303 lines
9.3 KiB
Groff
303 lines
9.3 KiB
Groff
.\" Copyright (c) 1995 Paul Kranenburg
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgment:
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.\" This product includes software developed by Paul Kranenburg.
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.\" 3. The name of the author may not be used to endorse or promote products
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.\" derived from this software without specific prior written permission
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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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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.\" $FreeBSD$
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.\"
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.Dd March 16, 2017
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.Dt RTLD 1
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.Os
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.Sh NAME
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.Nm ld-elf.so.1 ,
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.Nm ld.so ,
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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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The
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.Nm
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utility 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.
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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 using the
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.Xr mmap 2
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system call.
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.Pp
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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.
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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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This is useful for C++ libraries that contain static constructors.
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.Pp
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When resolving dependencies for the loaded objects,
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.Nm
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may be allowed to translate dynamic token strings in rpath and soname
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by setting
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.Fl "z origin"
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option of the static linker
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.Xr ld 1 .
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The following strings are recognized now:
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.Bl -tag -width ".Pa $PLATFORM"
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.It Pa $ORIGIN
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Translated to the full path of the loaded object.
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.It Pa $OSNAME
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Translated to the name of the operating system implementation.
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.It Pa $OSREL
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Translated to the release level of the operating system.
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.It Pa $PLATFORM
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Translated to the machine hardware platform.
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.El
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.Pp
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The
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.Nm
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utility itself is loaded by the kernel together with any dynamically-linked
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program that is to be executed.
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The kernel transfers control to the
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dynamic linker.
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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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The following search order is used to locate required shared objects:
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.Pp
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.Bl -enum -offset indent -compact
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.It
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.Dv DT_RPATH
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of the referencing object unless that object also contains a
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.Dv DT_RUNPATH
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tag
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.It
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.Dv DT_RPATH
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of the program unless the referencing object contains a
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.Dv DT_RUNPATH
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tag
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.It
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Path indicated by
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.Ev LD_LIBRARY_PATH
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environment variable
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.It
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.Dv DT_RUNPATH
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of the referencing object
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.It
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Hints file produced by the
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.Xr ldconfig 8
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utility
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.It
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The
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.Pa /lib
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and
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.Pa /usr/lib
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directories, unless the referencing object was linked using the
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.Dq Fl z Ar nodefaultlib
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option
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.El
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.Pp
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The
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.Nm
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utility
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recognizes a number of environment variables that can be used to modify
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its behaviour.
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On 64-bit architectures, the linker for 32-bit objects recognizes
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all the environment variables listed below, but is being prefixed with
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.Ev LD_32_ ,
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for example:
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.Ev LD_32_TRACE_LOADED_OBJECTS .
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.Bl -tag -width ".Ev LD_LIBMAP_DISABLE"
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.It Ev LD_DUMP_REL_POST
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If set,
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.Nm
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will print a table containing all relocations after symbol
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binding and relocation.
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.It Ev LD_DUMP_REL_PRE
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If set,
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.Nm
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will print a table containing all relocations before symbol
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binding and relocation.
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.It Ev LD_LIBMAP
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A library replacement list in the same format as
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.Xr libmap.conf 5 .
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For convenience, the characters
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.Ql =
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and
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.Ql \&,
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can be used instead of a space and a newline.
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This variable is parsed after
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.Xr libmap.conf 5 ,
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and will override its entries.
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This variable is unset for set-user-ID and set-group-ID programs.
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.It Ev LD_LIBMAP_DISABLE
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If set, disables the use of
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.Xr libmap.conf 5
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and
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.Ev LD_LIBMAP .
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This variable is unset for set-user-ID and set-group-ID programs.
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.It Ev LD_ELF_HINTS_PATH
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This variable will override the default location of
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.Dq hints
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file.
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This variable is unset for set-user-ID and set-group-ID programs.
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.It Ev LD_LIBRARY_PATH
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A colon separated list of directories, overriding the default search path
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for shared libraries.
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This variable is unset for set-user-ID and set-group-ID programs.
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.It Ev LD_LIBRARY_PATH_RPATH
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If the variable is specified and has a value starting with
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any of \'y\', \'Y\' or \'1\' symbols, the path specified by
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.Ev LD_LIBRARY_PATH
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variable is allowed to override the path from
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.Dv DT_RPATH
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for binaries which does not contain
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.Dv DT_RUNPATH
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tag.
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For such binaries, when the variable
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.Ev LD_LIBRARY_PATH_RPATH
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is set,
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.Dq Fl z Ar nodefaultlib
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link-time option is ignored as well.
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.It Ev LD_PRELOAD
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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.
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If the directory is not specified then
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the directories specified by
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.Ev LD_LIBRARY_PATH
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will be searched first
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followed by the set of built-in standard directories.
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This variable is unset for set-user-ID and set-group-ID programs.
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.Ev LD_LIBRARY_PATH_FDS
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A colon separated list of file descriptor numbers for library directories.
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This is intended for use within
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.Xr capsicum 4
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sandboxes, when global namespaces such as the filesystem are unavailable.
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It is consulted just after LD_LIBRARY_PATH.
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This variable is unset for set-user-ID and set-group-ID programs.
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.It Ev LD_BIND_NOT
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When set to a nonempty string, prevents modifications of the PLT slots when
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doing bindings.
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As result, each call of the PLT-resolved function is resolved.
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In combination with debug output, this provides complete account of
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all bind actions at runtime.
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This variable is unset for set-user-ID and set-group-ID programs.
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.It Ev LD_BIND_NOW
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When set to a nonempty string, causes
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.Nm
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to relocate all external function calls before starting execution of the
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program.
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Normally, function calls are bound lazily, at the first call
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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_TRACE_LOADED_OBJECTS
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When set to a nonempty string, causes
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.Nm
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to exit after loading the shared objects and printing a summary which includes
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the absolute pathnames of all objects, to standard output.
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.It Ev LD_TRACE_LOADED_OBJECTS_ALL
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When set to a nonempty string, causes
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.Nm
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to expand the summary to indicate which objects caused each object to
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be loaded.
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.It Ev LD_TRACE_LOADED_OBJECTS_FMT1
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.It Ev LD_TRACE_LOADED_OBJECTS_FMT2
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When set, these variables are interpreted as format strings a la
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.Xr printf 3
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to customize the trace output and are used by
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.Xr ldd 1 Ns 's
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.Fl f
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option and allows
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.Xr ldd 1
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to be operated as a filter more conveniently.
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If the dependency name starts with string
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.Pa lib ,
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.Ev LD_TRACE_LOADED_OBJECTS_FMT1
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is used, otherwise
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.Ev LD_TRACE_LOADED_OBJECTS_FMT2
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is used.
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The following conversions can be used:
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.Bl -tag -width 4n
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.It Li %a
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The main program's name
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(also known as
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.Dq __progname ) .
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.It Li \&%A
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The value of the environment variable
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.Ev LD_TRACE_LOADED_OBJECTS_PROGNAME .
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Typically used to print both the names of programs and shared libraries
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being inspected using
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.Xr ldd 1 .
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.It Li %o
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The library name.
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.It Li %p
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The full pathname as determined by
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.Nm rtld Ns 's
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library search rules.
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.It Li %x
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The library's load address.
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.El
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.Pp
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Additionally,
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.Ql \en
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and
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.Ql \et
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are recognized and have their usual meaning.
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.It Ev LD_UTRACE
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If set,
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.Nm
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will log events such as the loading and unloading of shared objects via
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.Xr utrace 2 .
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.It Ev LD_LOADFLTR
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If set,
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.Nm
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will process the filtee dependencies of the loaded objects immediately,
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instead of postponing it until required.
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Normally, the filtees are opened at the time of the first symbol resolution
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from the filter object.
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.El
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.Sh FILES
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.Bl -tag -width ".Pa /var/run/ld-elf32.so.hints" -compact
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.It Pa /var/run/ld-elf.so.hints
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Hints file.
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.It Pa /var/run/ld-elf32.so.hints
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Hints file for 32-bit binaries on 64-bit system.
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.It Pa /etc/libmap.conf
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The libmap configuration file.
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.It Pa /etc/libmap32.conf
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The libmap configuration file for 32-bit binaries on 64-bit system.
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.El
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.Sh SEE ALSO
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.Xr ld 1 ,
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.Xr ldd 1 ,
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.Xr capsicum 4 ,
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.Xr elf 5 ,
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.Xr libmap.conf 5 ,
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.Xr ldconfig 8
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