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RTLD(1)			FreeBSD	General	Commands Manual		       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 run-
     time support for loading and link-editing shared objects into a process'
     address space.  It	is also	commonly known as the dynamic linker.  It uses
     the data structures contained within dynamically linked programs 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 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 construc-
     tors.

     When resolving dependencies for the loaded	objects, ld-elf.so.1 may be
     allowed to	translate dynamic token	strings	in rpath and soname by setting
     -z	origin option of the static linker ld(1).  The following strings are
     recognized	now:

     $ORIGIN	Translated to the full path of the loaded object.

     $OSNAME	Translated to the name of the operating	system implementation.

     $OSREL	Translated to the release level	of the operating system.

     $PLATFORM	Translated to the machine hardware platform.

     The ld-elf.so.1 utility itself is loaded by the kernel together with any
     dynamically-linked	program	that is	to be executed.	 The kernel 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 program.  The
     following search order is used to locate required shared objects:

	   1.	DT_RPATH of the	referencing object unless that object also
		contains a DT_RUNPATH tag
	   2.	DT_RPATH of the	program	unless the referencing object contains
		a DT_RUNPATH tag
	   3.	Path indicated by LD_LIBRARY_PATH environment variable
	   4.	DT_RUNPATH of the referencing object
	   5.	Hints file produced by the ldconfig(8) utility
	   6.	The /lib and /usr/lib directories, unless the referencing
		object was linked using	the ``-z nodefaultlib''	option

     The ld-elf.so.1 utility recognizes	a number of environment	variables that
     can be used to modify its behaviour.  On 64-bit architectures, the	linker
     for 32-bit	objects	recognizes all the environment variables listed	below,
     but is being prefixed with	LD_32_,	for example:
     LD_32_TRACE_LOADED_OBJECTS.

     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	after libmap.conf(5), and will
			override its entries.  This variable is	unset for set-
			user-ID	and set-group-ID programs.

     LD_LIBMAP_DISABLE	If set,	disables the use of libmap.conf(5) and
			LD_LIBMAP.  This variable is unset for set-user-ID and
			set-group-ID programs.

     LD_ELF_HINTS_PATH	This variable will override the	default	location of
			``hints'' file.	 This variable is unset	for set-user-
			ID and set-group-ID programs.

     LD_LIBRARY_PATH	A colon	separated list of directories, overriding the
			default	search path for	shared libraries.  This	vari-
			able is	unset for set-user-ID and set-group-ID pro-
			grams.

     LD_LIBRARY_PATH_RPATH
			If the variable	is specified and has a value starting
			with any of 'y', 'Y' or	'1' symbols, the path speci-
			fied by	LD_LIBRARY_PATH	variable is allowed to over-
			ride the path from DT_RPATH for	binaries which does
			not contain DT_RUNPATH tag.  For such binaries,	when
			the variable LD_LIBRARY_PATH_RPATH is set, ``-z
			nodefaultlib'' link-time option	is ignored as well.

     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 directory is	not specified then the
			directories specified by LD_LIBRARY_PATH will be
			searched first followed	by the set of built-in stan-
			dard directories.  This	variable is unset 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 increases the start-up time	of a program,
			but it avoids run-time surprises caused	by unexpect-
			edly undefined functions.

     LD_TRACE_LOADED_OBJECTS
			When set to a nonempty string, causes ld-elf.so.1 to
			exit after loading the shared objects 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 interpreted as format
			strings	a la printf(3) to customize the	trace output
			and are	used by	ldd(1)'s -f option and allows ldd(1)
			to be operated as a filter more	conveniently.  If the
			dependency name	starts with string lib,
			LD_TRACE_LOADED_OBJECTS_FMT1 is	used, otherwise
			LD_TRACE_LOADED_OBJECTS_FMT2 is	used.  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_PROGNAME.	 Typically
			      used to print both the names of programs and
			      shared libraries being inspected using ldd(1).

			%o    The library name.

			%p    The full pathname	as determined by rtld's
			      library search rules.

			%x    The library's load address.

			Additionally, `\n' and `\t' are	recognized and have
			their usual meaning.

     LD_UTRACE		If set,	ld-elf.so.1 will log events such as the	load-
			ing and	unloading of shared objects via	utrace(2).

     LD_LOADFLTR	If set,	ld-elf.so.1 will process the filtee dependen-
			cies of	the loaded objects immediately,	instead	of
			postponing it until required.  Normally, the filtees
			are opened at the time of the first symbol resolution
			from the filter	object.

FILES
     /var/run/ld-elf.so.hints	 Hints file.
     /var/run/ld-elf32.so.hints	 Hints file for	32-bit binaries	on 64-bit sys-
				 tem.
     /etc/libmap.conf		 The libmap configuration file.
     /etc/libmap32.conf		 The libmap configuration file for 32-bit
				 binaries on 64-bit system.

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

FreeBSD	9.2			 June 28, 2012			   FreeBSD 9.2

NAME | DESCRIPTION | FILES | SEE ALSO

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