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.
61 When resolving dependencies for the loaded objects,
63 may be allowed to translate dynamic token strings in rpath and soname
66 option of the static linker
68 The following strings are recognized now:
69 .Bl -tag -width ".Pa $PLATFORM"
71 Translated to the full path of the loaded object.
73 Translated to the name of the operating system implementation.
75 Translated to the release level of the operating system.
77 Translated to the machine hardware platform.
82 utility itself is loaded by the kernel together with any dynamically-linked
83 program that is to be executed.
84 The kernel transfers control to the
86 After the dynamic linker has finished loading,
87 relocating, and initializing the program and its required shared
88 objects, it transfers control to the entry point of the program.
90 To locate the required shared objects in the file system,
101 recognizes a number of environment variables that can be used to modify
103 On 64-bit architectures, the linker for 32-bit objects recognizes
104 all the environment variables listed below, but is being prefixed with
107 .Ev LD_32_TRACE_LOADED_OBJECTS .
108 .Bl -tag -width ".Ev LD_LIBMAP_DISABLE"
109 .It Ev LD_DUMP_REL_POST
112 will print a table containing all relocations after symbol
113 binding and relocation.
114 .It Ev LD_DUMP_REL_PRE
117 will print a table containing all relocations before symbol
118 binding and relocation.
120 A library replacement list in the same format as
122 For convenience, the characters
126 can be used instead of a space and a newline.
127 This variable is parsed after
129 and will override its entries.
130 This variable is unset for set-user-ID and set-group-ID programs.
131 .It Ev LD_LIBMAP_DISABLE
132 If set, disables the use of
136 This variable is unset for set-user-ID and set-group-ID programs.
137 .It Ev LD_ELF_HINTS_PATH
138 This variable will override the default location of
141 This variable is unset for set-user-ID and set-group-ID programs.
142 .It Ev LD_LIBRARY_PATH
143 A colon separated list of directories, overriding the default search path
144 for shared libraries.
145 This variable is unset for set-user-ID and set-group-ID programs.
147 A list of shared libraries, separated by colons and/or white space,
148 to be linked in before any
149 other shared libraries.
150 If the directory is not specified then
151 the directories specified by
153 will be searched first
154 followed by the set of built-in standard directories.
155 This variable is unset for set-user-ID and set-group-ID programs.
157 When set to a nonempty string, causes
159 to relocate all external function calls before starting execution of the
161 Normally, function calls are bound lazily, at the first call
164 increases the start-up time of a program, but it avoids run-time
165 surprises caused by unexpectedly undefined functions.
166 .It Ev LD_TRACE_LOADED_OBJECTS
167 When set to a nonempty string, causes
169 to exit after loading the shared objects and printing a summary which includes
170 the absolute pathnames of all objects, to standard output.
171 .It Ev LD_TRACE_LOADED_OBJECTS_ALL
172 When set to a nonempty string, causes
174 to expand the summary to indicate which objects caused each object to
176 .It Ev LD_TRACE_LOADED_OBJECTS_FMT1
177 .It Ev LD_TRACE_LOADED_OBJECTS_FMT2
178 When set, these variables are interpreted as format strings a la
180 to customize the trace output and are used by
185 to be operated as a filter more conveniently.
186 If the dependency name starts with string
188 .Ev LD_TRACE_LOADED_OBJECTS_FMT1
190 .Ev LD_TRACE_LOADED_OBJECTS_FMT2
192 The following conversions can be used:
195 The main program's name
199 The value of the environment variable
200 .Ev LD_TRACE_LOADED_OBJECTS_PROGNAME .
201 Typically used to print both the names of programs and shared libraries
202 being inspected using
207 The full pathname as determined by
209 library search rules.
211 The library's load address.
218 are recognized and have their usual meaning.
222 will log events such as the loading and unloading of shared objects via
228 will process the filtee dependencies of the loaded objects immediately,
229 instead of postponing it until required.
230 Normally, the filtees are opened at the time of the first symbol resolution
231 from the filter object.
234 .Bl -tag -width ".Pa /var/run/ld-elf32.so.hints" -compact
235 .It Pa /var/run/ld-elf.so.hints
237 .It Pa /var/run/ld-elf32.so.hints
238 Hints file for 32-bit binaries on 64-bit system.
239 .It Pa /etc/libmap.conf
240 The libmap configuration file.
241 .It Pa /etc/libmap32.conf
242 The libmap configuration file for 32-bit binaries on 64-bit system.