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