rtld(1)

NAME

ld-elf.so.1, ld.so, rtld - run-time link-editor

DESCRIPTION

The ld-elf.so.1 utility is a self-contained shared object

providing runtime support for loading and link-editing shared objects in

to a process'
address space. It is also commonly known as the dynamic

linker. It uses
the data structures contained within dynamically linked pro

grams to
determine which shared libraries are needed and loads them

using the
mmap(2) system call.

After all shared libraries have been successfully loaded,

ld-elf.so.1
proceeds to resolve external references from both the main

program and
all objects loaded. A mechanism is provided for initializa

tion 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 stat

ic constructors.

The ld-elf.so.1 utility itself is loaded by the kernel to

gether with any
dynamically-linked program that is to be executed. The ker

nel transfers
control to the dynamic linker. After the dynamic linker has

finished
loading, relocating, and initializing the program and its

required shared
objects, it transfers control to the entry point of the pro

gram.

To locate the required shared objects in the file system,

ld-elf.so.1 may
use a ``hints'' file prepared by the ldconfig(8) utility.

The ld-elf.so.1 utility recognizes a number of environment

variables that
can be used to modify its behaviour as follows:

LD_DUMP_REL_POST If set ld-elf.so.1 will print a table

containing

all relocations after symbol binding

and relocation.

LD_DUMP_REL_PRE If set ld-elf.so.1 will print a table

containing

all relocations before symbol binding

and relocation.

LD_LIBMAP A library replacement list in the

same format as

libmap.conf(5). For convenience, the

characters
`=' and `,' can be used instead of a

space and a
newline. This variable is parsed af

ter
libmap.conf(5), and will override its

entries.

LD_LIBMAP_DISABLE If set, disables the use of

libmap.conf(5) and

LD_LIBMAP.

LD_LIBRARY_PATH A colon separated list of directo

ries, overriding

the default search path for shared

libraries.
This is ignored for set-user-ID and

set-group-ID
programs.

LD_PRELOAD A list of shared libraries, separated

by colons

and/or white space, to be linked in

before any
other shared libraries. If the di

rectory is not
specified then the directories speci

fied by
LD_LIBRARY_PATH will be searched

first followed by
the set of built-in standard directo

ries. This is
ignored for set-user-ID and set

group-ID programs.

LD_BIND_NOW When set to a nonempty string, causes

ld-elf.so.1

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. LD_BIND_NOW in

creases the
start-up time of a program, but it

avoids run-time
surprises caused by unexpectedly un

defined functions.

LD_TRACE_LOADED_OBJECTS

When set to a nonempty string, causes

ld-elf.so.1
to exit after loading the shared ob

jects and
printing a summary which includes the

absolute
pathnames of all objects, to standard

output.

LD_TRACE_LOADED_OBJECTS_ALL

When set to a nonempty string, causes

ld-elf.so.1
to expand the summary to indicate

which objects
caused each object to be loaded.

LD_TRACE_LOADED_OBJECTS_FMT1

LD_TRACE_LOADED_OBJECTS_FMT2

When set, these variables are inter

preted as format strings a la printf(3) to cus

tomize the trace
output and are used by ldd(1)'s -f

option and
allows ldd(1) to be operated as a

filter more conveniently. The following conversions

can be used:

%a The main program's name (also

known as

``__progname'').

%A The value of the environment

variable

LD_TRACE_LOADED_OBJECTS_PROG

NAME

%o The library name.

%m The library's major version

number.

%p The full pathname as determined

by rtld's

library search rules.

%x The library's load address.

Additionally, `0 and `' are recog

nized and
have their usual meaning.

FILES

/var/run/ld-elf.so.hints Hints file.
/etc/libmap.conf The libmap configuration file.

SEE ALSO

ld(1), ldd(1), elf(5), libmap.conf(5), ldconfig(8)

BSD May 31, 2003

BSD