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.Bl -tag -width ".Ev LD_LIBMAP_DISABLE" 109.It Ev LD_DUMP_REL_POST 110If set, 111.Nm 112will print a table containing all relocations after symbol 113binding and relocation. 114.It Ev LD_DUMP_REL_PRE 115If set, 116.Nm 117will print a table containing all relocations before symbol 118binding and relocation. 119.It Ev LD_LIBMAP 120A library replacement list in the same format as 121.Xr libmap.conf 5 . 122For convenience, the characters 123.Ql = 124and 125.Ql \&, 126can be used instead of a space and a newline. 127This variable is parsed after 128.Xr libmap.conf 5 , 129and will override its entries. 130This variable is unset for set-user-ID and set-group-ID programs. 131.It Ev LD_LIBMAP_DISABLE 132If set, disables the use of 133.Xr libmap.conf 5 134and 135.Ev LD_LIBMAP . 136This variable is unset for set-user-ID and set-group-ID programs. 137.It Ev LD_ELF_HINTS_PATH 138This variable will override the default location of 139.Dq hints 140file. 141This variable is unset for set-user-ID and set-group-ID programs. 142.It Ev LD_LIBRARY_PATH 143A colon separated list of directories, overriding the default search path 144for shared libraries. 145This variable is unset for set-user-ID and set-group-ID programs. 146.It Ev LD_PRELOAD 147A list of shared libraries, separated by colons and/or white space, 148to be linked in before any 149other shared libraries. 150If the directory is not specified then 151the directories specified by 152.Ev LD_LIBRARY_PATH 153will be searched first 154followed by the set of built-in standard directories. 155This variable is unset for set-user-ID and set-group-ID programs. 156.It Ev LD_BIND_NOW 157When set to a nonempty string, causes 158.Nm 159to relocate all external function calls before starting execution of the 160program. 161Normally, function calls are bound lazily, at the first call 162of each function. 163.Ev LD_BIND_NOW 164increases the start-up time of a program, but it avoids run-time 165surprises caused by unexpectedly undefined functions. 166.It Ev LD_TRACE_LOADED_OBJECTS 167When set to a nonempty string, causes 168.Nm 169to exit after loading the shared objects and printing a summary which includes 170the absolute pathnames of all objects, to standard output. 171.It Ev LD_TRACE_LOADED_OBJECTS_ALL 172When set to a nonempty string, causes 173.Nm 174to expand the summary to indicate which objects caused each object to 175be loaded. 176.It Ev LD_TRACE_LOADED_OBJECTS_FMT1 177.It Ev LD_TRACE_LOADED_OBJECTS_FMT2 178When set, these variables are interpreted as format strings a la 179.Xr printf 3 180to customize the trace output and are used by 181.Xr ldd 1 Ns 's 182.Fl f 183option and allows 184.Xr ldd 1 185to be operated as a filter more conveniently. 186If the dependency name starts with string 187.Pa lib , 188.Ev LD_TRACE_LOADED_OBJECTS_FMT1 189is used, otherwise 190.Ev LD_TRACE_LOADED_OBJECTS_FMT2 191is used. 192The following conversions can be used: 193.Bl -tag -width 4n 194.It Li %a 195The main program's name 196(also known as 197.Dq __progname ) . 198.It Li \&%A 199The value of the environment variable 200.Ev LD_TRACE_LOADED_OBJECTS_PROGNAME . 201Typically used to print both the names of programs and shared libraries 202being inspected using 203.Xr ldd 1 . 204.It Li %o 205The library name. 206.It Li %p 207The full pathname as determined by 208.Nm rtld Ns 's 209library search rules. 210.It Li %x 211The library's load address. 212.El 213.Pp 214Additionally, 215.Ql \en 216and 217.Ql \et 218are recognized and have their usual meaning. 219.It Ev LD_UTRACE 220If set, 221.Nm 222will log events such as the loading and unloading of shared objects via 223.Xr utrace 2 . 224.Pp 225.It Ev LD_LOADFLTR 226If set, 227.Nm 228will process the filtee dependencies of the loaded objects immediately, 229instead of postponing it until required. 230Normally, the filtees are opened at the time of the first symbol resolution 231from the filter object. 232.El 233.Sh FILES 234.Bl -tag -width ".Pa /var/run/ld-elf32.so.hints" -compact 235.It Pa /var/run/ld-elf.so.hints 236Hints file. 237.It Pa /var/run/ld-elf32.so.hints 238Hints file for 32-bit binaries on 64-bit system. 239.It Pa /etc/libmap.conf 240The libmap configuration file. 241.It Pa /etc/libmap32.conf 242The libmap configuration file for 32-bit binaries on 64-bit system. 243.El 244.Sh SEE ALSO 245.Xr ld 1 , 246.Xr ldd 1 , 247.Xr elf 5 , 248.Xr libmap.conf 5 , 249.Xr ldconfig 8 250