kern/i386/dl.c

/* dl-386.c - arch-dependent part of loadable module support */
/*
 *  GRUB  --  GRand Unified Bootloader
 *  Copyright (C) 2002,2005,2007,2009  Free Software Foundation, Inc.
 *
 *  GRUB is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  GRUB is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with GRUB.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <grub/dl.h>
#include <grub/elf.h>
#include <grub/misc.h>
#include <grub/err.h>

/* Check if EHDR is a valid ELF header.  */
grub_err_t
grub_arch_dl_check_header (void *ehdr)
{
  Elf_Ehdr *e = ehdr;

  /* Check the magic numbers.  */
  if (e->e_ident[EI_CLASS] != ELFCLASS32
      || e->e_ident[EI_DATA] != ELFDATA2LSB
      || e->e_machine != EM_386)
    return grub_error (GRUB_ERR_BAD_OS, "invalid arch specific ELF magic");

  return GRUB_ERR_NONE;
}

/* Relocate symbols.  */
grub_err_t
grub_arch_dl_relocate_symbols (grub_dl_t mod, void *ehdr)
{
  Elf_Ehdr *e = ehdr;
  Elf_Shdr *s;
  Elf_Word entsize;
  unsigned i;

  /* Find a symbol table.  */
  for (i = 0, s = (Elf_Shdr *) ((char *) e + e->e_shoff);
       i < e->e_shnum;
       i++, s = (Elf_Shdr *) ((char *) s + e->e_shentsize))
    if (s->sh_type == SHT_SYMTAB)
      break;

  if (i == e->e_shnum)
    return grub_error (GRUB_ERR_BAD_MODULE, "no symtab found");

  entsize = s->sh_entsize;

  for (i = 0, s = (Elf_Shdr *) ((char *) e + e->e_shoff);
       i < e->e_shnum;
       i++, s = (Elf_Shdr *) ((char *) s + e->e_shentsize))
    if (s->sh_type == SHT_REL)
      {
    grub_dl_segment_t seg;

    /* Find the target segment.  */
    for (seg = mod->segment; seg; seg = seg->next)
      if (seg->section == s->sh_info)
        break;

    if (seg)
      {
        Elf_Rel *rel, *max;

        for (rel = (Elf_Rel *) ((char *) e + s->sh_offset),
           max = rel + s->sh_size / s->sh_entsize;
         rel < max;
         rel++)
          {
        Elf_Word *addr;
        Elf_Sym *sym;

        if (seg->size < rel->r_offset)
          return grub_error (GRUB_ERR_BAD_MODULE,
                     "reloc offset is out of the segment");

        addr = (Elf_Word *) ((char *) seg->addr + rel->r_offset);
        sym = (Elf_Sym *) ((char *) mod->symtab
                     + entsize * ELF_R_SYM (rel->r_info));

        switch (ELF_R_TYPE (rel->r_info))
          {
          case R_386_32:
            *addr += sym->st_value;
            break;

          case R_386_PC32:
            *addr += (sym->st_value - (Elf_Word) seg->addr
                  - rel->r_offset);
            break;
          }
          }
      }
      }

  return GRUB_ERR_NONE;
}