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 .Lhere\n"
  59        ".Lhere: popl %0\n"
  60        "        subl $.Lhere, %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 `.Lhere'.
  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 #ifndef PROF
  74 /* We add a declaration of this function here so that in dl-runtime.c
  75    the ELF_MACHINE_RUNTIME_TRAMPOLINE macro really can pass the parameters
  76    in registers.
  77
  78    We cannot use this scheme for profiling because the _mcount call
  79    destroys the passed register information.  */
  80 static ElfW(Addr) fixup (struct link_map *l, ElfW(Word) reloc_offset)
  81      __attribute__ ((regparm (2), unused));
  82 #endif
  83
  84 /* Set up the loaded object described by L so its unrelocated PLT
  85    entries will jump to the on-demand fixup code in dl-runtime.c.  */
  86
  87 static inline void __attribute__ ((unused))
  88 elf_machine_runtime_setup (struct link_map *l, int lazy)
  89 {
  90   Elf32_Addr *got;
  91   extern void _dl_runtime_resolve (Elf32_Word);
  92
  93   if (l->l_info[DT_JMPREL] && lazy)
  94     {
  95       /* The GOT entries for functions in the PLT have not yet been filled
  96          in.  Their initial contents will arrange when called to push an
  97          offset into the .rel.plt section, push _GLOBAL_OFFSET_TABLE_[1],
  98          and then jump to _GLOBAL_OFFSET_TABLE[2].  */
  99       got = (Elf32_Addr *) (l->l_addr + l->l_info[DT_PLTGOT]->d_un.d_ptr);
 100       got[1] = (Elf32_Addr) l;  /* Identify this shared object.  */
 101       /* This function will get called to fix up the GOT entry indicated by
 102          the offset on the stack, and then jump to the resolved address.  */
 103       got[2] = (Elf32_Addr) &_dl_runtime_resolve;
 104     }
 105
 106
 107   /* This code is used in dl-runtime.c to call the `fixup' function
 108      and then redirect to the address it returns.  */
 109 #ifndef PROF
 110 # define ELF_MACHINE_RUNTIME_TRAMPOLINE asm ("\
 111         .globl _dl_runtime_resolve
 112         .type _dl_runtime_resolve, @function
 113 _dl_runtime_resolve:
 114         pushl %eax              # Preserve registers otherwise clobbered.
 115         pushl %ecx
 116         pushl %edx
 117         movl 16(%esp), %edx     # Copy args pushed by PLT in register.  Note
 118         movl 12(%esp), %eax     # that `fixup' takes its parameters in regs.
 119         call fixup              # Call resolver.
 120         popl %edx               # Get register content back.
 121         popl %ecx
 122         xchgl %eax, (%esp)      # Get %eax contents end store function address.
 123         ret $8                  # Jump to function address.
 124         .size _dl_runtime_resolve, .-_dl_runtime_resolve
 125 ");
 126 #else
 127 # define ELF_MACHINE_RUNTIME_TRAMPOLINE asm ("\
 128         .globl _dl_runtime_resolve
 129         .type _dl_runtime_resolve, @function
 130 _dl_runtime_resolve:
 131         pushl %eax              # Preserve registers otherwise clobbered.
 132         pushl %ecx
 133         pushl %edx
 134         movl 16(%esp), %edx     # Push the arguments for `fixup'
 135         movl 12(%esp), %eax
 136         pushl %edx
 137         pushl %eax
 138         call fixup              # Call resolver.
 139         popl %edx               # Pop the parameters
 140         popl %ecx
 141         popl %edx               # Get register content back.
 142         popl %ecx
 143         xchgl %eax, (%esp)      # Get %eax contents end store function address.
 144         ret $8                  # Jump to function address.
 145         .size _dl_runtime_resolve, .-_dl_runtime_resolve
 146 ");
 147 #endif
 148 /* The PLT uses Elf32_Rel relocs.  */
 149 #define elf_machine_relplt elf_machine_rel
 150 }
 151
 152 /* Mask identifying addresses reserved for the user program,
 153    where the dynamic linker should not map anything.  */
 154 #define ELF_MACHINE_USER_ADDRESS_MASK   0xf8000000UL
 155
 156
 157
 158 /* Initial entry point code for the dynamic linker.
 159    The C function `_dl_start' is the real entry point;
 160    its return value is the user program's entry point.  */
 161
 162 #define RTLD_START asm ("\
 163 .text\n\
 164 .globl _start\n\
 165 .globl _dl_start_user\n\
 166 _start:\n\
 167         pushl %esp\n\
 168         call _dl_start\n\
 169         popl %ebx\n\
 170 _dl_start_user:\n\
 171         # Save the user entry point address in %edi.\n\
 172         movl %eax, %edi\n\
 173         # Point %ebx at the GOT.
 174         call 0f\n\
 175 0:      popl %ebx\n\
 176         addl $_GLOBAL_OFFSET_TABLE_+[.-0b], %ebx\n\
 177         # See if we were run as a command with the executable file\n\
 178         # name as an extra leading argument.\n\
 179         movl _dl_skip_args@GOT(%ebx), %eax\n\
 180         movl (%eax), %eax\n\
 181         # Pop the original argument count.\n\
 182         popl %ecx\n\
 183         # Subtract _dl_skip_args from it.\n\
 184         subl %eax, %ecx\n\
 185         # Adjust the stack pointer to skip _dl_skip_args words.\n\
 186         leal (%esp,%eax,4), %esp\n\
 187         # Push back the modified argument count.\n\
 188         pushl %ecx\n\
 189         # Push _dl_default_scope[2] as argument in _dl_init_next call below.\n\
 190         movl _dl_default_scope@GOT(%ebx), %eax\n\
 191         movl 8(%eax), %esi\n\
 192 0:      pushl %esi\n\
 193         # Call _dl_init_next to return the address of an initializer\n\
 194         # function to run.\n\
 195         call _dl_init_next@PLT\n\
 196         addl $4, %esp # Pop argument.\n\
 197         # Check for zero return, when out of initializers.\n\
 198         testl %eax, %eax\n\
 199         jz 1f\n\
 200         # Call the shared object initializer function.\n\
 201         # NOTE: We depend only on the registers (%ebx, %esi and %edi)\n\
 202         # and the return address pushed by this call;\n\
 203         # the initializer is called with the stack just\n\
 204         # as it appears on entry, and it is free to move\n\
 205         # the stack around, as long as it winds up jumping to\n\
 206         # the return address on the top of the stack.\n\
 207         call *%eax\n\
 208         # Loop to call _dl_init_next for the next initializer.\n\
 209         jmp 0b\n\
 210 1:      # Clear the startup flag.\n\
 211         movl _dl_starting_up@GOT(%ebx), %eax\n\
 212         movl $0, (%eax)\n\
 213         # Pass our finalizer function to the user in %edx, as per ELF ABI.\n\
 214         movl _dl_fini@GOT(%ebx), %edx\n\
 215         # Jump to the user's entry point.\n\
 216         jmp *%edi\n\
 217 ");
 218
 219 /* Nonzero iff TYPE should not be allowed to resolve to one of
 220    the main executable's symbols, as for a COPY reloc.  */
 221 #define elf_machine_lookup_noexec_p(type) ((type) == R_386_COPY)
 222
 223 /* Nonzero iff TYPE describes relocation of a PLT entry, so
 224    PLT entries should not be allowed to define the value.  */
 225 #define elf_machine_lookup_noplt_p(type) ((type) == R_386_JMP_SLOT)
 226
 227 /* A reloc type used for ld.so cmdline arg lookups to reject PLT entries.  */
 228 #define ELF_MACHINE_RELOC_NOPLT R_386_JMP_SLOT
 229
 230 /* The i386 never uses Elf32_Rela relocations.  */
 231 #define ELF_MACHINE_NO_RELA 1
 232
 233 #endif /* !dl_machine_h */
 234
 235 #ifdef RESOLVE
 236
 237 /* Perform the relocation specified by RELOC and SYM (which is fully resolved).
 238    MAP is the object containing the reloc.  */
 239
 240 static inline void
 241 elf_machine_rel (struct link_map *map, const Elf32_Rel *reloc,
 242                  const Elf32_Sym *sym, const struct r_found_version *version)
 243 {
 244   Elf32_Addr *const reloc_addr = (void *) (map->l_addr + reloc->r_offset);
 245
 246   if (ELF32_R_TYPE (reloc->r_info) == R_386_RELATIVE)
 247     {
 248 #ifndef RTLD_BOOTSTRAP
 249       if (map != &_dl_rtld_map) /* Already done in rtld itself.  */
 250 #endif
 251         *reloc_addr += map->l_addr;
 252     }
 253   else
 254     {
 255 #ifndef RTLD_BOOTSTRAP
 256       const Elf32_Sym *const refsym = sym;
 257 #endif
 258       Elf32_Addr value = RESOLVE (&sym, version, ELF32_R_TYPE (reloc->r_info));
 259       if (sym)
 260         value += sym->st_value;
 261
 262       switch (ELF32_R_TYPE (reloc->r_info))
 263         {
 264         case R_386_COPY:
 265           memcpy (reloc_addr, (void *) value, sym->st_size);
 266           break;
 267         case R_386_GLOB_DAT:
 268         case R_386_JMP_SLOT:
 269           *reloc_addr = value;
 270           break;
 271         case R_386_32:
 272           {
 273 #ifndef RTLD_BOOTSTRAP
 274            /* This is defined in rtld.c, but nowhere in the static
 275               libc.a; make the reference weak so static programs can
 276               still link.  This declaration cannot be done when
 277               compiling rtld.c (i.e.  #ifdef RTLD_BOOTSTRAP) because
 278               rtld.c contains the common defn for _dl_rtld_map, which
 279               is incompatible with a weak decl in the same file.  */
 280             weak_extern (_dl_rtld_map);
 281             if (map == &_dl_rtld_map)
 282               /* Undo the relocation done here during bootstrapping.
 283                  Now we will relocate it anew, possibly using a
 284                  binding found in the user program or a loaded library
 285                  rather than the dynamic linker's built-in definitions
 286                  used while loading those libraries.  */
 287               value -= map->l_addr + refsym->st_value;
 288 #endif
 289             *reloc_addr += value;
 290             break;
 291           }
 292         case R_386_PC32:
 293           *reloc_addr += (value - (Elf32_Addr) reloc_addr);
 294           break;
 295         case R_386_NONE:                /* Alright, Wilbur.  */
 296           break;
 297         default:
 298           assert (! "unexpected dynamic reloc type");
 299           break;
 300         }
 301     }
 302 }
 303
 304 static inline void
 305 elf_machine_lazy_rel (struct link_map *map, const Elf32_Rel *reloc)
 306 {
 307   Elf32_Addr *const reloc_addr = (void *) (map->l_addr + reloc->r_offset);
 308   switch (ELF32_R_TYPE (reloc->r_info))
 309     {
 310     case R_386_JMP_SLOT:
 311       *reloc_addr += map->l_addr;
 312       break;
 313     default:
 314       assert (! "unexpected PLT reloc type");
 315       break;
 316     }
 317 }
 318
 319 #endif /* RESOLVE */