sysdeps/generic/dl-machine.h

   1 /* Machine-dependent ELF dynamic relocation inline functions.  Stub version.
   2    Copyright (C) 1995-2023 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 Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the 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    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 #define ELF_MACHINE_NAME "stub"
  20
  21 #include <string.h>
  22 #include <link.h>
  23 #include <dl-static-tls.h>
  24 #include <dl-machine-rel.h>
  25
  26
  27 /* Return nonzero iff ELF header is compatible with the running host.  */
  28 static inline int
  29 elf_machine_matches_host (const Elf32_Ehdr *ehdr)
  30 {
  31   switch (ehdr->e_machine)
  32     {
  33     default:
  34       return 0;
  35     }
  36 }
  37
  38
  39 /* Return the link-time address of _DYNAMIC.  */
  40 static inline Elf32_Addr
  41 elf_machine_dynamic (void)
  42 {
  43 #error "Damn, no _DYNAMIC"
  44 }
  45
  46
  47 /* Return the run-time load address of the shared object.  */
  48 static inline Elf32_Addr
  49 elf_machine_load_address (void)
  50 {
  51 #error "Where am I?"
  52 }
  53
  54 /* Fixup a PLT entry to bounce directly to the function at VALUE.  */
  55
  56 static inline ElfW(Addr)
  57 elf_machine_fixup_plt (struct link_map *map, lookup_t t,
  58                        const ElfW(Sym) *refsym, const ElfW(Sym) *sym,
  59                        const ElfW(Rel) *reloc,
  60                        ElfW(Addr) *reloc_addr, ElfW(Addr) value)
  61 {
  62   return *reloc_addr = value;
  63 }
  64
  65 /* Perform the relocation specified by RELOC and SYM (which is fully resolved).
  66    LOADADDR is the load address of the object; INFO is an array indexed
  67    by DT_* of the .dynamic section info.  */
  68
  69 auto inline void
  70 __attribute__ ((always_inline))
  71 elf_machine_rel (Elf32_Addr loadaddr, Elf32_Dyn *info[DT_NUM],
  72                  const Elf32_Rel *reloc, const Elf32_Sym *sym,
  73                  Elf32_Addr (*resolve) (const Elf32_Sym **ref,
  74                                         Elf32_Addr reloc_addr,
  75                                         int noplt))
  76 {
  77   Elf32_Addr *const reloc_addr = (Elf32_Addr *) reloc->r_offset;
  78   Elf32_Addr loadbase;
  79
  80   switch (ELF32_R_TYPE (reloc->r_info))
  81     {
  82     case R_MACHINE_COPY:
  83       loadbase = (*resolve) (&sym, (Elf32_Addr) reloc_addr, 0);
  84       memcpy (reloc_addr, (void *) (loadbase + sym->st_value), sym->st_size);
  85       break;
  86     default:
  87       _dl_reloc_bad_type (map, ELF32_R_TYPE (reloc->r_info), 0);
  88       break;
  89     }
  90 }
  91
  92
  93 auto inline Elf32_Addr
  94 __attribute__ ((always_inline))
  95 elf_machine_rela (Elf32_Addr loadaddr, Elf32_Dyn *info[DT_NUM],
  96                   const Elf32_Rel *reloc, const Elf32_Sym *sym,
  97                   Elf32_Addr (*resolve) (const Elf32_Sym **ref,
  98                                          Elf32_Addr reloc_addr,
  99                                          int noplt))
 100 {
 101   _dl_signal_error (0, "Elf32_Rela relocation requested -- unused on "
 102                     NULL, ELF_MACHINE_NAME);
 103 }
 104
 105
 106 /* Set up the loaded object described by L so its unrelocated PLT
 107    entries will jump to the on-demand fixup code in dl-runtime.c.  */
 108
 109 static inline int
 110 elf_machine_runtime_setup (struct link_map *l, int lazy)
 111 {
 112   extern void _dl_runtime_resolve (Elf32_Word);
 113
 114   if (lazy)
 115     {
 116       /* The GOT entries for functions in the PLT have not yet been filled
 117          in.  Their initial contents will arrange when called to push an
 118          offset into the .rel.plt section, push _GLOBAL_OFFSET_TABLE_[1],
 119          and then jump to _GLOBAL_OFFSET_TABLE[2].  */
 120       Elf32_Addr *got = (Elf32_Addr *) D_PTR (l, l_info[DT_PLTGOT]);
 121       got[1] = (Elf32_Addr) l;  /* Identify this shared object.  */
 122
 123       /* This function will get called to fix up the GOT entry indicated by
 124          the offset on the stack, and then jump to the resolved address.  */
 125       got[2] = (Elf32_Addr) &_dl_runtime_resolve;
 126     }
 127
 128   return lazy;
 129 }
 130
 131
 132 /* Initial entry point code for the dynamic linker.
 133    The C function `_dl_start' is the real entry point;
 134    its return value is the user program's entry point.  */
 135
 136 #define RTLD_START #error need some startup code