8569deaf1c
filters are implemented. Filtees are loaded on demand, unless LD_LOADFLTR environment variable is set or -z loadfltr was specified during the linking. This forces rtld to upgrade read-locked rtld_bind_lock to write lock when it encounters an object with filter during symbol lookup. Consolidate common arguments of the symbol lookup functions in the SymLook structure. Track the state of the rtld locks in the RtldLockState structure. Pass local RtldLockState through the rtld symbol lookup calls to allow lock upgrades. Reviewed by: kan Tested by: Mykola Dzham <i levsha me>, nwhitehorn (powerpc)
250 lines
7.8 KiB
Groff
250 lines
7.8 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 April 1, 2009
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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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.Pp
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To locate the required shared objects in the file system,
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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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.Xr ldconfig 8
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utility.
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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_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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.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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.Pp
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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 elf 5 ,
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.Xr libmap.conf 5 ,
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.Xr ldconfig 8
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