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