ld.so - run-time link-editor
ld.so 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 (see
link(5)) contained
within dynamically linked programs to determine which
shared libraries
are needed and loads them at a convenient virtual
address using
the mmap(2) system call.
After all shared libraries have been successfully loaded,
ld.so 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.
ld.so is itself a shared object that is initially loaded by
the kernel.
To quickly locate the required shared objects in the
filesystem, ld.so
may use a ``hints'' file, prepared by the ldconfig(8) utility, in which
the full path specification of the shared objects can be
looked up by
hashing on the 3-tuple <library-name, major-version-number,
minorversion-number>.
ld.so recognises a number of environment variables that can
be used to
modify its behaviour as follows:
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.
LD_PRELOAD
A colon separate list of library names to load before any of the
regular libraries are loaded. This variable is ignored for setuser-ID
and set-group-ID executables.
LD_BIND_NOW
Specifies that the dynamic linker should process all
relocations
before transferring control to the program. Normally, the procedure
linkage table entries are handled lazily,
avoiding symbol
lookup and relocation for unused functions. This
variable is ignored
for set-user-ID and set-group-ID executables.
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>
LD_SUPPRESS_WARNINGS
When set, no warning messages of any kind are issued. Normally,
a warning is given if a satisfactorily versioned library could
not be found. <not yet supported>
LD_TRACE_LOADED_OBJECTS
When set, causes ld.so 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_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. <not yet
supported>
%o The library name.
%m The library's major version number.
%n The library's minor version number.
%p The full pathname as determined by ld.so's library search
rules.
%x The library's load address.
Additionally,n ant are recognised and have their
usual meaning.
<not yet supported>
LD_NO_INTERN_SEARCH
When set, ld.so does not process any internal search
paths that
were recorded in the executable. <not yet supported>
LD_NORANDOM
When set, do not load shared objects or libraries
dependent objects
in random order. This variable is ignored for
set-user-ID
and set-group-ID executables.
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.
LD_DEBUG
When set, be verbose about what ld.so does.
/var/run/ld.so.hints library location hints built by ldconfig(8)
ld(1), link(5), ldconfig(8)
The shared library model employed first appeared in SunOS
4.0.
OpenBSD 3.6 June 27, 1995
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