HP-UX Reference (11i v2 07/12) - 3 Library Functions A-M (vol 6)

d
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 available.
Any object loaded by dlopen() that requires relocations against global symbols can reference the symbols
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
dlopen()
invocation that specified the RTLD_GLOBAL flag. To determine the scope of visibility for the symbols
loaded with a
dlopen() invocation, the mode parameter should be bitwise or’ed with one of the following
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, how-
ever, 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 reloca-
tions 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 avail-
able 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() .
314 Hewlett-Packard Company − 2 − HP-UX 11i Version 2: December 2007 Update