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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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.
93 The following search order is used to locate required shared objects:
95 .Bd -literal -offset "XX"
96 1. DT_RPATH of the referencing object unless that object also
97 contains a DT_RUNPATH tag
98 2. DT_RPATH of the program unless the referencing object contains
100 3. Path indicated by LD_LIBRARY_PATH environment variable
101 4. DT_RUNPATH of the referencing object
102 5. Hints file produced by the ldconfig utility
103 6. The /usr/lib directory unless the referencing object was linked
104 using the "-z nodefaultlib" option
110 recognizes a number of environment variables that can be used to modify
111 its behaviour as follows:
112 .Bl -tag -width ".Ev LD_LIBMAP_DISABLE"
113 .It Ev LD_DUMP_REL_POST
116 will print a table containing all relocations after symbol
117 binding and relocation.
118 .It Ev LD_DUMP_REL_PRE
121 will print a table containing all relocations before symbol
122 binding and relocation.
124 A library replacement list in the same format as
126 For convenience, the characters
130 can be used instead of a space and a newline.
131 This variable is parsed after
133 and will override its entries.
134 This variable is unset for set-user-ID and set-group-ID programs.
135 .It Ev LD_LIBMAP_DISABLE
136 If set, disables the use of
140 This variable is unset for set-user-ID and set-group-ID programs.
141 .It Ev LD_ELF_HINTS_PATH
142 This variable will override the default location of
145 This variable is unset for set-user-ID and set-group-ID programs.
146 .It Ev LD_LIBRARY_PATH
147 A colon separated list of directories, overriding the default search path
148 for shared libraries.
149 This variable is unset for set-user-ID and set-group-ID programs.
151 A list of shared libraries, separated by colons and/or white space,
152 to be linked in before any
153 other shared libraries.
154 If the directory is not specified then
155 the directories specified by
157 will be searched first
158 followed by the set of built-in standard directories.
159 This variable is unset for set-user-ID and set-group-ID programs.
161 When set to a nonempty string, causes
163 to relocate all external function calls before starting execution of the
165 Normally, function calls are bound lazily, at the first call
168 increases the start-up time of a program, but it avoids run-time
169 surprises caused by unexpectedly undefined functions.
170 .It Ev LD_TRACE_LOADED_OBJECTS
171 When set to a nonempty string, causes
173 to exit after loading the shared objects and printing a summary which includes
174 the absolute pathnames of all objects, to standard output.
175 .It Ev LD_TRACE_LOADED_OBJECTS_ALL
176 When set to a nonempty string, causes
178 to expand the summary to indicate which objects caused each object to
180 .It Ev LD_TRACE_LOADED_OBJECTS_FMT1
181 .It Ev LD_TRACE_LOADED_OBJECTS_FMT2
182 When set, these variables are interpreted as format strings a la
184 to customize the trace output and are used by
189 to be operated as a filter more conveniently.
190 If the dependency name starts with string
192 .Ev LD_TRACE_LOADED_OBJECTS_FMT1
194 .Ev LD_TRACE_LOADED_OBJECTS_FMT2
196 The following conversions can be used:
199 The main program's name
203 The value of the environment variable
204 .Ev LD_TRACE_LOADED_OBJECTS_PROGNAME .
205 Typically used to print both the names of programs and shared libraries
206 being inspected using
211 The full pathname as determined by
213 library search rules.
215 The library's load address.
222 are recognized and have their usual meaning.
226 will log events such as the loading and unloading of shared objects via
232 will process the filtee dependencies of the loaded objects immediately,
233 instead of postponing it until required.
234 Normally, the filtees are opened at the time of the first symbol resolution
235 from the filter object.
238 If a shared object preloaded by the
240 mechanism contains a public symbol
241 .Dq _rtld_functrace ,
243 will transfer control to this function each time
244 it needs to resolve an unbound function symbol.
245 By returning a non-zero value,
247 can advise the linker to keep tracing the specified
248 combination of caller shared object and called function;
249 returning 0 will prevent
251 to be called for this combination again.
253 When implementing a custom
255 function, be aware of the possibility that
257 might be called for functions called on its behalf,
258 or that multiple threads could enter
261 .Sh DIFFERENCES BETWEEN .1 and .2
262 ABI changes have been made to support TLS allocation and initialization
263 and to give threading libraries a chance to complete initialization of the
264 TCB prior to the calling of the _init() functions for the dynamically loaded
267 .Bl -tag -width ".Pa /var/run/ld-elf.so.hints" -compact
268 .It Pa /var/run/ld-elf.so.hints
270 .It Pa /etc/libmap.conf
271 The libmap configuration file.
276 for printing out the functions as they are called, this code can be used:
277 .Bd -literal -offset indent
283 _rtld_functrace(const char *callerso, const char *calleeso,
284 const char *calleefun, void *stack)
286 write(2, "calling ", 8);
287 write(2, calleefun, strlen(calleefun));
293 If put in a file named
296 .Bd -literal -offset indent
297 $ cc -shared -fPIC ft.c -o ft.so