1DLINFO(3)                  Linux Programmer's Manual                 DLINFO(3)
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NAME

6       dlinfo - obtain information about a dynamically loaded object
7

SYNOPSIS

9       #define _GNU_SOURCE
10       #include <link.h>
11       #include <dlfcn.h>
12
13       int dlinfo(void *handle, int request, void *info);
14
15       Link with -ldl.
16

DESCRIPTION

18       The  dlinfo() function obtains information about the dynamically loaded
19       object referred to by handle (typically obtained by an earlier call  to
20       dlopen(3)  or dlmopen(3)).  The request argument specifies which infor‐
21       mation is to be returned.  The info argument is a pointer to  a  buffer
22       used  to store information returned by the call; the type of this argu‐
23       ment depends on request.
24
25       The following values are supported for request (with the  corresponding
26       type for info shown in parentheses):
27
28       RTLD_DI_LMID (Lmid_t *)
29              Obtain  the  ID of the link-map list (namespace) in which handle
30              is loaded.
31
32       RTLD_DI_LINKMAP (struct link_map **)
33              Obtain a pointer to the link_map structure corresponding to han‐
34              dle.  The info argument points to a pointer to a link_map struc‐
35              ture, defined in <link.h> as:
36
37                  struct link_map {
38                      ElfW(Addr) l_addr;  /* Difference between the
39                                             address in the ELF file and
40                                             the address in memory */
41                      char      *l_name;  /* Absolute pathname where
42                                             object was found */
43                      ElfW(Dyn) *l_ld;    /* Dynamic section of the
44                                             shared object */
45                      struct link_map *l_next, *l_prev;
46                                          /* Chain of loaded objects */
47
48                      /* Plus additional fields private to the
49                         implementation */
50                  };
51
52       RTLD_DI_ORIGIN (char *)
53              Copy the pathname of the origin of the shared object correspond‐
54              ing to handle to the location pointed to by info.
55
56       RTLD_DI_SERINFO (Dl_serinfo *)
57              Obtain  the  library search paths for the shared object referred
58              to by handle.  The info argument is a pointer  to  a  Dl_serinfo
59              that  contains  the  search paths.  Because the number of search
60              paths may vary, the size of the structure pointed to by info can
61              vary.   The  RTLD_DI_SERINFOSIZE  request described below allows
62              applications to size the buffer suitably.  The caller must  per‐
63              form the following steps:
64
65              1. Use  a  RTLD_DI_SERINFOSIZE  request to populate a Dl_serinfo
66                 structure with the size (dls_size) of  the  structure  needed
67                 for the subsequent RTLD_DI_SERINFO request.
68
69              2. Allocate a Dl_serinfo buffer of the correct size (dls_size).
70
71              3. Use  a  further  RTLD_DI_SERINFOSIZE  request to populate the
72                 dls_size and dls_cnt fields of the buffer  allocated  in  the
73                 previous step.
74
75              4. Use a RTLD_DI_SERINFO to obtain the library search paths.
76
77              The Dl_serinfo structure is defined as follows:
78
79                  typedef struct {
80                      size_t dls_size;           /* Size in bytes of
81                                                    the whole buffer */
82                      unsigned int dls_cnt;      /* Number of elements
83                                                    in 'dls_serpath' */
84                      Dl_serpath dls_serpath[1]; /* Actually longer,
85                                                    'dls_cnt' elements */
86                  } Dl_serinfo;
87
88              Each  of  the  dls_serpath  elements in the above structure is a
89              structure of the following form:
90
91                  typedef struct {
92                      char *dls_name;            /* Name of library search
93                                                    path directory */
94                      unsigned int dls_flags;    /* Indicates where this
95                                                    directory came from */
96                  } Dl_serpath;
97
98              The dls_flags field is currently  unused,  and  always  contains
99              zero.
100
101       RTLD_DI_SERINFOSIZE (Dl_serinfo *)
102              Populate  the  dls_size  and  dls_cnt  fields  of the Dl_serinfo
103              structure pointed to by info with values suitable for allocating
104              a buffer for use in a subsequent RTLD_DI_SERINFO request.
105
106       RTLD_DI_TLS_MODID (size_t *, since glibc 2.4)
107              Obtain  the  module ID of this shared object's TLS (thread-local
108              storage) segment, as used in TLS relocations.   If  this  object
109              does not define a TLS segment, zero is placed in *info.
110
111       RTLD_DI_TLS_DATA (void **, since glibc 2.4)
112              Obtain a pointer to the calling thread's TLS block corresponding
113              to this shared object's TLS segment.  If this  object  does  not
114              define  a PT_TLS segment, or if the calling thread has not allo‐
115              cated a block for it, NULL is placed in *info.
116

RETURN VALUE

118       On success, dlinfo() returns 0.  On failure, it returns -1;  the  cause
119       of the error can be diagnosed using dlerror(3).
120

VERSIONS

122       dlinfo() first appeared in glibc 2.3.3.
123

ATTRIBUTES

125       For  an  explanation  of  the  terms  used  in  this  section,  see at‐
126       tributes(7).
127
128       ┌──────────┬───────────────┬─────────┐
129Interface Attribute     Value   
130       ├──────────┼───────────────┼─────────┤
131dlinfo()  │ Thread safety │ MT-Safe │
132       └──────────┴───────────────┴─────────┘

CONFORMING TO

134       This function is a nonstandard GNU extension.
135

NOTES

137       This function derives from the Solaris function of the  same  name  and
138       also  appears on some other systems.  The sets of requests supported by
139       the various implementations overlaps only partially.
140

EXAMPLES

142       The program below opens a shared objects using dlopen(3) and then  uses
143       the  RTLD_DI_SERINFOSIZE and RTLD_DI_SERINFO requests to obtain the li‐
144       brary search path list for the library.  Here is an example of what  we
145       might see when running the program:
146
147           $ ./a.out /lib64/libm.so.6
148           dls_serpath[0].dls_name = /lib64
149           dls_serpath[1].dls_name = /usr/lib64
150
151   Program source
152
153       #define _GNU_SOURCE
154       #include <dlfcn.h>
155       #include <link.h>
156       #include <stdio.h>
157       #include <stdlib.h>
158
159       int
160       main(int argc, char *argv[])
161       {
162           void *handle;
163           Dl_serinfo serinfo;
164           Dl_serinfo *sip;
165
166           if (argc != 2) {
167               fprintf(stderr, "Usage: %s <libpath>\n", argv[0]);
168               exit(EXIT_FAILURE);
169           }
170
171           /* Obtain a handle for shared object specified on command line */
172
173           handle = dlopen(argv[1], RTLD_NOW);
174           if (handle == NULL) {
175               fprintf(stderr, "dlopen() failed: %s\n", dlerror());
176               exit(EXIT_FAILURE);
177           }
178
179           /* Discover the size of the buffer that we must pass to
180              RTLD_DI_SERINFO */
181
182           if (dlinfo(handle, RTLD_DI_SERINFOSIZE, &serinfo) == -1) {
183               fprintf(stderr, "RTLD_DI_SERINFOSIZE failed: %s\n", dlerror());
184               exit(EXIT_FAILURE);
185           }
186
187           /* Allocate the buffer for use with RTLD_DI_SERINFO */
188
189           sip = malloc(serinfo.dls_size);
190           if (sip == NULL) {
191               perror("malloc");
192               exit(EXIT_FAILURE);
193           }
194
195           /* Initialize the 'dls_size' and 'dls_cnt' fields in the newly
196              allocated buffer */
197
198           if (dlinfo(handle, RTLD_DI_SERINFOSIZE, sip) == -1) {
199               fprintf(stderr, "RTLD_DI_SERINFOSIZE failed: %s\n", dlerror());
200               exit(EXIT_FAILURE);
201           }
202
203           /* Fetch and print library search list */
204
205           if (dlinfo(handle, RTLD_DI_SERINFO, sip) == -1) {
206               fprintf(stderr, "RTLD_DI_SERINFO failed: %s\n", dlerror());
207               exit(EXIT_FAILURE);
208           }
209
210           for (int j = 0; j < serinfo.dls_cnt; j++)
211               printf("dls_serpath[%d].dls_name = %s\n",
212                       j, sip->dls_serpath[j].dls_name);
213
214           exit(EXIT_SUCCESS);
215       }
216

SEE ALSO

218       dl_iterate_phdr(3),   dladdr(3),   dlerror(3),   dlopen(3),   dlsym(3),
219       ld.so(8)
220

COLOPHON

222       This page is part of release 5.10 of the Linux  man-pages  project.   A
223       description  of  the project, information about reporting bugs, and the
224       latest    version    of    this    page,    can     be     found     at
225       https://www.kernel.org/doc/man-pages/.
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229Linux                             2020-11-01                         DLINFO(3)
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