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1/* Data structure for communication from the run-time dynamic linker for
2 loaded ELF shared objects.
3 Copyright (C) 1995-2025 Free Software Foundation, Inc.
4 This file is part of the GNU C Library.
5
6 The GNU C Library is free software; you can redistribute it and/or
7 modify it under the terms of the GNU Lesser General Public
8 License as published by the Free Software Foundation; either
9 version 2.1 of the License, or (at your option) any later version.
10
11 The GNU C Library is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 Lesser General Public License for more details.
15
16 You should have received a copy of the GNU Lesser General Public
17 License along with the GNU C Library; if not, see
18 <https://www.gnu.org/licenses/>. */
19
20#ifndef _LINK_H
21#define _LINK_H 1
22
23#include <features.h>
24#include <elf.h>
25#include <dlfcn.h>
26#include <sys/types.h>
27
28/* We use this macro to refer to ELF types independent of the native wordsize.
29 `ElfW(TYPE)' is used in place of `Elf32_TYPE' or `Elf64_TYPE'. */
30#define ElfW(type) _ElfW (Elf, __ELF_NATIVE_CLASS, type)
31#define _ElfW(e,w,t) _ElfW_1 (e, w, _##t)
32#define _ElfW_1(e,w,t) e##w##t
33
34#include <bits/elfclass.h> /* Defines __ELF_NATIVE_CLASS. */
35#include <bits/link.h>
36
37/* The legacy rendezvous structure used by the run-time dynamic linker to
38 communicate details of shared object loading to the debugger. */
39
40struct r_debug
41 {
42 /* Version number for this protocol. It should be greater than 0. */
43 int r_version;
44
45 struct link_map *r_map; /* Head of the chain of loaded objects. */
46
47 /* This is the address of a function internal to the run-time linker,
48 that will always be called when the linker begins to map in a
49 library or unmap it, and again when the mapping change is complete.
50 The debugger can set a breakpoint at this address if it wants to
51 notice shared object mapping changes. */
52 ElfW(Addr) r_brk;
53 enum
54 {
55 /* This state value describes the mapping change taking place when
56 the `r_brk' address is called. */
57 RT_CONSISTENT, /* Mapping change is complete. */
58 RT_ADD, /* Beginning to add a new object. */
59 RT_DELETE /* Beginning to remove an object mapping. */
60 } r_state;
61
62 ElfW(Addr) r_ldbase; /* Base address the linker is loaded at. */
63 };
64
65/* This is the symbol of that structure provided by the dynamic linker. */
66extern struct r_debug _r_debug;
67
68/* The extended rendezvous structure used by the run-time dynamic linker
69 to communicate details of shared object loading to the debugger. If
70 the executable's dynamic section has a DT_DEBUG element, the run-time
71 linker sets that element's value to the address where this structure
72 can be found. */
73
74struct r_debug_extended
75 {
76 struct r_debug base;
77
78 /* The following field is added by r_version == 2. */
79
80 /* Link to the next r_debug_extended structure. Each r_debug_extended
81 structure represents a different namespace. The first
82 r_debug_extended structure is for the default namespace. */
83 struct r_debug_extended *r_next;
84 };
85
86/* This symbol refers to the "dynamic structure" in the `.dynamic' section
87 of whatever module refers to `_DYNAMIC'. So, to find its own
88 `struct r_debug_extended', a program could do:
89 for (dyn = _DYNAMIC; dyn->d_tag != DT_NULL; ++dyn)
90 if (dyn->d_tag == DT_DEBUG)
91 r_debug_extended = (struct r_debug_extended *) dyn->d_un.d_ptr;
92 */
93extern ElfW(Dyn) _DYNAMIC[];
94
95/* Structure describing a loaded shared object. The `l_next' and `l_prev'
96 members form a chain of all the shared objects loaded at startup.
97
98 These data structures exist in space used by the run-time dynamic linker;
99 modifying them may have disastrous results. */
100
101struct link_map
102 {
103 /* These first few members are part of the protocol with the debugger.
104 This is the same format used in SVR4. */
105
106 ElfW(Addr) l_addr; /* Difference between the address in the ELF
107 file and the addresses in memory. */
108 char *l_name; /* Absolute file name object was found in. */
109 ElfW(Dyn) *l_ld; /* Dynamic section of the shared object. */
110 struct link_map *l_next, *l_prev; /* Chain of loaded objects. */
111 };
112
113#ifdef __USE_GNU
114
115/* Version numbers for la_version handshake interface. */
116#include <bits/link_lavcurrent.h>
117
118/* Activity types signaled through la_activity. */
119enum
120 {
121 LA_ACT_CONSISTENT, /* Link map consistent again. */
122 LA_ACT_ADD, /* New object will be added. */
123 LA_ACT_DELETE /* Objects will be removed. */
124 };
125
126/* Values representing origin of name for dynamic loading. */
127enum
128 {
129 LA_SER_ORIG = 0x01, /* Original name. */
130 LA_SER_LIBPATH = 0x02, /* Directory from LD_LIBRARY_PATH. */
131 LA_SER_RUNPATH = 0x04, /* Directory from RPATH/RUNPATH. */
132 LA_SER_CONFIG = 0x08, /* Found through ldconfig. */
133 LA_SER_DEFAULT = 0x40, /* Default directory. */
134 LA_SER_SECURE = 0x80 /* Unused. */
135 };
136
137/* Values for la_objopen return value. */
138enum
139 {
140 LA_FLG_BINDTO = 0x01, /* Audit symbols bound to this object. */
141 LA_FLG_BINDFROM = 0x02 /* Audit symbols bound from this object. */
142 };
143
144/* Values for la_symbind flags parameter. */
145enum
146 {
147 LA_SYMB_NOPLTENTER = 0x01, /* la_pltenter will not be called. */
148 LA_SYMB_NOPLTEXIT = 0x02, /* la_pltexit will not be called. */
149 LA_SYMB_STRUCTCALL = 0x04, /* Return value is a structure. */
150 LA_SYMB_DLSYM = 0x08, /* Binding due to dlsym call. */
151 LA_SYMB_ALTVALUE = 0x10 /* Value has been changed by a previous
152 la_symbind call. */
153 };
154
155struct dl_phdr_info
156 {
157 ElfW(Addr) dlpi_addr;
158 const char *dlpi_name;
159 const ElfW(Phdr) *dlpi_phdr;
160 ElfW(Half) dlpi_phnum;
161
162 /* Note: Following members were introduced after the first
163 version of this structure was available. Check the SIZE
164 argument passed to the dl_iterate_phdr callback to determine
165 whether or not each later member is available. */
166
167 /* Incremented when a new object may have been added. */
168 __extension__ unsigned long long int dlpi_adds;
169 /* Incremented when an object may have been removed. */
170 __extension__ unsigned long long int dlpi_subs;
171
172 /* If there is a PT_TLS segment, its module ID as used in
173 TLS relocations, else zero. */
174 size_t dlpi_tls_modid;
175
176 /* The address of the calling thread's instance of this module's
177 PT_TLS segment, if it has one and it has been allocated
178 in the calling thread, otherwise a null pointer. */
179 void *dlpi_tls_data;
180 };
181
182__BEGIN_DECLS
183
184extern int dl_iterate_phdr (int (*__callback) (struct dl_phdr_info *,
185 size_t, void *),
186 void *__data);
187
188
189/* Prototypes for the ld.so auditing interfaces. These are not
190 defined anywhere in ld.so but instead have to be provided by the
191 auditing DSO. */
192extern unsigned int la_version (unsigned int __version);
193extern void la_activity (uintptr_t *__cookie, unsigned int __flag);
194extern char *la_objsearch (const char *__name, uintptr_t *__cookie,
195 unsigned int __flag);
196extern unsigned int la_objopen (struct link_map *__map, Lmid_t __lmid,
197 uintptr_t *__cookie);
198extern void la_preinit (uintptr_t *__cookie);
199extern uintptr_t la_symbind32 (Elf32_Sym *__sym, unsigned int __ndx,
200 uintptr_t *__refcook, uintptr_t *__defcook,
201 unsigned int *__flags, const char *__symname);
202extern uintptr_t la_symbind64 (Elf64_Sym *__sym, unsigned int __ndx,
203 uintptr_t *__refcook, uintptr_t *__defcook,
204 unsigned int *__flags, const char *__symname);
205extern unsigned int la_objclose (uintptr_t *__cookie);
206
207__END_DECLS
208
209#endif
210
211#endif /* link.h */