linux/scripts/recordmcount.h
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   1/*
   2 * recordmcount.h
   3 *
   4 * This code was taken out of recordmcount.c written by
   5 * Copyright 2009 John F. Reiser <jreiser@BitWagon.com>.  All rights reserved.
   6 *
   7 * The original code had the same algorithms for both 32bit
   8 * and 64bit ELF files, but the code was duplicated to support
   9 * the difference in structures that were used. This
  10 * file creates a macro of everything that is different between
  11 * the 64 and 32 bit code, such that by including this header
  12 * twice we can create both sets of functions by including this
  13 * header once with RECORD_MCOUNT_64 undefined, and again with
  14 * it defined.
  15 *
  16 * This conversion to macros was done by:
  17 * Copyright 2010 Steven Rostedt <srostedt@redhat.com>, Red Hat Inc.
  18 *
  19 * Licensed under the GNU General Public License, version 2 (GPLv2).
  20 */
  21#undef append_func
  22#undef is_fake_mcount
  23#undef fn_is_fake_mcount
  24#undef MIPS_is_fake_mcount
  25#undef sift_rel_mcount
  26#undef find_secsym_ndx
  27#undef __has_rel_mcount
  28#undef has_rel_mcount
  29#undef tot_relsize
  30#undef do_func
  31#undef Elf_Addr
  32#undef Elf_Ehdr
  33#undef Elf_Shdr
  34#undef Elf_Rel
  35#undef Elf_Rela
  36#undef Elf_Sym
  37#undef ELF_R_SYM
  38#undef Elf_r_sym
  39#undef ELF_R_INFO
  40#undef Elf_r_info
  41#undef ELF_ST_BIND
  42#undef fn_ELF_R_SYM
  43#undef fn_ELF_R_INFO
  44#undef uint_t
  45#undef _w
  46#undef _align
  47#undef _size
  48
  49#ifdef RECORD_MCOUNT_64
  50# define append_func            append64
  51# define sift_rel_mcount        sift64_rel_mcount
  52# define find_secsym_ndx        find64_secsym_ndx
  53# define __has_rel_mcount       __has64_rel_mcount
  54# define has_rel_mcount         has64_rel_mcount
  55# define tot_relsize            tot64_relsize
  56# define do_func                do64
  57# define is_fake_mcount         is_fake_mcount64
  58# define fn_is_fake_mcount      fn_is_fake_mcount64
  59# define MIPS_is_fake_mcount    MIPS64_is_fake_mcount
  60# define Elf_Addr               Elf64_Addr
  61# define Elf_Ehdr               Elf64_Ehdr
  62# define Elf_Shdr               Elf64_Shdr
  63# define Elf_Rel                Elf64_Rel
  64# define Elf_Rela               Elf64_Rela
  65# define Elf_Sym                Elf64_Sym
  66# define ELF_R_SYM              ELF64_R_SYM
  67# define Elf_r_sym              Elf64_r_sym
  68# define ELF_R_INFO             ELF64_R_INFO
  69# define Elf_r_info             Elf64_r_info
  70# define ELF_ST_BIND            ELF64_ST_BIND
  71# define fn_ELF_R_SYM           fn_ELF64_R_SYM
  72# define fn_ELF_R_INFO          fn_ELF64_R_INFO
  73# define uint_t                 uint64_t
  74# define _w                     w8
  75# define _align                 7u
  76# define _size                  8
  77#else
  78# define append_func            append32
  79# define sift_rel_mcount        sift32_rel_mcount
  80# define find_secsym_ndx        find32_secsym_ndx
  81# define __has_rel_mcount       __has32_rel_mcount
  82# define has_rel_mcount         has32_rel_mcount
  83# define tot_relsize            tot32_relsize
  84# define do_func                do32
  85# define is_fake_mcount         is_fake_mcount32
  86# define fn_is_fake_mcount      fn_is_fake_mcount32
  87# define MIPS_is_fake_mcount    MIPS32_is_fake_mcount
  88# define Elf_Addr               Elf32_Addr
  89# define Elf_Ehdr               Elf32_Ehdr
  90# define Elf_Shdr               Elf32_Shdr
  91# define Elf_Rel                Elf32_Rel
  92# define Elf_Rela               Elf32_Rela
  93# define Elf_Sym                Elf32_Sym
  94# define ELF_R_SYM              ELF32_R_SYM
  95# define Elf_r_sym              Elf32_r_sym
  96# define ELF_R_INFO             ELF32_R_INFO
  97# define Elf_r_info             Elf32_r_info
  98# define ELF_ST_BIND            ELF32_ST_BIND
  99# define fn_ELF_R_SYM           fn_ELF32_R_SYM
 100# define fn_ELF_R_INFO          fn_ELF32_R_INFO
 101# define uint_t                 uint32_t
 102# define _w                     w
 103# define _align                 3u
 104# define _size                  4
 105#endif
 106
 107/* Functions and pointers that do_file() may override for specific e_machine. */
 108static int fn_is_fake_mcount(Elf_Rel const *rp)
 109{
 110        return 0;
 111}
 112static int (*is_fake_mcount)(Elf_Rel const *rp) = fn_is_fake_mcount;
 113
 114static uint_t fn_ELF_R_SYM(Elf_Rel const *rp)
 115{
 116        return ELF_R_SYM(_w(rp->r_info));
 117}
 118static uint_t (*Elf_r_sym)(Elf_Rel const *rp) = fn_ELF_R_SYM;
 119
 120static void fn_ELF_R_INFO(Elf_Rel *const rp, unsigned sym, unsigned type)
 121{
 122        rp->r_info = _w(ELF_R_INFO(sym, type));
 123}
 124static void (*Elf_r_info)(Elf_Rel *const rp, unsigned sym, unsigned type) = fn_ELF_R_INFO;
 125
 126/*
 127 * MIPS mcount long call has 2 _mcount symbols, only the position of the 1st
 128 * _mcount symbol is needed for dynamic function tracer, with it, to disable
 129 * tracing(ftrace_make_nop), the instruction in the position is replaced with
 130 * the "b label" instruction, to enable tracing(ftrace_make_call), replace the
 131 * instruction back. So, here, we set the 2nd one as fake and filter it.
 132 *
 133 * c:   3c030000        lui     v1,0x0          <-->    b       label
 134 *              c: R_MIPS_HI16  _mcount
 135 *              c: R_MIPS_NONE  *ABS*
 136 *              c: R_MIPS_NONE  *ABS*
 137 * 10:  64630000        daddiu  v1,v1,0
 138 *              10: R_MIPS_LO16 _mcount
 139 *              10: R_MIPS_NONE *ABS*
 140 *              10: R_MIPS_NONE *ABS*
 141 * 14:  03e0082d        move    at,ra
 142 * 18:  0060f809        jalr    v1
 143 * label:
 144 */
 145#define MIPS_FAKEMCOUNT_OFFSET  4
 146
 147static int MIPS_is_fake_mcount(Elf_Rel const *rp)
 148{
 149        static Elf_Addr old_r_offset;
 150        Elf_Addr current_r_offset = _w(rp->r_offset);
 151        int is_fake;
 152
 153        is_fake = old_r_offset &&
 154                (current_r_offset - old_r_offset == MIPS_FAKEMCOUNT_OFFSET);
 155        old_r_offset = current_r_offset;
 156
 157        return is_fake;
 158}
 159
 160/* Append the new shstrtab, Elf_Shdr[], __mcount_loc and its relocations. */
 161static void append_func(Elf_Ehdr *const ehdr,
 162                        Elf_Shdr *const shstr,
 163                        uint_t const *const mloc0,
 164                        uint_t const *const mlocp,
 165                        Elf_Rel const *const mrel0,
 166                        Elf_Rel const *const mrelp,
 167                        unsigned int const rel_entsize,
 168                        unsigned int const symsec_sh_link)
 169{
 170        /* Begin constructing output file */
 171        Elf_Shdr mcsec;
 172        char const *mc_name = (sizeof(Elf_Rela) == rel_entsize)
 173                ? ".rela__mcount_loc"
 174                :  ".rel__mcount_loc";
 175        unsigned const old_shnum = w2(ehdr->e_shnum);
 176        uint_t const old_shoff = _w(ehdr->e_shoff);
 177        uint_t const old_shstr_sh_size   = _w(shstr->sh_size);
 178        uint_t const old_shstr_sh_offset = _w(shstr->sh_offset);
 179        uint_t t = 1 + strlen(mc_name) + _w(shstr->sh_size);
 180        uint_t new_e_shoff;
 181
 182        shstr->sh_size = _w(t);
 183        shstr->sh_offset = _w(sb.st_size);
 184        t += sb.st_size;
 185        t += (_align & -t);  /* word-byte align */
 186        new_e_shoff = t;
 187
 188        /* body for new shstrtab */
 189        ulseek(fd_map, sb.st_size, SEEK_SET);
 190        uwrite(fd_map, old_shstr_sh_offset + (void *)ehdr, old_shstr_sh_size);
 191        uwrite(fd_map, mc_name, 1 + strlen(mc_name));
 192
 193        /* old(modified) Elf_Shdr table, word-byte aligned */
 194        ulseek(fd_map, t, SEEK_SET);
 195        t += sizeof(Elf_Shdr) * old_shnum;
 196        uwrite(fd_map, old_shoff + (void *)ehdr,
 197               sizeof(Elf_Shdr) * old_shnum);
 198
 199        /* new sections __mcount_loc and .rel__mcount_loc */
 200        t += 2*sizeof(mcsec);
 201        mcsec.sh_name = w((sizeof(Elf_Rela) == rel_entsize) + strlen(".rel")
 202                + old_shstr_sh_size);
 203        mcsec.sh_type = w(SHT_PROGBITS);
 204        mcsec.sh_flags = _w(SHF_ALLOC);
 205        mcsec.sh_addr = 0;
 206        mcsec.sh_offset = _w(t);
 207        mcsec.sh_size = _w((void *)mlocp - (void *)mloc0);
 208        mcsec.sh_link = 0;
 209        mcsec.sh_info = 0;
 210        mcsec.sh_addralign = _w(_size);
 211        mcsec.sh_entsize = _w(_size);
 212        uwrite(fd_map, &mcsec, sizeof(mcsec));
 213
 214        mcsec.sh_name = w(old_shstr_sh_size);
 215        mcsec.sh_type = (sizeof(Elf_Rela) == rel_entsize)
 216                ? w(SHT_RELA)
 217                : w(SHT_REL);
 218        mcsec.sh_flags = 0;
 219        mcsec.sh_addr = 0;
 220        mcsec.sh_offset = _w((void *)mlocp - (void *)mloc0 + t);
 221        mcsec.sh_size   = _w((void *)mrelp - (void *)mrel0);
 222        mcsec.sh_link = w(symsec_sh_link);
 223        mcsec.sh_info = w(old_shnum);
 224        mcsec.sh_addralign = _w(_size);
 225        mcsec.sh_entsize = _w(rel_entsize);
 226        uwrite(fd_map, &mcsec, sizeof(mcsec));
 227
 228        uwrite(fd_map, mloc0, (void *)mlocp - (void *)mloc0);
 229        uwrite(fd_map, mrel0, (void *)mrelp - (void *)mrel0);
 230
 231        ehdr->e_shoff = _w(new_e_shoff);
 232        ehdr->e_shnum = w2(2 + w2(ehdr->e_shnum));  /* {.rel,}__mcount_loc */
 233        ulseek(fd_map, 0, SEEK_SET);
 234        uwrite(fd_map, ehdr, sizeof(*ehdr));
 235}
 236
 237/*
 238 * Look at the relocations in order to find the calls to mcount.
 239 * Accumulate the section offsets that are found, and their relocation info,
 240 * onto the end of the existing arrays.
 241 */
 242static uint_t *sift_rel_mcount(uint_t *mlocp,
 243                               unsigned const offbase,
 244                               Elf_Rel **const mrelpp,
 245                               Elf_Shdr const *const relhdr,
 246                               Elf_Ehdr const *const ehdr,
 247                               unsigned const recsym,
 248                               uint_t const recval,
 249                               unsigned const reltype)
 250{
 251        uint_t *const mloc0 = mlocp;
 252        Elf_Rel *mrelp = *mrelpp;
 253        Elf_Shdr *const shdr0 = (Elf_Shdr *)(_w(ehdr->e_shoff)
 254                + (void *)ehdr);
 255        unsigned const symsec_sh_link = w(relhdr->sh_link);
 256        Elf_Shdr const *const symsec = &shdr0[symsec_sh_link];
 257        Elf_Sym const *const sym0 = (Elf_Sym const *)(_w(symsec->sh_offset)
 258                + (void *)ehdr);
 259
 260        Elf_Shdr const *const strsec = &shdr0[w(symsec->sh_link)];
 261        char const *const str0 = (char const *)(_w(strsec->sh_offset)
 262                + (void *)ehdr);
 263
 264        Elf_Rel const *const rel0 = (Elf_Rel const *)(_w(relhdr->sh_offset)
 265                + (void *)ehdr);
 266        unsigned rel_entsize = _w(relhdr->sh_entsize);
 267        unsigned const nrel = _w(relhdr->sh_size) / rel_entsize;
 268        Elf_Rel const *relp = rel0;
 269
 270        unsigned mcountsym = 0;
 271        unsigned t;
 272
 273        for (t = nrel; t; --t) {
 274                if (!mcountsym) {
 275                        Elf_Sym const *const symp =
 276                                &sym0[Elf_r_sym(relp)];
 277                        char const *symname = &str0[w(symp->st_name)];
 278                        char const *mcount = '_' == gpfx ? "_mcount" : "mcount";
 279
 280                        if ('.' == symname[0])
 281                                ++symname;  /* ppc64 hack */
 282                        if (0 == strcmp(mcount, symname) ||
 283                            (altmcount && 0 == strcmp(altmcount, symname)))
 284                                mcountsym = Elf_r_sym(relp);
 285                }
 286
 287                if (mcountsym == Elf_r_sym(relp) && !is_fake_mcount(relp)) {
 288                        uint_t const addend = _w(_w(relp->r_offset) - recval);
 289
 290                        mrelp->r_offset = _w(offbase
 291                                + ((void *)mlocp - (void *)mloc0));
 292                        Elf_r_info(mrelp, recsym, reltype);
 293                        if (sizeof(Elf_Rela) == rel_entsize) {
 294                                ((Elf_Rela *)mrelp)->r_addend = addend;
 295                                *mlocp++ = 0;
 296                        } else
 297                                *mlocp++ = addend;
 298
 299                        mrelp = (Elf_Rel *)(rel_entsize + (void *)mrelp);
 300                }
 301                relp = (Elf_Rel const *)(rel_entsize + (void *)relp);
 302        }
 303        *mrelpp = mrelp;
 304        return mlocp;
 305}
 306
 307
 308/*
 309 * Find a symbol in the given section, to be used as the base for relocating
 310 * the table of offsets of calls to mcount.  A local or global symbol suffices,
 311 * but avoid a Weak symbol because it may be overridden; the change in value
 312 * would invalidate the relocations of the offsets of the calls to mcount.
 313 * Often the found symbol will be the unnamed local symbol generated by
 314 * GNU 'as' for the start of each section.  For example:
 315 *    Num:    Value  Size Type    Bind   Vis      Ndx Name
 316 *      2: 00000000     0 SECTION LOCAL  DEFAULT    1
 317 */
 318static unsigned find_secsym_ndx(unsigned const txtndx,
 319                                char const *const txtname,
 320                                uint_t *const recvalp,
 321                                Elf_Shdr const *const symhdr,
 322                                Elf_Ehdr const *const ehdr)
 323{
 324        Elf_Sym const *const sym0 = (Elf_Sym const *)(_w(symhdr->sh_offset)
 325                + (void *)ehdr);
 326        unsigned const nsym = _w(symhdr->sh_size) / _w(symhdr->sh_entsize);
 327        Elf_Sym const *symp;
 328        unsigned t;
 329
 330        for (symp = sym0, t = nsym; t; --t, ++symp) {
 331                unsigned int const st_bind = ELF_ST_BIND(symp->st_info);
 332
 333                if (txtndx == w2(symp->st_shndx)
 334                        /* avoid STB_WEAK */
 335                    && (STB_LOCAL == st_bind || STB_GLOBAL == st_bind)) {
 336                        *recvalp = _w(symp->st_value);
 337                        return symp - sym0;
 338                }
 339        }
 340        fprintf(stderr, "Cannot find symbol for section %d: %s.\n",
 341                txtndx, txtname);
 342        fail_file();
 343}
 344
 345
 346/* Evade ISO C restriction: no declaration after statement in has_rel_mcount. */
 347static char const *
 348__has_rel_mcount(Elf_Shdr const *const relhdr,  /* is SHT_REL or SHT_RELA */
 349                 Elf_Shdr const *const shdr0,
 350                 char const *const shstrtab,
 351                 char const *const fname)
 352{
 353        /* .sh_info depends on .sh_type == SHT_REL[,A] */
 354        Elf_Shdr const *const txthdr = &shdr0[w(relhdr->sh_info)];
 355        char const *const txtname = &shstrtab[w(txthdr->sh_name)];
 356
 357        if (0 == strcmp("__mcount_loc", txtname)) {
 358                fprintf(stderr, "warning: __mcount_loc already exists: %s\n",
 359                        fname);
 360                succeed_file();
 361        }
 362        if (SHT_PROGBITS != w(txthdr->sh_type) ||
 363            !is_mcounted_section_name(txtname))
 364                return NULL;
 365        return txtname;
 366}
 367
 368static char const *has_rel_mcount(Elf_Shdr const *const relhdr,
 369                                  Elf_Shdr const *const shdr0,
 370                                  char const *const shstrtab,
 371                                  char const *const fname)
 372{
 373        if (SHT_REL  != w(relhdr->sh_type) && SHT_RELA != w(relhdr->sh_type))
 374                return NULL;
 375        return __has_rel_mcount(relhdr, shdr0, shstrtab, fname);
 376}
 377
 378
 379static unsigned tot_relsize(Elf_Shdr const *const shdr0,
 380                            unsigned nhdr,
 381                            const char *const shstrtab,
 382                            const char *const fname)
 383{
 384        unsigned totrelsz = 0;
 385        Elf_Shdr const *shdrp = shdr0;
 386
 387        for (; nhdr; --nhdr, ++shdrp) {
 388                if (has_rel_mcount(shdrp, shdr0, shstrtab, fname))
 389                        totrelsz += _w(shdrp->sh_size);
 390        }
 391        return totrelsz;
 392}
 393
 394
 395/* Overall supervision for Elf32 ET_REL file. */
 396static void
 397do_func(Elf_Ehdr *const ehdr, char const *const fname, unsigned const reltype)
 398{
 399        Elf_Shdr *const shdr0 = (Elf_Shdr *)(_w(ehdr->e_shoff)
 400                + (void *)ehdr);
 401        unsigned const nhdr = w2(ehdr->e_shnum);
 402        Elf_Shdr *const shstr = &shdr0[w2(ehdr->e_shstrndx)];
 403        char const *const shstrtab = (char const *)(_w(shstr->sh_offset)
 404                + (void *)ehdr);
 405
 406        Elf_Shdr const *relhdr;
 407        unsigned k;
 408
 409        /* Upper bound on space: assume all relevant relocs are for mcount. */
 410        unsigned const totrelsz = tot_relsize(shdr0, nhdr, shstrtab, fname);
 411        Elf_Rel *const mrel0 = umalloc(totrelsz);
 412        Elf_Rel *      mrelp = mrel0;
 413
 414        /* 2*sizeof(address) <= sizeof(Elf_Rel) */
 415        uint_t *const mloc0 = umalloc(totrelsz>>1);
 416        uint_t *      mlocp = mloc0;
 417
 418        unsigned rel_entsize = 0;
 419        unsigned symsec_sh_link = 0;
 420
 421        for (relhdr = shdr0, k = nhdr; k; --k, ++relhdr) {
 422                char const *const txtname = has_rel_mcount(relhdr, shdr0,
 423                        shstrtab, fname);
 424                if (txtname) {
 425                        uint_t recval = 0;
 426                        unsigned const recsym = find_secsym_ndx(
 427                                w(relhdr->sh_info), txtname, &recval,
 428                                &shdr0[symsec_sh_link = w(relhdr->sh_link)],
 429                                ehdr);
 430
 431                        rel_entsize = _w(relhdr->sh_entsize);
 432                        mlocp = sift_rel_mcount(mlocp,
 433                                (void *)mlocp - (void *)mloc0, &mrelp,
 434                                relhdr, ehdr, recsym, recval, reltype);
 435                }
 436        }
 437        if (mloc0 != mlocp) {
 438                append_func(ehdr, shstr, mloc0, mlocp, mrel0, mrelp,
 439                            rel_entsize, symsec_sh_link);
 440        }
 441        free(mrel0);
 442        free(mloc0);
 443}
 444