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.
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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 .Bl -enum -offset indent -compact
98 of the referencing object unless that object also contains a
103 of the program unless the referencing object contains a
112 of the referencing object
114 Hints file produced by the
122 directory unless the referencing object was linked using the
123 .Dq Fl z Ar nodefaultlib
130 recognizes a number of environment variables that can be used to modify
131 its behaviour as follows:
132 .Bl -tag -width ".Ev LD_LIBMAP_DISABLE"
133 .It Ev LD_DUMP_REL_POST
136 will print a table containing all relocations after symbol
137 binding and relocation.
138 .It Ev LD_DUMP_REL_PRE
141 will print a table containing all relocations before symbol
142 binding and relocation.
144 A library replacement list in the same format as
146 For convenience, the characters
150 can be used instead of a space and a newline.
151 This variable is parsed after
153 and will override its entries.
154 This variable is unset for set-user-ID and set-group-ID programs.
155 .It Ev LD_LIBMAP_DISABLE
156 If set, disables the use of
160 This variable is unset for set-user-ID and set-group-ID programs.
161 .It Ev LD_ELF_HINTS_PATH
162 This variable will override the default location of
165 This variable is unset for set-user-ID and set-group-ID programs.
166 .It Ev LD_LIBRARY_PATH
167 A colon separated list of directories, overriding the default search path
168 for shared libraries.
169 This variable is unset for set-user-ID and set-group-ID programs.
171 A list of shared libraries, separated by colons and/or white space,
172 to be linked in before any
173 other shared libraries.
174 If the directory is not specified then
175 the directories specified by
177 will be searched first
178 followed by the set of built-in standard directories.
179 This variable is unset for set-user-ID and set-group-ID programs.
181 When set to a nonempty string, causes
183 to relocate all external function calls before starting execution of the
185 Normally, function calls are bound lazily, at the first call
188 increases the start-up time of a program, but it avoids run-time
189 surprises caused by unexpectedly undefined functions.
190 .It Ev LD_TRACE_LOADED_OBJECTS
191 When set to a nonempty string, causes
193 to exit after loading the shared objects and printing a summary which includes
194 the absolute pathnames of all objects, to standard output.
195 .It Ev LD_TRACE_LOADED_OBJECTS_ALL
196 When set to a nonempty string, causes
198 to expand the summary to indicate which objects caused each object to
200 .It Ev LD_TRACE_LOADED_OBJECTS_FMT1
201 .It Ev LD_TRACE_LOADED_OBJECTS_FMT2
202 When set, these variables are interpreted as format strings a la
204 to customize the trace output and are used by
209 to be operated as a filter more conveniently.
210 If the dependency name starts with string
212 .Ev LD_TRACE_LOADED_OBJECTS_FMT1
214 .Ev LD_TRACE_LOADED_OBJECTS_FMT2
216 The following conversions can be used:
219 The main program's name
223 The value of the environment variable
224 .Ev LD_TRACE_LOADED_OBJECTS_PROGNAME .
225 Typically used to print both the names of programs and shared libraries
226 being inspected using
231 The full pathname as determined by
233 library search rules.
235 The library's load address.
242 are recognized and have their usual meaning.
246 will log events such as the loading and unloading of shared objects via
251 will process the filtee dependencies of the loaded objects immediately,
252 instead of postponing it until required.
253 Normally, the filtees are opened at the time of the first symbol resolution
254 from the filter object.
257 If a shared object preloaded by the
259 mechanism contains a public symbol
260 .Dq _rtld_functrace ,
262 will transfer control to this function each time
263 it needs to resolve an unbound function symbol.
264 By returning a non-zero value,
266 can advise the linker to keep tracing the specified
267 combination of caller shared object and called function;
268 returning 0 will prevent
270 to be called for this combination again.
272 When implementing a custom
274 function, be aware of the possibility that
276 might be called for functions called on its behalf,
277 or that multiple threads could enter
280 .Sh DIFFERENCES BETWEEN .1 and .2
281 ABI changes have been made to support TLS allocation and initialization
282 and to give threading libraries a chance to complete initialization of the
283 TCB prior to the calling of the _init() functions for the dynamically loaded
286 .Bl -tag -width ".Pa /var/run/ld-elf.so.hints" -compact
287 .It Pa /var/run/ld-elf.so.hints
289 .It Pa /etc/libmap.conf
290 The libmap configuration file.
295 for printing out the functions as they are called, this code can be used:
296 .Bd -literal -offset indent
302 _rtld_functrace(const char *callerso, const char *calleeso,
303 const char *calleefun, void *stack)
305 write(2, "calling ", 8);
306 write(2, calleefun, strlen(calleefun));
312 If put in a file named
315 .Bd -literal -offset indent
316 $ cc -shared -fPIC ft.c -o ft.so