1.\" $FreeBSD: src/libexec/rtld-elf/rtld.1,v 1.18.2.7 2002/01/10 17:51:28 ru Exp $ 2.\" $DragonFly: src/libexec/rtld-elf/rtld.1,v 1.3 2005/05/11 19:47:06 dillon Exp $ 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.2 , 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 DIFFERENCES BETWEEN .1 and .2 149.Pp 150ABI changes have been made to support TLS allocation and initialization 151and to give threading libraries a chance to complete initialization of the 152TCB prior to the calling of the _init() functions for the dynamically loaded 153libraries. 154.Sh FILES 155.Bl -tag -width indent 156.It Pa /var/run/ld-elf.so.hints 157.El 158.Sh SEE ALSO 159.Xr ld 1 , 160.Xr ldd 1 , 161.Xr elf 5 , 162.Xr ldconfig 8 163