libelf/elf_newdata.c

   1 /* Create new, empty section data.
   2    Copyright (C) 1998, 1999, 2000, 2001, 2002, 2015 Red Hat, Inc.
   3    This file is part of elfutils.
   4    Contributed by Ulrich Drepper <drepper@redhat.com>, 1998.
   5
   6    This file is free software; you can redistribute it and/or modify
   7    it under the terms of either
   8
   9      * the GNU Lesser General Public License as published by the Free
  10        Software Foundation; either version 3 of the License, or (at
  11        your option) any later version
  12
  13    or
  14
  15      * the GNU General Public License as published by the Free
  16        Software Foundation; either version 2 of the License, or (at
  17        your option) any later version
  18
  19    or both in parallel, as here.
  20
  21    elfutils is distributed in the hope that it will be useful, but
  22    WITHOUT ANY WARRANTY; without even the implied warranty of
  23    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  24    General Public License for more details.
  25
  26    You should have received copies of the GNU General Public License and
  27    the GNU Lesser General Public License along with this program.  If
  28    not, see <http://www.gnu.org/licenses/>.  */
  29
  30 #ifdef HAVE_CONFIG_H
  31 # include <config.h>
  32 #endif
  33
  34 #include <stddef.h>
  35 #include <stdlib.h>
  36
  37 #include "libelfP.h"
  38
  39
  40 Elf_Data *
  41 elf_newdata (Elf_Scn *scn)
  42 {
  43   Elf_Data_List *result = NULL;
  44
  45   if (scn == NULL)
  46     return NULL;
  47
  48   if (unlikely (scn->index == 0))
  49     {
  50       /* It is not allowed to add something to the 0th section.  */
  51       __libelf_seterrno (ELF_E_NOT_NUL_SECTION);
  52       return NULL;
  53     }
  54
  55   if (scn->elf->class == ELFCLASS32
  56       || (offsetof (struct Elf, state.elf32.ehdr)
  57           == offsetof (struct Elf, state.elf64.ehdr))
  58       ? scn->elf->state.elf32.ehdr == NULL
  59       : scn->elf->state.elf64.ehdr == NULL)
  60     {
  61       __libelf_seterrno (ELF_E_WRONG_ORDER_EHDR);
  62       return NULL;
  63     }
  64
  65   rwlock_wrlock (scn->elf->lock);
  66
  67   /* data_read is set when data has been read from the ELF image or
  68      when a new section has been created by elf_newscn.  If data has
  69      been read from the ELF image, then rawdata_base will point to raw
  70      data.  If data_read has been set by elf_newscn, then rawdata_base
  71      will be NULL.  data_list_rear will be set by elf_getdata if the
  72      data has been converted, or by this function, elf_newdata, when
  73      new data has been added.
  74
  75      Currently elf_getdata and elf_update rely on the fact that when
  76      data_list_read is not NULL all they have to do is walk the data
  77      list. They will ignore any (unread) raw data in that case.
  78
  79      So we need to make sure the data list is setup if there is
  80      already data available.  */
  81   if (scn->data_read
  82       && scn->rawdata_base != NULL
  83       && scn->data_list_rear == NULL)
  84     __libelf_set_data_list_rdlock (scn, 1);
  85
  86   if (scn->data_read && scn->data_list_rear == NULL)
  87     {
  88       /* This means the section was created by the user and this is the
  89          first data.  */
  90       result = &scn->data_list;
  91       result->flags = ELF_F_DIRTY;
  92     }
  93   else
  94     {
  95       /* It would be more efficient to create new data without
  96          reading/converting the data from the file.  But then we
  97          have to remember this.  Currently elf_getdata and
  98          elf_update rely on the fact that they don't have to
  99          load/convert any data if data_list_rear is set.  */
 100       if (scn->data_read == 0)
 101         {
 102           if (__libelf_set_rawdata_wrlock (scn) != 0)
 103             /* Something went wrong.  The error value is already set.  */
 104             goto out;
 105           __libelf_set_data_list_rdlock (scn, 1);
 106         }
 107
 108       /* Create a new, empty data descriptor.  */
 109       result = calloc (1, sizeof (Elf_Data_List));
 110       if (result == NULL)
 111         {
 112           __libelf_seterrno (ELF_E_NOMEM);
 113           goto out;
 114         }
 115
 116       result->flags = ELF_F_DIRTY | ELF_F_MALLOCED;
 117     }
 118
 119   /* Set the predefined values.  */
 120   result->data.d.d_version = EV_CURRENT;
 121
 122   result->data.s = scn;
 123
 124   /* Add to the end of the list.  */
 125   if (scn->data_list_rear != NULL)
 126     scn->data_list_rear->next = result;
 127
 128   scn->data_list_rear = result;
 129
 130  out:
 131   rwlock_unlock (scn->elf->lock);
 132
 133   /* Please note that the following is thread safe and is also defined
 134      for RESULT == NULL since it still return NULL.  */
 135   return &result->data.d;
 136 }