ld-elf.so.1, ld.so, rtld -- run-time link-editor
The ld-elf.so.1 utility is a self-contained shared object providing runtime
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 constructors.
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.
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_DISABLE If set, disables the use of libmap.conf(5).
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.
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 standard
directories. 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 increases the start-up time of a program,
but it avoids run-time surprises caused by unexpectedly
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. 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
%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, `\n' and `\t' are recognized and have
their usual meaning.
/var/run/ld-elf.so.hints Hints file.
/etc/libmap.conf The libmap configuration file.
ld(1), ldd(1), elf(5), libmap.conf(5), ldconfig(8)
FreeBSD 5.2.1 May 31, 2003 FreeBSD 5.2.1 [ Back ] |
