sysdeps/arm/dl-machine.h

   1 /* Machine-dependent ELF dynamic relocation inline functions.  ARM version.
   2    Copyright (C) 1995-2024 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 "ARM"
  23
  24 #include <assert.h>
  25 #include <sys/param.h>
  26 #include <tls.h>
  27 #include <dl-tlsdesc.h>
  28 #include <dl-irel.h>
  29 #include <dl-static-tls.h>
  30 #include <dl-machine-rel.h>
  31
  32 #ifndef CLEAR_CACHE
  33 # error CLEAR_CACHE definition required to handle TEXTREL
  34 #endif
  35
  36 /* Return nonzero iff ELF header is compatible with the running host.  */
  37 static inline int __attribute__ ((unused))
  38 elf_machine_matches_host (const Elf32_Ehdr *ehdr)
  39 {
  40   return ehdr->e_machine == EM_ARM;
  41 }
  42
  43 /* Return the run-time load address of the shared object.  */
  44 static inline ElfW(Addr) __attribute__ ((unused))
  45 elf_machine_load_address (void)
  46 {
  47   extern const ElfW(Ehdr) __ehdr_start attribute_hidden;
  48   return (ElfW(Addr)) &__ehdr_start;
  49 }
  50
  51 /* Return the link-time address of _DYNAMIC.  */
  52 static inline ElfW(Addr) __attribute__ ((unused))
  53 elf_machine_dynamic (void)
  54 {
  55   extern ElfW(Dyn) _DYNAMIC[] attribute_hidden;
  56   return (ElfW(Addr)) _DYNAMIC - elf_machine_load_address ();
  57 }
  58
  59 /* Set up the loaded object described by L so its unrelocated PLT
  60    entries will jump to the on-demand fixup code in dl-runtime.c.  */
  61
  62 static inline int __attribute__ ((unused))
  63 elf_machine_runtime_setup (struct link_map *l, struct r_scope_elem *scope[],
  64                            int lazy, int profile)
  65 {
  66   Elf32_Addr *got;
  67   extern void _dl_runtime_resolve (Elf32_Word);
  68
  69   if (l->l_info[DT_JMPREL] && lazy)
  70     {
  71       /* patb: this is different than i386 */
  72       /* The GOT entries for functions in the PLT have not yet been filled
  73          in.  Their initial contents will arrange when called to push an
  74          index into the .got section, load ip with &_GLOBAL_OFFSET_TABLE_[3],
  75          and then jump to _GLOBAL_OFFSET_TABLE[2].  */
  76       got = (Elf32_Addr *) D_PTR (l, l_info[DT_PLTGOT]);
  77       /* If a library is prelinked but we have to relocate anyway,
  78          we have to be able to undo the prelinking of .got.plt.
  79          The prelinker saved us here address of .plt.  */
  80       if (got[1])
  81         l->l_mach.plt = got[1] + l->l_addr;
  82       got[1] = (Elf32_Addr) l;  /* Identify this shared object.  */
  83
  84       /* The got[2] entry contains the address of a function which gets
  85          called to get the address of a so far unresolved function and
  86          jump to it.  The profiling extension of the dynamic linker allows
  87          to intercept the calls to collect information.  In this case we
  88          don't store the address in the GOT so that all future calls also
  89          end in this function.  */
  90 #ifdef SHARED
  91       extern void _dl_runtime_profile (Elf32_Word);
  92       if (profile)
  93         {
  94           got[2] = (Elf32_Addr) &_dl_runtime_profile;
  95
  96           if (GLRO(dl_profile) != NULL
  97               && _dl_name_match_p (GLRO(dl_profile), l))
  98             /* Say that we really want profiling and the timers are
  99                started.  */
 100             GL(dl_profile_map) = l;
 101         }
 102       else
 103 #endif
 104         /* This function will get called to fix up the GOT entry indicated by
 105            the offset on the stack, and then jump to the resolved address.  */
 106         got[2] = (Elf32_Addr) &_dl_runtime_resolve;
 107     }
 108
 109   return lazy;
 110 }
 111
 112 #if defined(ARCH_HAS_BX)
 113 #define BX(x) "bx\t" #x
 114 #else
 115 #define BX(x) "mov\tpc, " #x
 116 #endif
 117
 118 /* Mask identifying addresses reserved for the user program,
 119    where the dynamic linker should not map anything.  */
 120 #define ELF_MACHINE_USER_ADDRESS_MASK   0xf8000000UL
 121
 122 /* Initial entry point code for the dynamic linker.
 123    The C function `_dl_start' is the real entry point;
 124    its return value is the user program's entry point.  */
 125
 126 #define RTLD_START asm ("\
 127 .text\n\
 128 .globl _start\n\
 129 .type _start, %function\n\
 130 .globl _dl_start_user\n\
 131 .type _dl_start_user, %function\n\
 132 _start:\n\
 133         @ we are PIC code, so get global offset table\n\
 134         ldr     sl, .L_GET_GOT\n\
 135         @ at start time, all the args are on the stack\n\
 136         mov     r0, sp\n\
 137         bl      _dl_start\n\
 138         @ returns user entry point in r0\n\
 139 _dl_start_user:\n\
 140         adr     r6, .L_GET_GOT\n\
 141         add     sl, sl, r6\n\
 142         ldr     r4, [sl, r4]\n\
 143         @ save the entry point in another register\n\
 144         mov     r6, r0\n\
 145         @ get the original arg count\n\
 146         ldr     r1, [sp]\n\
 147         @ get the argv address\n\
 148         add     r2, sp, #4\n\
 149         @ compute envp\n\
 150         add     r3, r2, r1, lsl #2\n\
 151         add     r3, r3, #4\n\
 152         @ now we call _dl_init\n\
 153         ldr     r0, .L_LOADED\n\
 154         ldr     r0, [sl, r0]\n\
 155         @ call _dl_init\n\
 156         bl      _dl_init(PLT)\n\
 157         @ load the finalizer function\n\
 158         ldr     r0, .L_FINI_PROC\n\
 159         add     r0, sl, r0\n\
 160         @ jump to the user_s entry point\n\
 161         " BX(r6) "\n\
 162 \n\
 163 .L_GET_GOT:\n\
 164         .word   _GLOBAL_OFFSET_TABLE_ - .L_GET_GOT\n\
 165 .L_FINI_PROC:\n\
 166         .word   _dl_fini(GOTOFF)\n\
 167 .L_ARGV:\n\
 168         .word   __GI__dl_argv(GOTOFF)\n\
 169 .L_LOADED:\n\
 170         .word   _rtld_local(GOTOFF)\n\
 171 .previous\n\
 172 ");
 173
 174 /* ELF_RTYPE_CLASS_PLT iff TYPE describes relocation of a PLT entry or
 175    TLS variable, so undefined references should not be allowed to
 176    define the value.
 177    ELF_RTYPE_CLASS_COPY iff TYPE should not be allowed to resolve to one
 178    of the main executable's symbols, as for a COPY reloc.  */
 179 #ifndef RTLD_BOOTSTRAP
 180 # define elf_machine_type_class(type) \
 181   ((((type) == R_ARM_JUMP_SLOT || (type) == R_ARM_TLS_DTPMOD32          \
 182      || (type) == R_ARM_TLS_DTPOFF32 || (type) == R_ARM_TLS_TPOFF32     \
 183      || (type) == R_ARM_TLS_DESC)                                       \
 184     * ELF_RTYPE_CLASS_PLT)                                              \
 185    | (((type) == R_ARM_COPY) * ELF_RTYPE_CLASS_COPY))
 186 #else
 187 #define elf_machine_type_class(type) \
 188   ((((type) == R_ARM_JUMP_SLOT) * ELF_RTYPE_CLASS_PLT)  \
 189    | (((type) == R_ARM_COPY) * ELF_RTYPE_CLASS_COPY))
 190 #endif
 191
 192 /* A reloc type used for ld.so cmdline arg lookups to reject PLT entries.  */
 193 #define ELF_MACHINE_JMP_SLOT    R_ARM_JUMP_SLOT
 194
 195 /* We define an initialization functions.  This is called very early in
 196    _dl_sysdep_start.  */
 197 #define DL_PLATFORM_INIT dl_platform_init ()
 198
 199 static inline void __attribute__ ((unused))
 200 dl_platform_init (void)
 201 {
 202   if (GLRO(dl_platform) != NULL && *GLRO(dl_platform) == '\0')
 203     /* Avoid an empty string which would disturb us.  */
 204     GLRO(dl_platform) = NULL;
 205 }
 206
 207 static inline Elf32_Addr
 208 elf_machine_fixup_plt (struct link_map *map, lookup_t t,
 209                        const ElfW(Sym) *refsym, const ElfW(Sym) *sym,
 210                        const Elf32_Rel *reloc,
 211                        Elf32_Addr *reloc_addr, Elf32_Addr value)
 212 {
 213   return *reloc_addr = value;
 214 }
 215
 216 /* Return the final value of a plt relocation.  */
 217 static inline Elf32_Addr
 218 elf_machine_plt_value (struct link_map *map, const Elf32_Rel *reloc,
 219                        Elf32_Addr value)
 220 {
 221   return value;
 222 }
 223
 224 #endif /* !dl_machine_h */
 225
 226
 227 /* Names of the architecture-specific auditing callback functions.  */
 228 #define ARCH_LA_PLTENTER arm_gnu_pltenter
 229 #define ARCH_LA_PLTEXIT arm_gnu_pltexit
 230
 231 #ifdef RESOLVE_MAP
 232 /* Set NEW_VALUE based on V, and return true iff it overflows 24 bits.  */
 233 static inline bool set_new_value (Elf32_Addr *new_value, Elf32_Addr v,
 234                                   Elf32_Addr *const reloc_addr,
 235                                   Elf32_Sword addend)
 236 {
 237   *new_value = v + addend - (Elf32_Addr) reloc_addr;
 238   Elf32_Addr topbits = *new_value & 0xfe000000;
 239   return topbits != 0xfe000000 && topbits != 0x00000000;
 240 }
 241
 242 /* Handle a PC24 reloc, including the out-of-range case.  */
 243 static void
 244 relocate_pc24 (struct link_map *map, Elf32_Addr value,
 245                Elf32_Addr *const reloc_addr, Elf32_Sword addend)
 246 {
 247   Elf32_Addr new_value;
 248
 249   if (set_new_value (&new_value, value, reloc_addr, addend))
 250     {
 251       /* The PC-relative address doesn't fit in 24 bits!  */
 252
 253       static void *fix_page;
 254       static size_t fix_offset;
 255       if (fix_page == NULL)
 256         {
 257           void *new_page = __mmap (NULL, GLRO(dl_pagesize),
 258                                    PROT_READ | PROT_WRITE | PROT_EXEC,
 259                                    MAP_PRIVATE | MAP_ANON, -1, 0);
 260           if (new_page == MAP_FAILED)
 261             _dl_signal_error (0, map->l_name, NULL,
 262                               "could not map page for fixup");
 263           fix_page = new_page;
 264           assert (fix_offset == 0);
 265         }
 266
 267       Elf32_Word *fix_address = fix_page + fix_offset;
 268       fix_address[0] = 0xe51ff004;      /* ldr pc, [pc, #-4] */
 269       fix_address[1] = value;
 270
 271       fix_offset += sizeof fix_address[0] * 2;
 272       if (fix_offset >= GLRO(dl_pagesize))
 273         {
 274           fix_page = NULL;
 275           fix_offset = 0;
 276         }
 277
 278       if (set_new_value (&new_value, (Elf32_Addr) fix_address, reloc_addr,
 279                          addend))
 280         _dl_signal_error (0, map->l_name, NULL,
 281                           "R_ARM_PC24 relocation out of range");
 282     }
 283
 284   *reloc_addr = (*reloc_addr & 0xff000000) | ((new_value >> 2) & 0x00ffffff);
 285 }
 286
 287 /* Perform the relocation specified by RELOC and SYM (which is fully resolved).
 288    MAP is the object containing the reloc.  */
 289
 290 static inline void
 291 __attribute__ ((always_inline))
 292 elf_machine_rel (struct link_map *map, struct r_scope_elem *scope[],
 293                  const Elf32_Rel *reloc, const Elf32_Sym *sym,
 294                  const struct r_found_version *version,
 295                  void *const reloc_addr_arg, int skip_ifunc)
 296 {
 297   Elf32_Addr *const reloc_addr = reloc_addr_arg;
 298   const unsigned int r_type = ELF32_R_TYPE (reloc->r_info);
 299
 300 #if !defined RTLD_BOOTSTRAP
 301   if (__builtin_expect (r_type == R_ARM_RELATIVE, 0))
 302     *reloc_addr += map->l_addr;
 303 # ifndef RTLD_BOOTSTRAP
 304   else if (__builtin_expect (r_type == R_ARM_NONE, 0))
 305     return;
 306 # endif
 307   else
 308 #endif
 309     {
 310       const Elf32_Sym *const refsym = sym;
 311       struct link_map *sym_map = RESOLVE_MAP (map, scope, &sym, version,
 312                                               r_type);
 313       Elf32_Addr value = SYMBOL_ADDRESS (sym_map, sym, true);
 314
 315       if (sym != NULL
 316           && __builtin_expect (ELFW(ST_TYPE) (sym->st_info) == STT_GNU_IFUNC, 0)
 317           && __builtin_expect (sym->st_shndx != SHN_UNDEF, 1)
 318           && __builtin_expect (!skip_ifunc, 1))
 319         value = elf_ifunc_invoke (value);
 320
 321       switch (r_type)
 322         {
 323         case R_ARM_COPY:
 324           if (sym == NULL)
 325             /* This can happen in trace mode if an object could not be
 326                found.  */
 327             break;
 328           if (sym->st_size > refsym->st_size
 329               || (GLRO(dl_verbose) && sym->st_size < refsym->st_size))
 330             {
 331               const char *strtab;
 332
 333               strtab = (const void *) D_PTR (map, l_info[DT_STRTAB]);
 334               _dl_error_printf ("\
 335 %s: Symbol `%s' has different size in shared object, consider re-linking\n",
 336                                 RTLD_PROGNAME, strtab + refsym->st_name);
 337             }
 338           memcpy (reloc_addr_arg, (void *) value,
 339                   MIN (sym->st_size, refsym->st_size));
 340           break;
 341         case R_ARM_GLOB_DAT:
 342         case R_ARM_JUMP_SLOT:
 343 # ifdef RTLD_BOOTSTRAP
 344           /* Fix weak undefined references.  */
 345           if (sym != NULL && sym->st_value == 0)
 346             *reloc_addr = 0;
 347           else
 348 # endif
 349             *reloc_addr = value;
 350           break;
 351         case R_ARM_ABS32:
 352           {
 353             struct unaligned
 354               {
 355                 Elf32_Addr x;
 356               } __attribute__ ((packed, may_alias));
 357 # ifndef RTLD_BOOTSTRAP
 358            /* This is defined in rtld.c, but nowhere in the static
 359               libc.a; make the reference weak so static programs can
 360               still link.  This declaration cannot be done when
 361               compiling rtld.c (i.e.  #ifdef RTLD_BOOTSTRAP) because
 362               rtld.c contains the common defn for _dl_rtld_map, which
 363               is incompatible with a weak decl in the same file.  */
 364 #  ifndef SHARED
 365             weak_extern (_dl_rtld_map);
 366 #  endif
 367             if (map == &GL(dl_rtld_map))
 368               /* Undo the relocation done here during bootstrapping.
 369                  Now we will relocate it anew, possibly using a
 370                  binding found in the user program or a loaded library
 371                  rather than the dynamic linker's built-in definitions
 372                  used while loading those libraries.  */
 373               value -= SYMBOL_ADDRESS (map, refsym, true);
 374 # endif
 375             /* Support relocations on mis-aligned offsets.  */
 376             ((struct unaligned *) reloc_addr)->x += value;
 377             break;
 378           }
 379         case R_ARM_TLS_DESC:
 380           {
 381             struct tlsdesc *td = (struct tlsdesc *)reloc_addr;
 382
 383 # ifndef RTLD_BOOTSTRAP
 384             if (! sym)
 385               td->entry = _dl_tlsdesc_undefweak;
 386             else
 387 # endif
 388               {
 389                 if (ELF32_R_SYM (reloc->r_info) == STN_UNDEF)
 390                   value = td->argument.value;
 391                 else
 392                   value = sym->st_value;
 393
 394 # ifndef RTLD_BOOTSTRAP
 395 #  ifndef SHARED
 396                 CHECK_STATIC_TLS (map, sym_map);
 397 #  else
 398                 if (!TRY_STATIC_TLS (map, sym_map))
 399                   {
 400                     td->argument.pointer
 401                       = _dl_make_tlsdesc_dynamic (sym_map, value);
 402                     td->entry = _dl_tlsdesc_dynamic;
 403                   }
 404                 else
 405 #  endif
 406 # endif
 407                 {
 408                   td->argument.value = value + sym_map->l_tls_offset;
 409                   td->entry = _dl_tlsdesc_return;
 410                 }
 411               }
 412             }
 413             break;
 414         case R_ARM_PC24:
 415           relocate_pc24 (map, value, reloc_addr,
 416                          /* Sign-extend the 24-bit addend in the
 417                             instruction (which counts instructions), and
 418                             then shift it up two so as to count bytes.  */
 419                          (((Elf32_Sword) *reloc_addr << 8) >> 8) << 2);
 420           break;
 421 #if !defined RTLD_BOOTSTRAP
 422         case R_ARM_TLS_DTPMOD32:
 423           /* Get the information from the link map returned by the
 424              resolv function.  */
 425           if (sym_map != NULL)
 426             *reloc_addr = sym_map->l_tls_modid;
 427           break;
 428
 429         case R_ARM_TLS_DTPOFF32:
 430           if (sym != NULL)
 431             *reloc_addr += sym->st_value;
 432           break;
 433
 434         case R_ARM_TLS_TPOFF32:
 435           if (sym != NULL)
 436             {
 437               CHECK_STATIC_TLS (map, sym_map);
 438               *reloc_addr += sym->st_value + sym_map->l_tls_offset;
 439             }
 440           break;
 441         case R_ARM_IRELATIVE:
 442           value = map->l_addr + *reloc_addr;
 443           if (__glibc_likely (!skip_ifunc))
 444             value = ((Elf32_Addr (*) (int)) value) (GLRO(dl_hwcap));
 445           *reloc_addr = value;
 446           break;
 447 #endif
 448         default:
 449           _dl_reloc_bad_type (map, r_type, 0);
 450           break;
 451         }
 452     }
 453 }
 454
 455
 456 static inline void
 457 __attribute__ ((always_inline))
 458 elf_machine_rel_relative (Elf32_Addr l_addr, const Elf32_Rel *reloc,
 459                           void *const reloc_addr_arg)
 460 {
 461   Elf32_Addr *const reloc_addr = reloc_addr_arg;
 462   *reloc_addr += l_addr;
 463 }
 464
 465
 466 static inline void
 467 __attribute__ ((always_inline))
 468 elf_machine_lazy_rel (struct link_map *map, struct r_scope_elem *scope[],
 469                       Elf32_Addr l_addr, const Elf32_Rel *reloc,
 470                       int skip_ifunc)
 471 {
 472   Elf32_Addr *const reloc_addr = (void *) (l_addr + reloc->r_offset);
 473   const unsigned int r_type = ELF32_R_TYPE (reloc->r_info);
 474   /* Check for unexpected PLT reloc type.  */
 475   if (__builtin_expect (r_type == R_ARM_JUMP_SLOT, 1))
 476     {
 477       if (__builtin_expect (map->l_mach.plt, 0) == 0)
 478         *reloc_addr += l_addr;
 479       else
 480         *reloc_addr = map->l_mach.plt;
 481     }
 482   else if (__builtin_expect (r_type == R_ARM_TLS_DESC, 1))
 483     {
 484       const Elf_Symndx symndx = ELFW (R_SYM) (reloc->r_info);
 485       const ElfW (Sym) *symtab = (const void *)D_PTR (map, l_info[DT_SYMTAB]);
 486       const ElfW (Sym) *sym = &symtab[symndx];
 487       const struct r_found_version *version = NULL;
 488
 489       if (map->l_info[VERSYMIDX (DT_VERSYM)] != NULL)
 490         {
 491           const ElfW (Half) *vernum =
 492             (const void *)D_PTR (map, l_info[VERSYMIDX (DT_VERSYM)]);
 493           version = &map->l_versions[vernum[symndx] & 0x7fff];
 494         }
 495
 496       /* Always initialize TLS descriptors completely, because lazy
 497          initialization requires synchronization at every TLS access.  */
 498       elf_machine_rel (map, scope, reloc, sym, version, reloc_addr, skip_ifunc);
 499     }
 500   else
 501     _dl_reloc_bad_type (map, r_type, 1);
 502 }
 503
 504 #endif /* RESOLVE_MAP */