linux/scripts/recordmcount.c
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   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
  36static int fd_map;      /* File descriptor for file being modified. */
  37static int mmap_failed; /* Boolean flag. */
  38static void *ehdr_curr; /* current ElfXX_Ehdr *  for resource cleanup */
  39static char gpfx;       /* prefix for global symbol name (sometimes '_') */
  40static struct stat sb;  /* Remember .st_size, etc. */
  41static jmp_buf jmpenv;  /* setjmp/longjmp per-file error escape */
  42static const char *altmcount;   /* alternate mcount symbol name */
  43static int warn_on_notrace_sect; /* warn when section has mcount not being recorded */
  44
  45/* setjmp() return values */
  46enum {
  47        SJ_SETJMP = 0,  /* hardwired first return */
  48        SJ_FAIL,
  49        SJ_SUCCEED
  50};
  51
  52/* Per-file resource cleanup when multiple files. */
  53static void
  54cleanup(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
  63static void __attribute__((noreturn))
  64fail_file(void)
  65{
  66        cleanup();
  67        longjmp(jmpenv, SJ_FAIL);
  68}
  69
  70static void __attribute__((noreturn))
  71succeed_file(void)
  72{
  73        cleanup();
  74        longjmp(jmpenv, SJ_SUCCEED);
  75}
  76
  77/* ulseek, uread, ...:  Check return value for errors. */
  78
  79static off_t
  80ulseek(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
  90static size_t
  91uread(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
 101static size_t
 102uwrite(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
 112static void *
 113umalloc(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
 123static unsigned char ideal_nop5_x86_64[5] = { 0x0f, 0x1f, 0x44, 0x00, 0x00 };
 124static unsigned char ideal_nop5_x86_32[5] = { 0x3e, 0x8d, 0x74, 0x26, 0x00 };
 125static unsigned char *ideal_nop;
 126
 127static char rel_type_nop;
 128
 129static int (*make_nop)(void *map, size_t const offset);
 130
 131static 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 */
 164static 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
 190static 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
 202static 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
 210static 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
 216static uint64_t w8nat(uint64_t const x)
 217{
 218        return x;
 219}
 220
 221static uint32_t w4nat(uint32_t const x)
 222{
 223        return x;
 224}
 225
 226static uint32_t w2nat(uint16_t const x)
 227{
 228        return x;
 229}
 230
 231static uint64_t (*w8)(uint64_t);
 232static uint32_t (*w)(uint32_t);
 233static uint32_t (*w2)(uint16_t);
 234
 235/* Names of the sections that could contain calls to mcount. */
 236static int
 237is_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
 261typedef uint8_t myElf64_Byte;           /* Type for a 8-bit quantity.  */
 262
 263union 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
 274static 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
 279static 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
 286static void
 287do_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
 407int
 408main(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
 472
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