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
  36/*
  37 * glibc synced up and added the metag number but didn't add the relocations.
  38 * Work around this in a crude manner for now.
  39 */
  40#ifndef EM_METAG
  41#define EM_METAG      174
  42#endif
  43#ifndef R_METAG_ADDR32
  44#define R_METAG_ADDR32                   2
  45#endif
  46#ifndef R_METAG_NONE
  47#define R_METAG_NONE                     3
  48#endif
  49
  50#ifndef EM_AARCH64
  51#define EM_AARCH64      183
  52#define R_AARCH64_NONE          0
  53#define R_AARCH64_ABS64 257
  54#endif
  55
  56static int fd_map;      /* File descriptor for file being modified. */
  57static int mmap_failed; /* Boolean flag. */
  58static char gpfx;       /* prefix for global symbol name (sometimes '_') */
  59static struct stat sb;  /* Remember .st_size, etc. */
  60static jmp_buf jmpenv;  /* setjmp/longjmp per-file error escape */
  61static const char *altmcount;   /* alternate mcount symbol name */
  62static int warn_on_notrace_sect; /* warn when section has mcount not being recorded */
  63static void *file_map;  /* pointer of the mapped file */
  64static void *file_end;  /* pointer to the end of the mapped file */
  65static int file_updated; /* flag to state file was changed */
  66static void *file_ptr;  /* current file pointer location */
  67static void *file_append; /* added to the end of the file */
  68static size_t file_append_size; /* how much is added to end of file */
  69
  70/* setjmp() return values */
  71enum {
  72        SJ_SETJMP = 0,  /* hardwired first return */
  73        SJ_FAIL,
  74        SJ_SUCCEED
  75};
  76
  77/* Per-file resource cleanup when multiple files. */
  78static void
  79cleanup(void)
  80{
  81        if (!mmap_failed)
  82                munmap(file_map, sb.st_size);
  83        else
  84                free(file_map);
  85        file_map = NULL;
  86        free(file_append);
  87        file_append = NULL;
  88        file_append_size = 0;
  89        file_updated = 0;
  90}
  91
  92static void __attribute__((noreturn))
  93fail_file(void)
  94{
  95        cleanup();
  96        longjmp(jmpenv, SJ_FAIL);
  97}
  98
  99static void __attribute__((noreturn))
 100succeed_file(void)
 101{
 102        cleanup();
 103        longjmp(jmpenv, SJ_SUCCEED);
 104}
 105
 106/* ulseek, uread, ...:  Check return value for errors. */
 107
 108static off_t
 109ulseek(int const fd, off_t const offset, int const whence)
 110{
 111        switch (whence) {
 112        case SEEK_SET:
 113                file_ptr = file_map + offset;
 114                break;
 115        case SEEK_CUR:
 116                file_ptr += offset;
 117                break;
 118        case SEEK_END:
 119                file_ptr = file_map + (sb.st_size - offset);
 120                break;
 121        }
 122        if (file_ptr < file_map) {
 123                fprintf(stderr, "lseek: seek before file\n");
 124                fail_file();
 125        }
 126        return file_ptr - file_map;
 127}
 128
 129static size_t
 130uread(int const fd, void *const buf, size_t const count)
 131{
 132        size_t const n = read(fd, buf, count);
 133        if (n != count) {
 134                perror("read");
 135                fail_file();
 136        }
 137        return n;
 138}
 139
 140static size_t
 141uwrite(int const fd, void const *const buf, size_t const count)
 142{
 143        size_t cnt = count;
 144        off_t idx = 0;
 145
 146        file_updated = 1;
 147
 148        if (file_ptr + count >= file_end) {
 149                off_t aoffset = (file_ptr + count) - file_end;
 150
 151                if (aoffset > file_append_size) {
 152                        file_append = realloc(file_append, aoffset);
 153                        file_append_size = aoffset;
 154                }
 155                if (!file_append) {
 156                        perror("write");
 157                        fail_file();
 158                }
 159                if (file_ptr < file_end) {
 160                        cnt = file_end - file_ptr;
 161                } else {
 162                        cnt = 0;
 163                        idx = aoffset - count;
 164                }
 165        }
 166
 167        if (cnt)
 168                memcpy(file_ptr, buf, cnt);
 169
 170        if (cnt < count)
 171                memcpy(file_append + idx, buf + cnt, count - cnt);
 172
 173        file_ptr += count;
 174        return count;
 175}
 176
 177static void *
 178umalloc(size_t size)
 179{
 180        void *const addr = malloc(size);
 181        if (addr == 0) {
 182                fprintf(stderr, "malloc failed: %zu bytes\n", size);
 183                fail_file();
 184        }
 185        return addr;
 186}
 187
 188static unsigned char ideal_nop5_x86_64[5] = { 0x0f, 0x1f, 0x44, 0x00, 0x00 };
 189static unsigned char ideal_nop5_x86_32[5] = { 0x3e, 0x8d, 0x74, 0x26, 0x00 };
 190static unsigned char *ideal_nop;
 191
 192static char rel_type_nop;
 193
 194static int (*make_nop)(void *map, size_t const offset);
 195
 196static int make_nop_x86(void *map, size_t const offset)
 197{
 198        uint32_t *ptr;
 199        unsigned char *op;
 200
 201        /* Confirm we have 0xe8 0x0 0x0 0x0 0x0 */
 202        ptr = map + offset;
 203        if (*ptr != 0)
 204                return -1;
 205
 206        op = map + offset - 1;
 207        if (*op != 0xe8)
 208                return -1;
 209
 210        /* convert to nop */
 211        ulseek(fd_map, offset - 1, SEEK_SET);
 212        uwrite(fd_map, ideal_nop, 5);
 213        return 0;
 214}
 215
 216static unsigned char ideal_nop4_arm64[4] = {0x1f, 0x20, 0x03, 0xd5};
 217static int make_nop_arm64(void *map, size_t const offset)
 218{
 219        uint32_t *ptr;
 220
 221        ptr = map + offset;
 222        /* bl <_mcount> is 0x94000000 before relocation */
 223        if (*ptr != 0x94000000)
 224                return -1;
 225
 226        /* Convert to nop */
 227        ulseek(fd_map, offset, SEEK_SET);
 228        uwrite(fd_map, ideal_nop, 4);
 229        return 0;
 230}
 231
 232/*
 233 * Get the whole file as a programming convenience in order to avoid
 234 * malloc+lseek+read+free of many pieces.  If successful, then mmap
 235 * avoids copying unused pieces; else just read the whole file.
 236 * Open for both read and write; new info will be appended to the file.
 237 * Use MAP_PRIVATE so that a few changes to the in-memory ElfXX_Ehdr
 238 * do not propagate to the file until an explicit overwrite at the last.
 239 * This preserves most aspects of consistency (all except .st_size)
 240 * for simultaneous readers of the file while we are appending to it.
 241 * However, multiple writers still are bad.  We choose not to use
 242 * locking because it is expensive and the use case of kernel build
 243 * makes multiple writers unlikely.
 244 */
 245static void *mmap_file(char const *fname)
 246{
 247        fd_map = open(fname, O_RDONLY);
 248        if (fd_map < 0 || fstat(fd_map, &sb) < 0) {
 249                perror(fname);
 250                fail_file();
 251        }
 252        if (!S_ISREG(sb.st_mode)) {
 253                fprintf(stderr, "not a regular file: %s\n", fname);
 254                fail_file();
 255        }
 256        file_map = mmap(0, sb.st_size, PROT_READ|PROT_WRITE, MAP_PRIVATE,
 257                        fd_map, 0);
 258        mmap_failed = 0;
 259        if (file_map == MAP_FAILED) {
 260                mmap_failed = 1;
 261                file_map = umalloc(sb.st_size);
 262                uread(fd_map, file_map, sb.st_size);
 263        }
 264        close(fd_map);
 265
 266        file_end = file_map + sb.st_size;
 267
 268        return file_map;
 269}
 270
 271static void write_file(const char *fname)
 272{
 273        char tmp_file[strlen(fname) + 4];
 274        size_t n;
 275
 276        if (!file_updated)
 277                return;
 278
 279        sprintf(tmp_file, "%s.rc", fname);
 280
 281        /*
 282         * After reading the entire file into memory, delete it
 283         * and write it back, to prevent weird side effects of modifying
 284         * an object file in place.
 285         */
 286        fd_map = open(tmp_file, O_WRONLY | O_TRUNC | O_CREAT, sb.st_mode);
 287        if (fd_map < 0) {
 288                perror(fname);
 289                fail_file();
 290        }
 291        n = write(fd_map, file_map, sb.st_size);
 292        if (n != sb.st_size) {
 293                perror("write");
 294                fail_file();
 295        }
 296        if (file_append_size) {
 297                n = write(fd_map, file_append, file_append_size);
 298                if (n != file_append_size) {
 299                        perror("write");
 300                        fail_file();
 301                }
 302        }
 303        close(fd_map);
 304        if (rename(tmp_file, fname) < 0) {
 305                perror(fname);
 306                fail_file();
 307        }
 308}
 309
 310/* w8rev, w8nat, ...: Handle endianness. */
 311
 312static uint64_t w8rev(uint64_t const x)
 313{
 314        return   ((0xff & (x >> (0 * 8))) << (7 * 8))
 315               | ((0xff & (x >> (1 * 8))) << (6 * 8))
 316               | ((0xff & (x >> (2 * 8))) << (5 * 8))
 317               | ((0xff & (x >> (3 * 8))) << (4 * 8))
 318               | ((0xff & (x >> (4 * 8))) << (3 * 8))
 319               | ((0xff & (x >> (5 * 8))) << (2 * 8))
 320               | ((0xff & (x >> (6 * 8))) << (1 * 8))
 321               | ((0xff & (x >> (7 * 8))) << (0 * 8));
 322}
 323
 324static uint32_t w4rev(uint32_t const x)
 325{
 326        return   ((0xff & (x >> (0 * 8))) << (3 * 8))
 327               | ((0xff & (x >> (1 * 8))) << (2 * 8))
 328               | ((0xff & (x >> (2 * 8))) << (1 * 8))
 329               | ((0xff & (x >> (3 * 8))) << (0 * 8));
 330}
 331
 332static uint32_t w2rev(uint16_t const x)
 333{
 334        return   ((0xff & (x >> (0 * 8))) << (1 * 8))
 335               | ((0xff & (x >> (1 * 8))) << (0 * 8));
 336}
 337
 338static uint64_t w8nat(uint64_t const x)
 339{
 340        return x;
 341}
 342
 343static uint32_t w4nat(uint32_t const x)
 344{
 345        return x;
 346}
 347
 348static uint32_t w2nat(uint16_t const x)
 349{
 350        return x;
 351}
 352
 353static uint64_t (*w8)(uint64_t);
 354static uint32_t (*w)(uint32_t);
 355static uint32_t (*w2)(uint16_t);
 356
 357/* Names of the sections that could contain calls to mcount. */
 358static int
 359is_mcounted_section_name(char const *const txtname)
 360{
 361        return strcmp(".text",           txtname) == 0 ||
 362                strcmp(".ref.text",      txtname) == 0 ||
 363                strcmp(".sched.text",    txtname) == 0 ||
 364                strcmp(".spinlock.text", txtname) == 0 ||
 365                strcmp(".irqentry.text", txtname) == 0 ||
 366                strcmp(".softirqentry.text", txtname) == 0 ||
 367                strcmp(".kprobes.text", txtname) == 0 ||
 368                strcmp(".cpuidle.text", txtname) == 0 ||
 369                strcmp(".text.unlikely", txtname) == 0;
 370}
 371
 372/* 32 bit and 64 bit are very similar */
 373#include "recordmcount.h"
 374#define RECORD_MCOUNT_64
 375#include "recordmcount.h"
 376
 377/* 64-bit EM_MIPS has weird ELF64_Rela.r_info.
 378 * http://techpubs.sgi.com/library/manuals/4000/007-4658-001/pdf/007-4658-001.pdf
 379 * We interpret Table 29 Relocation Operation (Elf64_Rel, Elf64_Rela) [p.40]
 380 * to imply the order of the members; the spec does not say so.
 381 *      typedef unsigned char Elf64_Byte;
 382 * fails on MIPS64 because their <elf.h> already has it!
 383 */
 384
 385typedef uint8_t myElf64_Byte;           /* Type for a 8-bit quantity.  */
 386
 387union mips_r_info {
 388        Elf64_Xword r_info;
 389        struct {
 390                Elf64_Word r_sym;               /* Symbol index.  */
 391                myElf64_Byte r_ssym;            /* Special symbol.  */
 392                myElf64_Byte r_type3;           /* Third relocation.  */
 393                myElf64_Byte r_type2;           /* Second relocation.  */
 394                myElf64_Byte r_type;            /* First relocation.  */
 395        } r_mips;
 396};
 397
 398static uint64_t MIPS64_r_sym(Elf64_Rel const *rp)
 399{
 400        return w(((union mips_r_info){ .r_info = rp->r_info }).r_mips.r_sym);
 401}
 402
 403static void MIPS64_r_info(Elf64_Rel *const rp, unsigned sym, unsigned type)
 404{
 405        rp->r_info = ((union mips_r_info){
 406                .r_mips = { .r_sym = w(sym), .r_type = type }
 407        }).r_info;
 408}
 409
 410static void
 411do_file(char const *const fname)
 412{
 413        Elf32_Ehdr *const ehdr = mmap_file(fname);
 414        unsigned int reltype = 0;
 415
 416        w = w4nat;
 417        w2 = w2nat;
 418        w8 = w8nat;
 419        switch (ehdr->e_ident[EI_DATA]) {
 420                static unsigned int const endian = 1;
 421        default:
 422                fprintf(stderr, "unrecognized ELF data encoding %d: %s\n",
 423                        ehdr->e_ident[EI_DATA], fname);
 424                fail_file();
 425                break;
 426        case ELFDATA2LSB:
 427                if (*(unsigned char const *)&endian != 1) {
 428                        /* main() is big endian, file.o is little endian. */
 429                        w = w4rev;
 430                        w2 = w2rev;
 431                        w8 = w8rev;
 432                }
 433                break;
 434        case ELFDATA2MSB:
 435                if (*(unsigned char const *)&endian != 0) {
 436                        /* main() is little endian, file.o is big endian. */
 437                        w = w4rev;
 438                        w2 = w2rev;
 439                        w8 = w8rev;
 440                }
 441                break;
 442        }  /* end switch */
 443        if (memcmp(ELFMAG, ehdr->e_ident, SELFMAG) != 0
 444        ||  w2(ehdr->e_type) != ET_REL
 445        ||  ehdr->e_ident[EI_VERSION] != EV_CURRENT) {
 446                fprintf(stderr, "unrecognized ET_REL file %s\n", fname);
 447                fail_file();
 448        }
 449
 450        gpfx = 0;
 451        switch (w2(ehdr->e_machine)) {
 452        default:
 453                fprintf(stderr, "unrecognized e_machine %d %s\n",
 454                        w2(ehdr->e_machine), fname);
 455                fail_file();
 456                break;
 457        case EM_386:
 458                reltype = R_386_32;
 459                rel_type_nop = R_386_NONE;
 460                make_nop = make_nop_x86;
 461                ideal_nop = ideal_nop5_x86_32;
 462                mcount_adjust_32 = -1;
 463                break;
 464        case EM_ARM:     reltype = R_ARM_ABS32;
 465                         altmcount = "__gnu_mcount_nc";
 466                         break;
 467        case EM_AARCH64:
 468                        reltype = R_AARCH64_ABS64;
 469                        make_nop = make_nop_arm64;
 470                        rel_type_nop = R_AARCH64_NONE;
 471                        ideal_nop = ideal_nop4_arm64;
 472                        gpfx = '_';
 473                        break;
 474        case EM_IA_64:   reltype = R_IA64_IMM64;   gpfx = '_'; break;
 475        case EM_METAG:   reltype = R_METAG_ADDR32;
 476                         altmcount = "_mcount_wrapper";
 477                         rel_type_nop = R_METAG_NONE;
 478                         /* We happen to have the same requirement as MIPS */
 479                         is_fake_mcount32 = MIPS32_is_fake_mcount;
 480                         break;
 481        case EM_MIPS:    /* reltype: e_class    */ gpfx = '_'; break;
 482        case EM_PPC:     reltype = R_PPC_ADDR32;   gpfx = '_'; break;
 483        case EM_PPC64:   reltype = R_PPC64_ADDR64; gpfx = '_'; break;
 484        case EM_S390:    /* reltype: e_class    */ gpfx = '_'; break;
 485        case EM_SH:      reltype = R_SH_DIR32;                 break;
 486        case EM_SPARCV9: reltype = R_SPARC_64;     gpfx = '_'; break;
 487        case EM_X86_64:
 488                make_nop = make_nop_x86;
 489                ideal_nop = ideal_nop5_x86_64;
 490                reltype = R_X86_64_64;
 491                rel_type_nop = R_X86_64_NONE;
 492                mcount_adjust_64 = -1;
 493                break;
 494        }  /* end switch */
 495
 496        switch (ehdr->e_ident[EI_CLASS]) {
 497        default:
 498                fprintf(stderr, "unrecognized ELF class %d %s\n",
 499                        ehdr->e_ident[EI_CLASS], fname);
 500                fail_file();
 501                break;
 502        case ELFCLASS32:
 503                if (w2(ehdr->e_ehsize) != sizeof(Elf32_Ehdr)
 504                ||  w2(ehdr->e_shentsize) != sizeof(Elf32_Shdr)) {
 505                        fprintf(stderr,
 506                                "unrecognized ET_REL file: %s\n", fname);
 507                        fail_file();
 508                }
 509                if (w2(ehdr->e_machine) == EM_MIPS) {
 510                        reltype = R_MIPS_32;
 511                        is_fake_mcount32 = MIPS32_is_fake_mcount;
 512                }
 513                do32(ehdr, fname, reltype);
 514                break;
 515        case ELFCLASS64: {
 516                Elf64_Ehdr *const ghdr = (Elf64_Ehdr *)ehdr;
 517                if (w2(ghdr->e_ehsize) != sizeof(Elf64_Ehdr)
 518                ||  w2(ghdr->e_shentsize) != sizeof(Elf64_Shdr)) {
 519                        fprintf(stderr,
 520                                "unrecognized ET_REL file: %s\n", fname);
 521                        fail_file();
 522                }
 523                if (w2(ghdr->e_machine) == EM_S390) {
 524                        reltype = R_390_64;
 525                        mcount_adjust_64 = -14;
 526                }
 527                if (w2(ghdr->e_machine) == EM_MIPS) {
 528                        reltype = R_MIPS_64;
 529                        Elf64_r_sym = MIPS64_r_sym;
 530                        Elf64_r_info = MIPS64_r_info;
 531                        is_fake_mcount64 = MIPS64_is_fake_mcount;
 532                }
 533                do64(ghdr, fname, reltype);
 534                break;
 535        }
 536        }  /* end switch */
 537
 538        write_file(fname);
 539        cleanup();
 540}
 541
 542int
 543main(int argc, char *argv[])
 544{
 545        const char ftrace[] = "/ftrace.o";
 546        int ftrace_size = sizeof(ftrace) - 1;
 547        int n_error = 0;  /* gcc-4.3.0 false positive complaint */
 548        int c;
 549        int i;
 550
 551        while ((c = getopt(argc, argv, "w")) >= 0) {
 552                switch (c) {
 553                case 'w':
 554                        warn_on_notrace_sect = 1;
 555                        break;
 556                default:
 557                        fprintf(stderr, "usage: recordmcount [-w] file.o...\n");
 558                        return 0;
 559                }
 560        }
 561
 562        if ((argc - optind) < 1) {
 563                fprintf(stderr, "usage: recordmcount [-w] file.o...\n");
 564                return 0;
 565        }
 566
 567        /* Process each file in turn, allowing deep failure. */
 568        for (i = optind; i < argc; i++) {
 569                char *file = argv[i];
 570                int const sjval = setjmp(jmpenv);
 571                int len;
 572
 573                /*
 574                 * The file kernel/trace/ftrace.o references the mcount
 575                 * function but does not call it. Since ftrace.o should
 576                 * not be traced anyway, we just skip it.
 577                 */
 578                len = strlen(file);
 579                if (len >= ftrace_size &&
 580                    strcmp(file + (len - ftrace_size), ftrace) == 0)
 581                        continue;
 582
 583                switch (sjval) {
 584                default:
 585                        fprintf(stderr, "internal error: %s\n", file);
 586                        exit(1);
 587                        break;
 588                case SJ_SETJMP:    /* normal sequence */
 589                        /* Avoid problems if early cleanup() */
 590                        fd_map = -1;
 591                        mmap_failed = 1;
 592                        file_map = NULL;
 593                        file_ptr = NULL;
 594                        file_updated = 0;
 595                        do_file(file);
 596                        break;
 597                case SJ_FAIL:    /* error in do_file or below */
 598                        fprintf(stderr, "%s: failed\n", file);
 599                        ++n_error;
 600                        break;
 601                case SJ_SUCCEED:    /* premature success */
 602                        /* do nothing */
 603                        break;
 604                }  /* end switch */
 605        }
 606        return !!n_error;
 607}
 608