1 .\" Copyright (c) 1995 Paul Kranenburg
2 .\" All rights reserved.
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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.
89 The following search order is used to locate required shared objects:
91 .Bl -enum -offset indent -compact
94 of the referencing object unless that object also contains a
99 of the program unless the referencing object contains a
108 of the referencing object
110 Hints file produced by the
118 directories, unless the referencing object was linked using the
119 .Dq Fl z Ar nodefaultlib
126 recognizes a number of environment variables that can be used to modify
128 On 64-bit architectures, the linker for 32-bit objects recognizes
129 all the environment variables listed below, but is being prefixed with
132 .Ev LD_32_TRACE_LOADED_OBJECTS .
133 .Bl -tag -width ".Ev LD_LIBMAP_DISABLE"
134 .It Ev LD_DUMP_REL_POST
137 will print a table containing all relocations after symbol
138 binding and relocation.
139 .It Ev LD_DUMP_REL_PRE
142 will print a table containing all relocations before symbol
143 binding and relocation.
145 A library replacement list in the same format as
147 For convenience, the characters
151 can be used instead of a space and a newline.
152 This variable is parsed after
154 and will override its entries.
155 This variable is unset for set-user-ID and set-group-ID programs.
156 .It Ev LD_LIBMAP_DISABLE
157 If set, disables the use of
161 This variable is unset for set-user-ID and set-group-ID programs.
162 .It Ev LD_ELF_HINTS_PATH
163 This variable will override the default location of
166 This variable is unset for set-user-ID and set-group-ID programs.
167 .It Ev LD_LIBRARY_PATH
168 A colon separated list of directories, overriding the default search path
169 for shared libraries.
170 This variable is unset for set-user-ID and set-group-ID programs.
171 .It Ev LD_LIBRARY_PATH_RPATH
172 If the variable is specified and has a value starting with
173 any of \'y\', \'Y\' or \'1\' symbols, the path specified by
175 variable is allowed to override the path from
177 for binaries which does not contain
180 For such binaries, when the variable
181 .Ev LD_LIBRARY_PATH_RPATH
183 .Dq Fl z Ar nodefaultlib
184 link-time option is ignored as well.
186 A list of shared libraries, separated by colons and/or white space,
187 to be linked in before any
188 other shared libraries.
189 If the directory is not specified then
190 the directories specified by
192 will be searched first
193 followed by the set of built-in standard directories.
194 This variable is unset for set-user-ID and set-group-ID programs.
195 .Ev LD_LIBRARY_PATH_FDS
196 A colon separated list of file descriptor numbers for library directories.
197 This is intended for use within
199 sandboxes, when global namespaces such as the filesystem are unavailable.
200 It is consulted just after LD_LIBRARY_PATH.
201 This variable is unset for set-user-ID and set-group-ID programs.
203 When set to a nonempty string, causes
205 to relocate all external function calls before starting execution of the
207 Normally, function calls are bound lazily, at the first call
210 increases the start-up time of a program, but it avoids run-time
211 surprises caused by unexpectedly undefined functions.
212 .It Ev LD_TRACE_LOADED_OBJECTS
213 When set to a nonempty string, causes
215 to exit after loading the shared objects and printing a summary which includes
216 the absolute pathnames of all objects, to standard output.
217 .It Ev LD_TRACE_LOADED_OBJECTS_ALL
218 When set to a nonempty string, causes
220 to expand the summary to indicate which objects caused each object to
222 .It Ev LD_TRACE_LOADED_OBJECTS_FMT1
223 .It Ev LD_TRACE_LOADED_OBJECTS_FMT2
224 When set, these variables are interpreted as format strings a la
226 to customize the trace output and are used by
231 to be operated as a filter more conveniently.
232 If the dependency name starts with string
234 .Ev LD_TRACE_LOADED_OBJECTS_FMT1
236 .Ev LD_TRACE_LOADED_OBJECTS_FMT2
238 The following conversions can be used:
241 The main program's name
245 The value of the environment variable
246 .Ev LD_TRACE_LOADED_OBJECTS_PROGNAME .
247 Typically used to print both the names of programs and shared libraries
248 being inspected using
253 The full pathname as determined by
255 library search rules.
257 The library's load address.
264 are recognized and have their usual meaning.
268 will log events such as the loading and unloading of shared objects via
273 will process the filtee dependencies of the loaded objects immediately,
274 instead of postponing it until required.
275 Normally, the filtees are opened at the time of the first symbol resolution
276 from the filter object.
279 .Bl -tag -width ".Pa /var/run/ld-elf32.so.hints" -compact
280 .It Pa /var/run/ld-elf.so.hints
282 .It Pa /var/run/ld-elf32.so.hints
283 Hints file for 32-bit binaries on 64-bit system.
284 .It Pa /etc/libmap.conf
285 The libmap configuration file.
286 .It Pa /etc/libmap32.conf
287 The libmap configuration file for 32-bit binaries on 64-bit system.