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_ABS64 257
  46 #endif
  47
  48 static int fd_map;      /* File descriptor for file being modified. */
  49 static int mmap_failed; /* Boolean flag. */
  50 static void *ehdr_curr; /* current ElfXX_Ehdr *  for resource cleanup */
  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
  57 /* setjmp() return values */
  58 enum {
  59         SJ_SETJMP = 0,  /* hardwired first return */
  60         SJ_FAIL,
  61         SJ_SUCCEED
  62 };
  63
  64 /* Per-file resource cleanup when multiple files. */
  65 static void
  66 cleanup(void)
  67 {
  68         if (!mmap_failed)
  69                 munmap(ehdr_curr, sb.st_size);
  70         else
  71                 free(ehdr_curr);
  72         close(fd_map);
  73 }
  74
  75 static void __attribute__((noreturn))
  76 fail_file(void)
  77 {
  78         cleanup();
  79         longjmp(jmpenv, SJ_FAIL);
  80 }
  81
  82 static void __attribute__((noreturn))
  83 succeed_file(void)
  84 {
  85         cleanup();
  86         longjmp(jmpenv, SJ_SUCCEED);
  87 }
  88
  89 /* ulseek, uread, ...:  Check return value for errors. */
  90
  91 static off_t
  92 ulseek(int const fd, off_t const offset, int const whence)
  93 {
  94         off_t const w = lseek(fd, offset, whence);
  95         if (w == (off_t)-1) {
  96                 perror("lseek");
  97                 fail_file();
  98         }
  99         return w;
 100 }
 101
 102 static size_t
 103 uread(int const fd, void *const buf, size_t const count)
 104 {
 105         size_t const n = read(fd, buf, count);
 106         if (n != count) {
 107                 perror("read");
 108                 fail_file();
 109         }
 110         return n;
 111 }
 112
 113 static size_t
 114 uwrite(int const fd, void const *const buf, size_t const count)
 115 {
 116         size_t const n = write(fd, buf, count);
 117         if (n != count) {
 118                 perror("write");
 119                 fail_file();
 120         }
 121         return n;
 122 }
 123
 124 static void *
 125 umalloc(size_t size)
 126 {
 127         void *const addr = malloc(size);
 128         if (addr == 0) {
 129                 fprintf(stderr, "malloc failed: %zu bytes\n", size);
 130                 fail_file();
 131         }
 132         return addr;
 133 }
 134
 135 static unsigned char ideal_nop5_x86_64[5] = { 0x0f, 0x1f, 0x44, 0x00, 0x00 };
 136 static unsigned char ideal_nop5_x86_32[5] = { 0x3e, 0x8d, 0x74, 0x26, 0x00 };
 137 static unsigned char *ideal_nop;
 138
 139 static char rel_type_nop;
 140
 141 static int (*make_nop)(void *map, size_t const offset);
 142
 143 static int make_nop_x86(void *map, size_t const offset)
 144 {
 145         uint32_t *ptr;
 146         unsigned char *op;
 147
 148         /* Confirm we have 0xe8 0x0 0x0 0x0 0x0 */
 149         ptr = map + offset;
 150         if (*ptr != 0)
 151                 return -1;
 152
 153         op = map + offset - 1;
 154         if (*op != 0xe8)
 155                 return -1;
 156
 157         /* convert to nop */
 158         ulseek(fd_map, offset - 1, SEEK_SET);
 159         uwrite(fd_map, ideal_nop, 5);
 160         return 0;
 161 }
 162
 163 /*
 164  * Get the whole file as a programming convenience in order to avoid
 165  * malloc+lseek+read+free of many pieces.  If successful, then mmap
 166  * avoids copying unused pieces; else just read the whole file.
 167  * Open for both read and write; new info will be appended to the file.
 168  * Use MAP_PRIVATE so that a few changes to the in-memory ElfXX_Ehdr
 169  * do not propagate to the file until an explicit overwrite at the last.
 170  * This preserves most aspects of consistency (all except .st_size)
 171  * for simultaneous readers of the file while we are appending to it.
 172  * However, multiple writers still are bad.  We choose not to use
 173  * locking because it is expensive and the use case of kernel build
 174  * makes multiple writers unlikely.
 175  */
 176 static void *mmap_file(char const *fname)
 177 {
 178         void *addr;
 179
 180         fd_map = open(fname, O_RDWR);
 181         if (fd_map < 0 || fstat(fd_map, &sb) < 0) {
 182                 perror(fname);
 183                 fail_file();
 184         }
 185         if (!S_ISREG(sb.st_mode)) {
 186                 fprintf(stderr, "not a regular file: %s\n", fname);
 187                 fail_file();
 188         }
 189         addr = mmap(0, sb.st_size, PROT_READ|PROT_WRITE, MAP_PRIVATE,
 190                     fd_map, 0);
 191         mmap_failed = 0;
 192         if (addr == MAP_FAILED) {
 193                 mmap_failed = 1;
 194                 addr = umalloc(sb.st_size);
 195                 uread(fd_map, addr, sb.st_size);
 196         }
 197         return addr;
 198 }
 199
 200 /* w8rev, w8nat, ...: Handle endianness. */
 201
 202 static uint64_t w8rev(uint64_t const x)
 203 {
 204         return   ((0xff & (x >> (0 * 8))) << (7 * 8))
 205                | ((0xff & (x >> (1 * 8))) << (6 * 8))
 206                | ((0xff & (x >> (2 * 8))) << (5 * 8))
 207                | ((0xff & (x >> (3 * 8))) << (4 * 8))
 208                | ((0xff & (x >> (4 * 8))) << (3 * 8))
 209                | ((0xff & (x >> (5 * 8))) << (2 * 8))
 210                | ((0xff & (x >> (6 * 8))) << (1 * 8))
 211                | ((0xff & (x >> (7 * 8))) << (0 * 8));
 212 }
 213
 214 static uint32_t w4rev(uint32_t const x)
 215 {
 216         return   ((0xff & (x >> (0 * 8))) << (3 * 8))
 217                | ((0xff & (x >> (1 * 8))) << (2 * 8))
 218                | ((0xff & (x >> (2 * 8))) << (1 * 8))
 219                | ((0xff & (x >> (3 * 8))) << (0 * 8));
 220 }
 221
 222 static uint32_t w2rev(uint16_t const x)
 223 {
 224         return   ((0xff & (x >> (0 * 8))) << (1 * 8))
 225                | ((0xff & (x >> (1 * 8))) << (0 * 8));
 226 }
 227
 228 static uint64_t w8nat(uint64_t const x)
 229 {
 230         return x;
 231 }
 232
 233 static uint32_t w4nat(uint32_t const x)
 234 {
 235         return x;
 236 }
 237
 238 static uint32_t w2nat(uint16_t const x)
 239 {
 240         return x;
 241 }
 242
 243 static uint64_t (*w8)(uint64_t);
 244 static uint32_t (*w)(uint32_t);
 245 static uint32_t (*w2)(uint16_t);
 246
 247 /* Names of the sections that could contain calls to mcount. */
 248 static int
 249 is_mcounted_section_name(char const *const txtname)
 250 {
 251         return strcmp(".text",           txtname) == 0 ||
 252                 strcmp(".ref.text",      txtname) == 0 ||
 253                 strcmp(".sched.text",    txtname) == 0 ||
 254                 strcmp(".spinlock.text", txtname) == 0 ||
 255                 strcmp(".irqentry.text", txtname) == 0 ||
 256                 strcmp(".kprobes.text", txtname) == 0 ||
 257                 strcmp(".text.unlikely", txtname) == 0;
 258 }
 259
 260 /* 32 bit and 64 bit are very similar */
 261 #include "recordmcount.h"
 262 #define RECORD_MCOUNT_64
 263 #include "recordmcount.h"
 264
 265 /* 64-bit EM_MIPS has weird ELF64_Rela.r_info.
 266  * http://techpubs.sgi.com/library/manuals/4000/007-4658-001/pdf/007-4658-001.pdf
 267  * We interpret Table 29 Relocation Operation (Elf64_Rel, Elf64_Rela) [p.40]
 268  * to imply the order of the members; the spec does not say so.
 269  *      typedef unsigned char Elf64_Byte;
 270  * fails on MIPS64 because their <elf.h> already has it!
 271  */
 272
 273 typedef uint8_t myElf64_Byte;           /* Type for a 8-bit quantity.  */
 274
 275 union mips_r_info {
 276         Elf64_Xword r_info;
 277         struct {
 278                 Elf64_Word r_sym;               /* Symbol index.  */
 279                 myElf64_Byte r_ssym;            /* Special symbol.  */
 280                 myElf64_Byte r_type3;           /* Third relocation.  */
 281                 myElf64_Byte r_type2;           /* Second relocation.  */
 282                 myElf64_Byte r_type;            /* First relocation.  */
 283         } r_mips;
 284 };
 285
 286 static uint64_t MIPS64_r_sym(Elf64_Rel const *rp)
 287 {
 288         return w(((union mips_r_info){ .r_info = rp->r_info }).r_mips.r_sym);
 289 }
 290
 291 static void MIPS64_r_info(Elf64_Rel *const rp, unsigned sym, unsigned type)
 292 {
 293         rp->r_info = ((union mips_r_info){
 294                 .r_mips = { .r_sym = w(sym), .r_type = type }
 295         }).r_info;
 296 }
 297
 298 static void
 299 do_file(char const *const fname)
 300 {
 301         Elf32_Ehdr *const ehdr = mmap_file(fname);
 302         unsigned int reltype = 0;
 303
 304         ehdr_curr = ehdr;
 305         w = w4nat;
 306         w2 = w2nat;
 307         w8 = w8nat;
 308         switch (ehdr->e_ident[EI_DATA]) {
 309                 static unsigned int const endian = 1;
 310         default:
 311                 fprintf(stderr, "unrecognized ELF data encoding %d: %s\n",
 312                         ehdr->e_ident[EI_DATA], fname);
 313                 fail_file();
 314                 break;
 315         case ELFDATA2LSB:
 316                 if (*(unsigned char const *)&endian != 1) {
 317                         /* main() is big endian, file.o is little endian. */
 318                         w = w4rev;
 319                         w2 = w2rev;
 320                         w8 = w8rev;
 321                 }
 322                 break;
 323         case ELFDATA2MSB:
 324                 if (*(unsigned char const *)&endian != 0) {
 325                         /* main() is little endian, file.o is big endian. */
 326                         w = w4rev;
 327                         w2 = w2rev;
 328                         w8 = w8rev;
 329                 }
 330                 break;
 331         }  /* end switch */
 332         if (memcmp(ELFMAG, ehdr->e_ident, SELFMAG) != 0
 333         ||  w2(ehdr->e_type) != ET_REL
 334         ||  ehdr->e_ident[EI_VERSION] != EV_CURRENT) {
 335                 fprintf(stderr, "unrecognized ET_REL file %s\n", fname);
 336                 fail_file();
 337         }
 338
 339         gpfx = 0;
 340         switch (w2(ehdr->e_machine)) {
 341         default:
 342                 fprintf(stderr, "unrecognized e_machine %d %s\n",
 343                         w2(ehdr->e_machine), fname);
 344                 fail_file();
 345                 break;
 346         case EM_386:
 347                 reltype = R_386_32;
 348                 make_nop = make_nop_x86;
 349                 ideal_nop = ideal_nop5_x86_32;
 350                 mcount_adjust_32 = -1;
 351                 break;
 352         case EM_ARM:     reltype = R_ARM_ABS32;
 353                          altmcount = "__gnu_mcount_nc";
 354                          break;
 355         case EM_AARCH64:
 356                          reltype = R_AARCH64_ABS64; gpfx = '_'; break;
 357         case EM_IA_64:   reltype = R_IA64_IMM64;   gpfx = '_'; break;
 358         case EM_METAG:   reltype = R_METAG_ADDR32;
 359                          altmcount = "_mcount_wrapper";
 360                          rel_type_nop = R_METAG_NONE;
 361                          /* We happen to have the same requirement as MIPS */
 362                          is_fake_mcount32 = MIPS32_is_fake_mcount;
 363                          break;
 364         case EM_MIPS:    /* reltype: e_class    */ gpfx = '_'; break;
 365         case EM_PPC:     reltype = R_PPC_ADDR32;   gpfx = '_'; break;
 366         case EM_PPC64:   reltype = R_PPC64_ADDR64; gpfx = '_'; break;
 367         case EM_S390:    /* reltype: e_class    */ gpfx = '_'; break;
 368         case EM_SH:      reltype = R_SH_DIR32;                 break;
 369         case EM_SPARCV9: reltype = R_SPARC_64;     gpfx = '_'; break;
 370         case EM_X86_64:
 371                 make_nop = make_nop_x86;
 372                 ideal_nop = ideal_nop5_x86_64;
 373                 reltype = R_X86_64_64;
 374                 mcount_adjust_64 = -1;
 375                 break;
 376         }  /* end switch */
 377
 378         switch (ehdr->e_ident[EI_CLASS]) {
 379         default:
 380                 fprintf(stderr, "unrecognized ELF class %d %s\n",
 381                         ehdr->e_ident[EI_CLASS], fname);
 382                 fail_file();
 383                 break;
 384         case ELFCLASS32:
 385                 if (w2(ehdr->e_ehsize) != sizeof(Elf32_Ehdr)
 386                 ||  w2(ehdr->e_shentsize) != sizeof(Elf32_Shdr)) {
 387                         fprintf(stderr,
 388                                 "unrecognized ET_REL file: %s\n", fname);
 389                         fail_file();
 390                 }
 391                 if (w2(ehdr->e_machine) == EM_S390) {
 392                         reltype = R_390_32;
 393                         mcount_adjust_32 = -4;
 394                 }
 395                 if (w2(ehdr->e_machine) == EM_MIPS) {
 396                         reltype = R_MIPS_32;
 397                         is_fake_mcount32 = MIPS32_is_fake_mcount;
 398                 }
 399                 do32(ehdr, fname, reltype);
 400                 break;
 401         case ELFCLASS64: {
 402                 Elf64_Ehdr *const ghdr = (Elf64_Ehdr *)ehdr;
 403                 if (w2(ghdr->e_ehsize) != sizeof(Elf64_Ehdr)
 404                 ||  w2(ghdr->e_shentsize) != sizeof(Elf64_Shdr)) {
 405                         fprintf(stderr,
 406                                 "unrecognized ET_REL file: %s\n", fname);
 407                         fail_file();
 408                 }
 409                 if (w2(ghdr->e_machine) == EM_S390) {
 410                         reltype = R_390_64;
 411                         mcount_adjust_64 = -8;
 412                 }
 413                 if (w2(ghdr->e_machine) == EM_MIPS) {
 414                         reltype = R_MIPS_64;
 415                         Elf64_r_sym = MIPS64_r_sym;
 416                         Elf64_r_info = MIPS64_r_info;
 417                         is_fake_mcount64 = MIPS64_is_fake_mcount;
 418                 }
 419                 do64(ghdr, fname, reltype);
 420                 break;
 421         }
 422         }  /* end switch */
 423
 424         cleanup();
 425 }
 426
 427 int
 428 main(int argc, char *argv[])
 429 {
 430         const char ftrace[] = "/ftrace.o";
 431         int ftrace_size = sizeof(ftrace) - 1;
 432         int n_error = 0;  /* gcc-4.3.0 false positive complaint */
 433         int c;
 434         int i;
 435
 436         while ((c = getopt(argc, argv, "w")) >= 0) {
 437                 switch (c) {
 438                 case 'w':
 439                         warn_on_notrace_sect = 1;
 440                         break;
 441                 default:
 442                         fprintf(stderr, "usage: recordmcount [-w] file.o...\n");
 443                         return 0;
 444                 }
 445         }
 446
 447         if ((argc - optind) < 1) {
 448                 fprintf(stderr, "usage: recordmcount [-w] file.o...\n");
 449                 return 0;
 450         }
 451
 452         /* Process each file in turn, allowing deep failure. */
 453         for (i = optind; i < argc; i++) {
 454                 char *file = argv[i];
 455                 int const sjval = setjmp(jmpenv);
 456                 int len;
 457
 458                 /*
 459                  * The file kernel/trace/ftrace.o references the mcount
 460                  * function but does not call it. Since ftrace.o should
 461                  * not be traced anyway, we just skip it.
 462                  */
 463                 len = strlen(file);
 464                 if (len >= ftrace_size &&
 465                     strcmp(file + (len - ftrace_size), ftrace) == 0)
 466                         continue;
 467
 468                 switch (sjval) {
 469                 default:
 470                         fprintf(stderr, "internal error: %s\n", file);
 471                         exit(1);
 472                         break;
 473                 case SJ_SETJMP:    /* normal sequence */
 474                         /* Avoid problems if early cleanup() */
 475                         fd_map = -1;
 476                         ehdr_curr = NULL;
 477                         mmap_failed = 1;
 478                         do_file(file);
 479                         break;
 480                 case SJ_FAIL:    /* error in do_file or below */
 481                         ++n_error;
 482                         break;
 483                 case SJ_SUCCEED:    /* premature success */
 484                         /* do nothing */
 485                         break;
 486                 }  /* end switch */
 487         }
 488         return !!n_error;
 489 }
 490
 491