1 /* Locating objects in the process image. ld.so implementation.
2 Copyright (C) 2021-2022 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
_dl_find_object_internal_copy(const struct dl_find_object_internal * source,struct dl_find_object_internal * copy)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 (©->map_start,
55 atomic_load_relaxed (&source->map_start));
56 atomic_store_relaxed (©->map_end,
57 atomic_load_relaxed (&source->map_end));
58 atomic_store_relaxed (©->map,
59 atomic_load_relaxed (&source->map));
60 atomic_store_relaxed (©->eh_frame,
61 atomic_load_relaxed (&source->eh_frame));
62 #if DLFO_STRUCT_HAS_EH_DBASE
63 atomic_store_relaxed (©->eh_dbase,
64 atomic_load_relaxed (&source->eh_dbase));
65 #endif
66 #if DLFO_STRUCT_HAS_EH_COUNT
67 atomic_store_relaxed (©->eh_count,
68 atomic_load_relaxed (&source->eh_count));
69 #endif
70 }
71
72 static inline void
_dl_find_object_to_external(struct dl_find_object_internal * internal,struct dl_find_object * external)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))
_dl_find_object_from_map(struct link_map * l,struct dl_find_object_internal * result)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 */
142