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