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Add a manual page for the ELF dynamic linker. I initially created
rtld.1 by means of a repository copy from "src/libexec/rtld-aout/rtld.1". Then I edited it to make it (more) accurate for the ELF dynamic linker.
This commit is contained in:
John Polstra
parent
ed6332a49e
commit
ea5cc7f114
2 changed files with 22 additions and 99 deletions
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@ -5,10 +5,11 @@ MAINTAINER= jdp
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PROG= ld-elf.so.1
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SRCS= rtld_start.S rtld.c lockdflt.c map_object.c malloc.c \
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xmalloc.c debug.c reloc.c
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NOMAN= true
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MAN1= rtld.1
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CFLAGS+= -Wall -DFREEBSD_ELF -I${.CURDIR}/${MACHINE_ARCH} -I${.CURDIR}
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LDFLAGS+= -nostdlib -e .rtld_start
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INSTALLFLAGS+= -fschg -C
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MLINKS= rtld.1 ld-elf.so.1.1
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.if exists(${.CURDIR}/${MACHINE_ARCH}/Makefile.inc)
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.include "${.CURDIR}/${MACHINE_ARCH}/Makefile.inc"
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@ -28,25 +28,21 @@
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.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd June 27, 1995
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.Dd January 28, 2000
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.Dt RTLD 1
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.Os FreeBSD
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.Sh NAME
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.Nm ld.so ,
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.Nm ld-elf.so.1 ,
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.Nm rtld
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.Nd run-time link-editor
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.Sh DESCRIPTION
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.Nm
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is a self-contained, position independent program image providing run-time
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is a self-contained shared object providing run-time
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support for loading and link-editing shared objects into a process'
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address space. It uses the data structures
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.Po
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see
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.Xr link 5
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.Pc
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address space. It is also commonly known as the dynamic linker.
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It uses the data structures
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contained within dynamically linked programs to determine which shared
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libraries are needed and loads them at a convenient virtual address
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using the
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libraries are needed and loads them using the
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.Xr mmap 2
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system call.
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.Pp
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@ -54,54 +50,24 @@ After all shared libraries have been successfully loaded,
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.Nm
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proceeds to resolve external references from both the main program and
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all objects loaded. A mechanism is provided for initialization routines
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to be called, on a per-object basis, giving a shared object an opportunity
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to perform any extra set-up, before execution of the program proper begins.
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to be called on a per-object basis, giving a shared object an opportunity
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to perform any extra set-up before execution of the program proper begins.
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This is useful for C++ libraries that contain static constructors.
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.Pp
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.Nm
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is itself a shared object that is initially loaded by the startup module
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.Em crt0 .
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Since
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.Xr a.out 5
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formats do not provide easy access to the file header from within a running
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process,
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.Em crt0
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uses the special symbol
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.Va _DYNAMIC
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to determine whether a program is in fact dynamically linked or not. Whenever
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the linker
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.Xr ld 1
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has relocated this symbol to a location other than 0,
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.Em crt0
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assumes the services of
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.Nm
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are needed
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.Po
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see
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.Xr link 5
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for details
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.Pc \&.
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.Em crt0
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passes control to
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.Nm
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\&'s entry point before the program's
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.Fn main
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routine is called. Thus,
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.Nm
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can complete the link-editing process before the dynamic program calls upon
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services of any dynamic library.
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itself is loaded by the kernel together with any dynamically-linked
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program that is to be executed. The kernel transfers control to the
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dynamic linker. After the dynamic linker has finished loading,
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relocating, and initializing the program and its required shared
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objects, it transfers control to the entry point of the program.
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.Pp
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To quickly locate the required shared objects in the filesystem,
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To locate the required shared objects in the filesystem,
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.Nm
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may use a
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.Dq hints
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file, prepared by the
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file prepared by the
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.Xr ldconfig 8
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utility, in which the full path specification of the shared objects can be
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looked up by hashing on the 3-tuple
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.Ao
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library-name, major-version-number, minor-version-number
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.Ac \&.
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utility.
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.Pp
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.Nm
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recognizes a number of environment variables that can be used to modify
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@ -113,7 +79,8 @@ A colon separated list of directories, overriding the default search path
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for shared libraries.
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This is ignored for set-user-ID and set-group-ID programs.
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.It Ev LD_PRELOAD
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A colon separated list of shared libraries, to be linked in before any
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A list of shared libraries, separated by colons and/or white space,
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to be linked in before any
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other shared libraries. If the directory is not specified then
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the directories specified by LD_LIBRARY_PATH will be searched first
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followed by the set of built-in standard directories.
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@ -127,38 +94,6 @@ of each function.
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.Ev LD_BIND_NOW
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increases the start-up time of a program, but it avoids run-time
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surprises caused by unexpectedly undefined functions.
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.It Ev LD_WARN_NON_PURE_CODE
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When set to a nonempty string, issue a warning whenever a link-editing
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operation requires modification of the text segment of some loaded
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object. This is usually indicative of an incorrectly built library.
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.It Ev LD_SUPPRESS_WARNINGS
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When set to a nonempty string, no warning messages of any kind are
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issued. Normally, a warning is given if satisfactorily versioned
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library could not be found.
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.It Ev LD_IGNORE_MISSING_OBJECTS
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When set to a nonempty string, makes it a nonfatal condition if
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one or more required shared objects cannot be loaded.
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Loading and execution proceeds using the objects that are
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available.
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A warning is produced for each missing object, unless the environment
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variable
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.Ev LD_SUPPRESS_WARNINGS
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is set to a nonempty string.
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.Pp
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This is ignored for set-user-ID and set-group-ID programs.
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.Pp
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Missing shared objects can be ignored without errors if all the
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following conditions hold:
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.Bl -bullet
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.It
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They do not supply definitions for any required data symbols.
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.It
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No functions defined by them are called during program execution.
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.It
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The environment variable
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.Ev LD_BIND_NOW
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is unset or is set to the empty string.
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.El
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.It Ev LD_TRACE_LOADED_OBJECTS
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When set to a nonempty string, causes
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.Nm
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@ -188,8 +123,6 @@ The value of the environment variable
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The library name.
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.It \&%m
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The library's major version number.
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.It \&%n
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The library's minor version number.
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.It \&%p
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The full pathname as determined by
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.Nm rtld Ns 's
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@ -203,23 +136,12 @@ Additionally,
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and
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.Sy \et
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are recognized and have their usual meaning.
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.\" .It Ev LD_NO_INTERN_SEARCH
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.\" When set,
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.\" .Nm
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.\" does not process any internal search paths that were recorded in the
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.\" executable.
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.\" .It Ev LD_NOSTD_PATH
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.\" When set, do not include a set of built-in standard directory paths for
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.\" searching. This might be useful when running on a system with a completely
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.\" non-standard filesystem layout.
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.El
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.Pp
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.Sh FILES
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/var/run/ld.so.hints
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/var/run/ld-elf.so.hints
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.Pp
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.Sh SEE ALSO
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.Xr elf 5 ,
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.Xr ld 1 ,
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.Xr link 5 ,
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.Xr ldconfig 8
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.Sh HISTORY
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The shared library model employed first appeared in SunOS 4.0
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