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 ld.so , 37.Nm rtld 38.Nd run-time link-editor 39.Sh DESCRIPTION 40The 41.Nm 42utility is a self-contained shared object providing run-time 43support for loading and link-editing shared objects into a process' 44address space. 45It is also commonly known as the dynamic linker. 46It uses the data structures 47contained within dynamically linked programs to determine which shared 48libraries are needed and loads them using the 49.Xr mmap 2 50system call. 51.Pp 52After all shared libraries have been successfully loaded, 53.Nm 54proceeds to resolve external references from both the main program and 55all objects loaded. 56A mechanism is provided for initialization routines 57to be called on a per-object basis, giving a shared object an opportunity 58to perform any extra set-up before execution of the program proper begins. 59This is useful for C++ libraries that contain static constructors. 60.Pp 61The 62.Nm 63utility itself is loaded by the kernel together with any dynamically-linked 64program that is to be executed. 65The kernel transfers control to the 66dynamic linker. 67After the dynamic linker has finished loading, 68relocating, and initializing the program and its required shared 69objects, it transfers control to the entry point of the program. 70.Pp 71To locate the required shared objects in the file system, 72.Nm 73may use a 74.Dq hints 75file prepared by the 76.Xr ldconfig 8 77utility. 78.Pp 79The 80.Nm 81utility 82recognizes a number of environment variables that can be used to modify 83its behaviour as follows: 84.Pp 85.Bl -tag -width ".Ev LD_LIBRARY_PATH" 86.It Ev LD_LIBRARY_PATH 87A colon separated list of directories, overriding the default search path 88for shared libraries. 89This is ignored for set-user-ID and set-group-ID programs. 90.It Ev LD_PRELOAD 91A list of shared libraries, separated by colons and/or white space, 92to be linked in before any 93other shared libraries. 94If the directory is not specified then 95the directories specified by 96.Ev LD_LIBRARY_PATH 97will be searched first 98followed by the set of built-in standard directories. 99This is ignored for set-user-ID and set-group-ID programs. 100.It Ev LD_BIND_NOW 101When set to a nonempty string, causes 102.Nm 103to relocate all external function calls before starting execution of the 104program. 105Normally, function calls are bound lazily, at the first call 106of each function. 107.Ev LD_BIND_NOW 108increases the start-up time of a program, but it avoids run-time 109surprises caused by unexpectedly undefined functions. 110.It Ev LD_TRACE_LOADED_OBJECTS 111When set to a nonempty string, causes 112.Nm 113to exit after loading the shared objects and printing a summary which includes 114the absolute pathnames of all objects, to standard output. 115.It Ev LD_TRACE_LOADED_OBJECTS_ALL 116When set to a nonempty string, causes 117.Nm 118to expand the summary to indicate which objects caused each object to 119be loaded. 120.It Ev LD_TRACE_LOADED_OBJECTS_FMT1 121.It Ev LD_TRACE_LOADED_OBJECTS_FMT2 122When set, these variables are interpreted as format strings a la 123.Xr printf 3 124to customize the trace output and are used by 125.Xr ldd 1 Ns 's 126.Fl f 127option and allows 128.Xr ldd 1 129to be operated as a filter more conveniently. 130The following conversions can be used: 131.Bl -tag -width 4n 132.It Li %a 133The main program's name 134(also known as 135.Dq __progname ) . 136.It Li \&%A 137The value of the environment variable 138.Ev LD_TRACE_LOADED_OBJECTS_PROGNAME 139.It Li %o 140The library name. 141.It Li %m 142The library's major version number. 143.It Li %p 144The full pathname as determined by 145.Nm rtld Ns 's 146library search rules. 147.It Li %x 148The library's load address. 149.El 150.Pp 151Additionally, 152.Ql \en 153and 154.Ql \et 155are recognized and have their usual meaning. 156.El 157.Sh FILES 158.Bl -tag -width indent 159.It Pa /var/run/ld-elf.so.hints 160.El 161.Sh SEE ALSO 162.Xr ld 1 , 163.Xr ldd 1 , 164.Xr elf 5 , 165.Xr ldconfig 8 166