elf/dl-find_object.h

   1 /* Locating objects in the process image.  ld.so implementation.
   2    Copyright (C) 2021-2023 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 #ifndef _DL_FIND_EH_FRAME_H
  20 #define _DL_FIND_EH_FRAME_H
  21
  22 #include <assert.h>
  23 #include <atomic.h>
  24 #include <dlfcn.h>
  25 #include <ldsodefs.h>
  26 #include <stdbool.h>
  27 #include <stdint.h>
  28
  29 /* Internal version of struct dl_find_object.  Does not include the
  30    (yet unused) flags member.  We need to make a copy of data also in
  31    struct link_map to support non-contiguous mappings, and to support
  32    software transactional memory (the link map is not covered by
  33    transactions).  */
  34 struct dl_find_object_internal
  35 {
  36   uintptr_t map_start;
  37   uintptr_t map_end;            /* Set to map_start by dlclose.  */
  38   struct link_map *map;         /* Set to NULL by dlclose.  */
  39   void *eh_frame;
  40 #if DLFO_STRUCT_HAS_EH_DBASE
  41   void *eh_dbase;
  42 #endif
  43 #if DLFO_STRUCT_HAS_EH_COUNT
  44   int eh_count;
  45 #endif
  46 };
  47
  48 /* Create a copy of *SOURCE in *COPY using relaxed MO loads and
  49    stores.  */
  50 static inline void
  51 _dl_find_object_internal_copy (const struct dl_find_object_internal *source,
  52                                struct dl_find_object_internal *copy)
  53 {
  54   atomic_store_relaxed (&copy->map_start,
  55                         atomic_load_relaxed (&source->map_start));
  56   atomic_store_relaxed (&copy->map_end,
  57                         atomic_load_relaxed (&source->map_end));
  58   atomic_store_relaxed (&copy->map,
  59                         atomic_load_relaxed (&source->map));
  60   atomic_store_relaxed (&copy->eh_frame,
  61                         atomic_load_relaxed (&source->eh_frame));
  62 #if DLFO_STRUCT_HAS_EH_DBASE
  63   atomic_store_relaxed (&copy->eh_dbase,
  64                         atomic_load_relaxed (&source->eh_dbase));
  65 #endif
  66 #if DLFO_STRUCT_HAS_EH_COUNT
  67   atomic_store_relaxed (&copy->eh_count,
  68                         atomic_load_relaxed (&source->eh_count));
  69 #endif
  70 }
  71
  72 static inline void
  73 _dl_find_object_to_external (struct dl_find_object_internal *internal,
  74                              struct dl_find_object *external)
  75 {
  76   external->dlfo_flags = 0;
  77   external->dlfo_map_start = (void *) internal->map_start;
  78   external->dlfo_map_end = (void *) internal->map_end;
  79   external->dlfo_link_map = internal->map;
  80   external->dlfo_eh_frame = internal->eh_frame;
  81 # if DLFO_STRUCT_HAS_EH_DBASE
  82   external->dlfo_eh_dbase = internal->eh_dbase;
  83 # endif
  84 # if DLFO_STRUCT_HAS_EH_COUNT
  85   external->dlfo_eh_count = internal->eh_count;
  86 # endif
  87 }
  88
  89 /* Extract the object location data from a link map and writes it to
  90    *RESULT using relaxed MO stores.  */
  91 static void __attribute__ ((unused))
  92 _dl_find_object_from_map (struct link_map *l,
  93                           struct dl_find_object_internal *result)
  94 {
  95   atomic_store_relaxed (&result->map_start, (uintptr_t) l->l_map_start);
  96   atomic_store_relaxed (&result->map_end, (uintptr_t) l->l_map_end);
  97   atomic_store_relaxed (&result->map, l);
  98
  99 #if DLFO_STRUCT_HAS_EH_DBASE
 100   atomic_store_relaxed (&result->eh_dbase, (void *) l->l_info[DT_PLTGOT]);
 101 #endif
 102
 103   for (const ElfW(Phdr) *ph = l->l_phdr, *ph_end = l->l_phdr + l->l_phnum;
 104        ph < ph_end; ++ph)
 105     if (ph->p_type == DLFO_EH_SEGMENT_TYPE)
 106       {
 107         atomic_store_relaxed (&result->eh_frame,
 108                               (void *) (ph->p_vaddr + l->l_addr));
 109 #if DLFO_STRUCT_HAS_EH_COUNT
 110         atomic_store_relaxed (&result->eh_count, ph->p_memsz / 8);
 111 #endif
 112         return;
 113       }
 114
 115   /* Object has no exception handling segment.  */
 116   atomic_store_relaxed (&result->eh_frame, NULL);
 117 #if DLFO_STRUCT_HAS_EH_COUNT
 118   atomic_store_relaxed (&result->eh_count, 0);
 119 #endif
 120 }
 121
 122 /* Called by the dynamic linker to set up the data structures for the
 123    initially loaded objects.  This creates a few persistent
 124    allocations, so it should be called with the minimal malloc.  */
 125 void _dl_find_object_init (void) attribute_hidden;
 126
 127 /* Called by dlopen/dlmopen to add new objects to the DWARF EH frame
 128    data structures.  NEW_MAP is the dlopen'ed link map.  Link maps on
 129    the l_next list are added if l_object_processed is 0.  Needs to
 130    be protected by loader write lock.  Returns true on success, false
 131    on malloc failure.  */
 132 bool _dl_find_object_update (struct link_map *new_map) attribute_hidden;
 133
 134 /* Called by dlclose to remove the link map from the DWARF EH frame
 135    data structures.  Needs to be protected by loader write lock.  */
 136 void _dl_find_object_dlclose (struct link_map *l) attribute_hidden;
 137
 138 /* Called from __libc_freeres to deallocate malloc'ed memory.  */
 139 void _dl_find_object_freeres (void) attribute_hidden;
 140
 141 #endif /* _DL_FIND_OBJECT_H */