DLINFO

NAME

SYNOPSIS

#define _GNU_SOURCE
#include <link.h>
#include <dlfcn.h>

int dlinfo(void *restrict handle, int request, void *restrict info);

Link with -ldl.

DESCRIPTION

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

VERSIONS

ATTRIBUTES

CONFORMING TO

NOTES

EXAMPLES

$ ./a.out /lib64/libm.so.6 dls_serpath[0].dls_name = /lib64 dls_serpath[1].dls_name = /usr/lib64  

Program source

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 (int 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

COLOPHON

Index

NAME

SYNOPSIS

DESCRIPTION

RETURN VALUE

VERSIONS

ATTRIBUTES

CONFORMING TO

NOTES

EXAMPLES

Program source

SEE ALSO

COLOPHON