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NAME

crle − configure runtime linking environment

SYNOPSIS

crle [-64] [-a name] [-c conf] [-e env] [-E env] [-f flags] [-i name] [-I name] [-g name] [-G name] [-l dir] [-o dir] [-s dir] [-t [ ELF | AOUT] ] [-u] [-v]

DESCRIPTION

The crle utility provides for the creation and display of a runtime linking configuration file. Without any arguments, or with just the -c option, crle displays the contents of a configuration file, any system defaults and the command-line required to regenerate the configuration file. When used with any other options, a new configuration file is created or updated. The configuration file is read and interpreted by the runtime linker, ld.so.1(1), during process start-up.

The default configuration file is /var/ld/ld.config for 32-bit objects and /var/ld/64/ld.config for 64-bit objects. Note: It is recommended that any new configuration file is first created in a temporary location. The environment variable LD_CONFIG can be set to this new configuration file to cause its use by the runtime linker instead of any default. After verification, the new configuration file can be moved to the default location if desired. Setting the environment variable LD_NOCONFIG to any value results in the runtime linker ignoring any configuration files, and may prove useful during experimentation.

The configuration file may contain the following information:
Default Search Paths

The runtime linker uses a prescribed search path for locating the dynamic dependencies of an object. This search path starts with the components of any LD_LIBRARY_PATH definition, followed by the components of an object’s runpath and finally any defaults specific to the object’s type. This last component of the search path can be expressed within the configuration file. Note: Typical use of this facility should augment any system defaults; see the -l option.

Trusted Directories

When processing a secure application the runtime linker restricts the use of LD_LIBRARY_PATH and the directories from which preload and audit libraries may be used to known trusted directories. These trusted directories can be expressed within the configuration file. Note: Typical use of this facility should augment any system defaults; see the -s option.

Directory Cache

The location of shared objects within defined directories can be maintained as a cache within the configuration file. This directory cache can reduce the overhead of searching for application dependencies.

Alternative Objects

In conjunction with the directory cache, shared objects may have alternative objects specified for use at runtime. These alternate objects may be supplied by the user, or can be created by crle as copies of shared objects fixed to known memory locations. These fixed alternative objects can require less processing at runtime than their original shared object counterpart.

Environment Variables

Any environment variable interpreted by the runtime linker can be specified within the configuration file.

Defining alternative default search paths, or additional trusted directories can be useful for administrators who wish to install third party software in a central location, or otherwise alter the search path of applications that may not have been coded with suitable runpaths.

Defining user supplied alternative objects provides a means of replacing dependencies other than via symbolic links or requiring LD_LIBRARY_PATH settings.

Defining runtime linker environment variables provides a means of centralizing their definition for all applications.

The directory cache and crle generated alternate objects can provide a means of reducing the runtime start-up overhead of applications that require many dependencies, or whose dependencies are expensive to relocate (this may be the case when shared objects contain position-dependent code).

When alternate objects generated by crle are specified within a configuration file, ld.so.1(1) performs some minimal consistency verification of the alternative objects against their originating objects. This verification is intended to avert application failure should an applications configuration information become out-of-sync with the underlying system components. When this situation arises the flexibility offered by dynamic linking system components may be compromised, and diagnosing the application failure may be difficult. Note: No verification of directory cache information is performed. Any changes to the directory structure will not be seen by a process until the cache is rebuilt.

System shared objects are often well tuned and may have no benefit being cached. The directory cache and alternative object features are typically applicable to user applications and shared objects.

crle creates alternate objects for the shared objects discovered when using the -I and -G options by calls to dldump(3DL). The alternate object is created in the directory specified by the preceding -o option, or defaults to the directory in which the configuration file is created. The flags used for the dldump() are specified using the -f option, or default to RTLD_REL_RELATIVE.

OPTIONS

The following options are supported:

-a name

This option adds an alternative to name to the configuration file. The actual alternative file must be supplied by the user. Multiple occurrences of this option are permitted. If name is a directory each shared object within the directory is added to the cache. If name does not exist, it is marked in the cache as a nonexistent file.

-c conf

Specifies to use the configuration file name conf. If this option is not supplied the default configuration file is used.

-e env

This option specifies a replaceable environment variable, env. Only environment variables applicable to the runtime linker are meaningful. Multiple occurrences of this option are permitted. This option is similar to the -E option, but differs in how configuration file definitions and process environment definitions of the same name are resolved at runtime.

A definition established in a configuration file can be overridden by a process environment definition, or be suppressed by a null-value process environment definition.

In other words, these configuration file definitions can be replaced or removed by the process environment at runtime.

-E env

This option specifies a permanent environment variable, env. Only environment variables applicable to the runtime linker are meaningful. Multiple occurrences of this option are permitted. This option is similar to the -e option, but differs in how configuration file definitions and process environment definitions of the same name are resolved at runtime.

Environment variable definitions meaningful to the runtime linker fall into one of two categories, that is, singular definitions such as LD_NOLAZYLOAD=1 and LD_DEBUG_OUTPUT=file, or list definitions which can take one or more values such as LD_LIBRARY_PATH=path, and LD_DEBUG=files,details.

A singular definition established in a configuration file will take precedence over a process environment definition. A list definition established in a configuration file will be appended to a process environment definition. Any definition established in a configuration file can not be suppressed by a null-value process environment definition.

In other words, these configuration file definitions can not be replaced or removed by the process environment at runtime.

-f flags

This option provides the symbolic flags argument to the dldump(3DL) calls used to generate alternate objects. Any of the RTLD_REL flags defined in /usr/include/dlfcn.h can be used. Multiple flags can be or’ed together using the "|" character, and in this case the string should be quoted to avoid expansion by the shell. If no flags values are provided the default flag is RTLD_REL_RELATIVE.

-i name

This option adds an individual name to the configuration cache. Multiple occurrences of this option are permitted. name may be a shared object or a directory. If name is a directory each shared object within the directory is added to the cache. Note: If name does not exist, it is marked in the cache as a nonexistent directory.

-I name

This option is the same as -i and in addition any shared objects have alternatives created via dldump(3DL). If the -f flag contains RTLD_REL_EXEC then name may be a dynamic executable, for which an alternative is created. Only one dynamic executable can be specified in this manner as the cache created is specific to this application.

-g name

This option adds the group name to the configuration cache. Each object is expanded to determine its dependencies. Multiple occurrences of this option are permitted. name may be a dynamic executable, shared object or a directory. The name itself, if it is a shared object, and its dependencies are added to the cache. If name is a directory each shared object within the directory, and its dependencies, are added to the cache.

-G name

This option is the same as -g and in addition any shared objects have alternatives created via dldump(3DL). If name is a dynamic executable, and the -f flag contains RTLD_REL_EXEC, then an alternative for the dynamic executable is also created. Only one dynamic executable can be specified in this manner as the cache created is specific to this application.

-l dir

This option specifies a new default search directory dir for ELF or AOUT objects. Multiple occurrences of this option are permitted. The type of object applicable to the search is specified by the preceding -t option, or defaults to ELF.

The system default search path for ELF objects is /usr/lib for 32-bit objects, and /usr/lib/64 for 64-bit objects. The system default search paths for AOUT objects is /usr/4lib, /usr/lib and /usr/local/lib.

Use of this option replaces the system default search path, and thus it is normally required that a -l option be used to specify the original system default in relation to any new paths being applied. However, if the -u option is in effect, and a configuration file does not exist, the system defaults are added to the new configuration file before the new paths specified with the -l option.

-o dir

This option specifies the directory dir in which any alternate objects must exist (in the case of using the -a option), or will be created (in the case of alternatives created by crle). Without this option, alternate objects will exist in the directory in which the configuration file is created. Multiple occurrences of this option are permitted, the directory dir being used to locate alternatives for any following command-line options. Alternative objects are not permitted to override their associated originals.

-s dir

This option specifies a new trusted directory dir for secure ELF or AOUT objects. See SECURITY in ld.so.1(1) for a definition of secure objects.

Multiple occurrences of this option are permitted. The type of object applicable to the search is specified by the preceding -t option, or defaults to ELF.

The system default trusted directory for secure ELF objects is /usr/lib/secure for 32-bit objects and /usr/lib/secure/64 for 64-bit objects. The system default trusted directories for secure AOUT objects are /usr/4lib, /usr/lib, /usr/ucblib, and /usr/local/lib.

Use of this option replaces the system default trusted directories, and thus it is normally required that a -s option be used to specify the original system default in relation to any new directories being applied. However, if the -u option is in effect, and a configuration file does not exist, the system defaults are added to the new configuration file before the new directories specified with the -s option.

-t ELF | AOUT

This option toggles the object type applicable to any -l or -s options that follow. The default object type is ELF.

If a configuration file does not exist it will be created as directed by the other arguments. In the case of the -l and -s options any system defaults will first be applied to the configuration file before the directories specified with these options.

By default the runtime linker attempts to read the configuration file /var/ld/ld.config for each 32-bit application it processes or /var/ld/64/ld.config for each 64-bit application. When processing an alternative application, the runtime linker will use a $ORIGIN/ld.config.app-name configuration file if present (see NOTES). Applications may reference an alternative configuration file either by setting the LD_CONFIG environment variable (see ld.so.1(1)), or by recording a configuration file name in the application at the time it is built using the link-editors -c option (see ld(1)).

EXAMPLES

Example 1: Update (and display) of a new default search path for ELF objects

example% crle -u -l /local/lib
example% crle

Configuration file [3]: /var/ld/ld.config
  Default Library Path (ELF):  /usr/lib:/local/lib
  Trusted Directories (ELF):   /usr/lib/secure  (system default)

Command line:
  crle  -l /usr/lib:/local/lib

example% crle  -u  -l /usr/local/lib
example% crle

Configuration file [3]: /var/ld/ld.config
  Default Library Path (ELF):  /usr/lib:/local/lib:/usr/local/lib
  Trusted Directories (ELF):   /usr/lib/secure  (system default)


Command line:
  crle  -l /usr/lib:/local/lib:/usr/local/lib

In this example, the default configuration file initially did not exist, and thus the new search path /local/lib is appended to the system default. The next update appends the search path /usr/local/lib to those already established in the configuration file.

Example 2: Creation (and display) of a new default search path and new trusted directory for ELF objects

example% crle -l /local/lib -l /usr/lib -s /local/lib
example% crle

Configuration file [2]: /var/ld/ld.config
  Default Library Path (ELF):  /local/lib:/usr/lib
  Trusted Directories (ELF):   /local/lib


Command line:
  crle  -l /local/lib:/usr/lib  -s /local/lib

With this configuration, third party applications may be installed in /local/bin and their associated dependencies in /local/lib. The default search path allows the applications to locate their dependencies without the need to set LD_LIBRARY_PATH. Note: The system default trusted directory has been replaced with this example.

Example 3: Creation of a directory cache for ELF objects

example% crle -i /usr/dt/lib -i /usr/openwin/lib -i /usr/lib \
-c config
example% ldd -s ./main

....
   find object=libc.so.1; required by ./main
    search path=/usr/dt/lib:/usr/openwin/lib  (RPATH ./main)
    trying path=/usr/dt/lib/libc.so.1
    trying path=/usr/openwin/lib/libc.so.1
    search path=/usr/lib  (default)
    trying path=/usr/lib/libc.so.1
        libc.so.1 =>     /usr/lib/libc.so.1


example% LD_CONFIG=config  ldd  -s  ./main
....
   find object=libc.so.1; required by ./main
    search path=/usr/dt/lib:/usr/openwin/lib  (RPATH ./main)
    search path=/usr/lib  (default)
    trying path=/usr/lib/libc.so.1
        libc.so.1 =>     /usr/lib/libc.so.1

With this configuration, the cache reflects that the system library libc.so.1 does not exist in the directories /usr/dt/lib or /usr/openwin/lib. Therefore, the search for this system file ignores these directories even though the application’s runpath indicates they should be searched.

Example 4: Creation of an alternative object cache for an ELF executable

example% crle -c /local/$HOST/.xterm/ld.config.xterm \
-f RTLD_REL_ALL -G /usr/openwin/bin/xterm
example% ln -s /local/$HOST/.xterm/xterm /local/$HOST/xterm
example% ldd /usr/local/$HOST/xterm

    libXaw.so.5 =>  /local/$HOST/.xterm/libWaw.so.5  (alternate)
    libXmu.so.4 =>  /local/$HOST/.xterm/libXmu.so.4  (alternate)
    ....
    libc.so.1 =>    /local/$HOST/.xterm/libc.so.1  (alternate)
    ....

With this configuration, a new xterm and its dependencies are created. These new objects are fully relocated to themselves and result in faster start-up than the originating objects. Note: The execution of this application uses its own specific configuration file. This model is generally more flexible than using the environment variable LD_CONFIG, as the configuration file will not be erroneously used by other applications such as ldd(1) or truss(1).

Example 5: Creating an alternative object cache to replace an ELF shared object

example% ldd /usr/bin/vi

    libcurses.so.1 =>  /usr/lib/libcurses.so.1
    ....

example% crle  -a /usr/lib/libcurses.so.1  -o  /usr/ucblib
example% crle

Configuration file [3]: /var/ld/ld.config
  Default Library Path (ELF):   /usr/lib  (system default)
  Trusted Directories (ELF):   /usr/lib/secure  (system default)

Directory: /usr/lib
  libcurses.so.1  (alternate: /usr/ucblib/libcurses.so.1)
....


example% ldd  /usr/bin/vi
    libcurses.so.1 =>  /usr/ucblib/libcurses.so.1  (alternate)
    ....

With this configuration, any dependency that would normally resolve to /usr/lib/libcurses.so.1 will instead resolve to /usr/ucblib/libcurses.so.1.

Example 6: Setting replaceable and permanent environment variables

example% crle -e LD_LIBRARY_PATH=/local/lib \
-E LD_PRELOAD=preload.so.1
example% crle

.....
Environment Variables:
  LD_LIBRARY_PATH=/local/lib  (replaceable)
  LD_PRELOAD=preload.so.1  (permanent)


.....
example% LD_DEBUG=files LD_PRELOAD=preload.so.2 ./main
.....
18764: file=preload.so.2;  preloaded
18764: file=/local/lib/preload.so.2  [ ELF ]; generating link map
.....
18764: file=preload.so.1;  preloaded
18764: file=/local/lib/preload.so.1  [ ELF ]; generating link map
.....

With this configuration file, a replaceable search path has been specified together with a permanent preload object which becomes appended to the process environment definition.

EXIT STATUS

The creation or display of a configuration file results in a 0 being returned; otherwise any error condition is accompanied with a diagnostic message and a non-zero value being returned.

NOTES

Tagging an alternative application to use an application specific configuration file can only be achieved if the original application contains one of the .dynamic tags DT_FLAGS_1 or DT_FEATURE_1. Without these entries any application specific configuration file must be specified using the LD_CONFIG environment variable. Care should be exercised with this latter method as this environment variable will be visible to any forked applications.

The use of the -u option requires at least version 2 of crle. This version level is evident from displaying the contents of a configuration file:

example% crle

Configuration file [2]: /var/ld/ld.config
  ......

With a version 2 configuration file, crle is capable of constructing the command-line arguments required to regenerate the configuration file and to provide full update capabilities. Although the update of a version 1 configuration file is possible, the contents of the configuration file may be insufficient for crle to compute the entire update requirements.

FILES

/var/ld/ld.config

Default configuration file for 32-bit applications.

/var/ld/64/ld.config

Default configuration file for 64-bit applications.

/var/tmp

Default location for temporary configuration file (see tempnam(3C)).

/usr/lib/lddstub

Stub application employed to dldump(3DL) 32-bit objects.

/usr/lib/64/lddstub

Stub application employed to dldump(3DL) 64-bit objects.

/usr/lib/libcrle.so.1

Audit library employed to dldump(3DL) 32-bit objects.

/usr/lib/64/libcrle.so.1

Audit library employed to dldump(3DL) 64-bit objects.

ATTRIBUTES

See attributes(5) for descriptions of the following attributes:

SEE ALSO

ld(1), ld.so.1(1), dldump(3DL), tempnam(3C), attributes(5)