dlopen_ia.3c (2010 09)

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dlopen_ia(3C) dlopen_ia(3C)

(Integrity Systems Only)

RTLD_TEXT_PRIVATE

Under this mode, the shared library loaded has its text segment mapped private.

This can be useful for debugging.

RTLD_LAZY Under this mode, only references to data symbols are relocated when the object is

loaded. References to functions are not relocated until a given function is invoked

for the ﬁrst time. This mode should result in better performance, since a process

may not reference all of the functions in any given shared object.

RTLD_NOW Under this mode, all necessary relocations are performed when the object is ﬁrst

loaded. This may result in some wasted effort, if relocations are performed for func-

tions that are never referenced, but is useful for applications that need to know as

soon as an object is loaded that all symbols referenced during execution are avail-

able.

Any object loaded by

dlopen() that requires relocations against global symbols can reference the sym-

bols in the original a.out, any objects loaded at program startup, from the object itself as well as any

other object included in the same dlopen() invocation, and any objects that were loaded in any

dlo-

pen() invocation that speciﬁed the RTLD_GLOBAL

ﬂag. To determine the scope of visibility for the sym-

bols loaded with a

dlopen() invocation, the mode parameter should be bitwise or’ed with one of the fol-

lowing values:

RTLD_GLOBAL The object’s symbols are made available for the relocation processing of any other

object. In addition, symbol lookup using dlopen(0,mode) and an associated

dlsym() allows objects loaded with RTLD_GLOBAL to be searched.

RTLD_LOCAL The object’s symbols are made available for relocation processing only to objects

loaded in the same dlopen() invocation.

If neither

RTLD_GLOBAL nor RTLD_LOCAL are speciﬁed, the default is RTLD_LOCAL.

If a ﬁle is speciﬁed in multiple

dlopen() invocations, mode is interpreted at each invocation. Note,

however, that once RTLD_NOW has been speciﬁed, all relocations will have been completed, rendering any

further RTLD_NOW operations redundant and any further RTLD_LAZY operations irrelevant.

Similarly, note that once

RTLD_GLOBAL has been speciﬁed, the object will maintain the RTLD_GLOBAL

status regardless of any previous or future speciﬁcation of RTLD_LOCAL, so long as the object remains in

the address space (see dlclose (3C)).

To determine the scope of symbols that are made available for relocation processing of objects loaded in a

dlopen() invocation, the mode parameter can be bitwise or’ed with one of the following values:

RTLD_GROUP Under this mode, the speciﬁed object, and its dependencies, behave as if they were

built with -B group (see ld(1)). Only symbols from objects loaded in the same

dlopen() invocation are made available for relocation. This ensures that all relo-

cations are satisﬁed using symbol deﬁnitions from the same dlopen() invocation.

RTLD_WORLD Under this mode, only symbols from global objects and from the object itself are

available for relocation processing. It does not use symbol deﬁnitions from other

objects loaded as part of the dlopen() invocation. This ﬂag has no effect on

objects build with -B group (see ld(1)).

RTLD_PARENT Under this mode, symbols from the object that invoked dlopen() are also made

available for relocation.

The default modes for

dlopen() are RTLD_WORLD|RTLD_GROUP. These ﬂags are OR’ed together

when the same object is loaded with different modes.

The following ﬂags do not affect relocation processing but provide other features:

RTLD_NODELETE Under this mode, the speciﬁed object and its dependencies behave as if they were

built with -B nodelete (see ld(1)). An explicit unload using dlclose() or

shl_load() returns success silently without detaching the shared library from

the process. Subsequently, the shared library handle is valid only for

shl_findsym(). It stays invalid for dlsym(), dlclose(), and

shl_unload() until the next explicit load using shl_load() or dlclose().

RTLD_NOLOAD Under this mode, the speciﬁed object is not loaded into the process’s address space,

but a valid handle is returned if the object already exists in the process address

space. If the speciﬁed object does not already exist, then an error is returned.

RTLD_NOLOAD can be used to query the presence, or for overriding the modes, of

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