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1 | '\" t |
2 | .\" Copyright (C) 2015 Michael Kerrisk <mtk.manpages@gmail.com> | |
3 | .\" and Copyright (C) 2008 Petr Baudis <pasky@suse.cz> (dladdr caveat) | |
4 | .\" | |
5 | .\" %%%LICENSE_START(VERBATIM) | |
6 | .\" Permission is granted to make and distribute verbatim copies of this | |
7 | .\" manual provided the copyright notice and this permission notice are | |
8 | .\" preserved on all copies. | |
9 | .\" | |
10 | .\" Permission is granted to copy and distribute modified versions of this | |
11 | .\" manual under the conditions for verbatim copying, provided that the | |
12 | .\" entire resulting derived work is distributed under the terms of a | |
13 | .\" permission notice identical to this one. | |
14 | .\" | |
15 | .\" Since the Linux kernel and libraries are constantly changing, this | |
16 | .\" manual page may be incorrect or out-of-date. The author(s) assume no | |
17 | .\" responsibility for errors or omissions, or for damages resulting from | |
18 | .\" the use of the information contained herein. The author(s) may not | |
19 | .\" have taken the same level of care in the production of this manual, | |
20 | .\" which is licensed free of charge, as they might when working | |
21 | .\" professionally. | |
22 | .\" | |
23 | .\" Formatted or processed versions of this manual, if unaccompanied by | |
24 | .\" the source, must acknowledge the copyright and authors of this work. | |
25 | .\" %%%LICENSE_END | |
26 | .\" | |
4b8c67d9 | 27 | .TH DLADDR 3 2017-09-15 "Linux" "Linux Programmer's Manual" |
affaa041 MK |
28 | .SH NAME |
29 | dladdr, dladdr1 \- translate address to symbolic information | |
30 | .SH SYNOPSIS | |
31 | .nf | |
32 | .B #define _GNU_SOURCE | |
33 | .B #include <dlfcn.h> | |
dbfe9c70 | 34 | .PP |
affaa041 | 35 | .BI "int dladdr(void *" addr ", Dl_info *" info ); |
dbfe9c70 | 36 | .PP |
affaa041 MK |
37 | .BI "int dladdr1(void *" addr ", Dl_info *" info ", void **" \ |
38 | extra_info ", int " flags ); | |
dbfe9c70 | 39 | .PP |
affaa041 MK |
40 | Link with \fI\-ldl\fP. |
41 | .fi | |
42 | .SH DESCRIPTION | |
43 | The function | |
44 | .BR dladdr () | |
45 | determines whether the address specified in | |
46 | .IR addr | |
47 | is located in one of the shared objects loaded by the calling application. | |
48 | If it is, then | |
49 | .BR dladdr () | |
50 | returns information about the shared object and symbol that overlaps | |
51 | .IR addr . | |
52 | This information is returned in a | |
53 | .I Dl_info | |
54 | structure: | |
51f5698d | 55 | .PP |
affaa041 | 56 | .in +4n |
b8302363 | 57 | .EX |
affaa041 MK |
58 | typedef struct { |
59 | const char *dli_fname; /* Pathname of shared object that | |
60 | contains address */ | |
61 | void *dli_fbase; /* Base address at which shared | |
62 | object is loaded */ | |
63 | const char *dli_sname; /* Name of symbol whose definition | |
64 | overlaps \fIaddr\fP */ | |
65 | void *dli_saddr; /* Exact address of symbol named | |
66 | in \fIdli_sname\fP */ | |
67 | } Dl_info; | |
b8302363 | 68 | .EE |
affaa041 MK |
69 | .in |
70 | .PP | |
71 | If no symbol matching | |
72 | .I addr | |
73 | could be found, then | |
74 | .I dli_sname | |
75 | and | |
76 | .I dli_saddr | |
77 | are set to NULL. | |
847e0d88 | 78 | .PP |
affaa041 MK |
79 | The function |
80 | .BR dladdr1 () | |
81 | is like | |
82 | .BR dladdr (), | |
83 | but returns additional information via the argument | |
84 | .IR extra_info . | |
85 | The information returned depends on the value specified in | |
86 | .IR flags , | |
87 | which can have one of the following values: | |
88 | .TP | |
89 | .B RTLD_DL_LINKMAP | |
10b22cd9 | 90 | Obtain a pointer to the link map for the matched file. |
affaa041 MK |
91 | The |
92 | .IR extra_info | |
93 | argument points to a pointer to a | |
94 | .I link_map | |
95 | structure (i.e., | |
96 | .IR "struct link_map\ **" ), | |
97 | defined in | |
98 | .I <link.h> | |
99 | as: | |
847e0d88 | 100 | .IP |
affaa041 | 101 | .in +4n |
b8302363 | 102 | .EX |
affaa041 MK |
103 | struct link_map { |
104 | ElfW(Addr) l_addr; /* Difference between the | |
105 | address in the ELF file and | |
106 | the address in memory */ | |
107 | char *l_name; /* Absolute pathname where | |
108 | object was found */ | |
109 | ElfW(Dyn) *l_ld; /* Dynamic section of the | |
110 | shared object */ | |
111 | struct link_map *l_next, *l_prev; | |
112 | /* Chain of loaded objects */ | |
113 | ||
114 | /* Plus additional fields private to the | |
115 | implementation */ | |
116 | }; | |
b8302363 | 117 | .EE |
affaa041 MK |
118 | .in |
119 | .TP | |
120 | .B RTLD_DL_SYMENT | |
10b22cd9 | 121 | Obtain a pointer to the ELF symbol table entry of the matching symbol. |
affaa041 MK |
122 | The |
123 | .IR extra_info | |
124 | argument is a pointer to a symbol pointer: | |
125 | .IR "const ElfW(Sym) **" . | |
126 | The | |
127 | .IR ElfW () | |
128 | macro definition turns its argument into the name of an ELF data | |
129 | type suitable for the hardware architecture. | |
130 | For example, on a 64-bit platform, | |
131 | .I ElfW(Sym) | |
132 | yields the data type name | |
133 | .IR Elf64_Sym , | |
134 | which is defined in | |
135 | .IR <elf.h> | |
136 | as: | |
847e0d88 | 137 | .IP |
affaa041 | 138 | .in +4n |
b8302363 | 139 | .EX |
30ea59e7 | 140 | typedef struct { |
affaa041 MK |
141 | Elf64_Word st_name; /* Symbol name */ |
142 | unsigned char st_info; /* Symbol type and binding */ | |
143 | unsigned char st_other; /* Symbol visibility */ | |
144 | Elf64_Section st_shndx; /* Section index */ | |
145 | Elf64_Addr st_value; /* Symbol value */ | |
146 | Elf64_Xword st_size; /* Symbol size */ | |
147 | } Elf64_Sym; | |
b8302363 | 148 | .EE |
affaa041 | 149 | .in |
847e0d88 | 150 | .IP |
affaa041 MK |
151 | The |
152 | .I st_name | |
153 | field is an index into the string table. | |
847e0d88 | 154 | .IP |
affaa041 MK |
155 | The |
156 | .I st_info | |
157 | field encodes the symbol's type and binding. | |
158 | The type can be extracted using the macro | |
159 | .BR ELF64_ST_TYPE(st_info) | |
160 | (or | |
161 | .BR ELF32_ST_TYPE() | |
162 | on 32-bit platforms), which yields one of the following values: | |
163 | .in +4n | |
164 | .TS | |
165 | lb lb | |
166 | lb l. | |
167 | Value Description | |
168 | STT_NOTYPE Symbol type is unspecified | |
169 | STT_OBJECT Symbol is a data object | |
170 | STT_FUNC Symbol is a code object | |
171 | STT_SECTION Symbol associated with a section | |
172 | STT_FILE Symbol's name is file name | |
173 | STT_COMMON Symbol is a common data object | |
174 | STT_TLS Symbol is thread-local data object | |
175 | STT_GNU_IFUNC Symbol is indirect code object | |
176 | .TE | |
177 | .in | |
178 | .IP | |
179 | The symbol binding can be extracted from the | |
180 | .I st_info | |
181 | field using the macro | |
182 | .BR ELF64_ST_BIND(st_info) | |
183 | (or | |
184 | .BR ELF32_ST_BIND() | |
185 | on 32-bit platforms), which yields one of the following values: | |
affaa041 MK |
186 | .in +4n |
187 | .TS | |
188 | lb lb | |
189 | lb l. | |
190 | Value Description | |
191 | STB_LOCAL Local symbol | |
192 | STB_GLOBAL Global symbol | |
193 | STB_WEAK Weak symbol | |
194 | STB_GNU_UNIQUE Unique symbol | |
195 | .TE | |
196 | .in | |
197 | .IP | |
198 | The | |
199 | .I st_other | |
200 | field contains the symbol's visibility, which can be extracted using the macro | |
201 | .BR ELF64_ST_VISIBILITY(st_info) | |
202 | (or | |
203 | .BR ELF32_ST_VISIBILITY() | |
204 | on 32-bit platforms), which yields one of the following values: | |
205 | .in +4n | |
206 | .TS | |
207 | lb lb | |
208 | lb l. | |
209 | Value Description | |
210 | STV_DEFAULT Default symbol visibility rules | |
211 | STV_INTERNAL Processor-specific hidden class | |
212 | STV_HIDDEN Symbol unavailable in other modules | |
213 | STV_PROTECTED Not preemptible, not exported | |
214 | .TE | |
215 | .in | |
216 | .SH RETURN VALUE | |
217 | On success, these functions return a nonzero value. | |
218 | If the address specified in | |
219 | .I addr | |
220 | could be matched to a shared object, | |
221 | but not to a symbol in the shared object, then the | |
222 | .I info->dli_sname | |
223 | and | |
224 | .I info->dli_saddr | |
225 | fields are set to NULL. | |
847e0d88 | 226 | .PP |
affaa041 MK |
227 | If the address specified in |
228 | .I addr | |
229 | could not be matched to a shared object, then these functions return 0. | |
230 | In this case, an error message is | |
231 | .I not | |
232 | .\" According to the FreeBSD man page, dladdr1() does signal an | |
233 | .\" error via dlerror() for this case. | |
234 | available via | |
235 | .BR dlerror (3). | |
236 | .SH VERSIONS | |
237 | .BR dladdr () | |
238 | is present in glibc 2.0 and later. | |
239 | .BR dladdr1 () | |
240 | first appeared in glibc 2.3.3. | |
06c0008d ZL |
241 | .SH ATTRIBUTES |
242 | For an explanation of the terms used in this section, see | |
243 | .BR attributes (7). | |
244 | .TS | |
245 | allbox; | |
246 | lbw19 lb lb | |
247 | l l l. | |
248 | Interface Attribute Value | |
249 | T{ | |
250 | .BR dladdr (), | |
251 | .BR dladdr1 () | |
252 | T} Thread safety MT-Safe | |
253 | .TE | |
affaa041 MK |
254 | .SH CONFORMING TO |
255 | These functions are nonstandard GNU extensions | |
256 | that are also present on Solaris. | |
257 | .SH BUGS | |
258 | Sometimes, the function pointers you pass to | |
259 | .BR dladdr () | |
260 | may surprise you. | |
9ea5bc66 | 261 | On some architectures (notably i386 and x86-64), |
affaa041 MK |
262 | .I dli_fname |
263 | and | |
264 | .I dli_fbase | |
265 | may end up pointing back at the object from which you called | |
266 | .BR dladdr (), | |
267 | even if the function used as an argument should come from | |
268 | a dynamically linked library. | |
269 | .PP | |
270 | The problem is that the function pointer will still be resolved | |
271 | at compile time, but merely point to the | |
272 | .I plt | |
273 | (Procedure Linkage Table) | |
274 | section of the original object (which dispatches the call after | |
275 | asking the dynamic linker to resolve the symbol). | |
276 | To work around this, | |
277 | you can try to compile the code to be position-independent: | |
278 | then, the compiler cannot prepare the pointer | |
ce65f81e | 279 | at compile time any more and |
affaa041 MK |
280 | .BR gcc (1) |
281 | will generate code that just loads the final symbol address from the | |
282 | .I got | |
283 | (Global Offset Table) at run time before passing it to | |
284 | .BR dladdr (). | |
285 | .SH SEE ALSO | |
286 | .BR dl_iterate_phdr (3), | |
9987012c | 287 | .BR dlinfo (3), |
affaa041 | 288 | .BR dlopen (3), |
de7d051d | 289 | .BR dlsym (3), |
affaa041 | 290 | .BR ld.so (8) |