sysdeps/alpha/dl-machine.h

   1 /* Machine-dependent ELF dynamic relocation inline functions.  Alpha version.
   2    Copyright (C) 1996-2022 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 /* This was written in the absence of an ABI -- don't expect
  20    it to remain unchanged.  */
  21
  22 #ifndef dl_machine_h
  23 #define dl_machine_h 1
  24
  25 #define ELF_MACHINE_NAME "alpha"
  26
  27 #include <string.h>
  28 #include <dl-static-tls.h>
  29 #include <dl-machine-rel.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, struct r_scope_elem *scope[],
  75                            int lazy, int profile)
  76 {
  77   extern char _dl_runtime_resolve_new[] attribute_hidden;
  78   extern char _dl_runtime_profile_new[] attribute_hidden;
  79   extern char _dl_runtime_resolve_old[] attribute_hidden;
  80   extern char _dl_runtime_profile_old[] attribute_hidden;
  81
  82   struct pltgot {
  83     char *resolve;
  84     struct link_map *link;
  85   };
  86
  87   struct pltgot *pg;
  88   long secureplt;
  89   char *resolve;
  90
  91   if (map->l_info[DT_JMPREL] == 0 || !lazy)
  92     return lazy;
  93
  94   /* Check to see if we're using the read-only plt form.  */
  95   secureplt = map->l_info[DT_ALPHA(PLTRO)] != 0;
  96
  97   /* If the binary uses the read-only secure plt format, PG points to
  98      the .got.plt section, which is the right place for ld.so to place
  99      its hooks.  Otherwise, PG is currently pointing at the start of
 100      the plt; the hooks go at offset 16.  */
 101   pg = (struct pltgot *) D_PTR (map, l_info[DT_PLTGOT]);
 102   pg += !secureplt;
 103
 104   /* This function will be called to perform the relocation.  They're
 105      not declared as functions to convince the compiler to use gp
 106      relative relocations for them.  */
 107   if (secureplt)
 108     resolve = _dl_runtime_resolve_new;
 109   else
 110     resolve = _dl_runtime_resolve_old;
 111
 112   if (__builtin_expect (profile, 0))
 113     {
 114       if (secureplt)
 115         resolve = _dl_runtime_profile_new;
 116       else
 117         resolve = _dl_runtime_profile_old;
 118
 119       if (GLRO(dl_profile) && _dl_name_match_p (GLRO(dl_profile), map))
 120         {
 121           /* This is the object we are looking for.  Say that we really
 122              want profiling and the timers are started.  */
 123           GL(dl_profile_map) = map;
 124         }
 125     }
 126
 127   pg->resolve = resolve;
 128   pg->link = map;
 129
 130   return lazy;
 131 }
 132
 133 /* Initial entry point code for the dynamic linker.
 134    The C function `_dl_start' is the real entry point;
 135    its return value is the user program's entry point.  */
 136
 137 #define RTLD_START asm ("\
 138         .section .text                                          \n\
 139         .set at                                                 \n\
 140         .globl _start                                           \n\
 141         .ent _start                                             \n\
 142 _start:                                                         \n\
 143         .frame $31,0,$31,0                                      \n\
 144         br      $gp, 0f                                         \n\
 145 0:      ldgp    $gp, 0($gp)                                     \n\
 146         .prologue 0                                             \n\
 147         /* Pass pointer to argument block to _dl_start.  */     \n\
 148         mov     $sp, $16                                        \n\
 149         bsr     $26, _dl_start          !samegp                 \n\
 150         .end _start                                             \n\
 151         /* FALLTHRU */                                          \n\
 152         .globl _dl_start_user                                   \n\
 153         .ent _dl_start_user                                     \n\
 154 _dl_start_user:                                                 \n\
 155         .frame $31,0,$31,0                                      \n\
 156         .prologue 0                                             \n\
 157         /* Save the user entry point address in s0.  */         \n\
 158         mov     $0, $9                                          \n\
 159         /* The special initializer gets called with the stack   \n\
 160            just as the application's entry point will see it;   \n\
 161            it can switch stacks if it moves these contents      \n\
 162            over.  */                                            \n\
 163 " RTLD_START_SPECIAL_INIT "                                     \n\
 164         /* Call _dl_init(_dl_loaded, argc, argv, envp) to run   \n\
 165            initializers.  */                                    \n\
 166         ldah    $16, _rtld_local($gp)   !gprelhigh              \n\
 167         ldq     $16, _rtld_local($16)   !gprellow               \n\
 168         ldq     $17, 0($sp)                                     \n\
 169         lda     $18, 8($sp)                                     \n\
 170         s8addq  $17, 8, $19                                     \n\
 171         addq    $19, $18, $19                                   \n\
 172         bsr     $26, _dl_init           !samegp                 \n\
 173         /* Pass our finalizer function to the user in $0. */    \n\
 174         ldah    $0, _dl_fini($gp)       !gprelhigh              \n\
 175         lda     $0, _dl_fini($0)        !gprellow               \n\
 176         /* Jump to the user's entry point.  */                  \n\
 177         mov     $9, $27                                         \n\
 178         jmp     ($9)                                            \n\
 179         .end _dl_start_user                                     \n\
 180         .set noat                                               \n\
 181 .previous");
 182
 183 #ifndef RTLD_START_SPECIAL_INIT
 184 #define RTLD_START_SPECIAL_INIT /* nothing */
 185 #endif
 186
 187 /* ELF_RTYPE_CLASS_PLT iff TYPE describes relocation of a PLT entry
 188    or TLS variables, so undefined references should not be allowed
 189    to define the value.
 190
 191    ELF_RTYPE_CLASS_COPY iff TYPE should not be allowed to resolve
 192    to one of the main executable's symbols, as for a COPY reloc.
 193    This is unused on Alpha.  */
 194
 195 # define elf_machine_type_class(type)   \
 196   (((type) == R_ALPHA_JMP_SLOT          \
 197     || (type) == R_ALPHA_DTPMOD64       \
 198     || (type) == R_ALPHA_DTPREL64       \
 199     || (type) == R_ALPHA_TPREL64) * ELF_RTYPE_CLASS_PLT)
 200
 201 /* A reloc type used for ld.so cmdline arg lookups to reject PLT entries.  */
 202 #define ELF_MACHINE_JMP_SLOT     R_ALPHA_JMP_SLOT
 203
 204 /* We define an initialization functions.  This is called very early in
 205  *    _dl_sysdep_start.  */
 206 #define DL_PLATFORM_INIT dl_platform_init ()
 207
 208 static inline void __attribute__ ((unused))
 209 dl_platform_init (void)
 210 {
 211         if (GLRO(dl_platform) != NULL && *GLRO(dl_platform) == '\0')
 212         /* Avoid an empty string which would disturb us.  */
 213                 GLRO(dl_platform) = NULL;
 214 }
 215
 216 /* Fix up the instructions of a PLT entry to invoke the function
 217    rather than the dynamic linker.  */
 218 static inline Elf64_Addr
 219 elf_machine_fixup_plt (struct link_map *map, lookup_t t,
 220                        const ElfW(Sym) *refsym, const ElfW(Sym) *sym,
 221                        const Elf64_Rela *reloc,
 222                        Elf64_Addr *got_addr, Elf64_Addr value)
 223 {
 224   const Elf64_Rela *rela_plt;
 225   Elf64_Word *plte;
 226   long int edisp;
 227
 228   /* Store the value we are going to load.  */
 229   *got_addr = value;
 230
 231   /* If this binary uses the read-only secure plt format, we're done.  */
 232   if (map->l_info[DT_ALPHA(PLTRO)])
 233     return value;
 234
 235   /* Otherwise we have to modify the plt entry in place to do the branch.  */
 236
 237   /* Recover the PLT entry address by calculating reloc's index into the
 238      .rela.plt, and finding that entry in the .plt.  */
 239   rela_plt = (const Elf64_Rela *) D_PTR (map, l_info[DT_JMPREL]);
 240   plte = (Elf64_Word *) (D_PTR (map, l_info[DT_PLTGOT]) + 32);
 241   plte += 3 * (reloc - rela_plt);
 242
 243   /* Find the displacement from the plt entry to the function.  */
 244   edisp = (long int) (value - (Elf64_Addr)&plte[3]) / 4;
 245
 246   if (edisp >= -0x100000 && edisp < 0x100000)
 247     {
 248       /* If we are in range, use br to perfect branch prediction and
 249          elide the dependency on the address load.  This case happens,
 250          e.g., when a shared library call is resolved to the same library.  */
 251
 252       int hi, lo;
 253       hi = value - (Elf64_Addr)&plte[0];
 254       lo = (short int) hi;
 255       hi = (hi - lo) >> 16;
 256
 257       /* Emit "lda $27,lo($27)" */
 258       plte[1] = 0x237b0000 | (lo & 0xffff);
 259
 260       /* Emit "br $31,function" */
 261       plte[2] = 0xc3e00000 | (edisp & 0x1fffff);
 262
 263       /* Think about thread-safety -- the previous instructions must be
 264          committed to memory before the first is overwritten.  */
 265       __asm__ __volatile__("wmb" : : : "memory");
 266
 267       /* Emit "ldah $27,hi($27)" */
 268       plte[0] = 0x277b0000 | (hi & 0xffff);
 269     }
 270   else
 271     {
 272       /* Don't bother with the hint since we already know the hint is
 273          wrong.  Eliding it prevents the wrong page from getting pulled
 274          into the cache.  */
 275
 276       int hi, lo;
 277       hi = (Elf64_Addr)got_addr - (Elf64_Addr)&plte[0];
 278       lo = (short)hi;
 279       hi = (hi - lo) >> 16;
 280
 281       /* Emit "ldq $27,lo($27)" */
 282       plte[1] = 0xa77b0000 | (lo & 0xffff);
 283
 284       /* Emit "jmp $31,($27)" */
 285       plte[2] = 0x6bfb0000;
 286
 287       /* Think about thread-safety -- the previous instructions must be
 288          committed to memory before the first is overwritten.  */
 289       __asm__ __volatile__("wmb" : : : "memory");
 290
 291       /* Emit "ldah $27,hi($27)" */
 292       plte[0] = 0x277b0000 | (hi & 0xffff);
 293     }
 294
 295   /* At this point, if we've been doing runtime resolution, Icache is dirty.
 296      This will be taken care of in _dl_runtime_resolve.  If instead we are
 297      doing this as part of non-lazy startup relocation, that bit of code
 298      hasn't made it into Icache yet, so there's nothing to clean up.  */
 299
 300   return value;
 301 }
 302
 303 /* Return the final value of a plt relocation.  */
 304 static inline Elf64_Addr
 305 elf_machine_plt_value (struct link_map *map, const Elf64_Rela *reloc,
 306                        Elf64_Addr value)
 307 {
 308   return value + reloc->r_addend;
 309 }
 310
 311 /* Names of the architecture-specific auditing callback functions.  */
 312 #define ARCH_LA_PLTENTER        alpha_gnu_pltenter
 313 #define ARCH_LA_PLTEXIT         alpha_gnu_pltexit
 314
 315 #endif /* !dl_machine_h */
 316
 317 #ifdef RESOLVE_MAP
 318
 319 /* Perform the relocation specified by RELOC and SYM (which is fully resolved).
 320    MAP is the object containing the reloc.  */
 321 static inline void
 322 __attribute__ ((always_inline))
 323 elf_machine_rela (struct link_map *map, struct r_scope_elem *scope[],
 324                   const Elf64_Rela *reloc,
 325                   const Elf64_Sym *sym,
 326                   const struct r_found_version *version,
 327                   void *const reloc_addr_arg,
 328                   int skip_ifunc)
 329 {
 330   Elf64_Addr *const reloc_addr = reloc_addr_arg;
 331   unsigned long int const r_type = ELF64_R_TYPE (reloc->r_info);
 332
 333   /* We cannot use a switch here because we cannot locate the switch
 334      jump table until we've self-relocated.  */
 335
 336 #if !defined RTLD_BOOTSTRAP
 337   if (__builtin_expect (r_type == R_ALPHA_RELATIVE, 0))
 338     {
 339         /* XXX Make some timings.  Maybe it's preferable to test for
 340            unaligned access and only do it the complex way if necessary.  */
 341         Elf64_Addr reloc_addr_val;
 342
 343         /* Load value without causing unaligned trap. */
 344         memcpy (&reloc_addr_val, reloc_addr_arg, 8);
 345         reloc_addr_val += map->l_addr;
 346
 347         /* Store value without causing unaligned trap. */
 348         memcpy (reloc_addr_arg, &reloc_addr_val, 8);
 349     }
 350   else
 351 #endif
 352     if (__builtin_expect (r_type == R_ALPHA_NONE, 0))
 353       return;
 354   else
 355     {
 356       struct link_map *sym_map = RESOLVE_MAP (map, scope, &sym, version,
 357                                               r_type);
 358       Elf64_Addr sym_value;
 359       Elf64_Addr sym_raw_value;
 360
 361       sym_raw_value = sym_value = reloc->r_addend;
 362       if (sym_map)
 363         {
 364           sym_raw_value += sym->st_value;
 365           sym_value += SYMBOL_ADDRESS (sym_map, sym, true);
 366         }
 367
 368       if (r_type == R_ALPHA_GLOB_DAT)
 369         *reloc_addr = sym_value;
 370       else if (r_type == R_ALPHA_JMP_SLOT)
 371         elf_machine_fixup_plt (map, 0, 0, 0, reloc, reloc_addr, sym_value);
 372 #ifndef RTLD_BOOTSTRAP
 373       else if (r_type == R_ALPHA_REFQUAD)
 374         {
 375           /* Store value without causing unaligned trap.  */
 376           memcpy (reloc_addr_arg, &sym_value, 8);
 377         }
 378 #endif
 379       else if (r_type == R_ALPHA_DTPMOD64)
 380         {
 381 # ifdef RTLD_BOOTSTRAP
 382           /* During startup the dynamic linker is always index 1.  */
 383           *reloc_addr = 1;
 384 # else
 385           /* Get the information from the link map returned by the
 386              resolv function.  */
 387           if (sym_map != NULL)
 388             *reloc_addr = sym_map->l_tls_modid;
 389 # endif
 390         }
 391       else if (r_type == R_ALPHA_DTPREL64)
 392         {
 393 # ifndef RTLD_BOOTSTRAP
 394           /* During relocation all TLS symbols are defined and used.
 395              Therefore the offset is already correct.  */
 396           *reloc_addr = sym_raw_value;
 397 # endif
 398         }
 399       else if (r_type == R_ALPHA_TPREL64)
 400         {
 401 # ifdef RTLD_BOOTSTRAP
 402           *reloc_addr = sym_raw_value + map->l_tls_offset;
 403 # else
 404           if (sym_map)
 405             {
 406               CHECK_STATIC_TLS (map, sym_map);
 407               *reloc_addr = sym_raw_value + sym_map->l_tls_offset;
 408             }
 409 # endif
 410         }
 411       else
 412         _dl_reloc_bad_type (map, r_type, 0);
 413     }
 414 }
 415
 416 /* Let do-rel.h know that on Alpha if l_addr is 0, all RELATIVE relocs
 417    can be skipped.  */
 418 #define ELF_MACHINE_REL_RELATIVE 1
 419
 420 static inline void
 421 __attribute__ ((always_inline))
 422 elf_machine_rela_relative (Elf64_Addr l_addr, const Elf64_Rela *reloc,
 423                            void *const reloc_addr_arg)
 424 {
 425   /* XXX Make some timings.  Maybe it's preferable to test for
 426      unaligned access and only do it the complex way if necessary.  */
 427   Elf64_Addr reloc_addr_val;
 428
 429   /* Load value without causing unaligned trap. */
 430   memcpy (&reloc_addr_val, reloc_addr_arg, 8);
 431   reloc_addr_val += l_addr;
 432
 433   /* Store value without causing unaligned trap. */
 434   memcpy (reloc_addr_arg, &reloc_addr_val, 8);
 435 }
 436
 437 static inline void
 438 __attribute__ ((always_inline))
 439 elf_machine_lazy_rel (struct link_map *map, struct r_scope_elem *scope[],
 440                       Elf64_Addr l_addr, const Elf64_Rela *reloc,
 441                       int skip_ifunc)
 442 {
 443   Elf64_Addr * const reloc_addr = (void *)(l_addr + reloc->r_offset);
 444   unsigned long int const r_type = ELF64_R_TYPE (reloc->r_info);
 445
 446   if (r_type == R_ALPHA_JMP_SLOT)
 447     {
 448       /* Perform a RELATIVE reloc on the .got entry that transfers
 449          to the .plt.  */
 450       *reloc_addr += l_addr;
 451     }
 452   else if (r_type == R_ALPHA_NONE)
 453     return;
 454   else
 455     _dl_reloc_bad_type (map, r_type, 1);
 456 }
 457
 458 #endif /* RESOLVE_MAP */