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 23, 2009 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. 112This variable is unset for set-user-ID and set-group-ID programs. 113.It Ev LD_LIBMAP_DISABLE 114If set, disables the use of 115.Xr libmap.conf 5 116and 117.Ev LD_LIBMAP . 118This variable is unset for set-user-ID and set-group-ID programs. 119.It Ev LD_ELF_HINTS_PATH 120This variable will override the default location of 121.Dq hints 122file. 123This variable is unset for set-user-ID and set-group-ID programs. 124.It Ev LD_LIBRARY_PATH 125A colon separated list of directories, overriding the default search path 126for shared libraries. 127This variable is unset for set-user-ID and set-group-ID programs. 128.It Ev LD_PRELOAD 129A list of shared libraries, separated by colons and/or white space, 130to be linked in before any 131other shared libraries. 132If the directory is not specified then 133the directories specified by 134.Ev LD_LIBRARY_PATH 135will be searched first 136followed by the set of built-in standard directories. 137This variable is unset for set-user-ID and set-group-ID programs. 138.It Ev LD_BIND_NOW 139When set to a nonempty string, causes 140.Nm 141to relocate all external function calls before starting execution of the 142program. 143Normally, function calls are bound lazily, at the first call 144of each function. 145.Ev LD_BIND_NOW 146increases the start-up time of a program, but it avoids run-time 147surprises caused by unexpectedly undefined functions. 148.It Ev LD_TRACE_LOADED_OBJECTS 149When set to a nonempty string, causes 150.Nm 151to exit after loading the shared objects and printing a summary which includes 152the absolute pathnames of all objects, to standard output. 153.It Ev LD_TRACE_LOADED_OBJECTS_ALL 154When set to a nonempty string, causes 155.Nm 156to expand the summary to indicate which objects caused each object to 157be loaded. 158.It Ev LD_TRACE_LOADED_OBJECTS_FMT1 159.It Ev LD_TRACE_LOADED_OBJECTS_FMT2 160When set, these variables are interpreted as format strings a la 161.Xr printf 3 162to customize the trace output and are used by 163.Xr ldd 1 Ns 's 164.Fl f 165option and allows 166.Xr ldd 1 167to be operated as a filter more conveniently. 168If the dependency name starts with string 169.Pa lib , 170.Ev LD_TRACE_LOADED_OBJECTS_FMT1 171is used, otherwise 172.Ev LD_TRACE_LOADED_OBJECTS_FMT2 173is used. 174The following conversions can be used: 175.Bl -tag -width 4n 176.It Li %a 177The main program's name 178(also known as 179.Dq __progname ) . 180.It Li \&%A 181The value of the environment variable 182.Ev LD_TRACE_LOADED_OBJECTS_PROGNAME . 183Typically used to print both the names of programs and shared libraries 184being inspected using 185.Xr ldd 1 . 186.It Li %o 187The library name. 188.It Li %p 189The full pathname as determined by 190.Nm rtld Ns 's 191library search rules. 192.It Li %x 193The library's load address. 194.El 195.Pp 196Additionally, 197.Ql \en 198and 199.Ql \et 200are recognized and have their usual meaning. 201.It Ev LD_UTRACE 202If set, 203.Nm 204will log events such as the loading and unloading of shared objects via 205.Xr utrace 2 . 206.El 207.Sh FILES 208.Bl -tag -width ".Pa /var/run/ld-elf32.so.hints" -compact 209.It Pa /var/run/ld-elf.so.hints 210Hints file. 211.It Pa /var/run/ld-elf32.so.hints 212Hints file for 32-bit binaries on 64-bit system. 213.It Pa /etc/libmap.conf 214The libmap configuration file. 215.It Pa /etc/libmap32.conf 216The libmap configuration file for 32-bit binaries on 64-bit system. 217.El 218.Sh SEE ALSO 219.Xr ld 1 , 220.Xr ldd 1 , 221.Xr elf 5 , 222.Xr libmap.conf 5 , 223.Xr ldconfig 8 224