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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | VERSIONS | ATTRIBUTES | CONFORMING TO | NOTES | EXAMPLE | SEE ALSO | COLOPHON |
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DLINFO(3) Linux Programmer's Manual DLINFO(3)
dlinfo - obtain information about a dynamically loaded object
#define _GNU_SOURCE
#include <link.h>
#include <dlfcn.h>
int dlinfo(void *handle, int request, void *info);
Link with -ldl.
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 corre‐
sponding 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 allocat‐
ing 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 correspond‐
ing 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.
On success, dlinfo() returns 0. On failure, it returns -1; the cause
of the error can be diagnosed using dlerror(3).
dlinfo() first appeared in glibc 2.3.3.
For an explanation of the terms used in this section, see
attributes(7).
┌──────────┬───────────────┬─────────┐
│Interface │ Attribute │ Value │
├──────────┼───────────────┼─────────┤
│dlinfo() │ Thread safety │ MT-Safe │
└──────────┴───────────────┴─────────┘
This function is a nonstandard GNU extension.
This function derives from the Solaris function of the same name and
also appears on some other systems. The sets of requests supported
by the various implementations overlaps only partially.
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;
int j;
if (argc != 2) {
fprintf(stderr, "Usage: %s <libpath>\n", argv[0]);
exit(EXIT_FAILURE);
}
/* Obtain a handle for shared objects 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 (j = 0; j < serinfo.dls_cnt; j++)
printf("dls_serpath[%d].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)
This page is part of release 4.15 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
Linux 2017-09-15 DLINFO(3)
Pages that refer to this page: dladdr(3), dlerror(3), dlopen(3), dlsym(3)
Copyright and license for this manual page
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