rtld: Allows return pathname in dl_iterate_phdr dlpi_name
[dragonfly.git] / libexec / rtld-elf / rtld.1
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1.\" Copyright (c) 1995 Paul Kranenburg
2.\" All rights reserved.
3.\"
4.\" Redistribution and use in source and binary forms, with or without
5.\" modification, are permitted provided that the following conditions
6.\" are met:
7.\" 1. Redistributions of source code must retain the above copyright
8.\" notice, this list of conditions and the following disclaimer.
9.\" 2. Redistributions in binary form must reproduce the above copyright
10.\" notice, this list of conditions and the following disclaimer in the
11.\" documentation and/or other materials provided with the distribution.
12.\" 3. All advertising materials mentioning features or use of this software
13.\" must display the following acknowledgment:
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
16.\" derived from this software without specific prior written permission
17.\"
18.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
19.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
20.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
21.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
22.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
23.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
24.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
25.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
26.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
27.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
28.\"
f4f4bfd5 29.\" $FreeBSD$
fcf53d9b 30.\"
f560f0d6 31.Dd May 6, 2012
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32.Dt RTLD 1
33.Os
34.Sh NAME
a1eee96a 35.Nm ld-elf.so.2 ,
fcf53d9b 36.Nm ld-elf.so.1 ,
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37.Nm rtld ,
38.Nm _rtld_functrace
984263bc 39.Nd run-time link-editor
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40.Sh SYNOPSIS
41.Ft int
42.Fn _rtld_functrace "const char *callerso" "const char *calleeso" "const char *calleefun" "void *stack"
984263bc 43.Sh DESCRIPTION
fcf53d9b 44The
984263bc 45.Nm
fcf53d9b 46utility is a self-contained shared object providing run-time
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47support for loading and link-editing shared objects into a process'
48address space.
49It is also commonly known as the dynamic linker.
50It uses the data structures
51contained within dynamically linked programs to determine which shared
52libraries are needed and loads them using the
53.Xr mmap 2
54system call.
55.Pp
56After all shared libraries have been successfully loaded,
57.Nm
58proceeds to resolve external references from both the main program and
59all objects loaded.
60A mechanism is provided for initialization routines
61to be called on a per-object basis, giving a shared object an opportunity
62to perform any extra set-up before execution of the program proper begins.
63This is useful for C++ libraries that contain static constructors.
64.Pp
fcf53d9b 65When resolving dependencies for the loaded objects,
984263bc 66.Nm
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67may be allowed to translate dynamic token strings in rpath and soname
68by setting
69.Fl "z origin"
70option of the static linker
71.Xr ld 1 .
72The following strings are recognized now:
73.Bl -tag -width ".Pa $PLATFORM"
74.It Pa $ORIGIN
75Translated to the full path of the loaded object.
76.It Pa $OSNAME
77Translated to the name of the operating system implementation.
78.It Pa $OSREL
79Translated to the release level of the operating system.
80.It Pa $PLATFORM
81Translated to the machine hardware platform.
82.El
83.Pp
84The
85.Nm
86utility itself is loaded by the kernel together with any dynamically-linked
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87program that is to be executed.
88The kernel transfers control to the
89dynamic linker.
90After the dynamic linker has finished loading,
91relocating, and initializing the program and its required shared
92objects, it transfers control to the entry point of the program.
f560f0d6 93The following search order is used to locate required shared objects:
984263bc 94.Pp
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95.Bl -enum -offset indent -compact
96.It
97.Dv DT_RPATH
98of the referencing object unless that object also contains a
99.Dv DT_RUNPATH
100tag
101.It
102.Dv DT_RPATH
103of the program unless the referencing object contains a
104.Dv DT_RUNPATH
105tag
106.It
107Path indicated by
108.Ev LD_LIBRARY_PATH
109environment variable
110.It
111.Dv DT_RUNPATH
112of the referencing object
113.It
114Hints file produced by the
115.Xr ldconfig 8
116utility
117.It
118The
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119.Pa /lib
120and
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121.Pa /usr/lib
122directory unless the referencing object was linked using the
123.Dq Fl z Ar nodefaultlib
124option
125.El
984263bc 126.Pp
fcf53d9b 127The
984263bc 128.Nm
fcf53d9b 129utility
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130recognizes a number of environment variables that can be used to modify
131its behaviour as follows:
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132.Bl -tag -width ".Ev LD_LIBMAP_DISABLE"
133.It Ev LD_DUMP_REL_POST
134If set,
135.Nm
136will print a table containing all relocations after symbol
137binding and relocation.
138.It Ev LD_DUMP_REL_PRE
139If set,
140.Nm
141will print a table containing all relocations before symbol
142binding and relocation.
143.It Ev LD_LIBMAP
144A library replacement list in the same format as
145.Xr libmap.conf 5 .
146For convenience, the characters
147.Ql =
148and
149.Ql \&,
150can be used instead of a space and a newline.
151This variable is parsed after
152.Xr libmap.conf 5 ,
153and will override its entries.
154This variable is unset for set-user-ID and set-group-ID programs.
155.It Ev LD_LIBMAP_DISABLE
156If set, disables the use of
157.Xr libmap.conf 5
158and
159.Ev LD_LIBMAP .
160This variable is unset for set-user-ID and set-group-ID programs.
161.It Ev LD_ELF_HINTS_PATH
162This variable will override the default location of
163.Dq hints
164file.
165This variable is unset for set-user-ID and set-group-ID programs.
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166.It Ev LD_LIBRARY_PATH
167A colon separated list of directories, overriding the default search path
168for shared libraries.
fcf53d9b 169This variable is unset for set-user-ID and set-group-ID programs.
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170.It Ev LD_PRELOAD
171A list of shared libraries, separated by colons and/or white space,
172to be linked in before any
173other shared libraries.
174If the directory is not specified then
175the directories specified by
176.Ev LD_LIBRARY_PATH
177will be searched first
178followed by the set of built-in standard directories.
fcf53d9b 179This variable is unset for set-user-ID and set-group-ID programs.
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180.It Ev LD_BIND_NOW
181When set to a nonempty string, causes
182.Nm
183to relocate all external function calls before starting execution of the
184program.
185Normally, function calls are bound lazily, at the first call
186of each function.
187.Ev LD_BIND_NOW
188increases the start-up time of a program, but it avoids run-time
189surprises caused by unexpectedly undefined functions.
190.It Ev LD_TRACE_LOADED_OBJECTS
191When set to a nonempty string, causes
192.Nm
193to exit after loading the shared objects and printing a summary which includes
194the absolute pathnames of all objects, to standard output.
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195.It Ev LD_TRACE_LOADED_OBJECTS_ALL
196When set to a nonempty string, causes
197.Nm
198to expand the summary to indicate which objects caused each object to
199be loaded.
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200.It Ev LD_TRACE_LOADED_OBJECTS_FMT1
201.It Ev LD_TRACE_LOADED_OBJECTS_FMT2
202When set, these variables are interpreted as format strings a la
203.Xr printf 3
204to customize the trace output and are used by
205.Xr ldd 1 Ns 's
206.Fl f
207option and allows
208.Xr ldd 1
209to be operated as a filter more conveniently.
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210If the dependency name starts with string
211.Pa lib ,
212.Ev LD_TRACE_LOADED_OBJECTS_FMT1
213is used, otherwise
214.Ev LD_TRACE_LOADED_OBJECTS_FMT2
215is used.
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216The following conversions can be used:
217.Bl -tag -width 4n
218.It Li %a
219The main program's name
220(also known as
221.Dq __progname ) .
222.It Li \&%A
223The value of the environment variable
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224.Ev LD_TRACE_LOADED_OBJECTS_PROGNAME .
225Typically used to print both the names of programs and shared libraries
226being inspected using
227.Xr ldd 1 .
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228.It Li %o
229The library name.
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230.It Li %p
231The full pathname as determined by
232.Nm rtld Ns 's
233library search rules.
234.It Li %x
235The library's load address.
236.El
237.Pp
238Additionally,
239.Ql \en
240and
241.Ql \et
242are recognized and have their usual meaning.
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243.It Ev LD_UTRACE
244If set,
245.Nm
246will log events such as the loading and unloading of shared objects via
247.Xr utrace 2 .
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JM
248.It Ev LD_LOADFLTR
249If set,
250.Nm
251will process the filtee dependencies of the loaded objects immediately,
252instead of postponing it until required.
253Normally, the filtees are opened at the time of the first symbol resolution
254from the filter object.
984263bc 255.El
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256.Pp
257If a shared object preloaded by the
258.Ev LD_PRELOAD
259mechanism contains a public symbol
260.Dq _rtld_functrace ,
261.Nm
262will transfer control to this function each time
263it needs to resolve an unbound function symbol.
264By returning a non-zero value,
265.Fn _rtld_functrace
266can advise the linker to keep tracing the specified
267combination of caller shared object and called function;
268returning 0 will prevent
269.Fn _rtld_functrace
270to be called for this combination again.
271.Pp
272When implementing a custom
273.Fn _rtld_functrace
274function, be aware of the possibility that
275.Fn _rtld_functrace
276might be called for functions called on its behalf,
277or that multiple threads could enter
278.Fn _rtld_functrace
279at the same time.
a1eee96a 280.Sh DIFFERENCES BETWEEN .1 and .2
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281ABI changes have been made to support TLS allocation and initialization
282and to give threading libraries a chance to complete initialization of the
283TCB prior to the calling of the _init() functions for the dynamically loaded
284libraries.
984263bc 285.Sh FILES
fcf53d9b 286.Bl -tag -width ".Pa /var/run/ld-elf.so.hints" -compact
984263bc 287.It Pa /var/run/ld-elf.so.hints
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288Hints file.
289.It Pa /etc/libmap.conf
290The libmap configuration file.
984263bc 291.El
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292.Sh EXAMPLES
293To set up an
294.Fn _rtld_functrace
295for printing out the functions as they are called, this code can be used:
296.Bd -literal -offset indent
297#include <string.h>
298
4ee0d876 299static int nl = 10;
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300
301int
302_rtld_functrace(const char *callerso, const char *calleeso,
303 const char *calleefun, void *stack)
304{
305 write(2, "calling ", 8);
306 write(2, calleefun, strlen(calleefun));
307 write(2, &nl, 1);
308 return 1;
309}
310.Ed
311.Pp
312If put in a file named
313.Pa ft.c
314and compiled with
315.Bd -literal -offset indent
0e759e7d 316$ cc -shared -fPIC ft.c -o ft.so
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317.Ed
318.Pp
319setting
320.Ev LD_PRELOAD
321to the path of
322.Pa ft.so
323will activate it.
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324.Sh SEE ALSO
325.Xr ld 1 ,
326.Xr ldd 1 ,
327.Xr elf 5 ,
fcf53d9b 328.Xr libmap.conf 5 ,
984263bc 329.Xr ldconfig 8