64_is_fake_mcount;
 549                 }
 550                 do64(ghdr, fname, reltype);
 551                 break;
 552         }
 553         }  /* end switch */
 554
 555         write_file(fname);
 556         cleanup();
 557 }
 558
 559 int
 560 main(int argc, char *argv[])
 561 {
 562         const char ftrace[] = "/ftrace.o";
 563         int ftrace_size = sizeof(ftrace) - 1;
 564         int n_error = 0;  /* gcc-4.3.0 false positive complaint */
 565         int c;
 566         int i;
 567
 568         while ((c = getopt(argc, argv, "w")) >= 0) {
 569                 switch (c) {
 570                 case 'w':
 571                         warn_on_notrace_sect = 1;
 572                         break;
 573                 default:
 574                         fprintf(stderr, "usage: recordmcount [-w] file.o...\n");
 575                         return 0;
 576                 }
 577         }
 578
 579         if ((argc - optind) < 1) {
 580                 fprintf(stderr, "usage: recordmcount [-w] file.o...\n");
 581                 return 0;
 582         }
 583
 584         /* Process each file in turn, allowing deep failure. */
 585         for (i = optind; i < argc; i++) {
 586                 char *file = argv[i];
 587                 int const sjval = setjmp(jmpenv);
 588                 int len;
 589
 590                 /*
 591                  * The file kernel/trace/ftrace.o references the mcount
 592                  * function but does not call it. Since ftrace.o should
 593                  * not be traced anyway, we just skip it.
 594                  */
 595                 len = strlen(file);
 596                 if (len >= ftrace_size &&
 597                     strcmp(file + (len - ftrace_size), ftrace) == 0)
 598                         continue;
 599
 600                 switch (sjval) {
 601                 default:
 602                         fprintf(stderr, "internal error: %s\n", file);
 603                         exit(1);
 604                         break;
 605                 case SJ_SETJMP:    /* normal sequence */
 606                         /* Avoid problems if early cleanup() */
 607                         fd_map = -1;
 608                         mmap_failed = 1;
 609                         file_map = NULL;
 610                         file_ptr = NULL;
 611                         file_updated = 0;
 612                         do_file(file);
 613                         break;
 614                 case SJ_FAIL:    /* error in do_file or below */
 615                         fprintf(stderr, "%s: failed\n", file);
 616                         ++n_error;
 617                         break;
 618                 case SJ_SUCCEED:    /* premature success */
 619                         /* do nothing */
 620                         break;
 621                 }  /* end switch */
 622         }
 623         return !!n_error;
 624 }