sysdeps/alpha/dl-machine.h

   1 /* Machine-dependent ELF dynamic relocation inline functions.  Alpha version.
   2    Copyright (C) 1996-2005, 2006 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4    Contributed by Richard Henderson <rth@tamu.edu>.
   5
   6    The GNU C Library is free software; you can redistribute it and/or
   7    modify it under the terms of the GNU Lesser General Public
   8    License as published by the Free Software Foundation; either
   9    version 2.1 of the 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    Lesser General Public License for more details.
  15
  16    You should have received a copy of the GNU Lesser General Public
  17    License along with the GNU C Library; if not, write to the Free
  18    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  19    02111-1307 USA.  */
  20
  21 /* This was written in the absence of an ABI -- don't expect
  22    it to remain unchanged.  */
  23
  24 #ifndef dl_machine_h
  25 #define dl_machine_h 1
  26
  27 #define ELF_MACHINE_NAME "alpha"
  28
  29 #include <string.h>
  30
  31
  32 /* Mask identifying addresses reserved for the user program,
  33    where the dynamic linker should not map anything.  */
  34 #define ELF_MACHINE_USER_ADDRESS_MASK   0x120000000UL
  35
  36 /* Translate a processor specific dynamic tag to the index in l_info array.  */
  37 #define DT_ALPHA(x) (DT_ALPHA_##x - DT_LOPROC + DT_NUM)
  38
  39 /* Return nonzero iff ELF header is compatible with the running host.  */
  40 static inline int
  41 elf_machine_matches_host (const Elf64_Ehdr *ehdr)
  42 {
  43   return ehdr->e_machine == EM_ALPHA;
  44 }
  45
  46 /* Return the link-time address of _DYNAMIC.  The multiple-got-capable
  47    linker no longer allocates the first .got entry for this.  But not to
  48    worry, no special tricks are needed.  */
  49 static inline Elf64_Addr
  50 elf_machine_dynamic (void)
  51 {
  52 #ifndef NO_AXP_MULTI_GOT_LD
  53   return (Elf64_Addr) &_DYNAMIC;
  54 #else
  55   register Elf64_Addr *gp __asm__ ("$29");
  56   return gp[-4096];
  57 #endif
  58 }
  59
  60 /* Return the run-time load address of the shared object.  */
  61
  62 static inline Elf64_Addr
  63 elf_machine_load_address (void)
  64 {
  65   /* This relies on the compiler using gp-relative addresses for static symbols.  */
  66   static void *dot = &dot;
  67   return (void *)&dot - dot;
  68 }
  69
  70 /* Set up the loaded object described by L so its unrelocated PLT
  71    entries will jump to the on-demand fixup code in dl-runtime.c.  */
  72
  73 static inline int
  74 elf_machine_runtime_setup (struct link_map *map, int lazy, int profile)
  75 {
  76   extern char _dl_runtime_resolve_new[] attribute_hidden;
  77   extern char _dl_runtime_profile_new[] attribute_hidden;
  78   extern char _dl_runtime_resolve_old[] attribute_hidden;
  79   extern char _dl_runtime_profile_old[] attribute_hidden;
  80
  81   struct pltgot {
  82     char *resolve;
  83     struct link_map *link;
  84   };
  85
  86   struct pltgot *pg;
  87   long secureplt;
  88   char *resolve;
  89
  90   if (map->l_info[DT_JMPREL] == 0 || !lazy)
  91     return lazy;
  92
  93   /* Check to see if we're using the read-only plt form.  */
  94   secureplt = map->l_info[DT_ALPHA(PLTRO)] != 0;
  95
  96   /* If the binary uses the read-only secure plt format, PG points to
  97      the .got.plt section, which is the right place for ld.so to place
  98      its hooks.  Otherwise, PG is currently pointing at the start of
  99      the plt; the hooks go at offset 16.  */
 100   pg = (struct pltgot *) D_PTR (map, l_info[DT_PLTGOT]);
 101   pg += !secureplt;
 102
 103   /* This function will be called to perform the relocation.  They're
 104      not declared as functions to convince the compiler to use gp
 105      relative relocations for them.  */
 106   if (secureplt)
 107     resolve = _dl_runtime_resolve_new;
 108   else
 109     resolve = _dl_runtime_resolve_old;
 110
 111   if (__builtin_expect (profile, 0))
 112     {
 113       if (secureplt)
 114         resolve = _dl_runtime_profile_new;
 115       else
 116         resolve = _dl_runtime_profile_old;
 117
 118       if (GLRO(dl_profile) && _dl_name_match_p (GLRO(dl_profile), map))
 119         {
 120           /* This is the object we are looking for.  Say that we really
 121              want profiling and the timers are started.  */
 122           GL(dl_profile_map) = map;
 123         }
 124     }
 125
 126   pg->resolve = resolve;
 127   pg->link = map;
 128
 129   return lazy;
 130 }
 131
 132 /* Initial entry point code for the dynamic linker.
 133    The C function `_dl_start' is the real entry point;
 134    its return value is the user program's entry point.  */
 135
 136 #define RTLD_START asm ("\
 137         .section .text                                          \n\
 138         .set at                                                 \n\
 139         .globl _start                                           \n\
 140         .ent _start                                             \n\
 141 _start:                                                         \n\
 142         .frame $31,0,$31,0                                      \n\
 143         br      $gp, 0f                                         \n\
 144 0:      ldgp    $gp, 0($gp)                                     \n\
 145         .prologue 0                                             \n\
 146         /* Pass pointer to argument block to _dl_start.  */     \n\
 147         mov     $sp, $16                                        \n\
 148         bsr     $26, _dl_start          !samegp                 \n\
 149         .end _start                                             \n\
 150         /* FALLTHRU */                                          \n\
 151         .globl _dl_start_user                                   \n\
 152         .ent _dl_start_user                                     \n\
 153 _dl_start_user:                                                 \n\
 154         .frame $31,0,$31,0                                      \n\
 155         .prologue 0                                             \n\
 156         /* Save the user entry point address in s0.  */         \n\
 157         mov     $0, $9                                          \n\
 158         /* See if we were run as a command with the executable  \n\
 159            file name as an extra leading argument.  */          \n\
 160         ldah    $1, _dl_skip_args($gp)  !gprelhigh              \n\
 161         ldl     $1, _dl_skip_args($1)   !gprellow               \n\
 162         bne     $1, $fixup_stack                                \n\
 163 $fixup_stack_ret:                                               \n\
 164         /* The special initializer gets called with the stack   \n\
 165            just as the application's entry point will see it;   \n\
 166            it can switch stacks if it moves these contents      \n\
 167            over.  */                                            \n\
 168 " RTLD_START_SPECIAL_INIT "                                     \n\
 169         /* Call _dl_init(_dl_loaded, argc, argv, envp) to run   \n\
 170            initializers.  */                                    \n\
 171         ldah    $16, _rtld_local($gp)   !gprelhigh              \n\
 172         ldq     $16, _rtld_local($16)   !gprellow               \n\
 173         ldq     $17, 0($sp)                                     \n\
 174         lda     $18, 8($sp)                                     \n\
 175         s8addq  $17, 8, $19                                     \n\
 176         addq    $19, $18, $19                                   \n\
 177         bsr     $26, _dl_init_internal  !samegp                 \n\
 178         /* Pass our finalizer function to the user in $0. */    \n\
 179         ldah    $0, _dl_fini($gp)       !gprelhigh              \n\
 180         lda     $0, _dl_fini($0)        !gprellow               \n\
 181         /* Jump to the user's entry point.  */                  \n\
 182         mov     $9, $27                                         \n\
 183         jmp     ($9)                                            \n\
 184 $fixup_stack:                                                   \n\
 185         /* Adjust the stack pointer to skip _dl_skip_args words.\n\
 186            This involves copying everything down, since the     \n\
 187            stack pointer must always be 16-byte aligned.  */    \n\
 188         ldah    $7, _dl_argv_internal($gp) !gprelhigh           \n\
 189         ldq     $2, 0($sp)                                      \n\
 190         ldq     $5, _dl_argv_internal($7) !gprellow             \n\
 191         subq    $31, $1, $6                                     \n\
 192         subq    $2, $1, $2                                      \n\
 193         s8addq  $6, $5, $5                                      \n\
 194         mov     $sp, $4                                         \n\
 195         s8addq  $1, $sp, $3                                     \n\
 196         stq     $2, 0($sp)                                      \n\
 197         stq     $5, _dl_argv_internal($7) !gprellow             \n\
 198         /* Copy down argv.  */                                  \n\
 199 0:      ldq     $5, 8($3)                                       \n\
 200         addq    $4, 8, $4                                       \n\
 201         addq    $3, 8, $3                                       \n\
 202         stq     $5, 0($4)                                       \n\
 203         bne     $5, 0b                                          \n\
 204         /* Copy down envp.  */                                  \n\
 205 1:      ldq     $5, 8($3)                                       \n\
 206         addq    $4, 8, $4                                       \n\
 207         addq    $3, 8, $3                                       \n\
 208         stq     $5, 0($4)                                       \n\
 209         bne     $5, 1b                                          \n\
 210         /* Copy down auxiliary table.  */                       \n\
 211 2:      ldq     $5, 8($3)                                       \n\
 212         ldq     $6, 16($3)                                      \n\
 213         addq    $4, 16, $4                                      \n\
 214         addq    $3, 16, $3                                      \n\
 215         stq     $5, -8($4)                                      \n\
 216         stq     $6, 0($4)                                       \n\
 217         bne     $5, 2b                                          \n\
 218         br      $fixup_stack_ret                                \n\
 219         .end _dl_start_user                                     \n\
 220         .set noat                                               \n\
 221 .previous");
 222
 223 #ifndef RTLD_START_SPECIAL_INIT
 224 #define RTLD_START_SPECIAL_INIT /* nothing */
 225 #endif
 226
 227 /* ELF_RTYPE_CLASS_PLT iff TYPE describes relocation of a PLT entry
 228    or TLS variables, so undefined references should not be allowed
 229    to define the value.
 230
 231    ELF_RTYPE_CLASS_NOCOPY iff TYPE should not be allowed to resolve
 232    to one of the main executable's symbols, as for a COPY reloc.
 233    This is unused on Alpha.  */
 234
 235 #if !defined RTLD_BOOTSTRAP || USE___THREAD
 236 # define elf_machine_type_class(type)   \
 237   (((type) == R_ALPHA_JMP_SLOT          \
 238     || (type) == R_ALPHA_DTPMOD64       \
 239     || (type) == R_ALPHA_DTPREL64       \
 240     || (type) == R_ALPHA_TPREL64) * ELF_RTYPE_CLASS_PLT)
 241 #else
 242 # define elf_machine_type_class(type)   \
 243   (((type) == R_ALPHA_JMP_SLOT) * ELF_RTYPE_CLASS_PLT)
 244 #endif
 245
 246 /* A reloc type used for ld.so cmdline arg lookups to reject PLT entries.  */
 247 #define ELF_MACHINE_JMP_SLOT     R_ALPHA_JMP_SLOT
 248
 249 /* The alpha never uses Elf64_Rel relocations.  */
 250 #define ELF_MACHINE_NO_REL 1
 251
 252 /* We define an initialization functions.  This is called very early in
 253  *    _dl_sysdep_start.  */
 254 #define DL_PLATFORM_INIT dl_platform_init ()
 255
 256 static inline void __attribute__ ((unused))
 257 dl_platform_init (void)
 258 {
 259         if (GLRO(dl_platform) != NULL && *GLRO(dl_platform) == '\0')
 260         /* Avoid an empty string which would disturb us.  */
 261                 GLRO(dl_platform) = NULL;
 262 }
 263
 264 /* Fix up the instructions of a PLT entry to invoke the function
 265    rather than the dynamic linker.  */
 266 static inline Elf64_Addr
 267 elf_machine_fixup_plt (struct link_map *map, lookup_t t,
 268                        const Elf64_Rela *reloc,
 269                        Elf64_Addr *got_addr, Elf64_Addr value)
 270 {
 271   const Elf64_Rela *rela_plt;
 272   Elf64_Word *plte;
 273   long int edisp;
 274
 275   /* Store the value we are going to load.  */
 276   *got_addr = value;
 277
 278   /* If this binary uses the read-only secure plt format, we're done.  */
 279   if (map->l_info[DT_ALPHA(PLTRO)])
 280     return value;
 281
 282   /* Otherwise we have to modify the plt entry in place to do the branch.  */
 283
 284   /* Recover the PLT entry address by calculating reloc's index into the
 285      .rela.plt, and finding that entry in the .plt.  */
 286   rela_plt = (const Elf64_Rela *) D_PTR (map, l_info[DT_JMPREL]);
 287   plte = (Elf64_Word *) (D_PTR (map, l_info[DT_PLTGOT]) + 32);
 288   plte += 3 * (reloc - rela_plt);
 289
 290   /* Find the displacement from the plt entry to the function.  */
 291   edisp = (long int) (value - (Elf64_Addr)&plte[3]) / 4;
 292
 293   if (edisp >= -0x100000 && edisp < 0x100000)
 294     {
 295       /* If we are in range, use br to perfect branch prediction and
 296          elide the dependency on the address load.  This case happens,
 297          e.g., when a shared library call is resolved to the same library.  */
 298
 299       int hi, lo;
 300       hi = value - (Elf64_Addr)&plte[0];
 301       lo = (short int) hi;
 302       hi = (hi - lo) >> 16;
 303
 304       /* Emit "lda $27,lo($27)" */
 305       plte[1] = 0x237b0000 | (lo & 0xffff);
 306
 307       /* Emit "br $31,function" */
 308       plte[2] = 0xc3e00000 | (edisp & 0x1fffff);
 309
 310       /* Think about thread-safety -- the previous instructions must be
 311          committed to memory before the first is overwritten.  */
 312       __asm__ __volatile__("wmb" : : : "memory");
 313
 314       /* Emit "ldah $27,hi($27)" */
 315       plte[0] = 0x277b0000 | (hi & 0xffff);
 316     }
 317   else
 318     {
 319       /* Don't bother with the hint since we already know the hint is
 320          wrong.  Eliding it prevents the wrong page from getting pulled
 321          into the cache.  */
 322
 323       int hi, lo;
 324       hi = (Elf64_Addr)got_addr - (Elf64_Addr)&plte[0];
 325       lo = (short)hi;
 326       hi = (hi - lo) >> 16;
 327
 328       /* Emit "ldq $27,lo($27)" */
 329       plte[1] = 0xa77b0000 | (lo & 0xffff);
 330
 331       /* Emit "jmp $31,($27)" */
 332       plte[2] = 0x6bfb0000;
 333
 334       /* Think about thread-safety -- the previous instructions must be
 335          committed to memory before the first is overwritten.  */
 336       __asm__ __volatile__("wmb" : : : "memory");
 337
 338       /* Emit "ldah $27,hi($27)" */
 339       plte[0] = 0x277b0000 | (hi & 0xffff);
 340     }
 341
 342   /* At this point, if we've been doing runtime resolution, Icache is dirty.
 343      This will be taken care of in _dl_runtime_resolve.  If instead we are
 344      doing this as part of non-lazy startup relocation, that bit of code
 345      hasn't made it into Icache yet, so there's nothing to clean up.  */
 346
 347   return value;
 348 }
 349
 350 /* Return the final value of a plt relocation.  */
 351 static inline Elf64_Addr
 352 elf_machine_plt_value (struct link_map *map, const Elf64_Rela *reloc,
 353                        Elf64_Addr value)
 354 {
 355   return value + reloc->r_addend;
 356 }
 357
 358 /* Names of the architecture-specific auditing callback functions.  */
 359 #define ARCH_LA_PLTENTER        alpha_gnu_pltenter
 360 #define ARCH_LA_PLTEXIT         alpha_gnu_pltexit
 361
 362 #endif /* !dl_machine_h */
 363
 364 #ifdef RESOLVE_MAP
 365
 366 /* Perform the relocation specified by RELOC and SYM (which is fully resolved).
 367    MAP is the object containing the reloc.  */
 368 auto inline void
 369 __attribute__ ((always_inline))
 370 elf_machine_rela (struct link_map *map,
 371                   const Elf64_Rela *reloc,
 372                   const Elf64_Sym *sym,
 373                   const struct r_found_version *version,
 374                   void *const reloc_addr_arg)
 375 {
 376   Elf64_Addr *const reloc_addr = reloc_addr_arg;
 377   unsigned long int const r_type = ELF64_R_TYPE (reloc->r_info);
 378
 379 #if !defined RTLD_BOOTSTRAP && !defined HAVE_Z_COMBRELOC && !defined SHARED
 380   /* This is defined in rtld.c, but nowhere in the static libc.a; make the
 381      reference weak so static programs can still link.  This declaration
 382      cannot be done when compiling rtld.c (i.e.  #ifdef RTLD_BOOTSTRAP)
 383      because rtld.c contains the common defn for _dl_rtld_map, which is
 384      incompatible with a weak decl in the same file.  */
 385   weak_extern (_dl_rtld_map);
 386 #endif
 387
 388   /* We cannot use a switch here because we cannot locate the switch
 389      jump table until we've self-relocated.  */
 390
 391 #if !defined RTLD_BOOTSTRAP || !defined HAVE_Z_COMBRELOC
 392   if (__builtin_expect (r_type == R_ALPHA_RELATIVE, 0))
 393     {
 394 # if !defined RTLD_BOOTSTRAP && !defined HAVE_Z_COMBRELOC
 395       /* Already done in dynamic linker.  */
 396       if (map != &GL(dl_rtld_map))
 397 # endif
 398         {
 399           /* XXX Make some timings.  Maybe it's preferable to test for
 400              unaligned access and only do it the complex way if necessary.  */
 401           Elf64_Addr reloc_addr_val;
 402
 403           /* Load value without causing unaligned trap. */
 404           memcpy (&reloc_addr_val, reloc_addr_arg, 8);
 405           reloc_addr_val += map->l_addr;
 406
 407           /* Store value without causing unaligned trap. */
 408           memcpy (reloc_addr_arg, &reloc_addr_val, 8);
 409         }
 410     }
 411   else
 412 #endif
 413     if (__builtin_expect (r_type == R_ALPHA_NONE, 0))
 414       return;
 415   else
 416     {
 417       struct link_map *sym_map = RESOLVE_MAP (&sym, version, r_type);
 418       Elf64_Addr sym_value;
 419       Elf64_Addr sym_raw_value;
 420
 421       sym_raw_value = sym_value = reloc->r_addend;
 422       if (sym_map)
 423         {
 424           sym_raw_value += sym->st_value;
 425           sym_value = sym_raw_value + sym_map->l_addr;
 426         }
 427
 428       if (r_type == R_ALPHA_GLOB_DAT)
 429         *reloc_addr = sym_value;
 430 #ifdef RESOLVE_CONFLICT_FIND_MAP
 431       /* In .gnu.conflict section, R_ALPHA_JMP_SLOT relocations have
 432          R_ALPHA_JMP_SLOT in lower 8 bits and the remaining 24 bits
 433          are .rela.plt index.  */
 434       else if ((r_type & 0xff) == R_ALPHA_JMP_SLOT)
 435         {
 436           /* elf_machine_fixup_plt needs the map reloc_addr points into,
 437              while in _dl_resolve_conflicts map is _dl_loaded.  */
 438           RESOLVE_CONFLICT_FIND_MAP (map, reloc_addr);
 439           reloc = ((const Elf64_Rela *) D_PTR (map, l_info[DT_JMPREL]))
 440                   + (r_type >> 8);
 441           elf_machine_fixup_plt (map, 0, reloc, reloc_addr, sym_value);
 442         }
 443 #else
 444       else if (r_type == R_ALPHA_JMP_SLOT)
 445         elf_machine_fixup_plt (map, 0, reloc, reloc_addr, sym_value);
 446 #endif
 447 #ifndef RTLD_BOOTSTRAP
 448       else if (r_type == R_ALPHA_REFQUAD)
 449         {
 450           /* Store value without causing unaligned trap.  */
 451           memcpy (reloc_addr_arg, &sym_value, 8);
 452         }
 453 #endif
 454 #if !defined RTLD_BOOTSTRAP || USE___THREAD
 455       else if (r_type == R_ALPHA_DTPMOD64)
 456         {
 457 # ifdef RTLD_BOOTSTRAP
 458           /* During startup the dynamic linker is always index 1.  */
 459           *reloc_addr = 1;
 460 # else
 461           /* Get the information from the link map returned by the
 462              resolv function.  */
 463           if (sym_map != NULL)
 464             *reloc_addr = sym_map->l_tls_modid;
 465 # endif
 466         }
 467       else if (r_type == R_ALPHA_DTPREL64)
 468         {
 469 # ifndef RTLD_BOOTSTRAP
 470           /* During relocation all TLS symbols are defined and used.
 471              Therefore the offset is already correct.  */
 472           *reloc_addr = sym_raw_value;
 473 # endif
 474         }
 475       else if (r_type == R_ALPHA_TPREL64)
 476         {
 477 # ifdef RTLD_BOOTSTRAP
 478           *reloc_addr = sym_raw_value + map->l_tls_offset;
 479 # else
 480           if (sym_map)
 481             {
 482               CHECK_STATIC_TLS (map, sym_map);
 483               *reloc_addr = sym_raw_value + sym_map->l_tls_offset;
 484             }
 485 # endif
 486         }
 487 #endif
 488       else
 489         _dl_reloc_bad_type (map, r_type, 0);
 490     }
 491 }
 492
 493 /* Let do-rel.h know that on Alpha if l_addr is 0, all RELATIVE relocs
 494    can be skipped.  */
 495 #define ELF_MACHINE_REL_RELATIVE 1
 496
 497 auto inline void
 498 __attribute__ ((always_inline))
 499 elf_machine_rela_relative (Elf64_Addr l_addr, const Elf64_Rela *reloc,
 500                            void *const reloc_addr_arg)
 501 {
 502   /* XXX Make some timings.  Maybe it's preferable to test for
 503      unaligned access and only do it the complex way if necessary.  */
 504   Elf64_Addr reloc_addr_val;
 505
 506   /* Load value without causing unaligned trap. */
 507   memcpy (&reloc_addr_val, reloc_addr_arg, 8);
 508   reloc_addr_val += l_addr;
 509
 510   /* Store value without causing unaligned trap. */
 511   memcpy (reloc_addr_arg, &reloc_addr_val, 8);
 512 }
 513
 514 auto inline void
 515 __attribute__ ((always_inline))
 516 elf_machine_lazy_rel (struct link_map *map,
 517                       Elf64_Addr l_addr, const Elf64_Rela *reloc)
 518 {
 519   Elf64_Addr * const reloc_addr = (void *)(l_addr + reloc->r_offset);
 520   unsigned long int const r_type = ELF64_R_TYPE (reloc->r_info);
 521
 522   if (r_type == R_ALPHA_JMP_SLOT)
 523     {
 524       /* Perform a RELATIVE reloc on the .got entry that transfers
 525          to the .plt.  */
 526       *reloc_addr += l_addr;
 527     }
 528   else if (r_type == R_ALPHA_NONE)
 529     return;
 530   else
 531     _dl_reloc_bad_type (map, r_type, 1);
 532 }
 533
 534 #endif /* RESOLVE_MAP */