path: root/libexec/ld.so/ld.so.1

.\"	$OpenBSD: ld.so.1,v 1.2 2003/07/09 15:34:07 jmc Exp $
.\"	$NetBSD: rtld.1,v 1.2 1995/10/08 23:43:28 pk Exp $
.\"
.\" Copyright (c) 1995 Paul Kranenburg
.\" All rights reserved.
.\"
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.\" modification, are permitted provided that the following conditions
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.\"    must display the following acknowledgement:
.\"      This product includes software developed by Paul Kranenburg.
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.Dd June 27, 1995
.Dt LD.SO 1
.Os
.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's
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.

<talk about CTORS/DTORS>

.Pp
.Nm
is itself a shared object that is initially loaded by the the kernel
<How it is run>
.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
.Aq library-name , major-version-number , minor-version-number .
.Pp
.Nm
recognises a number of environment variables that can be used to modify
its behaviour as follows:
.Bl -tag -width "LD_TRACE_LOADED_OBJECTS_PROGNAME"
.It Ev LD_LIBRARY_PATH
A colon separated list of directories, overriding the default search path
for shared libraries.
This variable is ignored for set-user-ID and set-group-ID executables.
.It Ev LD_PRELOAD
A colon separate list of library names to load before any of the regular
libraries are loaded.
This variable is ignored for set-user-ID and set-group-ID executables.
.It Ev LD_WARN_NON_PURE_CODE
When set, 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.
<not yet supported>
.It Ev LD_SUPPRESS_WARNINGS
When set, no warning messages of any kind are issued. Normally, a warning
is given if satisfactorily versioned library could not be found.
<not yet supported>
.It Ev LD_TRACE_LOADED_OBJECTS
When set, 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 Ns '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 -width "xxxx"
.It \&%a
The main program's name
.Pq also known as Dq __progname .
.It \&%A
The value of the environment variable
.Ev LD_TRACE_LOADED_OBJECTS_PROGNAME
<not yet supported>
.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 ld.so Ns 's
library search rules.
.It \&%x
The library's load address.
.El
.Pp
Additionally,
.Sy \en
and
.Sy \et
are recognised and have their usual meaning.
<not yet supported>
.It Ev LD_NO_INTERN_SEARCH
When set,
.Nm
does not process any internal search paths that were recorded in the
executable.
<not yet supported>
.It Ev LD_NOSTD_PATH
<not yet supported>
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
.Sh FILES
.Bl -tag -width /var/run/ld.so.hintsXXX -compact
.It Pa /var/run/ld.so.hints
library location hints built by
.Xr ldconfig 8
.El
.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.