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-Copyright (c) 1992,1993,1995,1996, Jens-Uwe Mager, Helios Software GmbH
-Not derived from licensed software.
-
-Permission is granted to freely use, copy, modify, and redistribute
-this software, provided that the author is not construed to be liable
-for any results of using the software, alterations are clearly marked
-as such, and this notice is not modified.
-
-libdl.a
--------
-
-This is an emulation library to emulate the SunOS/System V.4 functions
-to access the runtime linker. The functions are emulated by using the
-AIX load() function and by reading the .loader section of the loaded
-module to find the exports. The to be loaded module should be linked as
-follows (if using AIX 3):
-
- cc -o module.so -bM:SRE -bE:module.exp -e _nostart $(OBJS)
-
-For AIX 4:
-
- cc -o module.so -bM:SRE -bE:module.exp -bnoentry $(OBJS)
-
-If you want to reference symbols from the main part of the program in a
-loaded module, you will have to link against the export file of the
-main part:
-
- cc -o main -bE:main.exp $(MAIN_OBJS)
- cc -o module.so -bM:SRE -bI:main.exp -bE:module.exp -bnoentry $(OBJS)
-
-Note that you explicitely have to specify what functions are supposed
-to be accessible from your loaded modules, this is different from
-SunOS/System V.4 where any global is automatically exported. If you
-want to export all globals, the following script might be of help:
-
-#!/bin/sh
-/usr/ucb/nm -g $* | awk '$2 == "B" || $2 == "D" { print $3 }'
-
-The module export file contains the symbols to be exported. Because
-this library uses the loader section, the final module.so file can be
-stripped. C++ users should build their shared objects using the script
-makeC++SharedLib (part of the IBM C++ compiler), this will make sure
-that constructors and destructors for static and global objects will be
-called upon loading and unloading the module. GNU C++ users should use
-the -shared option to g++ to link the shared object:
-
- g++ -o module.so -shared $(OBJS)
-
-If the shared object does have permissions for anybody, the shared
-object will be loaded into the shared library segment and it will stay
-there even if the main application terminates. If you rebuild your
-shared object after a bugfix and you want to make sure that you really
-get the newest version you will have to use the "slibclean" command
-before starting the application again to garbage collect the shared
-library segment. If the performance utilities (bosperf) are installed
-you can use the following command to see what shared objects are
-loaded:
-
-/usr/lpp/bosperf/genkld | sort | uniq
-
-For easier debugging you can avoid loading the shared object into the
-shared library segment alltogether by removing permissions for others
-from the module.so file:
-
-chmod o-rwx module.so
-
-This will ensure you get a fresh copy of the shared object for every
-dlopen() call which is loaded into the application's data segment.
-
-Usage
------
-
-void *dlopen(const char *path, int mode);
-
-This routine loads the module pointed to by path and reads its export
-table. If the path does not contain a '/' character, dlopen will search
-for the module using the LIBPATH environment variable. It returns an
-opaque handle to the module or NULL on error. The mode parameter can be
-either RTLD_LAZY (for lazy function binding) or RTLD_NOW for immediate
-function binding. The AIX implementation currently does treat RTLD_NOW
-the same as RTLD_LAZY. The flag RTLD_GLOBAL might be or'ed into the
-mode parameter to allow loaded modules to bind to global variables or
-functions in other loaded modules loaded by dlopen(). If RTLD_GLOBAL is
-not specified, only globals from the main part of the executable or
-shared libraries are used to look for undefined symbols in loaded
-modules.
-
-
-void *dlsym(void *handle, const char *symbol);
-
-This routine searches for the symbol in the module referred to by
-handle and returns its address. If the symbol could not be found, the
-function returns NULL. The return value must be casted to a proper
-function pointer before it can be used. SunOS/System V.4 allows handle
-to be a NULL pointer to refer to the module the call is made from, this
-is not implemented.
-
-int dlclose(void *handle);
-
-This routine unloads the module referred to by the handle and disposes
-of any local storage. this function returns -1 on failure. Any function
-pointers obtained through dlsym() should be considered invalid after
-closing a module.
-
-As AIX caches shared objects in the shared library segment, function
-pointers obtained through dlsym() might still work even though the
-module has been unloaded. This can introduce subtle bugs that will
-segment fault later if AIX garbage collects or immediatly on
-SunOS/System V.4 as the text segment is unmapped.
-
-char *dlerror(void);
-
-This routine can be used to retrieve a text message describing the most
-recent error that occured on on of the above routines. This function
-returns NULL if there is no error information.
-
-Initialization and termination handlers
----------------------------------------
-
-The emulation provides for an initialization and a termination
-handler. The dlfcn.h file contains a structure declaration named
-dl_info with following members:
-
- void (*init)(void);
- void (*fini)(void);
-
-The init function is called upon first referencing the library. The
-fini function is called at dlclose() time or when the process exits.
-The module should declare a variable named dl_info that contains this
-structure which must be exported. These functions correspond to the
-documented _init() and _fini() functions of SunOS 4.x, but these are
-appearently not implemented in SunOS. When using SunOS 5.0, these
-correspond to #pragma init and #pragma fini respectively. At the same
-time any static or global C++ object's constructors or destructors will
-be called.
-
-BUGS
-----
-
-Please note that there is currently a problem with implicitely loaded
-shared C++ libaries: if you refer to a shared C++ library from a loaded
-module that is not yet used by the main program, the dlopen() emulator
-does not notice this and does not call the static constructors for the
-implicitely loaded library. This can be easily demonstrated by
-referencing the C++ standard streams from a loaded module if the main
-program is a plain C program.
-
-Jens-Uwe Mager
-
-HELIOS Software GmbH
-Lavesstr. 80
-30159 Hannover
-Germany
-
-Phone: +49 511 36482-0
-FAX: +49 511 36482-69
-AppleLink: helios.de/jum
-Internet: jum@helios.de
-
-Revison History
----------------
-
-SCCS/s.dlfcn.h:
-
-D 1.4 95/04/25 09:36:52 jum 4 3 00018/00004/00028
-MRs:
-COMMENTS:
-added RTLD_GLOBAL, include and C++ guards
-
-D 1.3 92/12/27 20:58:32 jum 3 2 00001/00001/00031
-MRs:
-COMMENTS:
-we always have prototypes on RS/6000
-
-D 1.2 92/08/16 17:45:11 jum 2 1 00009/00000/00023
-MRs:
-COMMENTS:
-added dl_info structure to implement initialize and terminate functions
-
-D 1.1 92/08/02 18:08:45 jum 1 0 00023/00000/00000
-MRs:
-COMMENTS:
-Erstellungsdatum und -uhrzeit 92/08/02 18:08:45 von jum
-
-SCCS/s.dlfcn.c:
-
-D 1.11 96/04/10 20:12:51 jum 13 12 00037/00000/00533
-MRs:
-COMMENTS:
-Integrated the changes from John W. Eaton <jwe@bevo.che.wisc.edu> to initialize
-g++ generated shared objects.
-
-D 1.10 96/02/15 17:42:44 jum 12 10 00012/00007/00521
-MRs:
-COMMENTS:
-the C++ constructor and destructor chains are now called properly for either
-xlC 2 or xlC 3 (CSet++).
-
-D 1.9 95/09/22 11:09:38 markus 10 9 00001/00008/00527
-MRs:
-COMMENTS:
-Fix version number
-
-D 1.8 95/09/22 10:14:34 markus 9 8 00008/00001/00527
-MRs:
-COMMENTS:
-Added version number for dl lib
-
-D 1.7 95/08/14 19:08:38 jum 8 6 00026/00004/00502
-MRs:
-COMMENTS:
-Integrated the fixes from Kirk Benell (kirk@rsinc.com) to allow loading of
-shared objects generated under AIX 4. Fixed bug that symbols with exactly
-8 characters would use garbage characters from the following symbol value.
-
-D 1.6 95/04/25 09:38:03 jum 6 5 00046/00006/00460
-MRs:
-COMMENTS:
-added handling of C++ static constructors and destructors, added RTLD_GLOBAL to bind against other loaded modules
-
-D 1.5 93/02/14 20:14:17 jum 5 4 00002/00000/00464
-MRs:
-COMMENTS:
-added path to dlopen error message to make clear where there error occured.
-
-D 1.4 93/01/03 19:13:56 jum 4 3 00061/00005/00403
-MRs:
-COMMENTS:
-to allow calling symbols in the main module call load with L_NOAUTODEFER and
-do a loadbind later with the main module.
-
-D 1.3 92/12/27 20:59:55 jum 3 2 00066/00008/00342
-MRs:
-COMMENTS:
-added search by L_GETINFO if module got loaded by LIBPATH
-
-D 1.2 92/08/16 17:45:43 jum 2 1 00074/00006/00276
-MRs:
-COMMENTS:
-implemented initialize and terminate functions, added reference counting to avoid multiple loads of the same library
-
-D 1.1 92/08/02 18:08:45 jum 1 0 00282/00000/00000
-MRs:
-COMMENTS:
-Erstellungsdatum und -uhrzeit 92/08/02 18:08:45 von jum
-
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