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 #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 }