sysdeps/i386/dl-machine.h

   1 /* Machine-dependent ELF dynamic relocation inline functions.  i386 version.
   2 Copyright (C) 1995, 1996 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 Library General Public License as
   7 published by the Free Software Foundation; either version 2 of the
   8 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 Library General Public License for more details.
  14
  15 You should have received a copy of the GNU Library General Public
  16 License along with the GNU C Library; see the file COPYING.LIB.  If
  17 not, write to the Free Software Foundation, Inc., 675 Mass Ave,
  18 Cambridge, MA 02139, USA.  */
  19
  20 #ifndef dl_machine_h
  21 #define dl_machine_h
  22
  23 #define ELF_MACHINE_NAME "i386"
  24
  25 #include <assert.h>
  26
  27 /* Return nonzero iff E_MACHINE is compatible with the running host.  */
  28 static inline int __attribute__ ((unused))
  29 elf_machine_matches_host (Elf32_Half e_machine)
  30 {
  31   switch (e_machine)
  32     {
  33     case EM_386:
  34     case EM_486:
  35       return 1;
  36     default:
  37       return 0;
  38     }
  39 }
  40
  41
  42 /* Return the run-time address of the _GLOBAL_OFFSET_TABLE_.
  43    Must be inlined in a function which uses global data.  */
  44 static inline Elf32_Addr * __attribute__ ((unused))
  45 elf_machine_got (void)
  46 {
  47   register Elf32_Addr *got asm ("%ebx");
  48   return got;
  49 }
  50
  51
  52 /* Return the run-time load address of the shared object.  */
  53 static inline Elf32_Addr __attribute__ ((unused))
  54 elf_machine_load_address (void)
  55 {
  56   Elf32_Addr addr;
  57   asm ("        call here\n"
  58        "here:   popl %0\n"
  59        "        subl $here, %0"
  60        : "=r" (addr));
  61   return addr;
  62 }
  63 /* The `subl' insn above will contain an R_386_32 relocation entry
  64    intended to insert the run-time address of the label `here'.
  65    This will be the first relocation in the text of the dynamic linker;
  66    we skip it to avoid trying to modify read-only text in this early stage.  */
  67 #define ELF_MACHINE_BEFORE_RTLD_RELOC(dynamic_info) \
  68   ++(const Elf32_Rel *) (dynamic_info)[DT_REL]->d_un.d_ptr; \
  69   (dynamic_info)[DT_RELSZ]->d_un.d_val -= sizeof (Elf32_Rel);
  70
  71
  72 /* Set up the loaded object described by L so its unrelocated PLT
  73    entries will jump to the on-demand fixup code in dl-runtime.c.  */
  74
  75 static inline void __attribute__ ((unused))
  76 elf_machine_runtime_setup (struct link_map *l, int lazy)
  77 {
  78   Elf32_Addr *got;
  79   extern void _dl_runtime_resolve (Elf32_Word);
  80
  81   if (l->l_info[DT_JMPREL] && lazy)
  82     {
  83       /* The GOT entries for functions in the PLT have not yet been filled
  84          in.  Their initial contents will arrange when called to push an
  85          offset into the .rel.plt section, push _GLOBAL_OFFSET_TABLE_[1],
  86          and then jump to _GLOBAL_OFFSET_TABLE[2].  */
  87       got = (Elf32_Addr *) (l->l_addr + l->l_info[DT_PLTGOT]->d_un.d_ptr);
  88       got[1] = (Elf32_Addr) l;  /* Identify this shared object.  */
  89       /* This function will get called to fix up the GOT entry indicated by
  90          the offset on the stack, and then jump to the resolved address.  */
  91       got[2] = (Elf32_Addr) &_dl_runtime_resolve;
  92     }
  93
  94   /* This code is used in dl-runtime.c to call the `fixup' function
  95      and then redirect to the address it returns.  */
  96 #define ELF_MACHINE_RUNTIME_TRAMPOLINE asm ("\
  97         .globl _dl_runtime_resolve
  98         .type _dl_runtime_resolve, @function
  99 _dl_runtime_resolve:
 100         call fixup      # Args pushed by PLT.
 101         addl $8, %esp   # Pop args.
 102         jmp *%eax       # Jump to function address.
 103 ");
 104 /* The PLT uses Elf32_Rel relocs.  */
 105 #define elf_machine_relplt elf_machine_rel
 106 }
 107
 108 /* Mask identifying addresses reserved for the user program,
 109    where the dynamic linker should not map anything.  */
 110 #define ELF_MACHINE_USER_ADDRESS_MASK   0xf8000000UL
 111
 112
 113
 114 /* Initial entry point code for the dynamic linker.
 115    The C function `_dl_start' is the real entry point;
 116    its return value is the user program's entry point.  */
 117
 118 #define RTLD_START asm ("\
 119 .text\n\
 120 .globl _start\n\
 121 .globl _dl_start_user\n\
 122 _start:\n\
 123         pushl %esp\n\
 124         call _dl_start\n\
 125         popl %ebx\n\
 126 _dl_start_user:\n\
 127         # Save the user entry point address in %edi.\n\
 128         movl %eax, %edi\n\
 129         # Point %ebx at the GOT.
 130         call 0f\n\
 131 0:      popl %ebx\n\
 132         addl $_GLOBAL_OFFSET_TABLE_+[.-0b], %ebx\n\
 133         # See if we were run as a command with the executable file\n\
 134         # name as an extra leading argument.\n\
 135         movl _dl_skip_args@GOT(%ebx), %eax\n\
 136         movl (%eax),%eax\n\
 137         # Pop the original argument count.\n\
 138         popl %ecx\n\
 139         # Subtract _dl_skip_args from it.\n\
 140         subl %eax, %ecx\n\
 141         # Adjust the stack pointer to skip _dl_skip_args words.\n\
 142         leal (%esp,%eax,4), %esp\n\
 143         # Push back the modified argument count.\n\
 144         pushl %ecx\n\
 145         # Push _dl_default_scope[2] as argument in _dl_init_next call below.\n\
 146         movl _dl_default_scope@GOT(%ebx), %eax\n\
 147         movl 8(%eax), %esi\n\
 148 0:      pushl %esi\n\
 149         # Call _dl_init_next to return the address of an initializer\n\
 150         # function to run.\n\
 151         call _dl_init_next@PLT\n\
 152         addl $4, %esp # Pop argument.\n\
 153         # Check for zero return, when out of initializers.\n\
 154         testl %eax,%eax\n\
 155         jz 1f\n\
 156         # Call the shared object initializer function.\n\
 157         # NOTE: We depend only on the registers (%ebx, %esi and %edi)\n\
 158         # and the return address pushed by this call;\n\
 159         # the initializer is called with the stack just\n\
 160         # as it appears on entry, and it is free to move\n\
 161         # the stack around, as long as it winds up jumping to\n\
 162         # the return address on the top of the stack.\n\
 163         call *%eax\n\
 164         # Loop to call _dl_init_next for the next initializer.\n\
 165         jmp 0b\n\
 166 1:      # Pass our finalizer function to the user in %edx, as per ELF ABI.\n\
 167         movl _dl_fini@GOT(%ebx), %edx\n\
 168         # Jump to the user's entry point.\n\
 169         jmp *%edi\n\
 170 ");
 171
 172 /* Nonzero iff TYPE describes relocation of a PLT entry, so
 173    PLT entries should not be allowed to define the value.  */
 174 #define elf_machine_pltrel_p(type) ((type) == R_386_JMP_SLOT)
 175
 176 /* The i386 never uses Elf32_Rela relocations.  */
 177 #define ELF_MACHINE_NO_RELA 1
 178
 179 #endif /* !dl_machine_h */
 180
 181 #ifdef RESOLVE
 182
 183 /* Perform the relocation specified by RELOC and SYM (which is fully resolved).
 184    MAP is the object containing the reloc.  */
 185
 186 static inline void
 187 elf_machine_rel (struct link_map *map,
 188                  const Elf32_Rel *reloc, const Elf32_Sym *sym)
 189 {
 190   Elf32_Addr *const reloc_addr = (void *) (map->l_addr + reloc->r_offset);
 191   Elf32_Addr loadbase;
 192
 193   switch (ELF32_R_TYPE (reloc->r_info))
 194     {
 195     case R_386_COPY:
 196       loadbase = RESOLVE (&sym, DL_LOOKUP_NOEXEC);
 197       memcpy (reloc_addr, (void *) (loadbase + sym->st_value), sym->st_size);
 198       break;
 199     case R_386_GLOB_DAT:
 200       loadbase = RESOLVE (&sym, 0);
 201       *reloc_addr = sym ? (loadbase + sym->st_value) : 0;
 202       break;
 203     case R_386_JMP_SLOT:
 204       loadbase = RESOLVE (&sym, DL_LOOKUP_NOPLT);
 205       *reloc_addr = sym ? (loadbase + sym->st_value) : 0;
 206       break;
 207     case R_386_32:
 208       {
 209         Elf32_Addr undo = 0;
 210 #ifndef RTLD_BOOTSTRAP
 211         /* This is defined in rtld.c, but nowhere in the static libc.a;
 212            make the reference weak so static programs can still link.  This
 213            declaration cannot be done when compiling rtld.c (i.e.  #ifdef
 214            RTLD_BOOTSTRAP) because rtld.c contains the common defn for
 215            _dl_rtld_map, which is incompatible with a weak decl in the same
 216            file.  */
 217         weak_extern (_dl_rtld_map);
 218         if (map == &_dl_rtld_map)
 219           /* Undo the relocation done here during bootstrapping.  Now we will
 220              relocate it anew, possibly using a binding found in the user
 221              program or a loaded library rather than the dynamic linker's
 222              built-in definitions used while loading those libraries.  */
 223           undo = map->l_addr + sym->st_value;
 224 #endif
 225         loadbase = RESOLVE (&sym, 0);
 226         *reloc_addr += (sym ? (loadbase + sym->st_value) : 0) - undo;
 227         break;
 228       }
 229     case R_386_RELATIVE:
 230 #ifndef RTLD_BOOTSTRAP
 231       if (map != &_dl_rtld_map) /* Already done in rtld itself.  */
 232 #endif
 233         *reloc_addr += map->l_addr;
 234       break;
 235     case R_386_PC32:
 236       loadbase = RESOLVE (&sym, 0);
 237       *reloc_addr += ((sym ? (loadbase + sym->st_value) : 0) -
 238                       (Elf32_Addr) reloc_addr);
 239       break;
 240     case R_386_NONE:            /* Alright, Wilbur.  */
 241       break;
 242     default:
 243       assert (! "unexpected dynamic reloc type");
 244       break;
 245     }
 246
 247 }
 248
 249 static inline void
 250 elf_machine_lazy_rel (struct link_map *map, const Elf32_Rel *reloc)
 251 {
 252   Elf32_Addr *const reloc_addr = (void *) (map->l_addr + reloc->r_offset);
 253   switch (ELF32_R_TYPE (reloc->r_info))
 254     {
 255     case R_386_JMP_SLOT:
 256       *reloc_addr += map->l_addr;
 257       break;
 258     default:
 259       assert (! "unexpected PLT reloc type");
 260       break;
 261     }
 262 }
 263
 264 #endif /* RESOLVE */