sysdeps/i386/dl-machine.h

   1 /* Machine-dependent ELF dynamic relocation inline functions.  i386 version.
   2    Copyright (C) 1995-2023 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 #ifndef dl_machine_h
  20 #define dl_machine_h
  21
  22 #define ELF_MACHINE_NAME "i386"
  23
  24 #include <assert.h>
  25 #include <sys/param.h>
  26 #include <sysdep.h>
  27 #include <tls.h>
  28 #include <dl-tlsdesc.h>
  29 #include <dl-static-tls.h>
  30 #include <dl-machine-rel.h>
  31
  32 /* Return nonzero iff ELF header is compatible with the running host.  */
  33 static inline int __attribute__ ((unused))
  34 elf_machine_matches_host (const Elf32_Ehdr *ehdr)
  35 {
  36   return ehdr->e_machine == EM_386;
  37 }
  38
  39
  40 /* Return the run-time load address of the shared object.  */
  41 static inline Elf32_Addr __attribute__ ((unused))
  42 elf_machine_load_address (void)
  43 {
  44   extern const Elf32_Ehdr __ehdr_start attribute_hidden;
  45   return (Elf32_Addr) &__ehdr_start;
  46 }
  47
  48 /* Return the link-time address of _DYNAMIC.  */
  49 static inline Elf32_Addr __attribute__ ((unused))
  50 elf_machine_dynamic (void)
  51 {
  52   extern Elf32_Dyn _DYNAMIC[] attribute_hidden;
  53   return (Elf32_Addr) _DYNAMIC - elf_machine_load_address ();
  54 }
  55
  56 /* Set up the loaded object described by L so its unrelocated PLT
  57    entries will jump to the on-demand fixup code in dl-runtime.c.  */
  58
  59 static inline int __attribute__ ((unused, always_inline))
  60 elf_machine_runtime_setup (struct link_map *l, struct r_scope_elem *scope[],
  61                            int lazy, int profile)
  62 {
  63   Elf32_Addr *got;
  64   extern void _dl_runtime_resolve (Elf32_Word) attribute_hidden;
  65   extern void _dl_runtime_profile (Elf32_Word) attribute_hidden;
  66   extern void _dl_runtime_resolve_shstk (Elf32_Word) attribute_hidden;
  67   extern void _dl_runtime_profile_shstk (Elf32_Word) attribute_hidden;
  68   /* Check if SHSTK is enabled by kernel.  */
  69   bool shstk_enabled
  70     = (GL(dl_x86_feature_1) & GNU_PROPERTY_X86_FEATURE_1_SHSTK) != 0;
  71
  72   if (l->l_info[DT_JMPREL] && lazy)
  73     {
  74       /* The GOT entries for functions in the PLT have not yet been filled
  75          in.  Their initial contents will arrange when called to push an
  76          offset into the .rel.plt section, push _GLOBAL_OFFSET_TABLE_[1],
  77          and then jump to _GLOBAL_OFFSET_TABLE[2].  */
  78       got = (Elf32_Addr *) D_PTR (l, l_info[DT_PLTGOT]);
  79       /* If a library is prelinked but we have to relocate anyway,
  80          we have to be able to undo the prelinking of .got.plt.
  81          The prelinker saved us here address of .plt + 0x16.  */
  82       if (got[1])
  83         {
  84           l->l_mach.plt = got[1] + l->l_addr;
  85           l->l_mach.gotplt = (Elf32_Addr) &got[3];
  86         }
  87       got[1] = (Elf32_Addr) l;  /* Identify this shared object.  */
  88
  89       /* The got[2] entry contains the address of a function which gets
  90          called to get the address of a so far unresolved function and
  91          jump to it.  The profiling extension of the dynamic linker allows
  92          to intercept the calls to collect information.  In this case we
  93          don't store the address in the GOT so that all future calls also
  94          end in this function.  */
  95 #ifdef SHARED
  96       if (__glibc_unlikely (profile))
  97         {
  98           got[2] = (shstk_enabled
  99                     ? (Elf32_Addr) &_dl_runtime_profile_shstk
 100                     : (Elf32_Addr) &_dl_runtime_profile);
 101
 102           if (GLRO(dl_profile) != NULL
 103               && _dl_name_match_p (GLRO(dl_profile), l))
 104             /* This is the object we are looking for.  Say that we really
 105                want profiling and the timers are started.  */
 106             GL(dl_profile_map) = l;
 107         }
 108       else
 109 #endif
 110         /* This function will get called to fix up the GOT entry indicated by
 111            the offset on the stack, and then jump to the resolved address.  */
 112         got[2] = (shstk_enabled
 113                   ? (Elf32_Addr) &_dl_runtime_resolve_shstk
 114                   : (Elf32_Addr) &_dl_runtime_resolve);
 115     }
 116
 117   return lazy;
 118 }
 119
 120 /* Mask identifying addresses reserved for the user program,
 121    where the dynamic linker should not map anything.  */
 122 #define ELF_MACHINE_USER_ADDRESS_MASK   0xf8000000UL
 123
 124 /* Initial entry point code for the dynamic linker.
 125    The C function `_dl_start' is the real entry point;
 126    its return value is the user program's entry point.  */
 127
 128 #define RTLD_START asm ("\n\
 129         .text\n\
 130         .align 16\n\
 131 0:      movl (%esp), %ebx\n\
 132         ret\n\
 133         .align 16\n\
 134 .globl _start\n\
 135 .globl _dl_start_user\n\
 136 _start:\n\
 137         movl %esp, %eax\n\
 138         subl $12, %esp\n\
 139         pushl %eax\n\
 140         call _dl_start\n\
 141         addl $16, %esp\n\
 142 _dl_start_user:\n\
 143         # Save the user entry point address in %edi.\n\
 144         movl %eax, %edi\n\
 145         # Point %ebx at the GOT.\n\
 146         call 0b\n\
 147         addl $_GLOBAL_OFFSET_TABLE_, %ebx\n\
 148         # Read the original argument count.\n\
 149         movl (%esp), %edx\n\
 150         # The special initializer gets called with the stack just\n\
 151         # as the application's entry point will see it; it can\n\
 152         # switch stacks if it moves these contents over.\n\
 153 " RTLD_START_SPECIAL_INIT "\n\
 154         # Load the parameters again.\n\
 155         # (eax, edx, ecx, esi) = (_dl_loaded, argc, argv, envp)\n\
 156         movl _rtld_local@GOTOFF(%ebx), %eax\n\
 157         leal 8(%esp,%edx,4), %esi\n\
 158         leal 4(%esp), %ecx\n\
 159         movl %esp, %ebp\n\
 160         # Make sure _dl_init is run with 16 byte aligned stack.\n\
 161         andl $-16, %esp\n\
 162         subl $12, %esp\n\
 163         pushl %ebp\n\
 164         # Arguments for _dl_init.\n\
 165         pushl %esi\n\
 166         pushl %ecx\n\
 167         pushl %edx\n\
 168         pushl %eax\n\
 169         # Clear %ebp, so that even constructors have terminated backchain.\n\
 170         xorl %ebp, %ebp\n\
 171         # Call the function to run the initializers.\n\
 172         call _dl_init\n\
 173         # Pass our finalizer function to the user in %edx, as per ELF ABI.\n\
 174         leal _dl_fini@GOTOFF(%ebx), %edx\n\
 175         # Restore %esp _start expects.\n\
 176         movl 16(%esp), %esp\n\
 177         # Jump to the user's entry point.\n\
 178         jmp *%edi\n\
 179         .previous\n\
 180 ");
 181
 182 #ifndef RTLD_START_SPECIAL_INIT
 183 # define RTLD_START_SPECIAL_INIT /* nothing */
 184 #endif
 185
 186 /* ELF_RTYPE_CLASS_PLT iff TYPE describes relocation of a PLT entry or
 187    TLS variable, so undefined references should not be allowed to
 188    define the value.
 189    ELF_RTYPE_CLASS_COPY iff TYPE should not be allowed to resolve to one
 190    of the main executable's symbols, as for a COPY reloc.  */
 191 # define elf_machine_type_class(type) \
 192   ((((type) == R_386_JMP_SLOT || (type) == R_386_TLS_DTPMOD32                 \
 193      || (type) == R_386_TLS_DTPOFF32 || (type) == R_386_TLS_TPOFF32           \
 194      || (type) == R_386_TLS_TPOFF || (type) == R_386_TLS_DESC)                \
 195     * ELF_RTYPE_CLASS_PLT)                                                    \
 196    | (((type) == R_386_COPY) * ELF_RTYPE_CLASS_COPY))
 197
 198 /* A reloc type used for ld.so cmdline arg lookups to reject PLT entries.  */
 199 #define ELF_MACHINE_JMP_SLOT    R_386_JMP_SLOT
 200
 201 /* We define an initialization functions.  This is called very early in
 202    _dl_sysdep_start.  */
 203 #define DL_PLATFORM_INIT dl_platform_init ()
 204
 205 static inline void __attribute__ ((unused))
 206 dl_platform_init (void)
 207 {
 208 #if IS_IN (rtld)
 209   /* _dl_x86_init_cpu_features is a wrapper for init_cpu_features which
 210      has been called early from __libc_start_main in static executable.  */
 211   _dl_x86_init_cpu_features ();
 212 #else
 213   if (GLRO(dl_platform) != NULL && *GLRO(dl_platform) == '\0')
 214     /* Avoid an empty string which would disturb us.  */
 215     GLRO(dl_platform) = NULL;
 216 #endif
 217 }
 218
 219 static inline Elf32_Addr
 220 elf_machine_fixup_plt (struct link_map *map, lookup_t t,
 221                        const ElfW(Sym) *refsym, const ElfW(Sym) *sym,
 222                        const Elf32_Rel *reloc,
 223                        Elf32_Addr *reloc_addr, Elf32_Addr value)
 224 {
 225   return *reloc_addr = value;
 226 }
 227
 228 /* Return the final value of a plt relocation.  */
 229 static inline Elf32_Addr
 230 elf_machine_plt_value (struct link_map *map, const Elf32_Rel *reloc,
 231                        Elf32_Addr value)
 232 {
 233   return value;
 234 }
 235
 236
 237 /* Names of the architecture-specific auditing callback functions.  */
 238 #define ARCH_LA_PLTENTER i86_gnu_pltenter
 239 #define ARCH_LA_PLTEXIT i86_gnu_pltexit
 240
 241 #endif /* !dl_machine_h */
 242
 243 #ifdef RESOLVE_MAP
 244
 245 /* Perform the relocation specified by RELOC and SYM (which is fully resolved).
 246    MAP is the object containing the reloc.  */
 247
 248 static inline void
 249 __attribute ((always_inline))
 250 elf_machine_rel (struct link_map *map, struct r_scope_elem *scope[],
 251                  const Elf32_Rel *reloc,
 252                  const Elf32_Sym *sym, const struct r_found_version *version,
 253                  void *const reloc_addr_arg, int skip_ifunc)
 254 {
 255   Elf32_Addr *const reloc_addr = reloc_addr_arg;
 256   const unsigned int r_type = ELF32_R_TYPE (reloc->r_info);
 257
 258 # if !defined RTLD_BOOTSTRAP
 259   if (__glibc_unlikely (r_type == R_386_RELATIVE))
 260     *reloc_addr += map->l_addr;
 261 #  ifndef RTLD_BOOTSTRAP
 262   else if (__glibc_unlikely (r_type == R_386_NONE))
 263     return;
 264 #  endif
 265   else
 266 # endif /* !RTLD_BOOTSTRAP */
 267     {
 268 # ifndef RTLD_BOOTSTRAP
 269       const Elf32_Sym *const refsym = sym;
 270 # endif
 271       struct link_map *sym_map = RESOLVE_MAP (map, scope, &sym, version,
 272                                               r_type);
 273       Elf32_Addr value = SYMBOL_ADDRESS (sym_map, sym, true);
 274
 275       if (sym != NULL
 276           && __glibc_unlikely (ELFW(ST_TYPE) (sym->st_info) == STT_GNU_IFUNC)
 277           && __glibc_likely (sym->st_shndx != SHN_UNDEF)
 278           && __glibc_likely (!skip_ifunc))
 279         {
 280 # ifndef RTLD_BOOTSTRAP
 281           if (sym_map != map
 282               && !sym_map->l_relocated)
 283             {
 284               const char *strtab
 285                 = (const char *) D_PTR (map, l_info[DT_STRTAB]);
 286               if (sym_map->l_type == lt_executable)
 287                 _dl_fatal_printf ("\
 288 %s: IFUNC symbol '%s' referenced in '%s' is defined in the executable \
 289 and creates an unsatisfiable circular dependency.\n",
 290                                   RTLD_PROGNAME, strtab + refsym->st_name,
 291                                   map->l_name);
 292               else
 293                 _dl_error_printf ("\
 294 %s: Relink `%s' with `%s' for IFUNC symbol `%s'\n",
 295                                   RTLD_PROGNAME, map->l_name,
 296                                   sym_map->l_name,
 297                                   strtab + refsym->st_name);
 298             }
 299 # endif
 300           value = ((Elf32_Addr (*) (void)) value) ();
 301         }
 302
 303       switch (r_type)
 304         {
 305 # ifndef RTLD_BOOTSTRAP
 306         case R_386_SIZE32:
 307           /* Set to symbol size plus addend.  */
 308           *reloc_addr += sym->st_size;
 309           break;
 310 # endif
 311         case R_386_GLOB_DAT:
 312         case R_386_JMP_SLOT:
 313           *reloc_addr = value;
 314           break;
 315
 316         case R_386_TLS_DTPMOD32:
 317 # ifdef RTLD_BOOTSTRAP
 318           /* During startup the dynamic linker is always the module
 319              with index 1.
 320              XXX If this relocation is necessary move before RESOLVE
 321              call.  */
 322           *reloc_addr = 1;
 323 # else
 324           /* Get the information from the link map returned by the
 325              resolv function.  */
 326           if (sym_map != NULL)
 327             *reloc_addr = sym_map->l_tls_modid;
 328 # endif
 329           break;
 330         case R_386_TLS_DTPOFF32:
 331 # ifndef RTLD_BOOTSTRAP
 332           /* During relocation all TLS symbols are defined and used.
 333              Therefore the offset is already correct.  */
 334           if (sym != NULL)
 335             *reloc_addr = sym->st_value;
 336 # endif
 337           break;
 338         case R_386_TLS_DESC:
 339           {
 340             struct tlsdesc volatile *td =
 341               (struct tlsdesc volatile *)reloc_addr;
 342
 343 # ifndef RTLD_BOOTSTRAP
 344             if (! sym)
 345               td->entry = _dl_tlsdesc_undefweak;
 346             else
 347 # endif
 348               {
 349 # ifndef RTLD_BOOTSTRAP
 350 #  ifndef SHARED
 351                 CHECK_STATIC_TLS (map, sym_map);
 352 #  else
 353                 if (!TRY_STATIC_TLS (map, sym_map))
 354                   {
 355                     td->arg = _dl_make_tlsdesc_dynamic
 356                       (sym_map, sym->st_value + (ElfW(Word))td->arg);
 357                     td->entry = _dl_tlsdesc_dynamic;
 358                   }
 359                 else
 360 #  endif
 361 # endif
 362                   {
 363                     td->arg = (void*)(sym->st_value - sym_map->l_tls_offset
 364                                       + (ElfW(Word))td->arg);
 365                     td->entry = _dl_tlsdesc_return;
 366                   }
 367               }
 368             break;
 369           }
 370         case R_386_TLS_TPOFF32:
 371           /* The offset is positive, backward from the thread pointer.  */
 372 #  ifdef RTLD_BOOTSTRAP
 373           *reloc_addr += map->l_tls_offset - sym->st_value;
 374 #  else
 375           /* We know the offset of object the symbol is contained in.
 376              It is a positive value which will be subtracted from the
 377              thread pointer.  To get the variable position in the TLS
 378              block we subtract the offset from that of the TLS block.  */
 379           if (sym != NULL)
 380             {
 381               CHECK_STATIC_TLS (map, sym_map);
 382               *reloc_addr += sym_map->l_tls_offset - sym->st_value;
 383             }
 384 # endif
 385           break;
 386         case R_386_TLS_TPOFF:
 387           /* The offset is negative, forward from the thread pointer.  */
 388 # ifdef RTLD_BOOTSTRAP
 389           *reloc_addr += sym->st_value - map->l_tls_offset;
 390 # else
 391           /* We know the offset of object the symbol is contained in.
 392              It is a negative value which will be added to the
 393              thread pointer.  */
 394           if (sym != NULL)
 395             {
 396               CHECK_STATIC_TLS (map, sym_map);
 397               *reloc_addr += sym->st_value - sym_map->l_tls_offset;
 398             }
 399 # endif
 400           break;
 401
 402 # ifndef RTLD_BOOTSTRAP
 403         case R_386_32:
 404           *reloc_addr += value;
 405           break;
 406         case R_386_PC32:
 407           *reloc_addr += (value - (Elf32_Addr) reloc_addr);
 408           break;
 409         case R_386_COPY:
 410           if (sym == NULL)
 411             /* This can happen in trace mode if an object could not be
 412                found.  */
 413             break;
 414           if (__glibc_unlikely (sym->st_size > refsym->st_size)
 415               || (__glibc_unlikely(sym->st_size < refsym->st_size)
 416                   && GLRO(dl_verbose)))
 417             {
 418               const char *strtab;
 419
 420               strtab = (const char *) D_PTR (map, l_info[DT_STRTAB]);
 421               _dl_error_printf ("\
 422 %s: Symbol `%s' has different size in shared object, consider re-linking\n",
 423                                 RTLD_PROGNAME, strtab + refsym->st_name);
 424             }
 425           memcpy (reloc_addr_arg, (void *) value,
 426                   MIN (sym->st_size, refsym->st_size));
 427           break;
 428         case R_386_IRELATIVE:
 429           value = map->l_addr + *reloc_addr;
 430           if (__glibc_likely (!skip_ifunc))
 431             value = ((Elf32_Addr (*) (void)) value) ();
 432           *reloc_addr = value;
 433           break;
 434         default:
 435           _dl_reloc_bad_type (map, r_type, 0);
 436           break;
 437 # endif /* !RTLD_BOOTSTRAP */
 438         }
 439     }
 440 }
 441
 442
 443 static inline void
 444 __attribute ((always_inline))
 445 elf_machine_rel_relative (Elf32_Addr l_addr, const Elf32_Rel *reloc,
 446                           void *const reloc_addr_arg)
 447 {
 448   Elf32_Addr *const reloc_addr = reloc_addr_arg;
 449   assert (ELF32_R_TYPE (reloc->r_info) == R_386_RELATIVE);
 450   *reloc_addr += l_addr;
 451 }
 452
 453 # ifndef RTLD_BOOTSTRAP
 454 static inline void
 455 __attribute__ ((always_inline))
 456 elf_machine_rela_relative (Elf32_Addr l_addr, const Elf32_Rela *reloc,
 457                            void *const reloc_addr_arg)
 458 {
 459   Elf32_Addr *const reloc_addr = reloc_addr_arg;
 460   *reloc_addr = l_addr + reloc->r_addend;
 461 }
 462 # endif /* !RTLD_BOOTSTRAP */
 463
 464 static inline void
 465 __attribute__ ((always_inline))
 466 elf_machine_lazy_rel (struct link_map *map, struct r_scope_elem *scope[],
 467                       Elf32_Addr l_addr, const Elf32_Rel *reloc,
 468                       int skip_ifunc)
 469 {
 470   Elf32_Addr *const reloc_addr = (void *) (l_addr + reloc->r_offset);
 471   const unsigned int r_type = ELF32_R_TYPE (reloc->r_info);
 472   /* Check for unexpected PLT reloc type.  */
 473   if (__glibc_likely (r_type == R_386_JMP_SLOT))
 474     {
 475       /* Prelink has been deprecated.  */
 476       if (__glibc_likely (map->l_mach.plt == 0))
 477         *reloc_addr += l_addr;
 478       else
 479         *reloc_addr = (map->l_mach.plt
 480                        + (((Elf32_Addr) reloc_addr) - map->l_mach.gotplt) * 4);
 481     }
 482   else if (__glibc_likely (r_type == R_386_TLS_DESC))
 483     {
 484       const Elf32_Rel *const r = reloc;
 485       /* The code below was borrowed from elf_dynamic_do_rel().  */
 486       const ElfW(Sym) *const symtab =
 487         (const void *) D_PTR (map, l_info[DT_SYMTAB]);
 488
 489       /* Always initialize TLS descriptors completely at load time, in
 490          case static TLS is allocated for it that requires locking.  */
 491 # ifdef RTLD_BOOTSTRAP
 492       /* The dynamic linker always uses versioning.  */
 493       assert (map->l_info[VERSYMIDX (DT_VERSYM)] != NULL);
 494 # else
 495       if (map->l_info[VERSYMIDX (DT_VERSYM)])
 496 # endif
 497         {
 498           const ElfW(Half) *const version =
 499             (const void *) D_PTR (map, l_info[VERSYMIDX (DT_VERSYM)]);
 500           ElfW(Half) ndx = version[ELFW(R_SYM) (r->r_info)] & 0x7fff;
 501           elf_machine_rel (map, scope, r, &symtab[ELFW(R_SYM) (r->r_info)],
 502                            &map->l_versions[ndx],
 503                            (void *) (l_addr + r->r_offset), skip_ifunc);
 504         }
 505 # ifndef RTLD_BOOTSTRAP
 506       else
 507         elf_machine_rel (map, scope, r, &symtab[ELFW(R_SYM) (r->r_info)], NULL,
 508                          (void *) (l_addr + r->r_offset), skip_ifunc);
 509 # endif
 510     }
 511   else if (__glibc_unlikely (r_type == R_386_IRELATIVE))
 512     {
 513       Elf32_Addr value = map->l_addr + *reloc_addr;
 514       if (__glibc_likely (!skip_ifunc))
 515         value = ((Elf32_Addr (*) (void)) value) ();
 516       *reloc_addr = value;
 517     }
 518   else
 519     _dl_reloc_bad_type (map, r_type, 1);
 520 }
 521
 522 #endif /* RESOLVE_MAP */