Simplify code by using IF_DRAIN.
[dragonfly.git] / libexec / rtld-elf / rtld.1
CommitLineData
984263bc 1.\" $FreeBSD: src/libexec/rtld-elf/rtld.1,v 1.18.2.7 2002/01/10 17:51:28 ru Exp $
1de703da 2.\" $DragonFly: src/libexec/rtld-elf/rtld.1,v 1.2 2003/06/17 04:27:08 dillon Exp $
984263bc
MD
3.\"
4.\" Copyright (c) 1995 Paul Kranenburg
5.\" All rights reserved.
6.\"
7.\" Redistribution and use in source and binary forms, with or without
8.\" modification, are permitted provided that the following conditions
9.\" are met:
10.\" 1. Redistributions of source code must retain the above copyright
11.\" notice, this list of conditions and the following disclaimer.
12.\" 2. Redistributions in binary form must reproduce the above copyright
13.\" notice, this list of conditions and the following disclaimer in the
14.\" documentation and/or other materials provided with the distribution.
15.\" 3. All advertising materials mentioning features or use of this software
16.\" must display the following acknowledgment:
17.\" This product includes software developed by Paul Kranenburg.
18.\" 3. The name of the author may not be used to endorse or promote products
19.\" derived from this software without specific prior written permission
20.\"
21.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
22.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
23.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
24.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
25.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
26.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
27.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
28.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
29.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
30.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
31.\"
32.Dd January 28, 2000
33.Dt RTLD 1
34.Os
35.Sh NAME
36.Nm ld-elf.so.1 ,
37.Nm rtld
38.Nd run-time link-editor
39.Sh DESCRIPTION
40.Nm
41is a self-contained shared object providing run-time
42support for loading and link-editing shared objects into a process'
43address space.
44It is also commonly known as the dynamic linker.
45It uses the data structures
46contained within dynamically linked programs to determine which shared
47libraries are needed and loads them using the
48.Xr mmap 2
49system call.
50.Pp
51After all shared libraries have been successfully loaded,
52.Nm
53proceeds to resolve external references from both the main program and
54all objects loaded.
55A mechanism is provided for initialization routines
56to be called on a per-object basis, giving a shared object an opportunity
57to perform any extra set-up before execution of the program proper begins.
58This is useful for C++ libraries that contain static constructors.
59.Pp
60.Nm
61itself is loaded by the kernel together with any dynamically-linked
62program that is to be executed.
63The kernel transfers control to the
64dynamic linker.
65After the dynamic linker has finished loading,
66relocating, and initializing the program and its required shared
67objects, it transfers control to the entry point of the program.
68.Pp
69To locate the required shared objects in the filesystem,
70.Nm
71may use a
72.Dq hints
73file prepared by the
74.Xr ldconfig 8
75utility.
76.Pp
77.Nm
78recognizes a number of environment variables that can be used to modify
79its behaviour as follows:
80.Pp
81.Bl -tag -width ".Ev LD_LIBRARY_PATH"
82.It Ev LD_LIBRARY_PATH
83A colon separated list of directories, overriding the default search path
84for shared libraries.
85This is ignored for set-user-ID and set-group-ID programs.
86.It Ev LD_PRELOAD
87A list of shared libraries, separated by colons and/or white space,
88to be linked in before any
89other shared libraries.
90If the directory is not specified then
91the directories specified by
92.Ev LD_LIBRARY_PATH
93will be searched first
94followed by the set of built-in standard directories.
95This is ignored for set-user-ID and set-group-ID programs.
96.It Ev LD_BIND_NOW
97When set to a nonempty string, causes
98.Nm
99to relocate all external function calls before starting execution of the
100program.
101Normally, function calls are bound lazily, at the first call
102of each function.
103.Ev LD_BIND_NOW
104increases the start-up time of a program, but it avoids run-time
105surprises caused by unexpectedly undefined functions.
106.It Ev LD_TRACE_LOADED_OBJECTS
107When set to a nonempty string, causes
108.Nm
109to exit after loading the shared objects and printing a summary which includes
110the absolute pathnames of all objects, to standard output.
111.It Ev LD_TRACE_LOADED_OBJECTS_FMT1
112.It Ev LD_TRACE_LOADED_OBJECTS_FMT2
113When set, these variables are interpreted as format strings a la
114.Xr printf 3
115to customize the trace output and are used by
116.Xr ldd 1 Ns 's
117.Fl f
118option and allows
119.Xr ldd 1
120to be operated as a filter more conveniently.
121The following conversions can be used:
122.Bl -tag -width 4n
123.It Li %a
124The main program's name
125(also known as
126.Dq __progname ) .
127.It Li \&%A
128The value of the environment variable
129.Ev LD_TRACE_LOADED_OBJECTS_PROGNAME
130.It Li %o
131The library name.
132.It Li %m
133The library's major version number.
134.It Li %p
135The full pathname as determined by
136.Nm rtld Ns 's
137library search rules.
138.It Li %x
139The library's load address.
140.El
141.Pp
142Additionally,
143.Ql \en
144and
145.Ql \et
146are recognized and have their usual meaning.
147.El
148.Sh FILES
149.Bl -tag -width indent
150.It Pa /var/run/ld-elf.so.hints
151.El
152.Sh SEE ALSO
153.Xr ld 1 ,
154.Xr ldd 1 ,
155.Xr elf 5 ,
156.Xr ldconfig 8