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 16, 2017 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. 89The following search order is used to locate required shared objects: 90.Pp 91.Bl -enum -offset indent -compact 92.It 93.Dv DT_RPATH 94of the referencing object unless that object also contains a 95.Dv DT_RUNPATH 96tag 97.It 98.Dv DT_RPATH 99of the program unless the referencing object contains a 100.Dv DT_RUNPATH 101tag 102.It 103Path indicated by 104.Ev LD_LIBRARY_PATH 105environment variable 106.It 107.Dv DT_RUNPATH 108of the referencing object 109.It 110Hints file produced by the 111.Xr ldconfig 8 112utility 113.It 114The 115.Pa /lib 116and 117.Pa /usr/lib 118directories, unless the referencing object was linked using the 119.Dq Fl z Ar nodefaultlib 120option 121.El 122.Pp 123The 124.Nm 125utility 126recognizes a number of environment variables that can be used to modify 127its behaviour. 128On 64-bit architectures, the linker for 32-bit objects recognizes 129all the environment variables listed below, but is being prefixed with 130.Ev LD_32_ , 131for example: 132.Ev LD_32_TRACE_LOADED_OBJECTS . 133.Bl -tag -width ".Ev LD_LIBMAP_DISABLE" 134.It Ev LD_DUMP_REL_POST 135If set, 136.Nm 137will print a table containing all relocations after symbol 138binding and relocation. 139.It Ev LD_DUMP_REL_PRE 140If set, 141.Nm 142will print a table containing all relocations before symbol 143binding and relocation. 144.It Ev LD_LIBMAP 145A library replacement list in the same format as 146.Xr libmap.conf 5 . 147For convenience, the characters 148.Ql = 149and 150.Ql \&, 151can be used instead of a space and a newline. 152This variable is parsed after 153.Xr libmap.conf 5 , 154and will override its entries. 155This variable is unset for set-user-ID and set-group-ID programs. 156.It Ev LD_LIBMAP_DISABLE 157If set, disables the use of 158.Xr libmap.conf 5 159and 160.Ev LD_LIBMAP . 161This variable is unset for set-user-ID and set-group-ID programs. 162.It Ev LD_ELF_HINTS_PATH 163This variable will override the default location of 164.Dq hints 165file. 166This variable is unset for set-user-ID and set-group-ID programs. 167.It Ev LD_LIBRARY_PATH 168A colon separated list of directories, overriding the default search path 169for shared libraries. 170This variable is unset for set-user-ID and set-group-ID programs. 171.It Ev LD_LIBRARY_PATH_RPATH 172If the variable is specified and has a value starting with 173any of \'y\', \'Y\' or \'1\' symbols, the path specified by 174.Ev LD_LIBRARY_PATH 175variable is allowed to override the path from 176.Dv DT_RPATH 177for binaries which does not contain 178.Dv DT_RUNPATH 179tag. 180For such binaries, when the variable 181.Ev LD_LIBRARY_PATH_RPATH 182is set, 183.Dq Fl z Ar nodefaultlib 184link-time option is ignored as well. 185.It Ev LD_PRELOAD 186A list of shared libraries, separated by colons and/or white space, 187to be linked in before any 188other shared libraries. 189If the directory is not specified then 190the directories specified by 191.Ev LD_LIBRARY_PATH 192will be searched first 193followed by the set of built-in standard directories. 194This variable is unset for set-user-ID and set-group-ID programs. 195.Ev LD_LIBRARY_PATH_FDS 196A colon separated list of file descriptor numbers for library directories. 197This is intended for use within 198.Xr capsicum 4 199sandboxes, when global namespaces such as the filesystem are unavailable. 200It is consulted just after LD_LIBRARY_PATH. 201This variable is unset for set-user-ID and set-group-ID programs. 202.It Ev LD_BIND_NOT 203When set to a nonempty string, prevents modifications of the PLT slots when 204doing bindings. 205As result, each call of the PLT-resolved function is resolved. 206In combination with debug output, this provides complete account of 207all bind actions at runtime. 208This variable is unset for set-user-ID and set-group-ID programs. 209.It Ev LD_BIND_NOW 210When set to a nonempty string, causes 211.Nm 212to relocate all external function calls before starting execution of the 213program. 214Normally, function calls are bound lazily, at the first call 215of each function. 216.Ev LD_BIND_NOW 217increases the start-up time of a program, but it avoids run-time 218surprises caused by unexpectedly undefined functions. 219.It Ev LD_TRACE_LOADED_OBJECTS 220When set to a nonempty string, causes 221.Nm 222to exit after loading the shared objects and printing a summary which includes 223the absolute pathnames of all objects, to standard output. 224.It Ev LD_TRACE_LOADED_OBJECTS_ALL 225When set to a nonempty string, causes 226.Nm 227to expand the summary to indicate which objects caused each object to 228be loaded. 229.It Ev LD_TRACE_LOADED_OBJECTS_FMT1 230.It Ev LD_TRACE_LOADED_OBJECTS_FMT2 231When set, these variables are interpreted as format strings a la 232.Xr printf 3 233to customize the trace output and are used by 234.Xr ldd 1 Ns 's 235.Fl f 236option and allows 237.Xr ldd 1 238to be operated as a filter more conveniently. 239If the dependency name starts with string 240.Pa lib , 241.Ev LD_TRACE_LOADED_OBJECTS_FMT1 242is used, otherwise 243.Ev LD_TRACE_LOADED_OBJECTS_FMT2 244is used. 245The following conversions can be used: 246.Bl -tag -width 4n 247.It Li %a 248The main program's name 249(also known as 250.Dq __progname ) . 251.It Li \&%A 252The value of the environment variable 253.Ev LD_TRACE_LOADED_OBJECTS_PROGNAME . 254Typically used to print both the names of programs and shared libraries 255being inspected using 256.Xr ldd 1 . 257.It Li %o 258The library name. 259.It Li %p 260The full pathname as determined by 261.Nm rtld Ns 's 262library search rules. 263.It Li %x 264The library's load address. 265.El 266.Pp 267Additionally, 268.Ql \en 269and 270.Ql \et 271are recognized and have their usual meaning. 272.It Ev LD_UTRACE 273If set, 274.Nm 275will log events such as the loading and unloading of shared objects via 276.Xr utrace 2 . 277.It Ev LD_LOADFLTR 278If set, 279.Nm 280will process the filtee dependencies of the loaded objects immediately, 281instead of postponing it until required. 282Normally, the filtees are opened at the time of the first symbol resolution 283from the filter object. 284.El 285.Sh FILES 286.Bl -tag -width ".Pa /var/run/ld-elf32.so.hints" -compact 287.It Pa /var/run/ld-elf.so.hints 288Hints file. 289.It Pa /var/run/ld-elf32.so.hints 290Hints file for 32-bit binaries on 64-bit system. 291.It Pa /etc/libmap.conf 292The libmap configuration file. 293.It Pa /etc/libmap32.conf 294The libmap configuration file for 32-bit binaries on 64-bit system. 295.El 296.Sh SEE ALSO 297.Xr ld 1 , 298.Xr ldd 1 , 299.Xr capsicum 4 , 300.Xr elf 5 , 301.Xr libmap.conf 5 , 302.Xr ldconfig 8 303