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