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 April 1, 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 61When resolving dependencies for the loaded objects, 62.Nm 63may be allowed to translate dynamic token strings in rpath and soname 64by setting 65.Fl "z origin" 66option of the static linker 67.Xr ld 1 . 68The following strings are recognized now: 69.Bl -tag -width ".Pa $PLATFORM" 70.It Pa $ORIGIN 71Translated to the full path of the loaded object. 72.It Pa $OSNAME 73Translated to the name of the operating system implementation. 74.It Pa $OSREL 75Translated to the release level of the operating system. 76.It Pa $PLATFORM 77Translated to the machine hardware platform. 78.El 79.Pp 80The 81.Nm 82utility itself is loaded by the kernel together with any dynamically-linked 83program that is to be executed. 84The kernel transfers control to the 85dynamic linker. 86After the dynamic linker has finished loading, 87relocating, and initializing the program and its required shared 88objects, it transfers control to the entry point of the program. 89.Pp 90To locate the required shared objects in the file system, 91.Nm 92may use a 93.Dq hints 94file prepared by the 95.Xr ldconfig 8 96utility. 97.Pp 98The 99.Nm 100utility 101recognizes a number of environment variables that can be used to modify 102its behaviour. 103On 64-bit architectures, the linker for 32-bit objects recognizes 104all the environment variables listed below, but is being prefixed with 105.Ev LD_32_ , 106for example: 107.Ev LD_32_TRACE_LOADED_OBJECTS . 108.Pp 109.Bl -tag -width ".Ev LD_LIBMAP_DISABLE" 110.It Ev LD_DUMP_REL_POST 111If set, 112.Nm 113will print a table containing all relocations after symbol 114binding and relocation. 115.It Ev LD_DUMP_REL_PRE 116If set, 117.Nm 118will print a table containing all relocations before symbol 119binding and relocation. 120.It Ev LD_LIBMAP 121A library replacement list in the same format as 122.Xr libmap.conf 5 . 123For convenience, the characters 124.Ql = 125and 126.Ql \&, 127can be used instead of a space and a newline. 128This variable is parsed after 129.Xr libmap.conf 5 , 130and will override its entries. 131This variable is unset for set-user-ID and set-group-ID programs. 132.It Ev LD_LIBMAP_DISABLE 133If set, disables the use of 134.Xr libmap.conf 5 135and 136.Ev LD_LIBMAP . 137This variable is unset for set-user-ID and set-group-ID programs. 138.It Ev LD_ELF_HINTS_PATH 139This variable will override the default location of 140.Dq hints 141file. 142This variable is unset for set-user-ID and set-group-ID programs. 143.It Ev LD_LIBRARY_PATH 144A colon separated list of directories, overriding the default search path 145for shared libraries. 146This variable is unset for set-user-ID and set-group-ID programs. 147.It Ev LD_PRELOAD 148A list of shared libraries, separated by colons and/or white space, 149to be linked in before any 150other shared libraries. 151If the directory is not specified then 152the directories specified by 153.Ev LD_LIBRARY_PATH 154will be searched first 155followed by the set of built-in standard directories. 156This variable is unset for set-user-ID and set-group-ID programs. 157.It Ev LD_BIND_NOW 158When set to a nonempty string, causes 159.Nm 160to relocate all external function calls before starting execution of the 161program. 162Normally, function calls are bound lazily, at the first call 163of each function. 164.Ev LD_BIND_NOW 165increases the start-up time of a program, but it avoids run-time 166surprises caused by unexpectedly undefined functions. 167.It Ev LD_TRACE_LOADED_OBJECTS 168When set to a nonempty string, causes 169.Nm 170to exit after loading the shared objects and printing a summary which includes 171the absolute pathnames of all objects, to standard output. 172.It Ev LD_TRACE_LOADED_OBJECTS_ALL 173When set to a nonempty string, causes 174.Nm 175to expand the summary to indicate which objects caused each object to 176be loaded. 177.It Ev LD_TRACE_LOADED_OBJECTS_FMT1 178.It Ev LD_TRACE_LOADED_OBJECTS_FMT2 179When set, these variables are interpreted as format strings a la 180.Xr printf 3 181to customize the trace output and are used by 182.Xr ldd 1 Ns 's 183.Fl f 184option and allows 185.Xr ldd 1 186to be operated as a filter more conveniently. 187If the dependency name starts with string 188.Pa lib , 189.Ev LD_TRACE_LOADED_OBJECTS_FMT1 190is used, otherwise 191.Ev LD_TRACE_LOADED_OBJECTS_FMT2 192is used. 193The following conversions can be used: 194.Bl -tag -width 4n 195.It Li %a 196The main program's name 197(also known as 198.Dq __progname ) . 199.It Li \&%A 200The value of the environment variable 201.Ev LD_TRACE_LOADED_OBJECTS_PROGNAME . 202Typically used to print both the names of programs and shared libraries 203being inspected using 204.Xr ldd 1 . 205.It Li %o 206The library name. 207.It Li %p 208The full pathname as determined by 209.Nm rtld Ns 's 210library search rules. 211.It Li %x 212The library's load address. 213.El 214.Pp 215Additionally, 216.Ql \en 217and 218.Ql \et 219are recognized and have their usual meaning. 220.It Ev LD_UTRACE 221If set, 222.Nm 223will log events such as the loading and unloading of shared objects via 224.Xr utrace 2 . 225.El 226.Sh FILES 227.Bl -tag -width ".Pa /var/run/ld-elf32.so.hints" -compact 228.It Pa /var/run/ld-elf.so.hints 229Hints file. 230.It Pa /var/run/ld-elf32.so.hints 231Hints file for 32-bit binaries on 64-bit system. 232.It Pa /etc/libmap.conf 233The libmap configuration file. 234.It Pa /etc/libmap32.conf 235The libmap configuration file for 32-bit binaries on 64-bit system. 236.El 237.Sh SEE ALSO 238.Xr ld 1 , 239.Xr ldd 1 , 240.Xr elf 5 , 241.Xr libmap.conf 5 , 242.Xr ldconfig 8 243