sysdeps/i386/dl-machine.h

   1 /* Machine-dependent ELF dynamic relocation inline functions.  i386 version.
   2    Copyright (C) 1995, 1996, 1997 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 not,
  17    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  18    Boston, MA 02111-1307, 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 link-time address of _DYNAMIC.  Conveniently, this is the
  43    first element of the GOT.  This must be inlined in a function which
  44    uses global data.  */
  45 static inline Elf32_Addr
  46 elf_machine_dynamic (void)
  47 {
  48   register Elf32_Addr *got asm ("%ebx");
  49   return *got;
  50 }
  51
  52
  53 /* Return the run-time load address of the shared object.  */
  54 static inline Elf32_Addr __attribute__ ((unused))
  55 elf_machine_load_address (void)
  56 {
  57   Elf32_Addr addr;
  58   asm ("        call here\n"
  59        "here:   popl %0\n"
  60        "        subl $here, %0"
  61        : "=r" (addr));
  62   return addr;
  63 }
  64 /* The `subl' insn above will contain an R_386_32 relocation entry
  65    intended to insert the run-time address of the label `here'.
  66    This will be the first relocation in the text of the dynamic linker;
  67    we skip it to avoid trying to modify read-only text in this early stage.  */
  68 #define ELF_MACHINE_BEFORE_RTLD_RELOC(dynamic_info) \
  69   ++(const Elf32_Rel *) (dynamic_info)[DT_REL]->d_un.d_ptr; \
  70   (dynamic_info)[DT_RELSZ]->d_un.d_val -= sizeof (Elf32_Rel);
  71
  72
  73 /* We add a declaration of this function here so that in dl-runtime.c
  74    the ELF_MACHINE_RUNTIME_TRAMPOLINE macro really can pass the parameters
  75    in registers.  */
  76 static ElfW(Addr) fixup (struct link_map *l, ElfW(Word) reloc_offset)
  77      __attribute__ ((regparm (2), unused));
  78
  79 /* Set up the loaded object described by L so its unrelocated PLT
  80    entries will jump to the on-demand fixup code in dl-runtime.c.  */
  81
  82 static inline void __attribute__ ((unused))
  83 elf_machine_runtime_setup (struct link_map *l, int lazy)
  84 {
  85   Elf32_Addr *got;
  86   extern void _dl_runtime_resolve (Elf32_Word);
  87
  88   if (l->l_info[DT_JMPREL] && lazy)
  89     {
  90       /* The GOT entries for functions in the PLT have not yet been filled
  91          in.  Their initial contents will arrange when called to push an
  92          offset into the .rel.plt section, push _GLOBAL_OFFSET_TABLE_[1],
  93          and then jump to _GLOBAL_OFFSET_TABLE[2].  */
  94       got = (Elf32_Addr *) (l->l_addr + l->l_info[DT_PLTGOT]->d_un.d_ptr);
  95       got[1] = (Elf32_Addr) l;  /* Identify this shared object.  */
  96       /* This function will get called to fix up the GOT entry indicated by
  97          the offset on the stack, and then jump to the resolved address.  */
  98       got[2] = (Elf32_Addr) &_dl_runtime_resolve;
  99     }
 100
 101
 102   /* This code is used in dl-runtime.c to call the `fixup' function
 103      and then redirect to the address it returns.  */
 104 #define ELF_MACHINE_RUNTIME_TRAMPOLINE asm ("\
 105         .globl _dl_runtime_resolve
 106         .type _dl_runtime_resolve, @function
 107 _dl_runtime_resolve:
 108         pushl %eax              # Preserve registers otherwise clobbered.
 109         pushl %ecx
 110         pushl %edx
 111         movl 16(%esp), %edx     # Copy args pushed by PLT in register.  Note
 112         movl 12(%esp), %eax     # that `fixup' takes its parameters in regs.
 113         call fixup              # Call resolver.
 114         popl %edx               # Get register content back.
 115         popl %ecx
 116         xchgl %eax, (%esp)      # Get %eax contents end store function address.
 117         ret $8                  # Jump to function address.
 118         .size _dl_runtime_resolve, .-_dl_runtime_resolve
 119 ");
 120 /* The PLT uses Elf32_Rel relocs.  */
 121 #define elf_machine_relplt elf_machine_rel
 122 }
 123
 124 /* Mask identifying addresses reserved for the user program,
 125    where the dynamic linker should not map anything.  */
 126 #define ELF_MACHINE_USER_ADDRESS_MASK   0xf8000000UL
 127
 128
 129
 130 /* Initial entry point code for the dynamic linker.
 131    The C function `_dl_start' is the real entry point;
 132    its return value is the user program's entry point.  */
 133
 134 #define RTLD_START asm ("\
 135 .text\n\
 136 .globl _start\n\
 137 .globl _dl_start_user\n\
 138 _start:\n\
 139         pushl %esp\n\
 140         call _dl_start\n\
 141         popl %ebx\n\
 142 _dl_start_user:\n\
 143         # Save the user entry point address in %edi.\n\
 144         movl %eax, %edi\n\
 145         # Point %ebx at the GOT.
 146         call 0f\n\
 147 0:      popl %ebx\n\
 148         addl $_GLOBAL_OFFSET_TABLE_+[.-0b], %ebx\n\
 149         # See if we were run as a command with the executable file\n\
 150         # name as an extra leading argument.\n\
 151         movl _dl_skip_args@GOT(%ebx), %eax\n\
 152         movl (%eax), %eax\n\
 153         # Pop the original argument count.\n\
 154         popl %ecx\n\
 155         # Subtract _dl_skip_args from it.\n\
 156         subl %eax, %ecx\n\
 157         # Adjust the stack pointer to skip _dl_skip_args words.\n\
 158         leal (%esp,%eax,4), %esp\n\
 159         # Push back the modified argument count.\n\
 160         pushl %ecx\n\
 161         # Push _dl_default_scope[2] as argument in _dl_init_next call below.\n\
 162         movl _dl_default_scope@GOT(%ebx), %eax\n\
 163         movl 8(%eax), %esi\n\
 164 0:      pushl %esi\n\
 165         # Call _dl_init_next to return the address of an initializer\n\
 166         # function to run.\n\
 167         call _dl_init_next@PLT\n\
 168         addl $4, %esp # Pop argument.\n\
 169         # Check for zero return, when out of initializers.\n\
 170         testl %eax, %eax\n\
 171         jz 1f\n\
 172         # Call the shared object initializer function.\n\
 173         # NOTE: We depend only on the registers (%ebx, %esi and %edi)\n\
 174         # and the return address pushed by this call;\n\
 175         # the initializer is called with the stack just\n\
 176         # as it appears on entry, and it is free to move\n\
 177         # the stack around, as long as it winds up jumping to\n\
 178         # the return address on the top of the stack.\n\
 179         call *%eax\n\
 180         # Loop to call _dl_init_next for the next initializer.\n\
 181         jmp 0b\n\
 182 1:      # Clear the startup flag.\n\
 183         movl _dl_starting_up@GOT(%ebx), %eax\n\
 184         movl $0, (%eax)\n\
 185         # Pass our finalizer function to the user in %edx, as per ELF ABI.\n\
 186         movl _dl_fini@GOT(%ebx), %edx\n\
 187         # Jump to the user's entry point.\n\
 188         jmp *%edi\n\
 189 ");
 190
 191 /* Nonzero iff TYPE describes relocation of a PLT entry, so
 192    PLT entries should not be allowed to define the value.  */
 193 #define elf_machine_pltrel_p(type) ((type) == R_386_JMP_SLOT)
 194
 195 /* The i386 never uses Elf32_Rela relocations.  */
 196 #define ELF_MACHINE_NO_RELA 1
 197
 198 #endif /* !dl_machine_h */
 199
 200 #ifdef RESOLVE
 201
 202 /* Perform the relocation specified by RELOC and SYM (which is fully resolved).
 203    MAP is the object containing the reloc.  */
 204
 205 static inline void
 206 elf_machine_rel (struct link_map *map, const Elf32_Rel *reloc,
 207                  const Elf32_Sym *sym, const hash_name_pair *version)
 208 {
 209   Elf32_Addr *const reloc_addr = (void *) (map->l_addr + reloc->r_offset);
 210   Elf32_Addr loadbase;
 211
 212   switch (ELF32_R_TYPE (reloc->r_info))
 213     {
 214     case R_386_COPY:
 215       loadbase = RESOLVE (&sym, version, DL_LOOKUP_NOEXEC);
 216       memcpy (reloc_addr, (void *) (loadbase + sym->st_value), sym->st_size);
 217       break;
 218     case R_386_GLOB_DAT:
 219       loadbase = RESOLVE (&sym, version, 0);
 220       *reloc_addr = sym ? (loadbase + sym->st_value) : 0;
 221       break;
 222     case R_386_JMP_SLOT:
 223       loadbase = RESOLVE (&sym, version, DL_LOOKUP_NOPLT);
 224       *reloc_addr = sym ? (loadbase + sym->st_value) : 0;
 225       break;
 226     case R_386_32:
 227       {
 228         Elf32_Addr undo = 0;
 229 #ifndef RTLD_BOOTSTRAP
 230         /* This is defined in rtld.c, but nowhere in the static libc.a;
 231            make the reference weak so static programs can still link.  This
 232            declaration cannot be done when compiling rtld.c (i.e.  #ifdef
 233            RTLD_BOOTSTRAP) because rtld.c contains the common defn for
 234            _dl_rtld_map, which is incompatible with a weak decl in the same
 235            file.  */
 236         weak_extern (_dl_rtld_map);
 237         if (map == &_dl_rtld_map)
 238           /* Undo the relocation done here during bootstrapping.  Now we will
 239              relocate it anew, possibly using a binding found in the user
 240              program or a loaded library rather than the dynamic linker's
 241              built-in definitions used while loading those libraries.  */
 242           undo = map->l_addr + sym->st_value;
 243 #endif
 244         loadbase = RESOLVE (&sym, version, 0);
 245         *reloc_addr += (sym ? (loadbase + sym->st_value) : 0) - undo;
 246         break;
 247       }
 248     case R_386_RELATIVE:
 249 #ifndef RTLD_BOOTSTRAP
 250       if (map != &_dl_rtld_map) /* Already done in rtld itself.  */
 251 #endif
 252         *reloc_addr += map->l_addr;
 253       break;
 254     case R_386_PC32:
 255       loadbase = RESOLVE (&sym, version, 0);
 256       *reloc_addr += ((sym ? (loadbase + sym->st_value) : 0) -
 257                       (Elf32_Addr) reloc_addr);
 258       break;
 259     case R_386_NONE:            /* Alright, Wilbur.  */
 260       break;
 261     default:
 262       assert (! "unexpected dynamic reloc type");
 263       break;
 264     }
 265
 266 }
 267
 268 static inline void
 269 elf_machine_lazy_rel (struct link_map *map, const Elf32_Rel *reloc)
 270 {
 271   Elf32_Addr *const reloc_addr = (void *) (map->l_addr + reloc->r_offset);
 272   switch (ELF32_R_TYPE (reloc->r_info))
 273     {
 274     case R_386_JMP_SLOT:
 275       *reloc_addr += map->l_addr;
 276       break;
 277     default:
 278       assert (! "unexpected PLT reloc type");
 279       break;
 280     }
 281 }
 282
 283 #endif /* RESOLVE */