1 .\" Copyright (c) 1995 Paul Kranenburg
2 .\" All rights reserved.
4 .\" Redistribution and use in source and binary forms, with or without
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38 .Nd run-time link-editor
42 utility is a self-contained shared object providing run-time
43 support for loading and link-editing shared objects into a process'
45 It is also commonly known as the dynamic linker.
46 It uses the data structures
47 contained within dynamically linked programs to determine which shared
48 libraries are needed and loads them using the
52 After all shared libraries have been successfully loaded,
54 proceeds to resolve external references from both the main program and
56 A mechanism is provided for initialization routines
57 to be called on a per-object basis, giving a shared object an opportunity
58 to perform any extra set-up before execution of the program proper begins.
59 This is useful for C++ libraries that contain static constructors.
63 utility itself is loaded by the kernel together with any dynamically-linked
64 program that is to be executed.
65 The kernel transfers control to the
67 After the dynamic linker has finished loading,
68 relocating, and initializing the program and its required shared
69 objects, it transfers control to the entry point of the program.
71 To locate the required shared objects in the file system,
82 recognizes a number of environment variables that can be used to modify
84 On 64-bit architectures, the linker for 32-bit objects recognizes
85 all the environment variables listed below, but is being prefixed with
88 .Ev LD_32_TRACE_LOADED_OBJECTS .
90 .Bl -tag -width ".Ev LD_LIBMAP_DISABLE"
91 .It Ev LD_DUMP_REL_POST
94 will print a table containing all relocations after symbol
95 binding and relocation.
96 .It Ev LD_DUMP_REL_PRE
99 will print a table containing all relocations before symbol
100 binding and relocation.
102 A library replacement list in the same format as
104 For convenience, the characters
108 can be used instead of a space and a newline.
109 This variable is parsed after
111 and will override its entries.
112 This variable is unset for set-user-ID and set-group-ID programs.
113 .It Ev LD_LIBMAP_DISABLE
114 If set, disables the use of
118 This variable is unset for set-user-ID and set-group-ID programs.
119 .It Ev LD_LIBRARY_PATH
120 A colon separated list of directories, overriding the default search path
121 for shared libraries.
122 This variable is unset for set-user-ID and set-group-ID programs.
124 A list of shared libraries, separated by colons and/or white space,
125 to be linked in before any
126 other shared libraries.
127 If the directory is not specified then
128 the directories specified by
130 will be searched first
131 followed by the set of built-in standard directories.
132 This variable is unset for set-user-ID and set-group-ID programs.
134 When set to a nonempty string, causes
136 to relocate all external function calls before starting execution of the
138 Normally, function calls are bound lazily, at the first call
141 increases the start-up time of a program, but it avoids run-time
142 surprises caused by unexpectedly undefined functions.
143 .It Ev LD_TRACE_LOADED_OBJECTS
144 When set to a nonempty string, causes
146 to exit after loading the shared objects and printing a summary which includes
147 the absolute pathnames of all objects, to standard output.
148 .It Ev LD_TRACE_LOADED_OBJECTS_ALL
149 When set to a nonempty string, causes
151 to expand the summary to indicate which objects caused each object to
153 .It Ev LD_TRACE_LOADED_OBJECTS_FMT1
154 .It Ev LD_TRACE_LOADED_OBJECTS_FMT2
155 When set, these variables are interpreted as format strings a la
157 to customize the trace output and are used by
162 to be operated as a filter more conveniently.
163 If the dependency name starts with string
165 .Ev LD_TRACE_LOADED_OBJECTS_FMT1
167 .Ev LD_TRACE_LOADED_OBJECTS_FMT2
169 The following conversions can be used:
172 The main program's name
176 The value of the environment variable
177 .Ev LD_TRACE_LOADED_OBJECTS_PROGNAME .
178 Typically used to print both the names of programs and shared libraries
179 being inspected using
184 The full pathname as determined by
186 library search rules.
188 The library's load address.
195 are recognized and have their usual meaning.
199 will log events such as the loading and unloading of shared objects via
203 .Bl -tag -width ".Pa /var/run/ld-elf32.so.hints" -compact
204 .It Pa /var/run/ld-elf.so.hints
206 .It Pa /var/run/ld-elf32.so.hints
207 Hints file for 32-bit binaries on 64-bit system.
208 .It Pa /etc/libmap.conf
209 The libmap configuration file.
210 .It Pa /etc/libmap32.conf
211 The libmap configuration file for 32-bit binaries on 64-bit system.