dlinfo(3)
NAME
dlinfo - obtain information about a dynamically loaded object
SYNOPSIS
#define _GNU_SOURCE
#include <link.h>
#include <dlfcn.h>
int dlinfo(void *handle, int request, void *info);
Link with -ldl.
DESCRIPTION
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.
RETURN VALUE
On success, dlinfo() returns 0. On failure, it returns -1; the cause
of the error can be diagnosed using dlerror(3).
VERSIONS
dlinfo() first appeared in glibc 2.3.3.
ATTRIBUTES
For an explanation of the terms used in this section, see
attributes(7).
Interface Attribute Value
dlinfo() Thread safety MT-Safe
CONFORMING TO
This function is a nonstandard GNU extension.
NOTES
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.
EXAMPLE
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);
}
SEE ALSO
dl_iterate_phdr(3), dladdr(3), dlerror(3), dlopen(3), dlsym(3),
ld.so(8)
COLOPHON
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