1.\" Copyright (c) 1995 Paul Kranenburg 2.\" All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. All advertising materials mentioning features or use of this software 13.\" must display the following acknowledgment: 14.\" This product includes software developed by Paul Kranenburg. 15.\" 3. The name of the author may not be used to endorse or promote products 16.\" derived from this software without specific prior written permission 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 19.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 20.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 21.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 22.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 23.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 24.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 25.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 26.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 27.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 28.\" 29.\" $FreeBSD$ 30.\" 31.Dd May 31, 2003 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_LIBMAP_DISABLE" 86.It Ev LD_DUMP_REL_POST 87If set 88.Nm 89will print a table containing all relocations after symbol 90binding and relocation. 91.It Ev LD_DUMP_REL_PRE 92If set 93.Nm 94will print a table containing all relocations before symbol 95binding and relocation. 96.It Ev LD_LIBMAP_DISABLE 97If set, disables the use of 98.Xr libmap.conf 5 . 99.It Ev LD_LIBRARY_PATH 100A colon separated list of directories, overriding the default search path 101for shared libraries. 102This is ignored for set-user-ID and set-group-ID programs. 103.It Ev LD_PRELOAD 104A list of shared libraries, separated by colons and/or white space, 105to be linked in before any 106other shared libraries. 107If the directory is not specified then 108the directories specified by 109.Ev LD_LIBRARY_PATH 110will be searched first 111followed by the set of built-in standard directories. 112This is ignored for set-user-ID and set-group-ID programs. 113.It Ev LD_BIND_NOW 114When set to a nonempty string, causes 115.Nm 116to relocate all external function calls before starting execution of the 117program. 118Normally, function calls are bound lazily, at the first call 119of each function. 120.Ev LD_BIND_NOW 121increases the start-up time of a program, but it avoids run-time 122surprises caused by unexpectedly undefined functions. 123.It Ev LD_TRACE_LOADED_OBJECTS 124When set to a nonempty string, causes 125.Nm 126to exit after loading the shared objects and printing a summary which includes 127the absolute pathnames of all objects, to standard output. 128.It Ev LD_TRACE_LOADED_OBJECTS_ALL 129When set to a nonempty string, causes 130.Nm 131to expand the summary to indicate which objects caused each object to 132be loaded. 133.It Ev LD_TRACE_LOADED_OBJECTS_FMT1 134.It Ev LD_TRACE_LOADED_OBJECTS_FMT2 135When set, these variables are interpreted as format strings a la 136.Xr printf 3 137to customize the trace output and are used by 138.Xr ldd 1 Ns 's 139.Fl f 140option and allows 141.Xr ldd 1 142to be operated as a filter more conveniently. 143The following conversions can be used: 144.Bl -tag -width 4n 145.It Li %a 146The main program's name 147(also known as 148.Dq __progname ) . 149.It Li \&%A 150The value of the environment variable 151.Ev LD_TRACE_LOADED_OBJECTS_PROGNAME 152.It Li %o 153The library name. 154.It Li %m 155The library's major version number. 156.It Li %p 157The full pathname as determined by 158.Nm rtld Ns 's 159library search rules. 160.It Li %x 161The library's load address. 162.El 163.Pp 164Additionally, 165.Ql \en 166and 167.Ql \et 168are recognized and have their usual meaning. 169.El 170.Sh FILES 171.Bl -tag -width ".Pa /var/run/ld-elf.so.hints" -compact 172.It Pa /var/run/ld-elf.so.hints 173Hints file. 174.It Pa /etc/libmap.conf 175The libmap configuration file. 176.El 177.Sh SEE ALSO 178.Xr ld 1 , 179.Xr ldd 1 , 180.Xr elf 5 , 181.Xr libmap.conf 5 , 182.Xr ldconfig 8 183