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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ATTRIBUTES | VERSIONS | STANDARDS | HISTORY | EXAMPLES | SEE ALSO | COLOPHON |
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dlinfo(3) Library Functions Manual dlinfo(3)
dlinfo - obtain information about a dynamically loaded object
Dynamic linking library (libdl, -ldl)
#define _GNU_SOURCE
#include <link.h>
#include <dlfcn.h>
int dlinfo(void *restrict handle, int request, void *restrict info);
The dlinfo() function obtains information about the dynamically
loaded object referred to by handle (typically obtained by an
earlier call to dlopen(3) or dlmopen(3)). The request argument
specifies which information is to be returned. The info argument
is a pointer to a buffer used to store information returned by the
call; the type of this argument depends on request.
The following values are supported for request (with the
corresponding type for info shown in parentheses):
RTLD_DI_LMID (Lmid_t *)
Obtain the ID of the link-map list (namespace) in which
handle is loaded.
RTLD_DI_LINKMAP (struct link_map **)
Obtain a pointer to the link_map structure corresponding to
handle. The info argument points to a pointer to a
link_map structure, defined in <link.h> as:
struct link_map {
ElfW(Addr) l_addr; /* Difference between the
address in the ELF file and
the address in memory */
char *l_name; /* Absolute pathname where
object was found */
ElfW(Dyn) *l_ld; /* Dynamic section of the
shared object */
struct link_map *l_next, *l_prev;
/* Chain of loaded objects */
/* Plus additional fields private to the
implementation */
};
RTLD_DI_ORIGIN (char *)
Copy the pathname of the origin of the shared object
corresponding to handle to the location pointed to by info.
RTLD_DI_SERINFO (Dl_serinfo *)
Obtain the library search paths for the shared object
referred to by handle. The info argument is a pointer to a
Dl_serinfo that contains the search paths. Because the
number of search paths may vary, the size of the structure
pointed to by info can vary. The RTLD_DI_SERINFOSIZE
request described below allows applications to size the
buffer suitably. The caller must perform the following
steps:
(1) Use a RTLD_DI_SERINFOSIZE request to populate a
Dl_serinfo structure with the size (dls_size) of the
structure needed for the subsequent RTLD_DI_SERINFO
request.
(2) Allocate a Dl_serinfo buffer of the correct size
(dls_size).
(3) Use a further RTLD_DI_SERINFOSIZE request to populate
the dls_size and dls_cnt fields of the buffer
allocated in the previous step.
(4) Use a RTLD_DI_SERINFO to obtain the library search
paths.
The Dl_serinfo structure is defined as follows:
typedef struct {
size_t dls_size; /* Size in bytes of
the whole buffer */
unsigned int dls_cnt; /* Number of elements
in 'dls_serpath' */
Dl_serpath dls_serpath[1]; /* Actually longer,
'dls_cnt' elements */
} Dl_serinfo;
Each of the dls_serpath elements in the above structure is
a structure of the following form:
typedef struct {
char *dls_name; /* Name of library search
path directory */
unsigned int dls_flags; /* Indicates where this
directory came from */
} Dl_serpath;
The dls_flags field is currently unused, and always
contains zero.
RTLD_DI_SERINFOSIZE (Dl_serinfo *)
Populate the dls_size and dls_cnt fields of the Dl_serinfo
structure pointed to by info with values suitable for
allocating a buffer for use in a subsequent RTLD_DI_SERINFO
request.
RTLD_DI_TLS_MODID (size_t *, since glibc 2.4)
Obtain the module ID of this shared object's TLS (thread-
local storage) segment, as used in TLS relocations. If
this object does not define a TLS segment, zero is placed
in *info.
RTLD_DI_TLS_DATA (void **, since glibc 2.4)
Obtain a pointer to the calling thread's TLS block
corresponding to this shared object's TLS segment. If this
object does not define a PT_TLS segment, or if the calling
thread has not allocated a block for it, NULL is placed in
*info.
RTLD_DI_PHDR (const ElfW(Phdr *), since glibc 2.34.1)
Obtain the address of this shared object's program header
and place it in *info. This dlinfo call returns the number
of program headers in the shared object.
On success, dlinfo() returns 0 (if not specified explicitly), or a
positive value corresponding to the request. On failure, it
returns -1; the error can be diagnosed using dlerror(3).
For an explanation of the terms used in this section, see
attributes(7).
┌──────────────────────────────────────┬───────────────┬─────────┐
│ Interface │ Attribute │ Value │
├──────────────────────────────────────┼───────────────┼─────────┤
│ dlinfo() │ Thread safety │ MT-Safe │
└──────────────────────────────────────┴───────────────┴─────────┘
The sets of requests supported by the various implementations
overlaps only partially.
GNU.
glibc 2.3.3. Solaris.
The program below opens a shared objects using dlopen(3) and then
uses the RTLD_DI_SERINFOSIZE and RTLD_DI_SERINFO requests to
obtain the library search path list for the library. Here is an
example of what we might see when running the program:
$ ./a.out /lib64/libm.so.6;
dls_serpath[0].dls_name = /lib64
dls_serpath[1].dls_name = /usr/lib64
Program source
#define _GNU_SOURCE
#include <dlfcn.h>
#include <link.h>
#include <stdio.h>
#include <stdlib.h>
int
main(int argc, char *argv[])
{
void *handle;
Dl_serinfo serinfo;
Dl_serinfo *sip;
if (argc != 2) {
fprintf(stderr, "Usage: %s <libpath>\n", argv[0]);
exit(EXIT_FAILURE);
}
/* Obtain a handle for shared object specified on command line. */
handle = dlopen(argv[1], RTLD_NOW);
if (handle == NULL) {
fprintf(stderr, "dlopen() failed: %s\n", dlerror());
exit(EXIT_FAILURE);
}
/* Discover the size of the buffer that we must pass to
RTLD_DI_SERINFO. */
if (dlinfo(handle, RTLD_DI_SERINFOSIZE, &serinfo) == -1) {
fprintf(stderr, "RTLD_DI_SERINFOSIZE failed: %s\n", dlerror());
exit(EXIT_FAILURE);
}
/* Allocate the buffer for use with RTLD_DI_SERINFO. */
sip = malloc(serinfo.dls_size);
if (sip == NULL) {
perror("malloc");
exit(EXIT_FAILURE);
}
/* Initialize the 'dls_size' and 'dls_cnt' fields in the newly
allocated buffer. */
if (dlinfo(handle, RTLD_DI_SERINFOSIZE, sip) == -1) {
fprintf(stderr, "RTLD_DI_SERINFOSIZE failed: %s\n", dlerror());
exit(EXIT_FAILURE);
}
/* Fetch and print library search list. */
if (dlinfo(handle, RTLD_DI_SERINFO, sip) == -1) {
fprintf(stderr, "RTLD_DI_SERINFO failed: %s\n", dlerror());
exit(EXIT_FAILURE);
}
for (size_t j = 0; j < serinfo.dls_cnt; j++)
printf("dls_serpath[%zu].dls_name = %s\n",
j, sip->dls_serpath[j].dls_name);
exit(EXIT_SUCCESS);
}
dl_iterate_phdr(3), dladdr(3), dlerror(3), dlopen(3), dlsym(3),
ld.so(8)
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Linux man-pages 6.15 2025-05-17 dlinfo(3)
Pages that refer to this page: dladdr(3), dlerror(3), dlopen(3), dlsym(3)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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