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 static int fd_map;      /* File descriptor for file being modified. */
  37 static int mmap_failed; /* Boolean flag. */
  38 static void *ehdr_curr; /* current ElfXX_Ehdr *  for resource cleanup */
  39 static char gpfx;       /* prefix for global symbol name (sometimes '_') */
  40 static struct stat sb;  /* Remember .st_size, etc. */
  41 static jmp_buf jmpenv;  /* setjmp/longjmp per-file error escape */
  42 static const char *altmcount;   /* alternate mcount symbol name */
  43 static int warn_on_notrace_sect; /* warn when section has mcount not being recorded */
  44
  45 /* setjmp() return values */
  46 enum {
  47         SJ_SETJMP = 0,  /* hardwired first return */
  48         SJ_FAIL,
  49         SJ_SUCCEED
  50 };
  51
  52 /* Per-file resource cleanup when multiple files. */
  53 static void
  54 cleanup(void)
  55 {
  56         if (!mmap_failed)
  57                 munmap(ehdr_curr, sb.st_size);
  58         else
  59                 free(ehdr_curr);
  60         close(fd_map);
  61 }
  62
  63 static void __attribute__((noreturn))
  64 fail_file(void)
  65 {
  66         cleanup();
  67         longjmp(jmpenv, SJ_FAIL);
  68 }
  69
  70 static void __attribute__((noreturn))
  71 succeed_file(void)
  72 {
  73         cleanup();
  74         longjmp(jmpenv, SJ_SUCCEED);
  75 }
  76
  77 /* ulseek, uread, ...:  Check return value for errors. */
  78
  79 static off_t
  80 ulseek(int const fd, off_t const offset, int const whence)
  81 {
  82         off_t const w = lseek(fd, offset, whence);
  83         if (w == (off_t)-1) {
  84                 perror("lseek");
  85                 fail_file();
  86         }
  87         return w;
  88 }
  89
  90 static size_t
  91 uread(int const fd, void *const buf, size_t const count)
  92 {
  93         size_t const n = read(fd, buf, count);
  94         if (n != count) {
  95                 perror("read");
  96                 fail_file();
  97         }
  98         return n;
  99 }
 100
 101 static size_t
 102 uwrite(int const fd, void const *const buf, size_t const count)
 103 {
 104         size_t const n = write(fd, buf, count);
 105         if (n != count) {
 106                 perror("write");
 107                 fail_file();
 108         }
 109         return n;
 110 }
 111
 112 static void *
 113 umalloc(size_t size)
 114 {
 115         void *const addr = malloc(size);
 116         if (addr == 0) {
 117                 fprintf(stderr, "malloc failed: %zu bytes\n", size);
 118                 fail_file();
 119         }
 120         return addr;
 121 }
 122
 123 static unsigned char ideal_nop5_x86_64[5] = { 0x0f, 0x1f, 0x44, 0x00, 0x00 };
 124 static unsigned char ideal_nop5_x86_32[5] = { 0x3e, 0x8d, 0x74, 0x26, 0x00 };
 125 static unsigned char *ideal_nop;
 126
 127 static char rel_type_nop;
 128
 129 static int (*make_nop)(void *map, size_t const offset);
 130
 131 static int make_nop_x86(void *map, size_t const offset)
 132 {
 133         uint32_t *ptr;
 134         unsigned char *op;
 135
 136         /* Confirm we have 0xe8 0x0 0x0 0x0 0x0 */
 137         ptr = map + offset;
 138         if (*ptr != 0)
 139                 return -1;
 140
 141         op = map + offset - 1;
 142         if (*op != 0xe8)
 143                 return -1;
 144
 145         /* convert to nop */
 146         ulseek(fd_map, offset - 1, SEEK_SET);
 147         uwrite(fd_map, ideal_nop, 5);
 148         return 0;
 149 }
 150
 151 /*
 152  * Get the whole file as a programming convenience in order to avoid
 153  * malloc+lseek+read+free of many pieces.  If successful, then mmap
 154  * avoids copying unused pieces; else just read the whole file.
 155  * Open for both read and write; new info will be appended to the file.
 156  * Use MAP_PRIVATE so that a few changes to the in-memory ElfXX_Ehdr
 157  * do not propagate to the file until an explicit overwrite at the last.
 158  * This preserves most aspects of consistency (all except .st_size)
 159  * for simultaneous readers of the file while we are appending to it.
 160  * However, multiple writers still are bad.  We choose not to use
 161  * locking because it is expensive and the use case of kernel build
 162  * makes multiple writers unlikely.
 163  */
 164 static void *mmap_file(char const *fname)
 165 {
 166         void *addr;
 167
 168         fd_map = open(fname, O_RDWR);
 169         if (fd_map < 0 || fstat(fd_map, &sb) < 0) {
 170                 perror(fname);
 171                 fail_file();
 172         }
 173         if (!S_ISREG(sb.st_mode)) {
 174                 fprintf(stderr, "not a regular file: %s\n", fname);
 175                 fail_file();
 176         }
 177         addr = mmap(0, sb.st_size, PROT_READ|PROT_WRITE, MAP_PRIVATE,
 178                     fd_map, 0);
 179         mmap_failed = 0;
 180         if (addr == MAP_FAILED) {
 181                 mmap_failed = 1;
 182                 addr = umalloc(sb.st_size);
 183                 uread(fd_map, addr, sb.st_size);
 184         }
 185         return addr;
 186 }
 187
 188 /* w8rev, w8nat, ...: Handle endianness. */
 189
 190 static uint64_t w8rev(uint64_t const x)
 191 {
 192         return   ((0xff & (x >> (0 * 8))) << (7 * 8))
 193                | ((0xff & (x >> (1 * 8))) << (6 * 8))
 194                | ((0xff & (x >> (2 * 8))) << (5 * 8))
 195                | ((0xff & (x >> (3 * 8))) << (4 * 8))
 196                | ((0xff & (x >> (4 * 8))) << (3 * 8))
 197                | ((0xff & (x >> (5 * 8))) << (2 * 8))
 198                | ((0xff & (x >> (6 * 8))) << (1 * 8))
 199                | ((0xff & (x >> (7 * 8))) << (0 * 8));
 200 }
 201
 202 static uint32_t w4rev(uint32_t const x)
 203 {
 204         return   ((0xff & (x >> (0 * 8))) << (3 * 8))
 205                | ((0xff & (x >> (1 * 8))) << (2 * 8))
 206                | ((0xff & (x >> (2 * 8))) << (1 * 8))
 207                | ((0xff & (x >> (3 * 8))) << (0 * 8));
 208 }
 209
 210 static uint32_t w2rev(uint16_t const x)
 211 {
 212         return   ((0xff & (x >> (0 * 8))) << (1 * 8))
 213                | ((0xff & (x >> (1 * 8))) << (0 * 8));
 214 }
 215
 216 static uint64_t w8nat(uint64_t const x)
 217 {
 218         return x;
 219 }
 220
 221 static uint32_t w4nat(uint32_t const x)
 222 {
 223         return x;
 224 }
 225
 226 static uint32_t w2nat(uint16_t const x)
 227 {
 228         return x;
 229 }
 230
 231 static uint64_t (*w8)(uint64_t);
 232 static uint32_t (*w)(uint32_t);
 233 static uint32_t (*w2)(uint16_t);
 234
 235 /* Names of the sections that could contain calls to mcount. */
 236 static int
 237 is_mcounted_section_name(char const *const txtname)
 238 {
 239         return strcmp(".text",           txtname) == 0 ||
 240                 strcmp(".ref.text",      txtname) == 0 ||
 241                 strcmp(".sched.text",    txtname) == 0 ||
 242                 strcmp(".spinlock.text", txtname) == 0 ||
 243                 strcmp(".irqentry.text", txtname) == 0 ||
 244                 strcmp(".kprobes.text", txtname) == 0 ||
 245                 strcmp(".text.unlikely", txtname) == 0;
 246 }
 247
 248 /* 32 bit and 64 bit are very similar */
 249 #include "recordmcount.h"
 250 #define RECORD_MCOUNT_64
 251 #include "recordmcount.h"
 252
 253 /* 64-bit EM_MIPS has weird ELF64_Rela.r_info.
 254  * http://techpubs.sgi.com/library/manuals/4000/007-4658-001/pdf/007-4658-001.pdf
 255  * We interpret Table 29 Relocation Operation (Elf64_Rel, Elf64_Rela) [p.40]
 256  * to imply the order of the members; the spec does not say so.
 257  *      typedef unsigned char Elf64_Byte;
 258  * fails on MIPS64 because their <elf.h> already has it!
 259  */
 260
 261 typedef uint8_t myElf64_Byte;           /* Type for a 8-bit quantity.  */
 262
 263 union mips_r_info {
 264         Elf64_Xword r_info;
 265         struct {
 266                 Elf64_Word r_sym;               /* Symbol index.  */
 267                 myElf64_Byte r_ssym;            /* Special symbol.  */
 268                 myElf64_Byte r_type3;           /* Third relocation.  */
 269                 myElf64_Byte r_type2;           /* Second relocation.  */
 270                 myElf64_Byte r_type;            /* First relocation.  */
 271         } r_mips;
 272 };
 273
 274 static uint64_t MIPS64_r_sym(Elf64_Rel const *rp)
 275 {
 276         return w(((union mips_r_info){ .r_info = rp->r_info }).r_mips.r_sym);
 277 }
 278
 279 static void MIPS64_r_info(Elf64_Rel *const rp, unsigned sym, unsigned type)
 280 {
 281         rp->r_info = ((union mips_r_info){
 282                 .r_mips = { .r_sym = w(sym), .r_type = type }
 283         }).r_info;
 284 }
 285
 286 static void
 287 do_file(char const *const fname)
 288 {
 289         Elf32_Ehdr *const ehdr = mmap_file(fname);
 290         unsigned int reltype = 0;
 291
 292         ehdr_curr = ehdr;
 293         w = w4nat;
 294         w2 = w2nat;
 295         w8 = w8nat;
 296         switch (ehdr->e_ident[EI_DATA]) {
 297                 static unsigned int const endian = 1;
 298         default:
 299                 fprintf(stderr, "unrecognized ELF data encoding %d: %s\n",
 300                         ehdr->e_ident[EI_DATA], fname);
 301                 fail_file();
 302                 break;
 303         case ELFDATA2LSB:
 304                 if (*(unsigned char const *)&endian != 1) {
 305                         /* main() is big endian, file.o is little endian. */
 306                         w = w4rev;
 307                         w2 = w2rev;
 308                         w8 = w8rev;
 309                 }
 310                 break;
 311         case ELFDATA2MSB:
 312                 if (*(unsigned char const *)&endian != 0) {
 313                         /* main() is little endian, file.o is big endian. */
 314                         w = w4rev;
 315                         w2 = w2rev;
 316                         w8 = w8rev;
 317                 }
 318                 break;
 319         }  /* end switch */
 320         if (memcmp(ELFMAG, ehdr->e_ident, SELFMAG) != 0
 321         ||  w2(ehdr->e_type) != ET_REL
 322         ||  ehdr->e_ident[EI_VERSION] != EV_CURRENT) {
 323                 fprintf(stderr, "unrecognized ET_REL file %s\n", fname);
 324                 fail_file();
 325         }
 326
 327         gpfx = 0;
 328         switch (w2(ehdr->e_machine)) {
 329         default:
 330                 fprintf(stderr, "unrecognized e_machine %d %s\n",
 331                         w2(ehdr->e_machine), fname);
 332                 fail_file();
 333                 break;
 334         case EM_386:
 335                 reltype = R_386_32;
 336                 make_nop = make_nop_x86;
 337                 ideal_nop = ideal_nop5_x86_32;
 338                 mcount_adjust_32 = -1;
 339                 break;
 340         case EM_ARM:     reltype = R_ARM_ABS32;
 341                          altmcount = "__gnu_mcount_nc";
 342                          break;
 343         case EM_IA_64:   reltype = R_IA64_IMM64;   gpfx = '_'; break;
 344         case EM_MIPS:    /* reltype: e_class    */ gpfx = '_'; break;
 345         case EM_PPC:     reltype = R_PPC_ADDR32;   gpfx = '_'; break;
 346         case EM_PPC64:   reltype = R_PPC64_ADDR64; gpfx = '_'; break;
 347         case EM_S390:    /* reltype: e_class    */ gpfx = '_'; break;
 348         case EM_SH:      reltype = R_SH_DIR32;                 break;
 349         case EM_SPARCV9: reltype = R_SPARC_64;     gpfx = '_'; break;
 350         case EM_X86_64:
 351                 make_nop = make_nop_x86;
 352                 ideal_nop = ideal_nop5_x86_64;
 353                 reltype = R_X86_64_64;
 354                 mcount_adjust_64 = -1;
 355                 break;
 356         }  /* end switch */
 357
 358         switch (ehdr->e_ident[EI_CLASS]) {
 359         default:
 360                 fprintf(stderr, "unrecognized ELF class %d %s\n",
 361                         ehdr->e_ident[EI_CLASS], fname);
 362                 fail_file();
 363                 break;
 364         case ELFCLASS32:
 365                 if (w2(ehdr->e_ehsize) != sizeof(Elf32_Ehdr)
 366                 ||  w2(ehdr->e_shentsize) != sizeof(Elf32_Shdr)) {
 367                         fprintf(stderr,
 368                                 "unrecognized ET_REL file: %s\n", fname);
 369                         fail_file();
 370                 }
 371                 if (w2(ehdr->e_machine) == EM_S390) {
 372                         reltype = R_390_32;
 373                         mcount_adjust_32 = -4;
 374                 }
 375                 if (w2(ehdr->e_machine) == EM_MIPS) {
 376                         reltype = R_MIPS_32;
 377                         is_fake_mcount32 = MIPS32_is_fake_mcount;
 378                 }
 379                 do32(ehdr, fname, reltype);
 380                 break;
 381         case ELFCLASS64: {
 382                 Elf64_Ehdr *const ghdr = (Elf64_Ehdr *)ehdr;
 383                 if (w2(ghdr->e_ehsize) != sizeof(Elf64_Ehdr)
 384                 ||  w2(ghdr->e_shentsize) != sizeof(Elf64_Shdr)) {
 385                         fprintf(stderr,
 386                                 "unrecognized ET_REL file: %s\n", fname);
 387                         fail_file();
 388                 }
 389                 if (w2(ghdr->e_machine) == EM_S390) {
 390                         reltype = R_390_64;
 391                         mcount_adjust_64 = -8;
 392                 }
 393                 if (w2(ghdr->e_machine) == EM_MIPS) {
 394                         reltype = R_MIPS_64;
 395                         Elf64_r_sym = MIPS64_r_sym;
 396                         Elf64_r_info = MIPS64_r_info;
 397                         is_fake_mcount64 = MIPS64_is_fake_mcount;
 398                 }
 399                 do64(ghdr, fname, reltype);
 400                 break;
 401         }
 402         }  /* end switch */
 403
 404         cleanup();
 405 }
 406
 407 int
 408 main(int argc, char *argv[])
 409 {
 410         const char ftrace[] = "/ftrace.o";
 411         int ftrace_size = sizeof(ftrace) - 1;
 412         int n_error = 0;  /* gcc-4.3.0 false positive complaint */
 413         int c;
 414         int i;
 415
 416         while ((c = getopt(argc, argv, "w")) >= 0) {
 417                 switch (c) {
 418                 case 'w':
 419                         warn_on_notrace_sect = 1;
 420                         break;
 421                 default:
 422                         fprintf(stderr, "usage: recordmcount [-w] file.o...\n");
 423                         return 0;
 424                 }
 425         }
 426
 427         if ((argc - optind) < 1) {
 428                 fprintf(stderr, "usage: recordmcount [-w] file.o...\n");
 429                 return 0;
 430         }
 431
 432         /* Process each file in turn, allowing deep failure. */
 433         for (i = optind; i < argc; i++) {
 434                 char *file = argv[i];
 435                 int const sjval = setjmp(jmpenv);
 436                 int len;
 437
 438                 /*
 439                  * The file kernel/trace/ftrace.o references the mcount
 440                  * function but does not call it. Since ftrace.o should
 441                  * not be traced anyway, we just skip it.
 442                  */
 443                 len = strlen(file);
 444                 if (len >= ftrace_size &&
 445                     strcmp(file + (len - ftrace_size), ftrace) == 0)
 446                         continue;
 447
 448                 switch (sjval) {
 449                 default:
 450                         fprintf(stderr, "internal error: %s\n", file);
 451                         exit(1);
 452                         break;
 453                 case SJ_SETJMP:    /* normal sequence */
 454                         /* Avoid problems if early cleanup() */
 455                         fd_map = -1;
 456                         ehdr_curr = NULL;
 457                         mmap_failed = 1;
 458                         do_file(file);
 459                         break;
 460                 case SJ_FAIL:    /* error in do_file or below */
 461                         ++n_error;
 462                         break;
 463                 case SJ_SUCCEED:    /* premature success */
 464                         /* do nothing */
 465                         break;
 466                 }  /* end switch */
 467         }
 468         return !!n_error;
 469 }
 470
 471