sysdeps/mips/dl-machine.h

   1 /* Machine-dependent ELF dynamic relocation inline functions.  mips version.
   2 Copyright (C) 1996 Free Software Foundation, Inc.
   3 This file is part of the GNU C Library.
   4 Contributed by Kazumoto Kojima <kkojima@info.kanagawa-u.ac.jp>.
   5
   6 The GNU C Library is free software; you can redistribute it and/or
   7 modify it under the terms of the GNU Library General Public License as
   8 published by the Free Software Foundation; either version 2 of the
   9 License, or (at your option) any later version.
  10
  11 The GNU C Library is distributed in the hope that it will be useful,
  12 but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14 Library General Public License for more details.
  15
  16 You should have received a copy of the GNU Library General Public
  17 License along with the GNU C Library; see the file COPYING.LIB.  If
  18 not, write to the Free Software Foundation, Inc., 675 Mass Ave,
  19 Cambridge, MA 02139, USA.  */
  20
  21 #define ELF_MACHINE_NAME "MIPS"
  22
  23 #include <assert.h>
  24 #include <string.h>
  25 #include <link.h>
  26 #include <sys/types.h>
  27 #include <sys/mman.h>
  28 #include <unistd.h>
  29
  30 /* DT_MIPS macro ranslate a processor specific dynamic tag to the index
  31    in l_info array.  */
  32 #define DT_MIPS(x) (DT_MIPS_##x - DT_LOPROC + DT_NUM)
  33
  34 #if 1
  35 /* XXX If FLAGS has the MAP_ALIGN bit, we need 64k alignement. */
  36 #ifndef MAP_ALIGN
  37 #define MAP_ALIGN 0x1000
  38 #endif
  39 #define ELF_MACHINE_ALIGN_MASK(flags) ((flags & MAP_ALIGN) ? 0xffff : 0)
  40 #endif
  41
  42 /* If there is a DT_MIPS_RLD_MAP entry in the dynamic section, fill it in
  43    with the run-time address of the r_debug structure  */
  44 #define ELF_MACHINE_SET_DEBUG(l,r) \
  45 do { if ((l)->l_info[DT_MIPS (RLD_MAP)]) \
  46        *(ElfW(Addr) *)((l)->l_info[DT_MIPS (RLD_MAP)]->d_un.d_ptr) = \
  47        (ElfW(Addr)) (r); \
  48    } while (0)
  49
  50 /* Return nonzero iff E_MACHINE is compatible with the running host.  */
  51 static inline int
  52 elf_machine_matches_host (ElfW(Half) e_machine)
  53 {
  54   switch (e_machine)
  55     {
  56     case EM_MIPS:
  57     case EM_MIPS_RS4_BE:
  58       return 1;
  59     default:
  60       return 0;
  61     }
  62 }
  63
  64 static inline ElfW(Addr) *
  65 elf_mips_got_from_gpreg (ElfW(Addr) gpreg)
  66 {
  67   /* FIXME: the offset of gp from GOT may be system-dependent. */
  68   return (ElfW(Addr) *) (gpreg - 0x7ff0);
  69 }
  70 /* Return the run-time address of the _GLOBAL_OFFSET_TABLE_.
  71    Must be inlined in a function which uses global data.  */
  72 static inline ElfW(Addr) *
  73 elf_machine_got (void)
  74 {
  75   register ElfW(Addr) gp asm ("$28");
  76   return (ElfW(Addr) *) (gp - 0x7ff0);
  77 }
  78
  79
  80 /* Return the run-time load address of the shared object.  */
  81 static inline ElfW(Addr)
  82 elf_machine_load_address (void)
  83 {
  84   ElfW(Addr) addr;
  85   asm ("        .set noreorder\n"
  86        "        la %0, here\n"
  87        "        bltzal $0, here\n"
  88        "        nop\n"
  89        "here:   subu %0, $31, %0\n"
  90        "        .set reorder\n"
  91        : "=r" (addr));
  92   return addr;
  93 }
  94
  95 /* The MSB of got[1] of a gnu object is set to identify gnu objects. */
  96 #define ELF_MIPS_GNU_GOT1_MASK 0x80000000
  97
  98 /* Relocate GOT. */
  99 static void
 100 elf_machine_got_rel (struct link_map *map)
 101 {
 102   ElfW(Addr) *got;
 103   ElfW(Sym) *sym;
 104   int i, n;
 105   struct link_map **scope;
 106   const char *strtab
 107     = ((void *) map->l_addr + map->l_info[DT_STRTAB]->d_un.d_ptr);
 108
 109   ElfW(Addr) resolve (const ElfW(Sym) *sym)
 110     {
 111       const ElfW(Sym) *ref = sym;
 112       ElfW(Addr) sym_loadaddr;
 113       sym_loadaddr = _dl_lookup_symbol (strtab + sym->st_name, &ref, scope,
 114                                         map->l_name, 0, 1);
 115       return (ref)? sym_loadaddr + ref->st_value: 0;
 116     }
 117
 118   got = (ElfW(Addr) *) ((void *) map->l_addr
 119                         + map->l_info[DT_PLTGOT]->d_un.d_ptr);
 120
 121   /* got[0] is reserved. got[1] is also reserved for the dynamic object
 122      generated by gnu ld. Skip these reserved entries from relocation.  */
 123   i = (got[1] & ELF_MIPS_GNU_GOT1_MASK)? 2: 1;
 124   n = map->l_info[DT_MIPS (LOCAL_GOTNO)]->d_un.d_val;
 125   /* Add the run-time display to all local got entries. */
 126   while (i < n)
 127     got[i++] += map->l_addr;
 128
 129   /* Set scope.  */
 130   scope = _dl_object_relocation_scope (map);
 131
 132   /* Handle global got entries. */
 133   got += n;
 134   sym = (ElfW(Sym) *) ((void *) map->l_addr
 135                        + map->l_info[DT_SYMTAB]->d_un.d_ptr);
 136   sym += map->l_info[DT_MIPS (GOTSYM)]->d_un.d_val;
 137   i = (map->l_info[DT_MIPS (SYMTABNO)]->d_un.d_val
 138        - map->l_info[DT_MIPS (GOTSYM)]->d_un.d_val);
 139
 140   while (i--)
 141     {
 142       if (sym->st_shndx == SHN_UNDEF)
 143         {
 144           if (ELFW(ST_TYPE) (sym->st_info) == STT_FUNC)
 145             {
 146               if (sym->st_value /* && maybe_stub (sym->st_value) */)
 147                 *got = sym->st_value + map->l_addr;
 148               else
 149                 *got = resolve (sym);
 150             }
 151           else /* if (*got == 0 || *got == QS) */
 152             *got = resolve (sym);
 153         }
 154       else if (sym->st_shndx == SHN_COMMON)
 155         *got = resolve (sym);
 156       else if (ELFW(ST_TYPE) (sym->st_info) == STT_FUNC
 157                && *got != sym->st_value
 158                /* && maybe_stub (*got) */)
 159         *got += map->l_addr;
 160       else if (ELFW(ST_TYPE) (sym->st_info) == STT_SECTION
 161                && ELFW(ST_BIND) (sym->st_info) == STB_GLOBAL)
 162         {
 163           if (sym->st_other == 0 && sym->st_shndx == SHN_ABS)
 164             *got = sym->st_value + map->l_addr; /* only for _gp_disp  */
 165           /* else SGI stuff ignored */
 166         }
 167       else
 168         *got = resolve (sym);
 169
 170       got++;
 171       sym++;
 172     }
 173
 174   *_dl_global_scope_end = NULL;
 175
 176   return;
 177 }
 178
 179 /* The MIPS never uses Elfxx_Rela relocations.  */
 180 #define ELF_MACHINE_NO_RELA 1
 181
 182 /* Set up the loaded object described by L so its stub function
 183    will jump to the on-demand fixup code in dl-runtime.c.  */
 184
 185 static inline void
 186 elf_machine_runtime_setup (struct link_map *l, int lazy)
 187 {
 188   ElfW(Addr) *got;
 189   extern void _dl_runtime_resolve (ElfW(Word));
 190
 191   if (lazy)
 192     {
 193       /* The GOT entries for functions have not yet been filled in.
 194          Their initial contents will arrange when called to put an
 195          offset into the .dynsym section in t8, the return address
 196          in t7 and then jump to _GLOBAL_OFFSET_TABLE[0].  */
 197       got = (ElfW(Addr) *) ((void *) l->l_addr
 198                             + l->l_info[DT_PLTGOT]->d_un.d_ptr);
 199
 200       /* This function will get called to fix up the GOT entry indicated by
 201          the register t8, and then jump to the resolved address.  */
 202       got[0] = (ElfW(Addr)) &_dl_runtime_resolve;
 203
 204       /* Store l to _GLOBAL_OFFSET_TABLE[1] for gnu object. The MSB
 205          of got[1] of a gnu object is set to identify gnu objects.
 206          Where we can store l for non gnu objects? XXX  */
 207       if ((got[1] & ELF_MIPS_GNU_GOT1_MASK) != 0)
 208         got[1] = (ElfW(Addr)) ((unsigned) l | ELF_MIPS_GNU_GOT1_MASK);
 209       else
 210         ; /* Do nothing. */
 211     }
 212
 213   /* Relocate global offset table.  */
 214   elf_machine_got_rel (l);
 215 }
 216
 217 /* Get link_map for this object.  */
 218 static inline struct link_map *
 219 elf_machine_runtime_link_map (ElfW(Addr) gpreg)
 220 {
 221   ElfW(Addr) *got = elf_mips_got_from_gpreg (gpreg);
 222   ElfW(Word) g1;
 223
 224   g1 = ((ElfW(Word) *) got)[1];
 225
 226   /* got[1] is reserved to keep its link map address for the shared
 227      object generated by gnu linker. If not so, we must search GOT
 228      in object list slowly. XXX  */
 229   if ((g1 & ELF_MIPS_GNU_GOT1_MASK) != 0)
 230     return (struct link_map *) (g1 & ~ELF_MIPS_GNU_GOT1_MASK);
 231   else
 232     {
 233       struct link_map *l = _dl_loaded;
 234       while (l)
 235         {
 236           if (got == (ElfW(Addr) *) ((void *) l->l_addr
 237                                      + l->l_info[DT_PLTGOT]->d_un.d_ptr))
 238             return l;
 239           l = l->l_next;
 240         }
 241     }
 242   _dl_signal_error (0, NULL, "cannot find runtime link map");
 243 }
 244
 245 /* Mips has no PLT but define elf_machine_relplt to be elf_machine_rel. */
 246 #define elf_machine_relplt elf_machine_rel
 247
 248 /* Define mips specific runtime resolver. The function __dl_runtime_resolve
 249    is called from assembler function _dl_runtime_resolve which converts
 250    special argument registers t7 ($15) and t8 ($24):
 251      t7  address to return to the caller of the function
 252      t8  index for this function symbol in .dynsym
 253    to usual c arguments.  */
 254
 255 #define ELF_MACHINE_RUNTIME_TRAMPOLINE \
 256 /* This is called from assembly stubs below which the compiler can't see.  */ \
 257 static ElfW(Addr) __dl_runtime_resolve (ElfW(Word), ElfW(Word), ElfW(Addr)) \
 258                   __attribute__ ((unused)); \
 259 \
 260 static ElfW(Addr) \
 261 __dl_runtime_resolve (ElfW(Word) sym_index,\
 262                       ElfW(Word) return_address,\
 263                       ElfW(Addr) old_gpreg)\
 264 {\
 265   struct link_map *l = elf_machine_runtime_link_map (old_gpreg);\
 266   const ElfW(Sym) *const symtab\
 267     = (const ElfW(Sym) *) (l->l_addr + l->l_info[DT_SYMTAB]->d_un.d_ptr);\
 268   const char *strtab\
 269     = (void *) (l->l_addr + l->l_info[DT_STRTAB]->d_un.d_ptr);\
 270   const ElfW(Addr) *got\
 271     = (const ElfW(Addr) *) (l->l_addr + l->l_info[DT_PLTGOT]->d_un.d_ptr);\
 272   const ElfW(Word) local_gotno\
 273     = (const ElfW(Word)) l->l_info[DT_MIPS (LOCAL_GOTNO)]->d_un.d_val;\
 274   const ElfW(Word) gotsym\
 275     = (const ElfW(Word)) l->l_info[DT_MIPS (GOTSYM)]->d_un.d_val;\
 276   const ElfW(Sym) *definer;\
 277   ElfW(Addr) loadbase;\
 278   ElfW(Addr) funcaddr;\
 279   struct link_map **scope;\
 280 \
 281   /* Look up the symbol's run-time value.  */\
 282   scope = _dl_object_relocation_scope (l);\
 283   definer = &symtab[sym_index];\
 284 \
 285   loadbase = _dl_lookup_symbol (strtab + definer->st_name, &definer,\
 286                                 scope, l->l_name, 0, 1);\
 287 \
 288   *_dl_global_scope_end = NULL;\
 289 \
 290   /* Apply the relocation with that value.  */\
 291   funcaddr = loadbase + definer->st_value;\
 292   *(got + local_gotno + sym_index - gotsym) = funcaddr;\
 293 \
 294   return funcaddr;\
 295 }\
 296 \
 297 asm ("\n\
 298         .text\n\
 299         .align  2\n\
 300         .globl  _dl_runtime_resolve\n\
 301         .type   _dl_runtime_resolve,@function\n\
 302         .ent    _dl_runtime_resolve\n\
 303 _dl_runtime_resolve:\n\
 304         .set noreorder\n\
 305         # Save old GP to $3.\n\
 306         move    $3,$28\n\
 307         # Modify t9 ($25) so as to point .cpload instruction.\n\
 308         addu    $25,8\n\
 309         # Compute GP.\n\
 310         .cpload $25\n\
 311         .set reorder\n\
 312         # Save arguments and sp value in stack.\n\
 313         subu    $29, 40\n\
 314         .cprestore 32\n\
 315         sw      $15, 36($29)\n\
 316         sw      $4, 12($29)\n\
 317         sw      $5, 16($29)\n\
 318         sw      $6, 20($29)\n\
 319         sw      $7, 24($29)\n\
 320         sw      $16, 28($29)\n\
 321         move    $16, $29\n\
 322         move    $4, $24\n\
 323         move    $5, $15\n\
 324         move    $6, $3\n\
 325         jal     __dl_runtime_resolve\n\
 326         move    $29, $16\n\
 327         lw      $31, 36($29)\n\
 328         lw      $4, 12($29)\n\
 329         lw      $5, 16($29)\n\
 330         lw      $6, 20($29)\n\
 331         lw      $7, 24($29)\n\
 332         lw      $16, 28($29)\n\
 333         addu    $29, 40\n\
 334         move    $25, $2\n\
 335         jr      $25\n\
 336         .end    _dl_runtime_resolve\n\
 337 ");
 338
 339 /* Mask identifying addresses reserved for the user program,
 340    where the dynamic linker should not map anything.  */
 341 #define ELF_MACHINE_USER_ADDRESS_MASK   0x00000000UL
 342
 343 /* Initial entry point code for the dynamic linker.
 344    The C function `_dl_start' is the real entry point;
 345    its return value is the user program's entry point.  */
 346
 347 #define RTLD_START asm ("\
 348         .text\n\
 349         .globl _start\n\
 350         .globl _dl_start_user\n\
 351         .ent _start\n\
 352 _start:\n\
 353         .set noreorder\n\
 354         bltzal $0, 0f\n\
 355         nop\n\
 356 0:      .cpload $31\n\
 357         .set reorder\n\
 358         # i386 ABI book says that the first entry of GOT holds\n\
 359         # the address of the dynamic structure. Though MIPS ABI\n\
 360         # doesn't say nothing about this, I emulate this here.\n\
 361         la $4, _DYNAMIC\n\
 362         sw $4, -0x7ff0($28)\n\
 363         move $4, $29\n\
 364         jal _dl_start\n\
 365         # Get the value of label '_dl_start_user' in t9 ($25).\n\
 366         la $25, _dl_start_user\n\
 367 _dl_start_user:\n\
 368         .set noreorder\n\
 369         .cpload $25\n\
 370         .set reorder\n\
 371         move $16, $28\n\
 372         # Save the user entry point address in saved register.\n\
 373         move $17, $2\n\
 374         # See if we were run as a command with the executable file\n\
 375         # name as an extra leading argument.\n\
 376         lw $2, _dl_skip_args\n\
 377         beq $2, $0, 1f\n\
 378         # Load the original argument count.\n\
 379         lw $4, 0($29)\n\
 380         # Subtract _dl_skip_args from it.\n\
 381         subu $4, $2\n\
 382         # Adjust the stack pointer to skip _dl_skip_args words.\n\
 383         sll $2,2\n\
 384         addu $29, $2\n\
 385         # Save back the modified argument count.\n\
 386         sw $4, 0($29)\n\
 387         # Get _dl_default_scope[2] as argument in _dl_init_next call below.\n\
 388 1:      la $2, _dl_default_scope\n\
 389         lw $4, 8($2)\n\
 390         # Call _dl_init_next to return the address of an initializer\n\
 391         # function to run.\n\
 392         jal _dl_init_next\n\
 393         move $28, $16\n\
 394         # Check for zero return,  when out of initializers.\n\
 395         beq $2, $0, 2f\n\
 396         # Call the shared object initializer function.\n\
 397         move $25, $2\n\
 398         lw $4, 0($29)\n\
 399         lw $5, 4($29)\n\
 400         lw $6, 8($29)\n\
 401         lw $7, 12($29)\n\
 402         jalr $25\n\
 403         move $28, $16\n\
 404         # Loop to call _dl_init_next for the next initializer.\n\
 405         b 1b\n\
 406         # Pass our finalizer function to the user in ra.\n\
 407 2:      la $31, _dl_fini\n\
 408         # Jump to the user entry point.\n\
 409         move $25, $17\n\
 410         lw $4, 0($29)\n\
 411         lw $5, 4($29)\n\
 412         lw $6, 8($29)\n\
 413         lw $7, 12($29)\n\
 414         jr $25\n\
 415         .end _start\n\
 416 ");
 417
 418 #ifdef RESOLVE
 419
 420 /* Perform the relocation specified by RELOC and SYM (which is fully resolved).
 421    MAP is the object containing the reloc.  */
 422
 423 static inline void
 424 elf_machine_rel (struct link_map *map,
 425                  const ElfW(Rel) *reloc, const ElfW(Sym) *sym)
 426 {
 427   ElfW(Addr) *const reloc_addr = (void *) (map->l_addr + reloc->r_offset);
 428   ElfW(Addr) loadbase, undo;
 429
 430   switch (ELFW(R_TYPE) (reloc->r_info))
 431     {
 432     case R_MIPS_REL32:
 433       if (ELFW(ST_BIND) (sym->st_info) == STB_LOCAL
 434           && (ELFW(ST_TYPE) (sym->st_info) == STT_SECTION
 435               || ELFW(ST_TYPE) (sym->st_info) == STT_NOTYPE))
 436         *reloc_addr += map->l_addr;
 437       else
 438         {
 439 #ifndef RTLD_BOOTSTRAP
 440           /* This is defined in rtld.c, but nowhere in the static libc.a;
 441              make the reference weak so static programs can still link.  This
 442              declaration cannot be done when compiling rtld.c (i.e.  #ifdef
 443              RTLD_BOOTSTRAP) because rtld.c contains the common defn for
 444              _dl_rtld_map, which is incompatible with a weak decl in the same
 445              file.  */
 446           weak_extern (_dl_rtld_map);
 447           if (map == &_dl_rtld_map)
 448             /* Undo the relocation done here during bootstrapping.  Now we will
 449                relocate it anew, possibly using a binding found in the user
 450                program or a loaded library rather than the dynamic linker's
 451                built-in definitions used while loading those libraries.  */
 452             undo = map->l_addr + sym->st_value;
 453           else
 454 #endif
 455             undo = 0;
 456           loadbase = RESOLVE (&sym, (ElfW(Addr)) reloc_addr, 0);
 457           *reloc_addr += (sym ? (loadbase + sym->st_value) : 0) - undo;
 458         }
 459       break;
 460     case R_MIPS_NONE:           /* Alright, Wilbur.  */
 461       break;
 462     default:
 463       assert (! "unexpected dynamic reloc type");
 464       break;
 465     }
 466 }
 467
 468 static inline void
 469 elf_machine_lazy_rel (struct link_map *map, const ElfW(Rel) *reloc)
 470 {
 471   /* Do nothing.  */
 472 }
 473
 474 #endif /* RESOLVE */