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 March 27, 2006 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. 84On 64-bit architectures, the linker for 32-bit objects recognizes 85all the environment variables listed below, but is being prefixed with 86.Ev LD_32_ , 87for example: 88.Ev LD_32_TRACE_LOADED_OBJECTS . 89.Pp 90.Bl -tag -width ".Ev LD_LIBMAP_DISABLE" 91.It Ev LD_DUMP_REL_POST 92If set, 93.Nm 94will print a table containing all relocations after symbol 95binding and relocation. 96.It Ev LD_DUMP_REL_PRE 97If set, 98.Nm 99will print a table containing all relocations before symbol 100binding and relocation. 101.It Ev LD_LIBMAP 102A library replacement list in the same format as 103.Xr libmap.conf 5 . 104For convenience, the characters 105.Ql = 106and 107.Ql \&, 108can be used instead of a space and a newline. 109This variable is parsed after 110.Xr libmap.conf 5 , 111and will override its entries. 112.It Ev LD_LIBMAP_DISABLE 113If set, disables the use of 114.Xr libmap.conf 5 115and 116.Ev LD_LIBMAP . 117.It Ev LD_LIBRARY_PATH 118A colon separated list of directories, overriding the default search path 119for shared libraries. 120This is ignored for set-user-ID and set-group-ID programs. 121.It Ev LD_PRELOAD 122A list of shared libraries, separated by colons and/or white space, 123to be linked in before any 124other shared libraries. 125If the directory is not specified then 126the directories specified by 127.Ev LD_LIBRARY_PATH 128will be searched first 129followed by the set of built-in standard directories. 130This is ignored for set-user-ID and set-group-ID programs. 131.It Ev LD_BIND_NOW 132When set to a nonempty string, causes 133.Nm 134to relocate all external function calls before starting execution of the 135program. 136Normally, function calls are bound lazily, at the first call 137of each function. 138.Ev LD_BIND_NOW 139increases the start-up time of a program, but it avoids run-time 140surprises caused by unexpectedly undefined functions. 141.It Ev LD_TRACE_LOADED_OBJECTS 142When set to a nonempty string, causes 143.Nm 144to exit after loading the shared objects and printing a summary which includes 145the absolute pathnames of all objects, to standard output. 146.It Ev LD_TRACE_LOADED_OBJECTS_ALL 147When set to a nonempty string, causes 148.Nm 149to expand the summary to indicate which objects caused each object to 150be loaded. 151.It Ev LD_TRACE_LOADED_OBJECTS_FMT1 152.It Ev LD_TRACE_LOADED_OBJECTS_FMT2 153When set, these variables are interpreted as format strings a la 154.Xr printf 3 155to customize the trace output and are used by 156.Xr ldd 1 Ns 's 157.Fl f 158option and allows 159.Xr ldd 1 160to be operated as a filter more conveniently. 161The following conversions can be used: 162.Bl -tag -width 4n 163.It Li %a 164The main program's name 165(also known as 166.Dq __progname ) . 167.It Li \&%A 168The value of the environment variable 169.Ev LD_TRACE_LOADED_OBJECTS_PROGNAME 170.It Li %o 171The library name. 172.It Li %m 173The library's major version number. 174.It Li %p 175The full pathname as determined by 176.Nm rtld Ns 's 177library search rules. 178.It Li %x 179The library's load address. 180.El 181.Pp 182Additionally, 183.Ql \en 184and 185.Ql \et 186are recognized and have their usual meaning. 187.It Ev LD_UTRACE 188If set, 189.Nm 190will log events such as the loading and unloading of shared objects via 191.Xr utrace 2 . 192.El 193.Sh FILES 194.Bl -tag -width ".Pa /var/run/ld-elf32.so.hints" -compact 195.It Pa /var/run/ld-elf.so.hints 196Hints file. 197.It Pa /var/run/ld-elf32.so.hints 198Hints file for 32-bit binaries on 64-bit system. 199.It Pa /etc/libmap.conf 200The libmap configuration file. 201.It Pa /etc/libmap32.conf 202The libmap configuration file for 32-bit binaries on 64-bit system. 203.El 204.Sh SEE ALSO 205.Xr ld 1 , 206.Xr ldd 1 , 207.Xr elf 5 , 208.Xr libmap.conf 5 , 209.Xr ldconfig 8 210