•file is not a shared object.
•An error occurs during the process of loading file or relocating its symbolic references. More detailed diagnostic information is available through dlerror.
Description
The dlopen routine is one of a family of routines that give the user direct access to the dynamic linking facilities. The dlopen routine makes a shared library specified by a file available to a running process. A shared library may specify other objects that it "needs" in order to execute properly. These dependencies are specified by DT_NEEDED entries in the .dynamic section of the original shared library. Each needed shared library may, in turn, specify other needed shared libraries. All such shared libraries are loaded along with the original shared library as a result of the call to dlopen.
If the value of file is 0, dlopen provides a handle on a "global symbol shared library." This shared library provides access to the symbols from an ordered set of shared libraries consisting of the original a.out, all of the shared libraries that were loaded at program startup along with the a.out, and all shared libraries loaded using a dlopen operation along with the RTLD_GLOBAL flag. As the latter set of shared libraries can change during execution, the set identified by handle can also change dynamically.
Only a single copy of a shared library file is brought into the address space, even if dlopen is invoked multiple times in reference to the file, and even if different pathnames are used to reference the file. When a shared library is brought into the address space of a process, it can contain references to symbols whose addresses are not known until the shared library is loaded. These references must be relocated before the symbols can be accessed. The mode parameter governs the relocations and may have the following values (defined in Parameters): RTLD_LAZY and RTLD_NOW.
Any shared library loaded by dlopen that requires relocations against global symbols can reference the following:
•Symbols in the original a.out.
•Any shared libraries loaded at program startup, from the shared library itself.
•Any shared library included in the same dlopen invocation.
•Any shared libraries that were loaded in any dlopen invocation that specified the RTLD_GLOBAL flag.
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 alternated with one of the following values:
RTLD_GROUP:Under this mode, the specified object and its dependencies behave as if they were built with
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 built with
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_WORLDRTLD_GROUP. These flags are alternated together when the same object is loaded with different modes.
The values RTLD_GROUP, RTLD_WORLD, and RTLD_PARENT are not available for PA32 systems.
150 Shared Library Management Routines