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 #define ELF_MACHINE_NAME "i386"
  21
  22 #include <assert.h>
  23 #include <string.h>
  24 #include <link.h>
  25
  26
  27 /* Return nonzero iff E_MACHINE is compatible with the running host.  */
  28 static inline int
  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 *
  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
  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 /* Perform the relocation specified by RELOC and SYM (which is fully resolved).
  72    MAP is the object containing the reloc.  */
  73
  74 static inline void
  75 elf_machine_rel (struct link_map *map,
  76                  const Elf32_Rel *reloc, const Elf32_Sym *sym,
  77                  Elf32_Addr (*resolve) (const Elf32_Sym **ref,
  78                                         Elf32_Addr reloc_addr,
  79                                         int noplt))
  80 {
  81   Elf32_Addr *const reloc_addr = (void *) (map->l_addr + reloc->r_offset);
  82   Elf32_Addr loadbase;
  83
  84   switch (ELF32_R_TYPE (reloc->r_info))
  85     {
  86     case R_386_COPY:
  87       loadbase = (*resolve) (&sym, (Elf32_Addr) reloc_addr, 0);
  88       memcpy (reloc_addr, (void *) (loadbase + sym->st_value), sym->st_size);
  89       break;
  90     case R_386_GLOB_DAT:
  91       loadbase = (resolve ? (*resolve) (&sym, (Elf32_Addr) reloc_addr, 0) :
  92                   /* RESOLVE is null during bootstrap relocation.  */
  93                   map->l_addr);
  94       *reloc_addr = sym ? (loadbase + sym->st_value) : 0;
  95       break;
  96     case R_386_JMP_SLOT:
  97       loadbase = (resolve ? (*resolve) (&sym, (Elf32_Addr) reloc_addr, 1) :
  98                   /* RESOLVE is null during bootstrap relocation.  */
  99                   map->l_addr);
 100       *reloc_addr = sym ? (loadbase + sym->st_value) : 0;
 101       break;
 102     case R_386_32:
 103       if (map->l_type == lt_interpreter)
 104         {
 105           /* Undo the relocation done here during bootstrapping.  Now we will
 106              relocate it anew, possibly using a binding found in the user
 107              program or a loaded library rather than the dynamic linker's
 108              built-in definitions used while loading those libraries.  */
 109           const Elf32_Sym *const dlsymtab
 110             = (void *) (map->l_addr + map->l_info[DT_SYMTAB]->d_un.d_ptr);
 111           *reloc_addr -= (map->l_addr +
 112                           dlsymtab[ELF32_R_SYM (reloc->r_info)].st_value);
 113         }
 114       loadbase = (*resolve) (&sym, (Elf32_Addr) reloc_addr, 0);
 115       *reloc_addr += sym ? (loadbase + sym->st_value) : 0;
 116       break;
 117     case R_386_RELATIVE:
 118       if (map->l_type != lt_interpreter) /* Already done in dynamic linker.  */
 119         *reloc_addr += map->l_addr;
 120       break;
 121     case R_386_PC32:
 122       loadbase = (*resolve) (&sym, (Elf32_Addr) reloc_addr, 0);
 123       *reloc_addr += ((sym ? (loadbase + sym->st_value) : 0) -
 124                       (Elf32_Addr) reloc_addr);
 125       break;
 126     case R_386_NONE:            /* Alright, Wilbur.  */
 127       break;
 128     default:
 129       assert (! "unexpected dynamic reloc type");
 130       break;
 131     }
 132 }
 133
 134 static inline void
 135 elf_machine_lazy_rel (struct link_map *map, const Elf32_Rel *reloc)
 136 {
 137   Elf32_Addr *const reloc_addr = (void *) (map->l_addr + reloc->r_offset);
 138   switch (ELF32_R_TYPE (reloc->r_info))
 139     {
 140     case R_386_JMP_SLOT:
 141       *reloc_addr += map->l_addr;
 142       break;
 143     default:
 144       assert (! "unexpected PLT reloc type");
 145       break;
 146     }
 147 }
 148
 149 /* Nonzero iff TYPE describes relocation of a PLT entry, so
 150    PLT entries should not be allowed to define the value.  */
 151 #define elf_machine_pltrel_p(type) ((type) == R_386_JMP_SLOT)
 152
 153 /* The i386 never uses Elf32_Rela relocations.  */
 154 #define ELF_MACHINE_NO_RELA 1
 155
 156
 157 /* Set up the loaded object described by L so its unrelocated PLT
 158    entries will jump to the on-demand fixup code in dl-runtime.c.  */
 159
 160 static inline void
 161 elf_machine_runtime_setup (struct link_map *l, int lazy)
 162 {
 163   Elf32_Addr *got;
 164   extern void _dl_runtime_resolve (Elf32_Word);
 165
 166   if (l->l_info[DT_JMPREL] && lazy)
 167     {
 168       /* The GOT entries for functions in the PLT have not yet been filled
 169          in.  Their initial contents will arrange when called to push an
 170          offset into the .rel.plt section, push _GLOBAL_OFFSET_TABLE_[1],
 171          and then jump to _GLOBAL_OFFSET_TABLE[2].  */
 172       got = (Elf32_Addr *) (l->l_addr + l->l_info[DT_PLTGOT]->d_un.d_ptr);
 173       got[1] = (Elf32_Addr) l;  /* Identify this shared object.  */
 174       /* This function will get called to fix up the GOT entry indicated by
 175          the offset on the stack, and then jump to the resolved address.  */
 176       got[2] = (Elf32_Addr) &_dl_runtime_resolve;
 177     }
 178
 179   /* This code is used in dl-runtime.c to call the `fixup' function
 180      and then redirect to the address it returns.  */
 181 #define ELF_MACHINE_RUNTIME_TRAMPOLINE asm ("\
 182         .globl _dl_runtime_resolve
 183         .type _dl_runtime_resolve, @function
 184 _dl_runtime_resolve:
 185         call fixup      # Args pushed by PLT.
 186         addl $8, %esp   # Pop args.
 187         jmp *%eax       # Jump to function address.
 188 ");
 189 /* The PLT uses Elf32_Rel relocs.  */
 190 #define elf_machine_relplt elf_machine_rel
 191 }
 192
 193 /* Mask identifying addresses reserved for the user program,
 194    where the dynamic linker should not map anything.  */
 195 #define ELF_MACHINE_USER_ADDRESS_MASK   0xf8000000UL
 196
 197
 198
 199 /* Initial entry point code for the dynamic linker.
 200    The C function `_dl_start' is the real entry point;
 201    its return value is the user program's entry point.  */
 202
 203 #define RTLD_START asm ("\
 204 .text\n\
 205 .globl _start\n\
 206 .globl _dl_start_user\n\
 207 _start:\n\
 208         call _dl_start\n\
 209 _dl_start_user:\n\
 210         # Save the user entry point address in %edi.\n\
 211         movl %eax, %edi\n\
 212         # Point %ebx at the GOT.
 213         call 0f\n\
 214 0:      popl %ebx\n\
 215         addl $_GLOBAL_OFFSET_TABLE_+[.-0b], %ebx\n\
 216         # See if we were run as a command with the executable file\n\
 217         # name as an extra leading argument.\n\
 218         movl _dl_skip_args@GOT(%ebx), %eax\n\
 219         movl (%eax),%eax\n\
 220         # Pop the original argument count.\n\
 221         popl %ecx\n\
 222         # Subtract _dl_skip_args from it.\n\
 223         subl %eax, %ecx\n\
 224         # Adjust the stack pointer to skip _dl_skip_args words.\n\
 225         leal (%esp,%eax,4), %esp\n\
 226         # Push back the modified argument count.\n\
 227         pushl %ecx\n\
 228         # Call _dl_init_next to return the address of an initializer\n\
 229         # function to run.\n\
 230 0:      call _dl_init_next@PLT\n\
 231         # Check for zero return, when out of initializers.\n\
 232         testl %eax,%eax\n\
 233         jz 1f\n\
 234         # Call the shared object initializer function.\n\
 235         # NOTE: We depend only on the registers (%ebx and %edi)\n\
 236         # and the return address pushed by this call;\n\
 237         # the initializer is called with the stack just\n\
 238         # as it appears on entry, and it is free to move\n\
 239         # the stack around, as long as it winds up jumping to\n\
 240         # the return address on the top of the stack.\n\
 241         call *%eax\n\
 242         # Loop to call _dl_init_next for the next initializer.\n\
 243         jmp 0b\n\
 244 1:      # Pass our finalizer function to the user in %edx, as per ELF ABI.\n\
 245         movl _dl_fini@GOT(%ebx), %edx\n\
 246         # Jump to the user's entry point.\n\
 247         jmp *%edi\n\
 248 ");