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#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
  43static int fd_map;      /* File descriptor for file being modified. */
  44static int mmap_failed; /* Boolean flag. */
  45static void *ehdr_curr; /* current ElfXX_Ehdr *  for resource cleanup */
  46static char gpfx;       /* prefix for global symbol name (sometimes '_') */
  47static struct stat sb;  /* Remember .st_size, etc. */
  48static jmp_buf jmpenv;  /* setjmp/longjmp per-file error escape */
  49static const char *altmcount;   /* alternate mcount symbol name */
  50static int warn_on_notrace_sect; /* warn when section has mcount not being recorded */
  51
  52/* setjmp() return values */
  53enum {
  54        SJ_SETJMP = 0,  /* hardwired first return */
  55        SJ_FAIL,
  56        SJ_SUCCEED
  57};
  58
  59/* Per-file resource cleanup when multiple files. */
  60static void
  61cleanup(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
  70static void __attribute__((noreturn))
  71fail_file(void)
  72{
  73        cleanup();
  74        longjmp(jmpenv, SJ_FAIL);
  75}
  76
  77static void __attribute__((noreturn))
  78succeed_file(void)
  79{
  80        cleanup();
  81        longjmp(jmpenv, SJ_SUCCEED);
  82}
  83
  84/* ulseek, uread, ...:  Check return value for errors. */
  85
  86static off_t
  87ulseek(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
  97static size_t
  98uread(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
 108static size_t
 109uwrite(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
 119static void *
 120umalloc(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
 130static unsigned char ideal_nop5_x86_64[5] = { 0x0f, 0x1f, 0x44, 0x00, 0x00 };
 131static unsigned char ideal_nop5_x86_32[5] = { 0x3e, 0x8d, 0x74, 0x26, 0x00 };
 132static unsigned char *ideal_nop;
 133
 134static char rel_type_nop;
 135
 136static int (*make_nop)(void *map, size_t const offset);
 137
 138static 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 */
 171static 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
 197static 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
 209static 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
 217static 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
 223static uint64_t w8nat(uint64_t const x)
 224{
 225        return x;
 226}
 227
 228static uint32_t w4nat(uint32_t const x)
 229{
 230        return x;
 231}
 232
 233static uint32_t w2nat(uint16_t const x)
 234{
 235        return x;
 236}
 237
 238static uint64_t (*w8)(uint64_t);
 239static uint32_t (*w)(uint32_t);
 240static uint32_t (*w2)(uint16_t);
 241
 242/* Names of the sections that could contain calls to mcount. */
 243static int
 244is_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
 268typedef uint8_t myElf64_Byte;           /* Type for a 8-bit quantity.  */
 269
 270union 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
 281static 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
 286static 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
 293static void
 294do_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
 420int
 421main(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
 485
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