LD.SO(1) BSD Reference Manual LD.SO(1)NAMEld.so - run-time link-editor
DESCRIPTIONld.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)) con-
tained within dynamically linked programs to determine which shared li-
braries 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, minor-version-
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 set-
user-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 pro-
cedure linkage table entries are handled lazily, avoiding symbol
lookup and relocation for unused functions. This variable is ig-
nored for set-user-ID and set-group-ID executables.
LD_WARN_NON_PURE_CODE
When set, issue a warning whenever a link-editing operation re-
quires 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 con-
veniently. 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 and \t are recognised and have their usual mean-
ing. <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 ob-
jects 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.
LD_NOPREBIND
When set, ignore any prebind data associated with the program or
libraries.
LD_PREBINDVALIDATE
When set, perform symbol relocation of the given binary and the
associated libraries, compare the results against the prebind
values, then exit.
FILES
/var/run/ld.so.hints library location hints built by ldconfig(8)SEE ALSOld(1), link(5), ldconfig(8)HISTORY
The shared library model employed first appeared in SunOS 4.0.
MirOS BSD #10-current June 27, 1995 1
