Copyright (c) 2003 Alexey Zelkin <phantom@FreeBSD.org>
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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 n link.h n 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.
p 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.
p Possible values for the .Fa request argument are: l -tag -width "Dv RTLD_" t 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
q 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.
p The .Vt Link_map structure is defined in n link.h and has the following members: d -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 l -tag -width Va t Va l_addr The base address of the object loaded into memory. t Va l_name The absolute pathname of the loaded shared object. t Va l_ld The address of the dynamic linking information segment
q Dv PT_DYNAMIC
loaded into memory.
t Va l_next The next
.Vt Link_map
structure on the link-map list.
t 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.
p
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.
d -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 .
p 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 .