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 static int fd_map;      /* File descriptor for file being modified. */
  51 static int mmap_failed; /* Boolean flag. */
  52 static void *ehdr_curr; /* current ElfXX_Ehdr *  for resource cleanup */
  53 static char gpfx;       /* prefix for global symbol name (sometimes '_') */
  54 static struct stat sb;  /* Remember .st_size, etc. */
  55 static jmp_buf jmpenv;  /* setjmp/longjmp per-file error escape */
  56 static const char *altmcount;   /* alternate mcount symbol name */
  57 static int warn_on_notrace_sect; /* warn when section has mcount not being recorded */
  58
  59 /* setjmp() return values */
  60 enum {
  61         SJ_SETJMP = 0,  /* hardwired first return */
  62         SJ_FAIL,
  63         SJ_SUCCEED
  64 };
  65
  66 /* Per-file resource cleanup when multiple files. */
  67 static void
  68 cleanup(void)
  69 {
  70         if (!mmap_failed)
  71                 munmap(ehdr_curr, sb.st_size);
  72         else
  73                 free(ehdr_curr);
  74         close(fd_map);
  75 }
  76
  77 static void __attribute__((noreturn))
  78 fail_file(void)
  79 {
  80         cleanup();
  81         longjmp(jmpenv, SJ_FAIL);
  82 }
  83
  84 static void __attribute__((noreturn))
  85 succeed_file(void)
  86 {
  87         cleanup();
  88         longjmp(jmpenv, SJ_SUCCEED);
  89 }
  90
  91 /* ulseek, uread, ...:  Check return value for errors. */
  92
  93 static off_t
  94 ulseek(int const fd, off_t const offset, int const whence)
  95 {
  96         off_t const w = lseek(fd, offset, whence);
  97         if (w == (off_t)-1) {
  98                 perror("lseek");
  99                 fail_file();
 100         }
 101         return w;
 102 }
 103
 104 static size_t
 105 uread(int const fd, void *const buf, size_t const count)
 106 {
 107         size_t const n = read(fd, buf, count);
 108         if (n != count) {
 109                 perror("read");
 110                 fail_file();
 111         }
 112         return n;
 113 }
 114
 115 static size_t
 116 uwrite(int const fd, void const *const buf, size_t const count)
 117 {
 118         size_t const n = write(fd, buf, count);
 119         if (n != count) {
 120                 perror("write");
 121                 fail_file();
 122         }
 123         return n;
 124 }
 125
 126 static void *
 127 umalloc(size_t size)
 128 {
 129         void *const addr = malloc(size);
 130         if (addr == 0) {
 131                 fprintf(stderr, "malloc failed: %zu bytes\n", size);
 132                 fail_file();
 133         }
 134         return addr;
 135 }
 136
 137 static unsigned char ideal_nop5_x86_64[5] = { 0x0f, 0x1f, 0x44, 0x00, 0x00 };
 138 static unsigned char ideal_nop5_x86_32[5] = { 0x3e, 0x8d, 0x74, 0x26, 0x00 };
 139 static unsigned char *ideal_nop;
 140
 141 static char rel_type_nop;
 142
 143 static int (*make_nop)(void *map, size_t const offset);
 144
 145 static int make_nop_x86(void *map, size_t const offset)
 146 {
 147         uint32_t *ptr;
 148         unsigned char *op;
 149
 150         /* Confirm we have 0xe8 0x0 0x0 0x0 0x0 */
 151         ptr = map + offset;
 152         if (*ptr != 0)
 153                 return -1;
 154
 155         op = map + offset - 1;
 156         if (*op != 0xe8)
 157                 return -1;
 158
 159         /* convert to nop */
 160         ulseek(fd_map, offset - 1, SEEK_SET);
 161         uwrite(fd_map, ideal_nop, 5);
 162         return 0;
 163 }
 164
 165 /*
 166  * Get the whole file as a programming convenience in order to avoid
 167  * malloc+lseek+read+free of many pieces.  If successful, then mmap
 168  * avoids copying unused pieces; else just read the whole file.
 169  * Open for both read and write; new info will be appended to the file.
 170  * Use MAP_PRIVATE so that a few changes to the in-memory ElfXX_Ehdr
 171  * do not propagate to the file until an explicit overwrite at the last.
 172  * This preserves most aspects of consistency (all except .st_size)
 173  * for simultaneous readers of the file while we are appending to it.
 174  * However, multiple writers still are bad.  We choose not to use
 175  * locking because it is expensive and the use case of kernel build
 176  * makes multiple writers unlikely.
 177  */
 178 static void *mmap_file(char const *fname)
 179 {
 180         void *addr;
 181
 182         fd_map = open(fname, O_RDWR);
 183         if (fd_map < 0 || fstat(fd_map, &sb) < 0) {
 184                 perror(fname);
 185                 fail_file();
 186         }
 187         if (!S_ISREG(sb.st_mode)) {
 188                 fprintf(stderr, "not a regular file: %s\n", fname);
 189                 fail_file();
 190         }
 191         addr = mmap(0, sb.st_size, PROT_READ|PROT_WRITE, MAP_PRIVATE,
 192                     fd_map, 0);
 193         mmap_failed = 0;
 194         if (addr == MAP_FAILED) {
 195                 mmap_failed = 1;
 196                 addr = umalloc(sb.st_size);
 197                 uread(fd_map, addr, sb.st_size);
 198         }
 199         if (sb.st_nlink != 1) {
 200                 /* file is hard-linked, break the hard link */
 201                 close(fd_map);
 202                 if (unlink(fname) < 0) {
 203                         perror(fname);
 204                         fail_file();
 205                 }
 206                 fd_map = open(fname, O_RDWR | O_CREAT, sb.st_mode);
 207                 if (fd_map < 0) {
 208                         perror(fname);
 209                         fail_file();
 210                 }
 211                 uwrite(fd_map, addr, sb.st_size);
 212         }
 213         return addr;
 214 }
 215
 216 /* w8rev, w8nat, ...: Handle endianness. */
 217
 218 static uint64_t w8rev(uint64_t const x)
 219 {
 220         return   ((0xff & (x >> (0 * 8))) << (7 * 8))
 221                | ((0xff & (x >> (1 * 8))) << (6 * 8))
 222                | ((0xff & (x >> (2 * 8))) << (5 * 8))
 223                | ((0xff & (x >> (3 * 8))) << (4 * 8))
 224                | ((0xff & (x >> (4 * 8))) << (3 * 8))
 225                | ((0xff & (x >> (5 * 8))) << (2 * 8))
 226                | ((0xff & (x >> (6 * 8))) << (1 * 8))
 227                | ((0xff & (x >> (7 * 8))) << (0 * 8));
 228 }
 229
 230 static uint32_t w4rev(uint32_t const x)
 231 {
 232         return   ((0xff & (x >> (0 * 8))) << (3 * 8))
 233                | ((0xff & (x >> (1 * 8))) << (2 * 8))
 234                | ((0xff & (x >> (2 * 8))) << (1 * 8))
 235                | ((0xff & (x >> (3 * 8))) << (0 * 8));
 236 }
 237
 238 static uint32_t w2rev(uint16_t const x)
 239 {
 240         return   ((0xff & (x >> (0 * 8))) << (1 * 8))
 241                | ((0xff & (x >> (1 * 8))) << (0 * 8));
 242 }
 243
 244 static uint64_t w8nat(uint64_t const x)
 245 {
 246         return x;
 247 }
 248
 249 static uint32_t w4nat(uint32_t const x)
 250 {
 251         return x;
 252 }
 253
 254 static uint32_t w2nat(uint16_t const x)
 255 {
 256         return x;
 257 }
 258
 259 static uint64_t (*w8)(uint64_t);
 260 static uint32_t (*w)(uint32_t);
 261 static uint32_t (*w2)(uint16_t);
 262
 263 /* Names of the sections that could contain calls to mcount. */
 264 static int
 265 is_mcounted_section_name(char const *const txtname)
 266 {
 267         return strcmp(".text",           txtname) == 0 ||
 268                 strcmp(".ref.text",      txtname) == 0 ||
 269                 strcmp(".sched.text",    txtname) == 0 ||
 270                 strcmp(".spinlock.text", txtname) == 0 ||
 271                 strcmp(".irqentry.text", txtname) == 0 ||
 272                 strcmp(".kprobes.text", txtname) == 0 ||
 273                 strcmp(".text.unlikely", txtname) == 0;
 274 }
 275
 276 /* 32 bit and 64 bit are very similar */
 277 #include "recordmcount.h"
 278 #define RECORD_MCOUNT_64
 279 #include "recordmcount.h"
 280
 281 /* 64-bit EM_MIPS has weird ELF64_Rela.r_info.
 282  * http://techpubs.sgi.com/library/manuals/4000/007-4658-001/pdf/007-4658-001.pdf
 283  * We interpret Table 29 Relocation Operation (Elf64_Rel, Elf64_Rela) [p.40]
 284  * to imply the order of the members; the spec does not say so.
 285  *      typedef unsigned char Elf64_Byte;
 286  * fails on MIPS64 because their <elf.h> already has it!
 287  */
 288
 289 typedef uint8_t myElf64_Byte;           /* Type for a 8-bit quantity.  */
 290
 291 union mips_r_info {
 292         Elf64_Xword r_info;
 293         struct {
 294                 Elf64_Word r_sym;               /* Symbol index.  */
 295                 myElf64_Byte r_ssym;            /* Special symbol.  */
 296                 myElf64_Byte r_type3;           /* Third relocation.  */
 297                 myElf64_Byte r_type2;           /* Second relocation.  */
 298                 myElf64_Byte r_type;            /* First relocation.  */
 299         } r_mips;
 300 };
 301
 302 static uint64_t MIPS64_r_sym(Elf64_Rel const *rp)
 303 {
 304         return w(((union mips_r_info){ .r_info = rp->r_info }).r_mips.r_sym);
 305 }
 306
 307 static void MIPS64_r_info(Elf64_Rel *const rp, unsigned sym, unsigned type)
 308 {
 309         rp->r_info = ((union mips_r_info){
 310                 .r_mips = { .r_sym = w(sym), .r_type = type }
 311         }).r_info;
 312 }
 313
 314 static void
 315 do_file(char const *const fname)
 316 {
 317         Elf32_Ehdr *const ehdr = mmap_file(fname);
 318         unsigned int reltype = 0;
 319
 320         ehdr_curr = ehdr;
 321         w = w4nat;
 322         w2 = w2nat;
 323         w8 = w8nat;
 324         switch (ehdr->e_ident[EI_DATA]) {
 325                 static unsigned int const endian = 1;
 326         default:
 327                 fprintf(stderr, "unrecognized ELF data encoding %d: %s\n",
 328                         ehdr->e_ident[EI_DATA], fname);
 329                 fail_file();
 330                 break;
 331         case ELFDATA2LSB:
 332                 if (*(unsigned char const *)&endian != 1) {
 333                         /* main() is big endian, file.o is little endian. */
 334                         w = w4rev;
 335                         w2 = w2rev;
 336                         w8 = w8rev;
 337                 }
 338                 break;
 339         case ELFDATA2MSB:
 340                 if (*(unsigned char const *)&endian != 0) {
 341                         /* main() is little endian, file.o is big endian. */
 342                         w = w4rev;
 343                         w2 = w2rev;
 344                         w8 = w8rev;
 345                 }
 346                 break;
 347         }  /* end switch */
 348         if (memcmp(ELFMAG, ehdr->e_ident, SELFMAG) != 0
 349         ||  w2(ehdr->e_type) != ET_REL
 350         ||  ehdr->e_ident[EI_VERSION] != EV_CURRENT) {
 351                 fprintf(stderr, "unrecognized ET_REL file %s\n", fname);
 352                 fail_file();
 353         }
 354
 355         gpfx = 0;
 356         switch (w2(ehdr->e_machine)) {
 357         default:
 358                 fprintf(stderr, "unrecognized e_machine %d %s\n",
 359                         w2(ehdr->e_machine), fname);
 360                 fail_file();
 361                 break;
 362         case EM_386:
 363                 reltype = R_386_32;
 364                 make_nop = make_nop_x86;
 365                 ideal_nop = ideal_nop5_x86_32;
 366                 mcount_adjust_32 = -1;
 367                 break;
 368         case EM_ARM:     reltype = R_ARM_ABS32;
 369                          altmcount = "__gnu_mcount_nc";
 370                          break;
 371         case EM_IA_64:   reltype = R_IA64_IMM64;   gpfx = '_'; break;
 372         case EM_METAG:   reltype = R_METAG_ADDR32;
 373                          altmcount = "_mcount_wrapper";
 374                          rel_type_nop = R_METAG_NONE;
 375                          /* We happen to have the same requirement as MIPS */
 376                          is_fake_mcount32 = MIPS32_is_fake_mcount;
 377                          break;
 378         case EM_MIPS:    /* reltype: e_class    */ gpfx = '_'; break;
 379         case EM_PPC:     reltype = R_PPC_ADDR32;   gpfx = '_'; break;
 380         case EM_PPC64:   reltype = R_PPC64_ADDR64; gpfx = '_'; break;
 381         case EM_S390:    /* reltype: e_class    */ gpfx = '_'; break;
 382         case EM_SH:      reltype = R_SH_DIR32;                 break;
 383         case EM_SPARCV9: reltype = R_SPARC_64;     gpfx = '_'; break;
 384         case EM_X86_64:
 385                 make_nop = make_nop_x86;
 386                 ideal_nop = ideal_nop5_x86_64;
 387                 reltype = R_X86_64_64;
 388                 mcount_adjust_64 = -1;
 389                 break;
 390         }  /* end switch */
 391
 392         switch (ehdr->e_ident[EI_CLASS]) {
 393         default:
 394                 fprintf(stderr, "unrecognized ELF class %d %s\n",
 395                         ehdr->e_ident[EI_CLASS], fname);
 396                 fail_file();
 397                 break;
 398         case ELFCLASS32:
 399                 if (w2(ehdr->e_ehsize) != sizeof(Elf32_Ehdr)
 400                 ||  w2(ehdr->e_shentsize) != sizeof(Elf32_Shdr)) {
 401                         fprintf(stderr,
 402                                 "unrecognized ET_REL file: %s\n", fname);
 403                         fail_file();
 404                 }
 405                 if (w2(ehdr->e_machine) == EM_S390) {
 406                         reltype = R_390_32;
 407                         mcount_adjust_32 = -4;
 408                 }
 409                 if (w2(ehdr->e_machine) == EM_MIPS) {
 410                         reltype = R_MIPS_32;
 411                         is_fake_mcount32 = MIPS32_is_fake_mcount;
 412                 }
 413                 do32(ehdr, fname, reltype);
 414                 break;
 415         case ELFCLASS64: {
 416                 Elf64_Ehdr *const ghdr = (Elf64_Ehdr *)ehdr;
 417                 if (w2(ghdr->e_ehsize) != sizeof(Elf64_Ehdr)
 418                 ||  w2(ghdr->e_shentsize) != sizeof(Elf64_Shdr)) {
 419                         fprintf(stderr,
 420                                 "unrecognized ET_REL file: %s\n", fname);
 421                         fail_file();
 422                 }
 423                 if (w2(ghdr->e_machine) == EM_S390) {
 424                         reltype = R_390_64;
 425                         mcount_adjust_64 = -8;
 426                 }
 427                 if (w2(ghdr->e_machine) == EM_MIPS) {
 428                         reltype = R_MIPS_64;
 429                         Elf64_r_sym = MIPS64_r_sym;
 430                         Elf64_r_info = MIPS64_r_info;
 431                         is_fake_mcount64 = MIPS64_is_fake_mcount;
 432                 }
 433                 do64(ghdr, fname, reltype);
 434                 break;
 435         }
 436         }  /* end switch */
 437
 438         cleanup();
 439 }
 440
 441 int
 442 main(int argc, char *argv[])
 443 {
 444         const char ftrace[] = "/ftrace.o";
 445         int ftrace_size = sizeof(ftrace) - 1;
 446         int n_error = 0;  /* gcc-4.3.0 false positive complaint */
 447         int c;
 448         int i;
 449
 450         while ((c = getopt(argc, argv, "w")) >= 0) {
 451                 switch (c) {
 452                 case 'w':
 453                         warn_on_notrace_sect = 1;
 454                         break;
 455                 default:
 456                         fprintf(stderr, "usage: recordmcount [-w] file.o...\n");
 457                         return 0;
 458                 }
 459         }
 460
 461         if ((argc - optind) < 1) {
 462                 fprintf(stderr, "usage: recordmcount [-w] file.o...\n");
 463                 return 0;
 464         }
 465
 466         /* Process each file in turn, allowing deep failure. */
 467         for (i = optind; i < argc; i++) {
 468                 char *file = argv[i];
 469                 int const sjval = setjmp(jmpenv);
 470                 int len;
 471
 472                 /*
 473                  * The file kernel/trace/ftrace.o references the mcount
 474                  * function but does not call it. Since ftrace.o should
 475                  * not be traced anyway, we just skip it.
 476                  */
 477                 len = strlen(file);
 478                 if (len >= ftrace_size &&
 479                     strcmp(file + (len - ftrace_size), ftrace) == 0)
 480                         continue;
 481
 482                 switch (sjval) {
 483                 default:
 484                         fprintf(stderr, "internal error: %s\n", file);
 485                         exit(1);
 486                         break;
 487                 case SJ_SETJMP:    /* normal sequence */
 488                         /* Avoid problems if early cleanup() */
 489                         fd_map = -1;
 490                         ehdr_curr = NULL;
 491                         mmap_failed = 1;
 492                         do_file(file);
 493                         break;
 494                 case SJ_FAIL:    /* error in do_file or below */
 495                         ++n_error;
 496                         break;
 497                 case SJ_SUCCEED:    /* premature success */
 498                         /* do nothing */
 499                         break;
 500                 }  /* end switch */
 501         }
 502         return !!n_error;
 503 }
 504
 505