225 lines
7.3 KiB
Plaintext
225 lines
7.3 KiB
Plaintext
.\" $Id: rtld.1,v 1.14 1997/05/27 13:46:40 max Exp $
|
|
.\"
|
|
.\" Copyright (c) 1995 Paul Kranenburg
|
|
.\" All rights reserved.
|
|
.\"
|
|
.\" Redistribution and use in source and binary forms, with or without
|
|
.\" modification, are permitted provided that the following conditions
|
|
.\" are met:
|
|
.\" 1. Redistributions of source code must retain the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer.
|
|
.\" 2. Redistributions in binary form must reproduce the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer in the
|
|
.\" documentation and/or other materials provided with the distribution.
|
|
.\" 3. All advertising materials mentioning features or use of this software
|
|
.\" must display the following acknowledgment:
|
|
.\" This product includes software developed by Paul Kranenburg.
|
|
.\" 3. The name of the author may not be used to endorse or promote products
|
|
.\" derived from this software without specific prior written permission
|
|
.\"
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
|
|
.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
|
|
.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
|
|
.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
|
|
.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
|
|
.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
|
|
.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
|
|
.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
|
|
.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
|
|
.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
|
|
.\"
|
|
.Dd June 27, 1995
|
|
.Dt RTLD 1
|
|
.Os FreeBSD
|
|
.Sh NAME
|
|
.Nm ld.so
|
|
.Nd run-time link-editor
|
|
.Sh DESCRIPTION
|
|
.Nm
|
|
is a self-contained, position independent program image providing run-time
|
|
support for loading and link-editing shared objects into a process'
|
|
address space. It uses the data structures
|
|
.Po
|
|
see
|
|
.Xr link 5
|
|
.Pc
|
|
contained within dynamically linked programs to determine which shared
|
|
libraries are needed and loads them at a convenient virtual address
|
|
using the
|
|
.Xr mmap 2
|
|
system call.
|
|
.Pp
|
|
After all shared libraries have been successfully loaded,
|
|
.Nm
|
|
proceeds to resolve external references from both the main program and
|
|
all objects loaded. A mechanism is provided for initialization routines
|
|
to be called, on a per-object basis, giving a shared object an opportunity
|
|
to perform any extra set-up, before execution of the program proper begins.
|
|
This is useful for C++ libraries that contain static constructors.
|
|
.Pp
|
|
.Nm
|
|
is itself a shared object that is initially loaded by the startup module
|
|
.Em crt0 .
|
|
Since
|
|
.Xr a.out 5
|
|
formats do not provide easy access to the file header from within a running
|
|
process,
|
|
.Em crt0
|
|
uses the special symbol
|
|
.Va _DYNAMIC
|
|
to determine whether a program is in fact dynamically linked or not. Whenever
|
|
the linker
|
|
.Xr ld 1
|
|
has relocated this symbol to a location other than 0,
|
|
.Em crt0
|
|
assumes the services of
|
|
.Nm
|
|
are needed
|
|
.Po
|
|
see
|
|
.Xr link 5
|
|
for details
|
|
.Pc \&.
|
|
.Em crt0
|
|
passes control to
|
|
.Nm
|
|
\&'s entry point before the program's
|
|
.Fn main
|
|
routine is called. Thus,
|
|
.Nm
|
|
can complete the link-editing process before the dynamic program calls upon
|
|
services of any dynamic library.
|
|
.Pp
|
|
To quickly locate the required shared objects in the filesystem,
|
|
.Nm
|
|
may use a
|
|
.Dq hints
|
|
file, prepared by the
|
|
.Xr ldconfig 8
|
|
utility, in which the full path specification of the shared objects can be
|
|
looked up by hashing on the 3-tuple
|
|
.Ao
|
|
library-name, major-version-number, minor-version-number
|
|
.Ac \&.
|
|
.Pp
|
|
.Nm
|
|
recognizes a number of environment variables that can be used to modify
|
|
its behaviour as follows:
|
|
.Pp
|
|
.Bl -tag -width "LD_IGNORE_MISSING_OBJECTS"
|
|
.It Ev LD_LIBRARY_PATH
|
|
A colon separated list of directories, overriding the default search path
|
|
for shared libraries.
|
|
This is ignored for set-user-ID and set-group-ID programs.
|
|
.It Ev LD_PRELOAD
|
|
A colon separated list of shared libraries, to be linked in before any
|
|
other shared libraries. If the directory is not specified then
|
|
the directories specified by LD_LIBRARY_PATH will be searched first
|
|
followed by the set of built-in standard directories.
|
|
This is ignored for set-user-ID and set-group-ID programs.
|
|
.It Ev LD_BIND_NOW
|
|
When set to a nonempty string, causes
|
|
.Nm
|
|
to relocate all external function calls before starting execution of the
|
|
program. Normally, function calls are bound lazily, at the first call
|
|
of each function.
|
|
.Ev LD_BIND_NOW
|
|
increases the start-up time of a program, but it avoids run-time
|
|
surprises caused by unexpectedly undefined functions.
|
|
.It Ev LD_WARN_NON_PURE_CODE
|
|
When set to a nonempty string, issue a warning whenever a link-editing
|
|
operation requires modification of the text segment of some loaded
|
|
object. This is usually indicative of an incorrectly built library.
|
|
.It Ev LD_SUPPRESS_WARNINGS
|
|
When set to a nonempty string, no warning messages of any kind are
|
|
issued. Normally, a warning is given if satisfactorily versioned
|
|
library could not be found.
|
|
.It Ev LD_IGNORE_MISSING_OBJECTS
|
|
When set to a nonempty string, makes it a nonfatal condition if
|
|
one or more required shared objects cannot be loaded.
|
|
Loading and execution proceeds using the objects that are
|
|
available.
|
|
A warning is produced for each missing object, unless the environment
|
|
variable
|
|
.Ev LD_SUPPRESS_WARNINGS
|
|
is set to a nonempty string.
|
|
.Pp
|
|
This is ignored for set-user-ID and set-group-ID programs.
|
|
.Pp
|
|
Missing shared objects can be ignored without errors if all the
|
|
following conditions hold:
|
|
.Bl -bullet
|
|
.It
|
|
They do not supply definitions for any required data symbols.
|
|
.It
|
|
No functions defined by them are called during program execution.
|
|
.It
|
|
The environment variable
|
|
.Ev LD_BIND_NOW
|
|
is unset or is set to the empty string.
|
|
.El
|
|
.It Ev LD_TRACE_LOADED_OBJECTS
|
|
When set to a nonempty string, causes
|
|
.Nm
|
|
to exit after loading the shared objects and printing a summary which includes
|
|
the absolute pathnames of all objects, to standard output.
|
|
.It Ev LD_TRACE_LOADED_OBJECTS_FMT1
|
|
.It Ev LD_TRACE_LOADED_OBJECTS_FMT2
|
|
When set, these variables are interpreted as format strings a la
|
|
.Xr printf 3
|
|
to customize the trace output and are used by
|
|
.Xr ldd 1 's
|
|
.Fl f
|
|
option and allows
|
|
.Xr ldd 1
|
|
to be operated as a filter more conveniently.
|
|
The following conversions can be used:
|
|
.Bl -tag -indent "LD_TRACE_LOADED_OBJECTS_FMT1 " -width "xxxx"
|
|
.It \&%a
|
|
The main program's name
|
|
.Po also known as
|
|
.Dq __progname
|
|
.Pc .
|
|
.It \&%A
|
|
The value of the environment variable
|
|
.Ev LD_TRACE_LOADED_OBJECTS_PROGNAME
|
|
.It \&%o
|
|
The library name.
|
|
.It \&%m
|
|
The library's major version number.
|
|
.It \&%n
|
|
The library's minor version number.
|
|
.It \&%p
|
|
The full pathname as determined by
|
|
.Nm rtld Ns 's
|
|
library search rules.
|
|
.It \&%x
|
|
The library's load address.
|
|
.El
|
|
.Pp
|
|
Additionally,
|
|
.Sy \en
|
|
and
|
|
.Sy \et
|
|
are recognized and have their usual meaning.
|
|
.\" .It Ev LD_NO_INTERN_SEARCH
|
|
.\" When set,
|
|
.\" .Nm
|
|
.\" does not process any internal search paths that were recorded in the
|
|
.\" executable.
|
|
.\" .It Ev LD_NOSTD_PATH
|
|
.\" When set, do not include a set of built-in standard directory paths for
|
|
.\" searching. This might be useful when running on a system with a completely
|
|
.\" non-standard filesystem layout.
|
|
.El
|
|
.Pp
|
|
.Sh FILES
|
|
/var/run/ld.so.hints
|
|
.Pp
|
|
.Sh SEE ALSO
|
|
.Xr ld 1 ,
|
|
.Xr link 5 ,
|
|
.Xr ldconfig 8
|
|
.Sh HISTORY
|
|
The shared library model employed first appeared in SunOS 4.0
|