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 <elf.h>
  28#include <fcntl.h>
  29#include <setjmp.h>
  30#include <stdio.h>
  31#include <stdlib.h>
  32#include <string.h>
  33#include <unistd.h>
  34
  35static int fd_map;      /* File descriptor for file being modified. */
  36static int mmap_failed; /* Boolean flag. */
  37static void *ehdr_curr; /* current ElfXX_Ehdr *  for resource cleanup */
  38static char gpfx;       /* prefix for global symbol name (sometimes '_') */
  39static struct stat sb;  /* Remember .st_size, etc. */
  40static jmp_buf jmpenv;  /* setjmp/longjmp per-file error escape */
  41
  42/* setjmp() return values */
  43enum {
  44        SJ_SETJMP = 0,  /* hardwired first return */
  45        SJ_FAIL,
  46        SJ_SUCCEED
  47};
  48
  49/* Per-file resource cleanup when multiple files. */
  50static void
  51cleanup(void)
  52{
  53        if (!mmap_failed)
  54                munmap(ehdr_curr, sb.st_size);
  55        else
  56                free(ehdr_curr);
  57        close(fd_map);
  58}
  59
  60static void __attribute__((noreturn))
  61fail_file(void)
  62{
  63        cleanup();
  64        longjmp(jmpenv, SJ_FAIL);
  65}
  66
  67static void __attribute__((noreturn))
  68succeed_file(void)
  69{
  70        cleanup();
  71        longjmp(jmpenv, SJ_SUCCEED);
  72}
  73
  74/* ulseek, uread, ...:  Check return value for errors. */
  75
  76static off_t
  77ulseek(int const fd, off_t const offset, int const whence)
  78{
  79        off_t const w = lseek(fd, offset, whence);
  80        if ((off_t)-1 == w) {
  81                perror("lseek");
  82                fail_file();
  83        }
  84        return w;
  85}
  86
  87static size_t
  88uread(int const fd, void *const buf, size_t const count)
  89{
  90        size_t const n = read(fd, buf, count);
  91        if (n != count) {
  92                perror("read");
  93                fail_file();
  94        }
  95        return n;
  96}
  97
  98static size_t
  99uwrite(int const fd, void const *const buf, size_t const count)
 100{
 101        size_t const n = write(fd, buf, count);
 102        if (n != count) {
 103                perror("write");
 104                fail_file();
 105        }
 106        return n;
 107}
 108
 109static void *
 110umalloc(size_t size)
 111{
 112        void *const addr = malloc(size);
 113        if (0 == addr) {
 114                fprintf(stderr, "malloc failed: %zu bytes\n", size);
 115                fail_file();
 116        }
 117        return addr;
 118}
 119
 120/*
 121 * Get the whole file as a programming convenience in order to avoid
 122 * malloc+lseek+read+free of many pieces.  If successful, then mmap
 123 * avoids copying unused pieces; else just read the whole file.
 124 * Open for both read and write; new info will be appended to the file.
 125 * Use MAP_PRIVATE so that a few changes to the in-memory ElfXX_Ehdr
 126 * do not propagate to the file until an explicit overwrite at the last.
 127 * This preserves most aspects of consistency (all except .st_size)
 128 * for simultaneous readers of the file while we are appending to it.
 129 * However, multiple writers still are bad.  We choose not to use
 130 * locking because it is expensive and the use case of kernel build
 131 * makes multiple writers unlikely.
 132 */
 133static void *mmap_file(char const *fname)
 134{
 135        void *addr;
 136
 137        fd_map = open(fname, O_RDWR);
 138        if (0 > fd_map || 0 > fstat(fd_map, &sb)) {
 139                perror(fname);
 140                fail_file();
 141        }
 142        if (!S_ISREG(sb.st_mode)) {
 143                fprintf(stderr, "not a regular file: %s\n", fname);
 144                fail_file();
 145        }
 146        addr = mmap(0, sb.st_size, PROT_READ|PROT_WRITE, MAP_PRIVATE,
 147                    fd_map, 0);
 148        mmap_failed = 0;
 149        if (MAP_FAILED == addr) {
 150                mmap_failed = 1;
 151                addr = umalloc(sb.st_size);
 152                uread(fd_map, addr, sb.st_size);
 153        }
 154        return addr;
 155}
 156
 157/* w8rev, w8nat, ...: Handle endianness. */
 158
 159static uint64_t w8rev(uint64_t const x)
 160{
 161        return   ((0xff & (x >> (0 * 8))) << (7 * 8))
 162               | ((0xff & (x >> (1 * 8))) << (6 * 8))
 163               | ((0xff & (x >> (2 * 8))) << (5 * 8))
 164               | ((0xff & (x >> (3 * 8))) << (4 * 8))
 165               | ((0xff & (x >> (4 * 8))) << (3 * 8))
 166               | ((0xff & (x >> (5 * 8))) << (2 * 8))
 167               | ((0xff & (x >> (6 * 8))) << (1 * 8))
 168               | ((0xff & (x >> (7 * 8))) << (0 * 8));
 169}
 170
 171static uint32_t w4rev(uint32_t const x)
 172{
 173        return   ((0xff & (x >> (0 * 8))) << (3 * 8))
 174               | ((0xff & (x >> (1 * 8))) << (2 * 8))
 175               | ((0xff & (x >> (2 * 8))) << (1 * 8))
 176               | ((0xff & (x >> (3 * 8))) << (0 * 8));
 177}
 178
 179static uint32_t w2rev(uint16_t const x)
 180{
 181        return   ((0xff & (x >> (0 * 8))) << (1 * 8))
 182               | ((0xff & (x >> (1 * 8))) << (0 * 8));
 183}
 184
 185static uint64_t w8nat(uint64_t const x)
 186{
 187        return x;
 188}
 189
 190static uint32_t w4nat(uint32_t const x)
 191{
 192        return x;
 193}
 194
 195static uint32_t w2nat(uint16_t const x)
 196{
 197        return x;
 198}
 199
 200static uint64_t (*w8)(uint64_t);
 201static uint32_t (*w)(uint32_t);
 202static uint32_t (*w2)(uint16_t);
 203
 204/* Names of the sections that could contain calls to mcount. */
 205static int
 206is_mcounted_section_name(char const *const txtname)
 207{
 208        return 0 == strcmp(".text",          txtname) ||
 209                0 == strcmp(".sched.text",    txtname) ||
 210                0 == strcmp(".spinlock.text", txtname) ||
 211                0 == strcmp(".irqentry.text", txtname) ||
 212                0 == strcmp(".text.unlikely", txtname);
 213}
 214
 215/* 32 bit and 64 bit are very similar */
 216#include "recordmcount.h"
 217#define RECORD_MCOUNT_64
 218#include "recordmcount.h"
 219
 220/* 64-bit EM_MIPS has weird ELF64_Rela.r_info.
 221 * http://techpubs.sgi.com/library/manuals/4000/007-4658-001/pdf/007-4658-001.pdf
 222 * We interpret Table 29 Relocation Operation (Elf64_Rel, Elf64_Rela) [p.40]
 223 * to imply the order of the members; the spec does not say so.
 224 *      typedef unsigned char Elf64_Byte;
 225 * fails on MIPS64 because their <elf.h> already has it!
 226 */
 227
 228typedef uint8_t myElf64_Byte;           /* Type for a 8-bit quantity.  */
 229
 230union mips_r_info {
 231        Elf64_Xword r_info;
 232        struct {
 233                Elf64_Word r_sym;               /* Symbol index.  */
 234                myElf64_Byte r_ssym;            /* Special symbol.  */
 235                myElf64_Byte r_type3;           /* Third relocation.  */
 236                myElf64_Byte r_type2;           /* Second relocation.  */
 237                myElf64_Byte r_type;            /* First relocation.  */
 238        } r_mips;
 239};
 240
 241static uint64_t MIPS64_r_sym(Elf64_Rel const *rp)
 242{
 243        return w(((union mips_r_info){ .r_info = rp->r_info }).r_mips.r_sym);
 244}
 245
 246static void MIPS64_r_info(Elf64_Rel *const rp, unsigned sym, unsigned type)
 247{
 248        rp->r_info = ((union mips_r_info){
 249                .r_mips = { .r_sym = w(sym), .r_type = type }
 250        }).r_info;
 251}
 252
 253static void
 254do_file(char const *const fname)
 255{
 256        Elf32_Ehdr *const ehdr = mmap_file(fname);
 257        unsigned int reltype = 0;
 258
 259        ehdr_curr = ehdr;
 260        w = w4nat;
 261        w2 = w2nat;
 262        w8 = w8nat;
 263        switch (ehdr->e_ident[EI_DATA]) {
 264                static unsigned int const endian = 1;
 265        default: {
 266                fprintf(stderr, "unrecognized ELF data encoding %d: %s\n",
 267                        ehdr->e_ident[EI_DATA], fname);
 268                fail_file();
 269        } break;
 270        case ELFDATA2LSB: {
 271                if (1 != *(unsigned char const *)&endian) {
 272                        /* main() is big endian, file.o is little endian. */
 273                        w = w4rev;
 274                        w2 = w2rev;
 275                        w8 = w8rev;
 276                }
 277        } break;
 278        case ELFDATA2MSB: {
 279                if (0 != *(unsigned char const *)&endian) {
 280                        /* main() is little endian, file.o is big endian. */
 281                        w = w4rev;
 282                        w2 = w2rev;
 283                        w8 = w8rev;
 284                }
 285        } break;
 286        }  /* end switch */
 287        if (0 != memcmp(ELFMAG, ehdr->e_ident, SELFMAG)
 288        ||  ET_REL != w2(ehdr->e_type)
 289        ||  EV_CURRENT != ehdr->e_ident[EI_VERSION]) {
 290                fprintf(stderr, "unrecognized ET_REL file %s\n", fname);
 291                fail_file();
 292        }
 293
 294        gpfx = 0;
 295        switch (w2(ehdr->e_machine)) {
 296        default: {
 297                fprintf(stderr, "unrecognized e_machine %d %s\n",
 298                        w2(ehdr->e_machine), fname);
 299                fail_file();
 300        } break;
 301        case EM_386:     reltype = R_386_32;                   break;
 302        case EM_ARM:     reltype = R_ARM_ABS32;                break;
 303        case EM_IA_64:   reltype = R_IA64_IMM64;   gpfx = '_'; break;
 304        case EM_MIPS:    /* reltype: e_class    */ gpfx = '_'; break;
 305        case EM_PPC:     reltype = R_PPC_ADDR32;   gpfx = '_'; break;
 306        case EM_PPC64:   reltype = R_PPC64_ADDR64; gpfx = '_'; break;
 307        case EM_S390:    /* reltype: e_class    */ gpfx = '_'; break;
 308        case EM_SH:      reltype = R_SH_DIR32;                 break;
 309        case EM_SPARCV9: reltype = R_SPARC_64;     gpfx = '_'; break;
 310        case EM_X86_64:  reltype = R_X86_64_64;                break;
 311        }  /* end switch */
 312
 313        switch (ehdr->e_ident[EI_CLASS]) {
 314        default: {
 315                fprintf(stderr, "unrecognized ELF class %d %s\n",
 316                        ehdr->e_ident[EI_CLASS], fname);
 317                fail_file();
 318        } break;
 319        case ELFCLASS32: {
 320                if (sizeof(Elf32_Ehdr) != w2(ehdr->e_ehsize)
 321                ||  sizeof(Elf32_Shdr) != w2(ehdr->e_shentsize)) {
 322                        fprintf(stderr,
 323                                "unrecognized ET_REL file: %s\n", fname);
 324                        fail_file();
 325                }
 326                if (EM_S390 == w2(ehdr->e_machine))
 327                        reltype = R_390_32;
 328                if (EM_MIPS == w2(ehdr->e_machine)) {
 329                        reltype = R_MIPS_32;
 330                        is_fake_mcount32 = MIPS32_is_fake_mcount;
 331                }
 332                do32(ehdr, fname, reltype);
 333        } break;
 334        case ELFCLASS64: {
 335                Elf64_Ehdr *const ghdr = (Elf64_Ehdr *)ehdr;
 336                if (sizeof(Elf64_Ehdr) != w2(ghdr->e_ehsize)
 337                ||  sizeof(Elf64_Shdr) != w2(ghdr->e_shentsize)) {
 338                        fprintf(stderr,
 339                                "unrecognized ET_REL file: %s\n", fname);
 340                        fail_file();
 341                }
 342                if (EM_S390 == w2(ghdr->e_machine))
 343                        reltype = R_390_64;
 344                if (EM_MIPS == w2(ghdr->e_machine)) {
 345                        reltype = R_MIPS_64;
 346                        Elf64_r_sym = MIPS64_r_sym;
 347                        Elf64_r_info = MIPS64_r_info;
 348                        is_fake_mcount64 = MIPS64_is_fake_mcount;
 349                }
 350                do64(ghdr, fname, reltype);
 351        } break;
 352        }  /* end switch */
 353
 354        cleanup();
 355}
 356
 357int
 358main(int argc, char const *argv[])
 359{
 360        const char ftrace[] = "kernel/trace/ftrace.o";
 361        int ftrace_size = sizeof(ftrace) - 1;
 362        int n_error = 0;  /* gcc-4.3.0 false positive complaint */
 363
 364        if (argc <= 1) {
 365                fprintf(stderr, "usage: recordmcount file.o...\n");
 366                return 0;
 367        }
 368
 369        /* Process each file in turn, allowing deep failure. */
 370        for (--argc, ++argv; 0 < argc; --argc, ++argv) {
 371                int const sjval = setjmp(jmpenv);
 372                int len;
 373
 374                /*
 375                 * The file kernel/trace/ftrace.o references the mcount
 376                 * function but does not call it. Since ftrace.o should
 377                 * not be traced anyway, we just skip it.
 378                 */
 379                len = strlen(argv[0]);
 380                if (len >= ftrace_size &&
 381                    strcmp(argv[0] + (len - ftrace_size), ftrace) == 0)
 382                        continue;
 383
 384                switch (sjval) {
 385                default: {
 386                        fprintf(stderr, "internal error: %s\n", argv[0]);
 387                        exit(1);
 388                } break;
 389                case SJ_SETJMP: {  /* normal sequence */
 390                        /* Avoid problems if early cleanup() */
 391                        fd_map = -1;
 392                        ehdr_curr = NULL;
 393                        mmap_failed = 1;
 394                        do_file(argv[0]);
 395                } break;
 396                case SJ_FAIL: {  /* error in do_file or below */
 397                        ++n_error;
 398                } break;
 399                case SJ_SUCCEED: {  /* premature success */
 400                        /* do nothing */
 401                } break;
 402                }  /* end switch */
 403        }
 404        return !!n_error;
 405}
 406
 407
 408