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.TH DLINFO 3 2017-09-15 "Linux" "Linux Programmer's Manual"

.SH NAME

dlinfo \- obtain information about a dynamically loaded object

.SH SYNOPSIS

.nf

.B #define _GNU_SOURCE

.B #include <link.h>

.B #include <dlfcn.h>

.PP

.BR "int dlinfo(void *" handle ", int " request ", void *" info );

.PP

Link with \fI\-ldl\fP.

.fi

.SH DESCRIPTION

The

.BR dlinfo ()

function obtains information about the dynamically loaded object

referred to by

.IR handle

(typically obtained by an earlier call to

.BR dlopen (3)

or

.BR dlmopen (3)).

The

.I request

argument specifies which information is to be returned.

The

.I info

argument is a pointer to a buffer used to store information

returned by the call; the type of this argument depends on

.IR request .

.PP

The following values are supported for

.IR request

(with the corresponding type for

.IR info

shown in parentheses):

.TP

.BR RTLD_DI_LMID " (\fILmid_t *\fP)"

Obtain the ID of the link-map list (namespace) in which

.I handle

is loaded.

.TP

.BR RTLD_DI_LINKMAP " (\fIstruct link_map **\fP)"

Obtain a pointer to the

.I link_map

structure corresponding to

.IR handle .

The

.IR info

argument points to a pointer to a

.I link_map

structure, defined in

.I <link.h>

as:

.IP

.in +4n

.EX

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 */

};

.EE

.in

.TP

.BR RTLD_DI_ORIGIN " (\fIchar *\fP)"

Copy the pathname of the origin of the shared object corresponding to

.IR handle

to the location pointed to by

.IR info .

.TP

.BR RTLD_DI_SERINFO " (\fIDl_serinfo *\fP)"

Obtain the library search paths for the shared object referred to by

.IR handle .

The

.I info

argument is a pointer to a

.I Dl_serinfo

that contains the search paths.

Because the number of search paths may vary,

the size of the structure pointed to by

.IR info

can vary.

The

.B RTLD_DI_SERINFOSIZE

request described below allows applications to size the buffer suitably.

The caller must perform the following steps:

.RS

.IP 1. 3

Use a

.B RTLD_DI_SERINFOSIZE

request to populate a

.I Dl_serinfo

structure with the size

.RI ( dls_size )

of the structure needed for the subsequent

.B RTLD_DI_SERINFO

request.

.IP 2.

Allocate a

.I Dl_serinfo

buffer of the correct size

.RI ( dls_size ).

.IP 3.

Use a further

.B RTLD_DI_SERINFOSIZE

request to populate the

.I dls_size

and

.I dls_cnt

fields of the buffer allocated in the previous step.

.IP 4.

Use a

.B RTLD_DI_SERINFO

to obtain the library search paths.

.IP

.RE

.IP

The

.I Dl_serinfo

structure is defined as follows:

.IP

.in +4n

.EX

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;

.EE

.in

.IP

Each of the

.I dls_serpath

elements in the above structure is a structure of the following form:

.IP

.in +4n

.EX

typedef struct {

    char *dls_name;            /* Name of library search

                                  path directory */

    unsigned int dls_flags;    /* Indicates where this

                                  directory came from */

} Dl_serpath;

.EE

.in

.IP

The

.I dls_flags

field is currently unused, and always contains zero.

.TP

.BR RTLD_DI_SERINFOSIZE " (\fIDl_serinfo *\fP)"

Populate the

.I dls_size

and

.I dls_cnt

fields of the

.I Dl_serinfo

structure pointed to by

.IR info

with values suitable for allocating a buffer for use in a subsequent

.B RTLD_DI_SERINFO

request.

.TP

.BR RTLD_DI_TLS_MODID " (\fIsize_t *\fP, 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

.IR *info .

.TP

.BR RTLD_DI_TLS_DATA " (\fIvoid **\fP, 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

.IR *info .

.SH RETURN VALUE

On success,

.BR dlinfo ()

returns 0.

On failure, it returns \-1; the cause of the error can be diagnosed using

.BR dlerror (3).

.SH VERSIONS

.BR dlinfo ()

first appeared in glibc 2.3.3.

.SH ATTRIBUTES

For an explanation of the terms used in this section, see

.BR attributes (7).

.TS

allbox;

lb lb lb

l l l.

Interface	Attribute	Value

T{

.BR dlinfo ()

T}	Thread safety	MT-Safe

.TE

.SH CONFORMING TO

This function is a nonstandard GNU extension.

.SH 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.

.SH EXAMPLE

The program below opens a shared objects using

.BR dlopen (3)

and then uses the

.B RTLD_DI_SERINFOSIZE

and

.B 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:

.PP

.in +4n

.EX

$ \fB./a.out /lib64/libm.so.6\fP

dls_serpath[0].dls_name = /lib64

dls_serpath[1].dls_name = /usr/lib64

.EE

.in

.SS Program source

\&

.EX

#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 \(aqdls_size\(aq and \(aqdls_cnt\(aq 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);

}

.EE

.SH SEE ALSO

.BR dl_iterate_phdr (3),

.BR dladdr (3),

.BR dlerror (3),

.BR dlopen (3),

.BR dlsym (3),

.BR ld.so (8)

.SH COLOPHON

This page is part of release 4.15 of the Linux

.I 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/.