SunOS man pages : ld.so.1 (1)
User Commands ld.so.1(1)
NAME
ld.so.1 - runtime linker for dynamic objects
SYNOPSIS
/usr/lib/ld.so.1
/etc/lib/ld.so.1
DESCRIPTION
Dynamic applications consist of one or more dynamic objects.
They are typically a dynamic executable and its shared
object dependencies. As part of the initialization and exe-
cution of a dynamic application, an interpreter is called to
complete 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 pathname specifying the
program's interpreter. The pathname to the interpreter can
be specified when the executable is being constructed by the
-I option to ld(1) the link-editor. The default name sup-
plied by the link-editor is that of the runtime linker,
/usr/lib/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 mmap(2). The kernel maps this interpreter
and transfers control to it, passing sufficient information
to allow the interpreter to continue binding the application
and then run it.
In addition to initializing an application, the runtime
linker provides services that allow the application to
extend its address space by mapping additional shared
objects and binding to symbols within them.
The runtime linker performs the following functions:
o It opens and processes any applicable configuration
file. Configuration files may be employed to alter
default search paths, provide a directory cache and
provide alternative object dependencies. See crle(1).
By default, the configuration file /var/ld/ld.config
is used for 32-bit objects and /var/ld/64/ld.config
for 64-bit objects. Alternative configuration files
can be specified with the LD_CONFIG environment vari-
able, or encoded within a dynamic executable using the
-c option of ld(1).
o It analyzes the application's dynamic information
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section (.dynamic) and determines which shared object
dependencies are required.
o It locates and maps in these dependencies, and then it
analyzes their dynamic information sections to deter-
mine if any additional shared object dependencies are
required.
o Once all shared object dependencies are located and
mapped, the runtime linker performs any necessary
relocations to bind these shared objects in prepara-
tion for process execution.
o It calls any initialization functions provided by the
shared object dependencies and, possibly, by the
dynamic executable. By default, these are called in
the reverse order of the topologically sorted depen-
dencies. If cyclic dependencies exist, the initiali-
zation functions are called using the sorted order
with the cycle removed. ldd(1) can be used to display
the initialization order of shared object dependen-
cies.
o It passes control to the application.
o During the application's execution, the runtime linker
can be called upon to perform any delayed function
binding.
o It calls any finalization functions on deletion of
shared objects from the process. By default these are
called in the order of the topologically sorted depen-
dencies.
o The application can also call upon the runtime
linker's services to acquire additional shared objects
by dlopen(3DL) and bind to symbols within these
objects with dlsym(3DL)
Further details on each of the above topics may be found in
the Linker and Libraries Guide.
The runtime linker uses a prescribed search path for locat-
ing the dynamic dependencies of an object. The default
search paths are the runpath recorded in the object, fol-
lowed by /usr/lib for 32-bit objects or /usr/lib/64 for 64-
bit objects. This latter component can be modified using a
configuration file created with crle(1). The runpath is
specified when the dynamic object is constructed using the
-R option to ld(1). LD_LIBRARY_PATH can be used to indicate
directories to be searched before the default directories.
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ENVIRONMENT VARIABLES
LD_AUDIT
A colon-separated list of objects that will be loaded
by the runtime linker. As each object is loaded, it
will be examined for Link-Auditing interfaces; the
routines that are present will be 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_NOW
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 set-
ting causes the runtime linker to perform both data
reference and function reference relocations during
process initialization, before transferring control to
the application. Also see the -z now option of ld(1).
LD_CONFIG
Provides an alternative configuration file. Configura-
tion files may be employed to alter default search
paths, provide a directory cache and provide alternate
object dependencies. See crle(1).
LD_DEBUG
Provides a comma, or colon-separated list of tokens to
cause the runtime linker to print debugging informa-
tion to the standard error. The special token help
indicates the full list of tokens available. The
environment variable LD_DEBUG_OUTPUT may also be sup-
plied to specify a file to which the debugging infor-
mation is sent. The filename will be suffixed with the
process id of the application generating the debugging
information.
LD_DEMANGLE
Any symbol name used as part of a diagnostic message
is shown as it is defined within an ELF file. When
LD_DEMANGLE is set to any non-null value, the runtime
linker will attempt to decode (demangle) any C++ sym-
bol name.
LD_FLAGS
Provides an alternative means of supplying environment
variable information. Any of the LD_XXX environment
variables can specified as a xxx token. Multiple
tokens can be supplied separated by commas. See EXAM-
PLES.
LD_LIBRARY_PATH
The LD_LIBRARY_PATH environment variable, if set, is
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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 to be searched before the default
directories. Also notice that LD_LIBRARY_PATH adds
additional semantics to ld(1).
LD_LOADFLTR
Filters are a form of shared object. They allow an
alternative shared object to be selected at runtime
and provide the implementation for any symbols 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,
the runtime linker will process filters immediately
when they are loaded. Also see the -z loadfltr option
of ld(1).
LD_NOAUDIT
Local auditing libraries can be defined within appli-
cations 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 will ignore any local audit-
ing libraries.
LD_NOAUXFLTR
Auxiliary filters are a form of shared object. They
allow an alternative shared object to be selected at
runtime which provides the implementation for any sym-
bols defined within the filter. See the -f option of
ld(1). When LD_NOAUXFLTR is set to any non-null
value, the runtime linker will disable this alterna-
tive shared object lookup.
LD_NOCONFIG
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 will disable
this configuration file processing.
LD_NODIRCONFIG
Provides a subset of LD_NOCONFIG in that any directory
cache information provided in a configuration file is
ignored.
LD_NODIRECT
Direct binding information instructs the runtime
linker to search directly for a symbol in an associ-
ated object, rather than carry out the default symbol
search model. See the -B direct option of ld(1). When
LD_NODIRECT is set to any non-null value, the runtime
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linker will ignore any direct binding information.
LD_NOLAZYLOAD
Dependencies labeled for lazy loading are not loaded
into memory until explicit reference has been made to
them. See the -z lazyload option of ld(1). When
LD_NOLAZYLOAD is set to any non-null value, the run-
time linker will ignore a dependencies lazy loading
label and load it immediately.
LD_NOOBJALTER
Provides a subset of LD_NOCONFIG in that any alterna-
tive object dependencies provided in a configuration
file are ignored.
LD_NOVERSION
By default the runtime linker verifies version depen-
dencies for the primary executable and all of its
dependencies. When LD_NOVERSION is set to any non-null
value, the runtime linker will disable this version
checking.
LD_ORIGIN
The immediate processing of $ORIGIN can be triggered
by setting the environment variable LD_ORIGIN to any
non-null value. This may be useful for applications
that invoke chdir(2) prior to locating dependencies
that employ the $ORIGIN string token.
LD_PRELOAD
Provides a whitespace-separated list of shared objects
that are to be interpreted by the runtime linker. The
specified shared objects are linked after the program
is executed but before any other shared objects that
the program references.
LD_PROFILE
Defines a shared object that will 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 vari-
able LD_PROFILE_OUTPUT may also be supplied to indi-
cate an alternative directory in which to place the
profiling buffer.
This buffer contains profil(2) and call count informa-
tion 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 will
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accumulate data in the profile buffer. The profile
buffer information may be examined using gprof(1).
Notice that this profiling technique is an alternative
to any that may 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.
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 and overrides
any non-suffixed version of the environment variable that
may be in effect.
Notice that environment variable names beginning with the
characters 'LD_' are reserved for possible future enhance-
ments 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
user is not a super-user, and either the real user and
effective user identifiers are not equal, or the real group
and effective group identifiers are not equal. See
getuid(2), geteuid(2), getgid(2), and getegid(2).
The default trusted directory known to the runtime linker is
/usr/lib/secure for 32-bit objects or /usr/lib/secure/64 for
64-bit objects. The utility crle(1) may be used to specify
additional trusted directories applicable for secure appli-
cations. Administrators who use this technique should ensure
that the target directories are suitably protected from mal-
icious intrusion.
If an LD_LIBRARY_PATH environment variable is in effect for
a secure process, then only the trusted directories speci-
fied by this variable will be used to augment the runtime
linker's search rules.
In a secure process, any runpath specifications provided by
the application or any of its dependencies will be used,
provided they are full pathnames, that is, the pathname
starts with a '/'.
In a secure process, the expansion of the $ORIGIN string is
allowed only if it expands to a trusted directory.
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Additional objects may be loaded with a secure process using
the LD_PRELOAD, or LD_AUDIT environment variables. These
objects must be specified as full pathnames or simple file
names. Full pathnames are restricted to known trusted direc-
tories. Simple file names, in which no '/' appears in the
name, are located subject to the search path restrictions
previously described, and thus will only resolve to known
trusted directories.
In a secure process, any dependencies that consist of simple
filenames will be processed using the pathname restrictions
previously described. Dependencies that are expressed as
full or relative pathnames will be used as is. Therefore,
the developer of a secure process should ensure that the
target directory referenced as a full or relative pathname
dependency is suitably protected from malicious intrusion.
When creating a secure process, it is recommended that rela-
tive pathnames not be used to express dependencies or to
construct dlopen(3DL) pathnames. 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,
example% LD_FLAGS_32=bind_now,library_path=/lib/one:/lib/two
example% LD_FLAGS_64=library_path=/lib/one/64,preload=foo.so
is equivalent to setting the individual environment vari-
ables LD_BIND_NOW and LD_LIBRARY_PATH for 32-bit applica-
tions, and LD_LIBRARY_PATH and LD_PRELOAD for 64-bit appli-
cations.
FILES
/usr/lib/ld.so.1
Default runtime linker.
/etc/lib/ld.so.1
Alternate runtime linker.
/usr/lib/libc.so.1
Alternate interpreter for SVID ABI compatibility.
/usr/lib/ld.so
AOUT(BCP) runtime linker.
/usr/lib/0@0.so.1
Null character pointer compatibility library. See
NOTES.
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/usr/lib/secure
LD_PRELOAD location for secure applications.
/usr/lib/secure/64
LD_PRELOAD location for secure 64-bit applications.
/usr/lib/64/ld.so.1
Default runtime linker for 64-bit applications.
/usr/lib/64/0@0.so.1
Null character pointer compatibility library for the
64-bit applications.
/var/ld/ld.config
Default configuration file for 32-bit applications.
/var/ld/64/ld.config
Default configuration file for 64-bit applications.
ATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:
____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|_____________________________|_____________________________|
| Availability | SUNWcsu |
|_____________________________|_____________________________|
SEE ALSO
crle(1), gprof(1), ld(1), ldd(1), exec(2), getegid(2),
geteuid(2), getuid(2), mmap(2), profil(2), dladdr(3DL),
dlclose(3DL), dldump(3DL), dlerror(3DL), dlopen(3DL),
dlsym(3DL), attributes(5)
Linker and Libraries Guide
NOTES
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 will occur in these appli-
cations when a null character pointer is accessed. If this
library is added to such an application at runtime using
LD_PRELOAD, it 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.
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