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.
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
#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)