1.\" $FreeBSD$ 2.\" 3.\" Copyright (c) 1995 Paul Kranenburg 4.\" All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. All advertising materials mentioning features or use of this software 15.\" must display the following acknowledgment: 16.\" This product includes software developed by Paul Kranenburg. 17.\" 3. The name of the author may not be used to endorse or promote products 18.\" derived from this software without specific prior written permission 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 21.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 22.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 23.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 24.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 25.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 26.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 27.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 28.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 29.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 30.\" 31.Dd January 28, 2000 32.Dt RTLD 1 33.Os 34.Sh NAME 35.Nm ld-elf.so.1 , 36.Nm rtld 37.Nd run-time link-editor 38.Sh DESCRIPTION 39The 40.Nm 41utility is 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 60The 61.Nm 62utility itself is loaded by the kernel together with any dynamically-linked 63program that is to be executed. 64The kernel transfers control to the 65dynamic linker. 66After the dynamic linker has finished loading, 67relocating, and initializing the program and its required shared 68objects, it transfers control to the entry point of the program. 69.Pp 70To locate the required shared objects in the filesystem, 71.Nm 72may use a 73.Dq hints 74file prepared by the 75.Xr ldconfig 8 76utility. 77.Pp 78The 79.Nm 80utility 81recognizes a number of environment variables that can be used to modify 82its behaviour as follows: 83.Pp 84.Bl -tag -width ".Ev LD_LIBRARY_PATH" 85.It Ev LD_LIBRARY_PATH 86A colon separated list of directories, overriding the default search path 87for shared libraries. 88This is ignored for set-user-ID and set-group-ID programs. 89.It Ev LD_PRELOAD 90A list of shared libraries, separated by colons and/or white space, 91to be linked in before any 92other shared libraries. 93If the directory is not specified then 94the directories specified by 95.Ev LD_LIBRARY_PATH 96will be searched first 97followed by the set of built-in standard directories. 98This is ignored for set-user-ID and set-group-ID programs. 99.It Ev LD_BIND_NOW 100When set to a nonempty string, causes 101.Nm 102to relocate all external function calls before starting execution of the 103program. 104Normally, function calls are bound lazily, at the first call 105of each function. 106.Ev LD_BIND_NOW 107increases the start-up time of a program, but it avoids run-time 108surprises caused by unexpectedly undefined functions. 109.It Ev LD_TRACE_LOADED_OBJECTS 110When set to a nonempty string, causes 111.Nm 112to exit after loading the shared objects and printing a summary which includes 113the absolute pathnames of all objects, to standard output. 114.It Ev LD_TRACE_LOADED_OBJECTS_ALL 115When set to a nonempty string, causes 116.Nm 117to expand the summary to indicate which objects caused each object to 118be loaded. 119.It Ev LD_TRACE_LOADED_OBJECTS_FMT1 120.It Ev LD_TRACE_LOADED_OBJECTS_FMT2 121When set, these variables are interpreted as format strings a la 122.Xr printf 3 123to customize the trace output and are used by 124.Xr ldd 1 Ns 's 125.Fl f 126option and allows 127.Xr ldd 1 128to be operated as a filter more conveniently. 129The following conversions can be used: 130.Bl -tag -width 4n 131.It Li %a 132The main program's name 133(also known as 134.Dq __progname ) . 135.It Li \&%A 136The value of the environment variable 137.Ev LD_TRACE_LOADED_OBJECTS_PROGNAME 138.It Li %o 139The library name. 140.It Li %m 141The library's major version number. 142.It Li %p 143The full pathname as determined by 144.Nm rtld Ns 's 145library search rules. 146.It Li %x 147The library's load address. 148.El 149.Pp 150Additionally, 151.Ql \en 152and 153.Ql \et 154are recognized and have their usual meaning. 155.El 156.Sh FILES 157.Bl -tag -width indent 158.It Pa /var/run/ld-elf.so.hints 159.El 160.Sh SEE ALSO 161.Xr ld 1 , 162.Xr ldd 1 , 163.Xr elf 5 , 164.Xr ldconfig 8 165