1 .\" Copyright (c) 1995 Paul Kranenburg
2 .\" All rights reserved.
4 .\" Redistribution and use in source and binary forms, with or without
5 .\" modification, are permitted provided that the following conditions
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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
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29 .\" $FreeBSD: src/libexec/rtld-elf/rtld.1 216695 2010-12-25 08:51:20Z kib $
39 .Nd run-time link-editor
42 .Fn _rtld_functrace "const char *callerso" "const char *calleeso" "const char *calleefun" "void *stack"
46 utility is a self-contained shared object providing run-time
47 support for loading and link-editing shared objects into a process'
49 It is also commonly known as the dynamic linker.
50 It uses the data structures
51 contained within dynamically linked programs to determine which shared
52 libraries are needed and loads them using the
56 After all shared libraries have been successfully loaded,
58 proceeds to resolve external references from both the main program and
60 A mechanism is provided for initialization routines
61 to be called on a per-object basis, giving a shared object an opportunity
62 to perform any extra set-up before execution of the program proper begins.
63 This is useful for C++ libraries that contain static constructors.
65 When resolving dependencies for the loaded objects,
67 may be allowed to translate dynamic token strings in rpath and soname
70 option of the static linker
72 The following strings are recognized now:
73 .Bl -tag -width ".Pa $PLATFORM"
75 Translated to the full path of the loaded object.
77 Translated to the name of the operating system implementation.
79 Translated to the release level of the operating system.
81 Translated to the machine hardware platform.
86 utility itself is loaded by the kernel together with any dynamically-linked
87 program that is to be executed.
88 The kernel transfers control to the
90 After the dynamic linker has finished loading,
91 relocating, and initializing the program and its required shared
92 objects, it transfers control to the entry point of the program.
94 To locate the required shared objects in the file system,
105 recognizes a number of environment variables that can be used to modify
106 its behaviour as follows:
107 .Bl -tag -width ".Ev LD_LIBMAP_DISABLE"
108 .It Ev LD_DUMP_REL_POST
111 will print a table containing all relocations after symbol
112 binding and relocation.
113 .It Ev LD_DUMP_REL_PRE
116 will print a table containing all relocations before symbol
117 binding and relocation.
119 A library replacement list in the same format as
121 For convenience, the characters
125 can be used instead of a space and a newline.
126 This variable is parsed after
128 and will override its entries.
129 This variable is unset for set-user-ID and set-group-ID programs.
130 .It Ev LD_LIBMAP_DISABLE
131 If set, disables the use of
135 This variable is unset for set-user-ID and set-group-ID programs.
136 .It Ev LD_ELF_HINTS_PATH
137 This variable will override the default location of
140 This variable is unset for set-user-ID and set-group-ID programs.
141 .It Ev LD_LIBRARY_PATH
142 A colon separated list of directories, overriding the default search path
143 for shared libraries.
144 This variable is unset for set-user-ID and set-group-ID programs.
146 A list of shared libraries, separated by colons and/or white space,
147 to be linked in before any
148 other shared libraries.
149 If the directory is not specified then
150 the directories specified by
152 will be searched first
153 followed by the set of built-in standard directories.
154 This variable is unset for set-user-ID and set-group-ID programs.
156 When set to a nonempty string, causes
158 to relocate all external function calls before starting execution of the
160 Normally, function calls are bound lazily, at the first call
163 increases the start-up time of a program, but it avoids run-time
164 surprises caused by unexpectedly undefined functions.
165 .It Ev LD_TRACE_LOADED_OBJECTS
166 When set to a nonempty string, causes
168 to exit after loading the shared objects and printing a summary which includes
169 the absolute pathnames of all objects, to standard output.
170 .It Ev LD_TRACE_LOADED_OBJECTS_ALL
171 When set to a nonempty string, causes
173 to expand the summary to indicate which objects caused each object to
175 .It Ev LD_TRACE_LOADED_OBJECTS_FMT1
176 .It Ev LD_TRACE_LOADED_OBJECTS_FMT2
177 When set, these variables are interpreted as format strings a la
179 to customize the trace output and are used by
184 to be operated as a filter more conveniently.
185 If the dependency name starts with string
187 .Ev LD_TRACE_LOADED_OBJECTS_FMT1
189 .Ev LD_TRACE_LOADED_OBJECTS_FMT2
191 The following conversions can be used:
194 The main program's name
198 The value of the environment variable
199 .Ev LD_TRACE_LOADED_OBJECTS_PROGNAME .
200 Typically used to print both the names of programs and shared libraries
201 being inspected using
206 The full pathname as determined by
208 library search rules.
210 The library's load address.
217 are recognized and have their usual meaning.
221 will log events such as the loading and unloading of shared objects via
225 If a shared object preloaded by the
227 mechanism contains a public symbol
228 .Dq _rtld_functrace ,
230 will transfer control to this function each time
231 it needs to resolve an unbound function symbol.
232 By returning a non-zero value,
234 can advise the linker to keep tracing the specified
235 combination of caller shared object and called function;
236 returning 0 will prevent
238 to be called for this combination again.
240 When implementing a custom
242 function, be aware of the possibility that
244 might be called for functions called on its behalf,
245 or that multiple threads could enter
248 .Sh DIFFERENCES BETWEEN .1 and .2
249 ABI changes have been made to support TLS allocation and initialization
250 and to give threading libraries a chance to complete initialization of the
251 TCB prior to the calling of the _init() functions for the dynamically loaded
254 .Bl -tag -width ".Pa /var/run/ld-elf.so.hints" -compact
255 .It Pa /var/run/ld-elf.so.hints
257 .It Pa /etc/libmap.conf
258 The libmap configuration file.
263 for printing out the functions as they are called, this code can be used:
264 .Bd -literal -offset indent
270 _rtld_functrace(const char *callerso, const char *calleeso,
271 const char *calleefun, void *stack)
273 write(2, "calling ", 8);
274 write(2, calleefun, strlen(calleefun));
280 If put in a file named
283 .Bd -literal -offset indent
284 $ cc -shared ft.c -o ft.so