.\"	$NetBSD: dlinfo.3,v 1.7 2022/03/06 23:36:01 andvar Exp $
.\"
.\" Copyright (c) 2003 Alexey Zelkin <phantom@FreeBSD.org>
.\" All rights reserved.
.\"
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.\" $FreeBSD: head/lib/libc/gen/dlinfo.3 267774 2014-06-23 08:25:03Z bapt $
.\"
.Dd January 13, 2020
.Dt DLINFO 3
.Os
.Sh NAME
.Nm dlinfo
.Nd information about a dynamically loaded object
.Sh LIBRARY
(These functions are not in a library.
They are included in every
dynamically linked program automatically.)
.Sh SYNOPSIS
.In link.h
.In dlfcn.h
.Ft int
.Fn dlinfo "void *handle" "int request" "void *p"
.Sh DESCRIPTION
The
.Fn dlinfo
function provides information about a dynamically loaded object.
The action taken by
.Fn dlinfo
and exact meaning and type of
.Fa p
argument depend on value of the
.Fa request
argument provided by caller.
.Pp
The
.Fa handle
argument is either the value returned from the
.Xr dlopen 3
function call or special handle
.Dv RTLD_SELF .
If
.Fa handle
is the value returned from
.Xr dlopen 3 ,
the information returned by the
.Fn dlinfo
function pertains to the specified object.
If
.Fa handle
is the special handle
.Dv RTLD_SELF ,
the information returned pertains to the caller itself.
.Pp
Possible values for the
.Fa request
argument are:
.Bl -tag -width "Dv RTLD_"
.It Dv RTLD_DI_LINKMAP
Retrieve the pointer to the
.Vt Link_map
for the specified
.Fa handle .
On successful return, the
.Fa p
argument is filled with the pointer to the
.Vt Link_map
structure
.Pq Fa "Link_map **p"
describing a shared object specified by the
.Fa handle
argument.
The
.Vt Link_map
structures are maintained as a doubly linked list by
.Xr ld.so 1 ,
in the same order as
.Xr dlopen 3
and
.Xr dlclose 3
are called.
.Pp
The
.Vt Link_map
structure is defined in
.In link.h
and has the following members:
.Bd -literal -offset indent
caddr_t         l_addr;    /* Base Address of library */
#ifdef __mips__
caddr_t         l_offs;    /* Load Offset of library */
#endif
const char      *l_name;   /* Absolute Path to Library */
void            *l_ld;     /* Pointer to .dynamic in memory */
struct link_map *l_next,   /* linked list of mapped libs */
                *l_prev;
.Ed
.Bl -tag -width Va
.It Va l_addr
The base address of the object loaded into memory.
.It Va l_name
The absolute pathname of the loaded shared object.
.It Va l_ld
The address of the dynamic linking information segment
.Pq Dv PT_DYNAMIC
loaded into memory.
.It Va l_next
The next
.Vt Link_map
structure on the link-map list.
.It Va l_prev
The previous
.Vt Link_map
structure on the link-map list.
.El
.\" .It Dv RTLD_DI_SERINFO
.\" Retrieve the library search paths associated with the given
.\" .Fa handle
.\" argument.
.\" The
.\" .Fa p
.\" argument should point to
.\" .Vt Dl_serinfo
.\" structure buffer
.\" .Pq Fa "Dl_serinfo *p" .
.\" The
.\" .Vt Dl_serinfo
.\" structure must be initialized first with the
.\" .Dv RTLD_DI_SERINFOSIZE
.\" request.
.\" .Pp
.\" The returned
.\" .Vt Dl_serinfo
.\" structure contains
.\" .Va dls_cnt
.\" .Vt Dl_serpath
.\" entries.
.\" Each entry's
.\" .Va dlp_name
.\" field points to the search path.
.\" The corresponding
.\" .Va dlp_info
.\" field contains one of more flags indicating the origin of the path (see the
.\" .Dv LA_SER_*
.\" flags defined in the
.\" .In link.h
.\" header file).
.\" See
.\" .Sx EXAMPLES ,
.\" example 2, for a usage example.
.\" .It Dv RTLD_DI_SERINFOSIZE
.\" Initialize a
.\" .Vt Dl_serinfo
.\" structure for use in a
.\" .Dv RTLD_DI_SERINFO
.\" request.
.\" Both the
.\" .Va dls_cnt
.\" and
.\" .Va dls_size
.\" fields are returned to indicate the number of search paths applicable
.\" to the handle, and the total size of a
.\" .Vt Dl_serinfo
.\" buffer required to hold
.\" .Va dls_cnt
.\" .Vt Dl_serpath
.\" entries and the associated search path strings.
.\" See
.\" .Sx EXAMPLES ,
.\" example 2, for a usage example.
.\" .It Va RTLD_DI_ORIGIN
.\" Retrieve the origin of the dynamic object associated with the handle.
.\" On successful return,
.\" .Fa p
.\" argument is filled with the
.\" .Vt char
.\" pointer
.\" .Pq Fa "char *p" .
.El
.Sh RETURN VALUES
The
.Fn dlinfo
function returns 0 on success, or \-1 if an error occurred.
Whenever an error has been detected, a message detailing it can
be retrieved via a call to
.Xr dlerror 3 .
.Sh EXAMPLES
Using
.Fn dlinfo
to retrieve
.Vt Link_map
structure.
.Pp
The following example shows how dynamic library can detect the list
of shared libraries loaded after caller's one.
For simplicity, error checking has been omitted.
.Bd -literal -offset indent
Link_map *map;

dlinfo(RTLD_SELF, RTLD_DI_LINKMAP, &map);

while (map != NULL) {
	printf("%p: %s\\n", map->l_addr, map->l_name);
	map = map->l_next;
}
.Ed
.\" .Pp
.\" Example 2: Using
.\" .Fn dlinfo
.\" to retrieve the library search paths.
.\" .Pp
.\" The following example shows how a dynamic object can inspect the library
.\" search paths that would be used to locate a simple filename with
.\" .Xr dlopen 3 .
.\" For simplicity, error checking has been omitted.
.\" .Bd -literal -offset indent
.\" Dl_serinfo	 _info, *info = &_info;
.\" Dl_serpath	*path;
.\" unsigned int	 cnt;
.\"
.\" /* determine search path count and required buffer size */
.\" dlinfo(RTLD_SELF, RTLD_DI_SERINFOSIZE, (void *)info);
.\"
.\" /* allocate new buffer and initialize */
.\" info = malloc(_info.dls_size);
.\" info->dls_size = _info.dls_size;
.\" info->dls_cnt = _info.dls_cnt;
.\"
.\" /* obtain search path information */
.\" dlinfo(RTLD_SELF, RTLD_DI_SERINFO, (void *)info);
.\"
.\" path = &info->dls_serpath[0];
.\"
.\" for (cnt = 1; cnt <= info->dls_cnt; cnt++, path++) {
.\" 	(void) printf("%2d: %s\\n", cnt, path->dls_name);
.\" }
.\" .Ed
.Sh SEE ALSO
.Xr rtld 1 ,
.Xr dladdr 3 ,
.Xr dlopen 3 ,
.Xr dlsym 3
.Sh HISTORY
The
.Fn dlinfo
function first appeared in the Solaris operating system.
In
.Nx ,
it first appeared in
.Nx 5.1 .
.Sh AUTHORS
.An -nosplit
The
.Nx
implementation of the
.Fn dlinfo
function was written by
.An Antti Kantee Aq Mt pooka@NetBSD.org .
.Pp
The manual page for this function was written by
.An Alexey Zelkin Aq Mt phantom@FreeBSD.org
and adapted to
.Nx
by
.An Kamil Rytarowski Aq Mt kamil@NetBSD.org .