LD.SO.1(1) User Commands LD.SO.1(1)

NAME

ld.so.1 - runtime linker for dynamic objects

SYNOPSIS

/lib/ld.so.1


/lib/ld.so.1 [-e envar] dynamic-object [object args]...

DESCRIPTION

Dynamic applications consist of one or more dynamic objects. A dynamic
application is typically a dynamic executable and one or more shared
object dependencies. As part of the initialization and execution of a
dynamic application, an interpreter is called. This interpreter completes
the binding of the application to its shared object dependencies. In
Solaris, this interpreter is referred to as the runtime linker.


During the link-editing of a dynamic executable, a special .interp
section, together with an associated program header, is created. This
section contains a path name specifying the program's interpreter. An
interpreter path name can be specified when the executable is constructed
using the -I option to ld(1), the link-editor. The default name supplied
by the link-editor is the name of the runtime linker, ld.so.1.


During the process of executing a dynamic executable, the kernel maps the
file, and locates the required interpreter. See exec(2) and mmapobj(2).
The kernel maps in, and transfers control to, this interpreter.
Sufficient information is passed to the interpreter to allow the
interpreter to continue to bind, and then execute the application.


In addition to initializing an application, the runtime linker provides
services that allow the application to extend its address space.
Additional shared objects can be mapped, and symbols within the shared
objects can be bound to.


The runtime linker performs the following functions:

o A configuration file, if in existence, is processed.
Configuration files can be employed to alter default search
paths, provide a directory cache, and provide alternative
object dependencies. See crle(1). By default, for 32-bit
objects, the configuration file /var/ld/ld.config is used. For
64-bit objects, the default configuration file
/var/ld/64/ld.config is used. Alternative configuration files
can be specified with the LD_CONFIG environment variable.
Alternative configuration files can also be encoded within a
dynamic executable by using the -c option of ld(1).

o The runtime linker analyzes the application's dynamic
information section, .dynamic, to determine which shared
object dependencies are required.

o The runtime linker then locates and maps in these
dependencies. The dynamic information section of each
dependency is then analyzed to determine if any additional
dependencies are required.

o Once all the shared object dependencies are loaded, the
runtime linker performs any necessary relocations. These
relocations bind the shared objects in preparation for process
execution.

o Any initialization functions provided by the shared object
dependencies and, possibly, by the dynamic executable are
called. The functions are called in the reverse order of the
topologically sorted dependencies. If cyclic dependencies
exist, the initialization functions are called using the
sorted order with the cycle removed. ldd(1) can be used to
display the initialization order of shared object
dependencies.

o Control is passed to the application.

o During the application's execution, the runtime linker can be
called upon to perform any delayed function binding.

o If any shared objects are deleted from the process,
finalization functions are called. By default, these functions
are called in the order of the topologically sorted
dependencies.

o The application can also call upon the services of the runtime
linker to acquire additional shared objects by using
dlopen(3C). Symbols provided by these objects, can be bound to
using dlsym(3C).


Further details on each of the previous topics can be found in the Linker
and Libraries Guide.


The runtime linker uses a prescribed search path for locating the dynamic
dependencies of an object. The default search paths are the runpath
recorded in the object, followed by a series of defaults. For 32-bit
objects, the defaults are /lib followed by /usr/lib. For 64-bit objects,
the defaults are /lib/64 followed by /usr/lib/64. These defaults
component can be modified using a configuration file that is created with
crle(1). The runpath is specified when the dynamic object is constructed
using the -R option to ld(1). The environment variable LD_LIBRARY_PATH
can be used to indicate directories to be searched before the default
directories.

Command Line Usage

Typically, the runtime linker is invoked indirectly through executing a
dynamic executable that declares the runtime linker as its interpreter.
The runtime linker can also be executed directly from the command line.
This mechanism is most often employed to experiment with new
implementations of the runtime linker. Arguments that are supplied on the
command line consist of options that are applicable to the runtime
linker. Following these options is the name of the dynamic object to be
executed, and any options required by this object. Effectively, the
runtime linker replaces any interpreter specified by the dynamic object.


The following option is supported:

-e envar
Specify a runtime linker specific environment variable. See
ENVIRONMENT VARIABLES.

ENVIRONMENT VARIABLES

Each environment variable can be specified with a _32 or _64 suffix. This
makes the environment variable specific, respectively, to 32-bit or
64-bit processes. This environment variable overrides any non-suffixed
version of the environment variable that might be in effect. Environment
variables specified without a value, that have a _32 or _64 suffix,
effectively cancel any associated generic environment variable setting.

LD_AUDIT, LD_AUDIT_32, and LD_AUDIT_64

A colon-separated list of objects that are loaded by the runtime
linker. As each object is loaded, the object is examined for Link-
Auditing interface routines. The routines that are present are called
as specified in the Link-Auditing interface described in the Linker
and Libraries Guide. Also, see the -p and -P options of ld(1).


LD_BIND_LAZY, LD_BIND_LAZY_32, and LD_BIND_LAZY_64

The runtime linker's default mode of performing lazy binding can be
enforced by setting the environment variable LD_BIND_LAZY to any non-
null value. This setting causes the runtime linker to perform only
lazy reference relocations for all objects that are loaded into the
process. Individual objects can request that lazy reference
relocations are performed when the object is loaded. See the -z now
option of ld(1), and dlopen(3C) with the mode RTLD_NOW. Such requests
to perform lazy reference relocations are suppressed when
LD_BIND_LAZY is in effect.

If both LD_BIND_LAZY and LD_BIND_NOW are specified, then LD_BIND_NOW
takes precedence.


LD_BIND_NOW, LD_BIND_NOW_32, and LD_BIND_NOW_64

The runtime linker's default mode of performing lazy binding can be
overridden by setting the environment variable LD_BIND_NOW to any
non-null value. This setting causes the runtime linker to perform
both immediate reference and lazy reference relocations for all
objects that are loaded into the process. Individual objects can
request that lazy reference relocations are performed when the object
is loaded. See the -z now option of ld(1), and dlopen(3C) with the
mode RTLD_NOW.

If both LD_BIND_NOW and LD_BIND_LAZY are specified, then LD_BIND_NOW
takes precedence.


LD_CAP_FILES, LD_CAP_FILES_32, and LD_CAP_FILES_64

A comma-separated list of executables and shared libraries to which
the alternative capabilities specified by LD_MACHCAP, LD_PLATCAP,
LD_HWCAP and LD_SFCAP should apply.

Executables and libraries may be specified either by their SONAME or
their full real pathname.


LD_CONFIG, LD_CONFIG_32, and LD_CONFIG_64

Provides an alternative configuration file. Configuration files can
be employed to alter default search paths, provide a directory cache,
and provide alternate object dependencies. See crle(1).


LD_DEBUG, LD_DEBUG_32, and LD_DEBUG_64

Provides a comma, or colon-separated list of tokens to cause the
runtime linker to print debugging information to standard error. The
special token help indicates the full list of tokens available. The
environment variable LD_DEBUG_OUTPUT can also be supplied to specify
a file to which the debugging information is sent. The filename is
suffixed with the process ID of the application generating the
debugging information. See lari(1).


LD_DEMANGLE, LD_DEMANGLE_32, and LD_DEMANGLE_64

Any symbol name used as part of a diagnostic message is shown as
defined within an ELF file. When LD_DEMANGLE is set to any non-null
value, the runtime linker attempts to decode (demangle) any C++
symbol name.


LD_FLAGS, LD_FLAGS_32, and LD_FLAGS_64

Provides an alternative means of supplying environment variable
information. Any of the LD_XXX environment variables can be
specified as a xxx token. Multiple tokens can be supplied separated
by commas. See EXAMPLES.


LD_HWCAP, LD_HWCAP_32, and LD_HWCAP_64

Specify a comma-separated set of alternative hardware capabilities.
A leading '+' indicates that the capabilities should be included in
addition to the default set, a leading '-' indicates that the
capabilities should be excluded from the default set, and neither
indicates that the set should replace the default set.

Capabilities may be specified either by name, or as hexadecimal
integers with an optional leading bracketed index number specifying
the capabilities family.
LD_HWCAP=[1]01 # Sets CA_SUN_HW_1 to 0x1
LD_HWCAP=[2]20 # Sets CA_SUN_HW_2 to 0x20


LD_MACHCAP

Specify an alternative machine hardware capability name.


LD_LIBRARY_PATH, LD_LIBRARY_PATH_32, and LD_LIBRARY_PATH_64

The LD_LIBRARY_PATH environment variable, if set, is used to enhance
the search path that the runtime linker uses to find dynamic
dependencies. LD_LIBRARY_PATH specifies a colon-separated list of
directories that are searched before the default directories. Also
notice that LD_LIBRARY_PATH adds additional semantics to ld(1).


LD_LOADFLTR, LD_LOADFLTR_32, and LD_LOADFLTR_64

Filters are a form of shared object. Filters allow an alternative
shared object to be selected at runtime that provide the
implementation for any symbols that are defined within the filter.
See the -f and -F options of ld(1). By default, the alternative
shared object processing is deferred until symbol resolution occurs
against the filter. When LD_LOADFLTR is set to any non-null value,
any filters are processed immediately when the filter is loaded.
Also, see the -z loadfltr option of ld(1).


LD_NOAUDIT, LD_NOAUDIT_32, and LD_NOAUDIT_64

Local auditing libraries can be defined within applications and
shared objects. See the -p and -P options of ld(1). When LD_NOAUDIT
is set to any non-null value, the runtime linker ignores any local
auditing libraries.


LD_NOAUXFLTR, LD_NOAUXFLTR_32, and LD_NOAUXFLTR_64

Auxiliary filters are a form of shared object. Auxiliary filters
allow an alternative shared object to be selected at runtime which
provides the implementation for any symbols that are defined within
the filter. See the -f option of ld(1). When LD_NOAUXFLTR is set to
any non-null value, the runtime linker disables this alternative
shared object lookup.


LD_NOCONFIG, LD_NOCONFIG_32, and LD_NOCONFIG_64

By default the runtime linker attempts to open and process a
configuration file. When LD_NOCONFIG is set to any non-null value,
the runtime linker disables this configuration file processing.


LD_NODIRCONFIG, LD_NODIRCONFIG_32, and LD_NODIRCONFIG_64

Provides a subset of LD_NOCONFIG in that any directory cache
information provided in a configuration file is ignored.


LD_NODIRECT, LD_NODIRECT_32, and LD_NODIRECT_64

Direct binding information instructs the runtime linker to search
directly for a symbol in an associated object. See the -B direct
option of ld(1). Without direct binding, the symbol search performed
by the runtime linker follows the default model. When LD_NODIRECT is
set to any non-null value, the runtime linker ignores any direct
binding information.


LD_NOENVCONFIG, LD_NOENVCONFIG_32, and LD_NOENVCONFIG_64

Provides a subset of LD_NOCONFIG in that any environment variables
provided in a configuration file are ignored.


LD_NOLAZYLOAD, LD_NOLAZYLOAD_32, and LD_NOLAZYLOAD_64

Dependencies that are labeled for lazy loading are not loaded into
memory until explicit reference to the dependency has been made. See
the -z lazyload option of ld(1). When LD_NOLAZYLOAD is set to any
non-null value, the runtime linker ignores a dependencies lazy
loading label and loads the dependency immediately.


LD_NOOBJALTER, LD_NOOBJALTER_32, and LD_NOOBJALTER_64

Provides a subset of LD_NOCONFIG in that any alternative object
dependencies provided in a configuration file are ignored.


LD_NOVERSION, LD_NOVERSION_32, and LD_NOVERSION_64

By default, the runtime linker verifies version dependencies for the
primary executable and all of its dependencies. When LD_NOVERSION is
set to any non-null value, the runtime linker disables this version
checking.


LD_ORIGIN, LD_ORIGIN_32, and LD_ORIGIN_64

The immediate processing of $ORIGIN can be triggered by setting the
environment variable LD_ORIGIN to any non-null value. Before Solaris
9, this option was useful for applications that invoked chdir(2)
prior to locating dependencies that employed the $ORIGIN string
token. The establishment of the current working directory by the
runtime linker is now default thus making this option redundant.


LD_PLATCAP

Specify an alternative platform hardware capability name.


LD_PRELOAD, LD_PRELOAD_32, and LD_PRELOAD_64

Provides a list of shared objects, separated by spaces. These objects
are loaded after the program being executed but before any other
shared objects that the program references. Symbol definitions
provided by the preloaded objects interpose on references made by the
shared objects that the program references. Symbol definitions
provided by the preloaded objects do not interpose on the symbol
definitions provided by the program.


LD_PROFILE, LD_PROFILE_32, and LD_PROFILE_64

Defines a shared object to be profiled by the runtime linker. When
profiling is enabled, a profiling buffer file is created and mapped.
The name of the buffer file is the name of the shared object being
profiled with a .profile extension. By default, this buffer is placed
under /var/tmp. The environment variable LD_PROFILE_OUTPUT can also
be supplied to indicate an alternative directory in which to place
the profiling buffer.

The profiling buffer contains profil(2) and call count information.
This information is similar to the gmon.out information generated by
programs that have been linked with the -xpg option of cc. Any
applications that use the named shared object and run while this
environment variable is set, accumulate data in the profile buffer.
See also NOTES. The profile buffer information can be examined using
gprof(1).

The LD_PROFILE profiling technique is an alternative to other
techniques that might be provided by the compilation system. The
shared object being profiled does not have to be instrumented in any
way, and LD_PROFILE should not be combined with a profile-
instrumented application. See the Linker and Libraries Guide for more
information on profiling shared objects.


LD_SFCAP, LD_SFCAP_32, and LD_SFCAP_64

Specify a comma-separated set of alternative software capabilities.
A leading '+' indicates that the capabilities should be included in
addition to the default set, a leading '-' indicates that the
capabilities should be excluded from the default set, and neither
indicates that the set should replace the default set.

Capabilities may be specified either by name, or as hexadecimal
integers.


LD_SIGNAL, LD_SIGNAL_32, and LD_SIGNAL_64

Provides a numeric signal number that the runtime linker uses to kill
the process in the event of a fatal runtime error. See thr_kill(3C).
By default, SIGKILL is used. For example, providing the alternative
signal number 6 (SIGABRT), can provide for the creation of a core
file to aid debugging. See also the RTLD_DI_SETSIGNAL request to
dlinfo(3C).


LD_TOXIC_PATH, LD_TOXIC_PATH_32, LD_TOXIC_PATH_64,

The toxic path refers to a set of paths where by, if ld.so.1 were to
load a dependency on that path, rather than loading it, it should
kill the process. This is useful when having built libraries that
while matching the native architecture of the system, are not
suitable to be used, for example, libraries that that correspond to
an alternate release of an operating system.


Notice that environment variable names beginning with the characters
'LD_' are reserved for possible future enhancements to ld(1) and ld.so.1.

SECURITY

Secure processes have some restrictions applied to the evaluation of
their dependencies and runpaths to prevent malicious dependency
substitution or symbol interposition.


The runtime linker categorizes a process as secure if the issetugid(2)
system call returns true for the process.


For 32-bit objects, the default trusted directories that are known to the
runtime linker are /lib/secure and /usr/lib/secure. For 64-bit objects,
the default trusted directories are /lib/secure/64 and
/usr/lib/secure/64. The utility crle(1) can be used to specify additional
trusted directories that are applicable for secure applications.
Administrators who use this technique should ensure that the target
directories are suitably protected from malicious intrusion.


If an LD_LIBRARY_PATH family environment variable is in effect for a
secure process, only the trusted directories specified by this variable
are used to augment the runtime linker's search rules.


In a secure process, runpath components that are provided by the
application or any of its dependencies are used, provided the component
is a full path name, that is, the path name starts with a '/'.


In a secure process, the expansion of the $ORIGIN string is allowed only
if the string expands to a trusted directory. However, should a $ORIGIN
expansion match a directory that has already provided dependencies, then
the directory is implicitly secure. This directory can be used to provide
additional dependencies.


In a secure process, LD_CONFIG is ignored. However, a configuration file
that is recorded in a secure application is used. See the -c option of
ld(1). A recorded configuration file must be a full path name, that is,
the path name starts with a '/'. A recorded configuration file that
employs the $ORIGIN string is restricted to known trusted directories.
Developers who record a configuration file within a secure application
should ensure that the configuration file directory is suitably protected
from malicious intrusion. In the absence of a recorded configuration
file, a secure process uses the default configuration file, if a
configuration file exists. See crle(1).


In a secure process, LD_SIGNAL is ignored.


Additional objects can be loaded with a secure process using the
LD_PRELOAD, or LD_AUDIT environment variables. These objects must be
specified as full path names or simple file names. Full path names are
restricted to known trusted directories. Simple file names, in which no
'/' appears in the name, are located subject to the search path
restrictions previously described. Simple file names resolve only to
known trusted directories.


In a secure process, any dependencies that consist of simple filenames
are processed using the path name restrictions previously described.
Dependencies expressed as full path names or relative path names are used
as is. Therefore, the developer of a secure process should ensure that
the target directory referenced as a full path name or relative path name
dependency is suitably protected from malicious intrusion.


When creating a secure process, relative path names should not be used to
express dependencies, or to construct dlopen(3C) path names. This
restriction should be applied to the application and to all dependencies.

EXAMPLES

Example 1: Using LD_FLAGS to group environment variable information

The following use of LD_FLAGS is equivalent to setting the individual
environment variables LD_BIND_NOW and LD_LIBRARY_PATH for 32-bit
applications:


example% LD_FLAGS_32=bind_now,library_path=/lib/one:/lib/two


The following use of LD_FLAGS is equivalent to setting the individual
environment variables LD_LIBRARY_PATH and LD_PRELOAD for 64-bit
applications:


example% LD_FLAGS_64=library_path=/lib/one/64,preload=foo.so

FILES

/lib/ld.so.1

Default runtime linker.


/lib/libc.so.1

Alternate interpreter for SVID ABI compatibility.


/usr/lib/ld.so

AOUT (BCP) runtime linker.


/usr/lib/0@0.so.1

A compatibility library to support null character pointers. See
NOTES.


/lib/secure and /usr/lib/secure

LD_PRELOAD location for secure applications.


/lib/secure/64 and /usr/lib/secure/64

LD_PRELOAD location for secure 64-bit applications.


/lib/64/ld.so.1

Default runtime linker for 64-bit applications.


/usr/lib/64/0@0.so.1

A 64-bit compatibility library to support null character pointers.
See NOTES.


/var/ld/ld.config

Default configuration file for 32-bit applications.


/var/ld/64/ld.config

Default configuration file for 64-bit applications.

SEE ALSO

crle(1), gprof(1), lari(1), ld(1), ldd(1), exec(2), issetugid(2),
mmapobj(2), profil(2), dladdr(3C), dlclose(3C), dldump(3C), dlerror(3C),
dlinfo(3C), dlopen(3C), dlsym(3C), thr_kill(3C), proc(5), attributes(7)


Linker and Libraries Guide

NOTES

Care should be exercised when using LD_PROFILE in combination with other
process monitoring techniques, such as users of proc(5). Multiple process
monitoring techniques can result in deadlock conditions that leave the
profile buffer locked. A locked buffer blocks any processes that try to
record profiling information. To reduce this likelihood, the runtime
linker's profile implementation determines if the process is being
monitored at startup. If so, profiling of the process is silently
disabled. However, this mechanism can not catch monitoring processes that
attach to the process during its execution.


The user compatibility library /usr/lib/0@0.so.1 provides a mechanism
that establishes a value of 0 at location 0. Some applications exist that
erroneously assume a null character pointer should be treated the same as
a pointer to a null string. A segmentation violation occurs in these
applications when a null character pointer is accessed. If this library
is added to such an application at runtime using LD_PRELOAD, the library
provides an environment that is sympathetic to this errant behavior.
However, the user compatibility library is intended neither to enable the
generation of such applications, nor to endorse this particular
programming practice.


In many cases, the presence of /usr/lib/0@0.so.1 is benign, and it can be
pre-loaded into programs that do not require it. However, there are
exceptions. Some applications, such as the JVM (Java Virtual Machine),
require that a segmentation violation be generated from a null pointer
access. Applications such as the JVM should not preload /usr/lib/0@0.so.

December 28, 2020 LD.SO.1(1)