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