424:. This problem cannot occur if each version of each library is uniquely identified and each program references libraries only by their full unique identifiers. The "DLL hell" problems with earlier Windows versions arose from using only the names of libraries, which were not guaranteed to be unique, to resolve dynamic links in programs. (To avoid "DLL hell", later versions of Windows rely largely on options for programs to install private DLLs—essentially a partial retreat from the use of shared libraries—along with mechanisms to prevent replacement of shared system DLLs with earlier versions of them.)
66:
36:
511:
and setgid programs, so that a user can't force such a program to run arbitrary code with root permissions. Developers of libraries are encouraged to place their dynamic libraries in places in the default search path. On the downside, this can make installation of new libraries problematic, and these
409:
Loaders for shared libraries vary widely in functionality. Some depend on the executable storing explicit paths to the libraries. Any change to the library naming or layout of the file system will cause these systems to fail. More commonly, only the name of the library (and not the path) is stored in
219:
Most modern operating systems use the same format for both shared libraries and executable files. This offers two main advantages: first, it requires only one loader (building and maintaining a single loader is considered well worth any added complexity). Secondly, it allows an executable file to be
383:
Since shared libraries on most systems do not change often, systems can compute a likely load address for each shared library on the system before it is needed and store that information in the libraries and executables. If every shared library that is loaded has undergone this process, then each
359:
when the executable file is created; it only records what library routines the program needs and the index names or numbers of the routines in the library. The majority of the work of linking is done at the time the application is loaded (load time) or during execution (runtime). Usually, the
530:
on request. Such a request may be made implicitly or explicitly. Implicit requests are made when a compiler or static linker adds library references that include file paths or simply file names. Explicit requests are made when applications make direct calls to an operating system's API.
478:
used a more flexible system, collecting a list of libraries from a number of known locations (similar to the PATH concept) when the system first starts. Moving libraries around causes no problems at all, although users incur a time cost when first starting the system.
215:
Shared libraries can be statically linked at compile-time, meaning that references to the library are resolved and the library is allocated memory when the executable file is created. But often linking of shared libraries is postponed until they are loaded.
300:
In some cases, different versions of shared libraries can cause problems, especially when libraries of different versions have the same file name, and different applications installed on a system each require a specific version. Such a scenario is known as
212:. For perspective, a program can alternatively be monolithic -- built to include the executable code of the library in its executable file, but the library code embedded in the program's executable file is not usable by other programs.
413:
If a shared library that an executable depends on is deleted, moved, or renamed, or if an incompatible version of the library is copied to a place that is earlier in the search, the executable would fail to load. This is called
364:. (However, it is possible, and not exceedingly difficult, to write a program that uses dynamic linking and includes its own dynamic linker, even for an operating system that itself provides no support for dynamic linking.)
392:
uses a similar technique, called "Discontinuous Saved
Segments" (DCSS). Disadvantages of this technique include the time required to precompute these addresses every time the shared libraries change, the inability to use
273:
system, applications were often only a few hundred kilobytes in size and loaded quickly; most of their code was located in libraries that had already been loaded for other purposes by the operating system.
269:, and on disk. If virtual memory is used, processes would execute the same physical page of RAM that is mapped into the different address spaces of the processes. This has advantages. For instance, on the
289:. These systems ensure, by various means, like pre-mapping the address space and reserving slots for each shared library, that code has a high probability of being shared. A third alternative is
297:
and its successors. This allows position-dependent code, but places no significant restrictions on where code can be placed or how it can be shared.
451:
function; the System32, System, and
Windows directories; then the current working directory; and finally the directories specified by the PATH
309:. Most modern operating systems after 2001 have clean-up methods to eliminate such situations or use application-specific "private" libraries.
503:
formats can specify additional directories in which to search for libraries for a particular program. This can usually be overridden with an
782:
251:, only stack-based data (local) was allowed in shared library code, or other significant restrictions were placed on shared library code.
443:, but for other DLLs it will check the directories in a defined order. First, Windows checks the directory where it loaded the program (
644:
394:
539:
535:
527:
332:
209:
194:
149:
750:
83:
563:
244:
225:
130:
87:
102:
397:, and the requirement of sufficient virtual address space for use (a problem that will be alleviated by the adoption of
534:
Most operating systems that support dynamically linked libraries also support dynamically loading such libraries via a
777:
384:
will load at its predetermined address, which speeds up the process of dynamic linking. This optimization is known as
109:
410:
the executable, with the operating system supplying a method to find the library on disk, based on some algorithm.
76:
278:
163:
512:"known" locations quickly become home to an increasing number of library files, making management more complex.
116:
372:
285:, which leads to a complex but flexible architecture, or by using common virtual addresses, as in Windows and
526:
Dynamic loading, a subset of dynamic linking, involves a dynamically linked library loading and unloading at
360:
necessary linking program, called a "dynamic linker" or "linking loader", is actually part of the underlying
98:
440:
492:
460:
660:
Private DLLs are DLLs that are installed with a specific application and used only by that application.
504:
452:
336:
266:
233:
190:
49:
496:
356:
355:
systems) is a library intended for dynamic linking. Only a minimal amount of work is done by the
290:
204:
loads the shared library from a file (other than the program's executable file) into memory at
543:
432:
340:
436:
361:
201:
186:
123:
648:
521:
416:
182:
716:
742:
456:
318:
240:
224:). Examples of file formats use for both shared libraries and executable files include
771:
672:
599:
294:
260:
178:
495:
in which to look for dynamic libraries. Some systems specify the default path in a
324:
221:
420:, existing on many platforms. The (infamous) Windows variant is commonly known as
335:), rather than when the executable file is created. A dynamically linked library (
619:
65:
17:
500:
385:
488:
352:
328:
205:
475:
464:
421:
306:
302:
270:
603:
368:
348:
248:
200:
When running a program that is configured to use a shared library, the
162:"Shared object" redirects here. For the synchronization mechanism, see
508:
398:
229:
567:
463:
as the primary store of shared dll files to remove the issue of
389:
344:
286:
282:
570:-based systems, including most UNIX and UNIX-like systems, use
59:
29:
439:
to determine the proper place to load DLLs that implement
27:
Code library designed for mutual use by multiple programs
367:
Programmers originally developed dynamic linking in the
327:
is linking performed while a program is being loaded (
499:, others hard-code it into the dynamic loader. Some
491:
systems have a "search path" specifying file-system
90:. Unsourced material may be challenged and removed.
582:. Some development systems automate this process.
371:operating system, starting in 1964, and the MTS (
265:Library code may be shared in memory by multiple
638:
636:
622:by Ulrich Drepper (with much background info)
401:architectures, at least for the time being).
277:Programs can accomplish RAM sharing by using
8:
718:Saved Segments Planning and Administration
150:Learn how and when to remove this message
632:
591:
351:; dynamic shared object, or DSO, under
45:may need to be cleaned up or summarized
447:); any directories set by calling the
388:on macOS and Linux, respectively. IBM
220:used as a shared library (if it has a
7:
88:adding citations to reliable sources
747:Microsoft Developer Network Library
743:"Dynamic-Link Library Search Order"
673:"VSI OpenVMS Linker Utility Manual"
305:, named after the Windows and OS/2
239:In some older environments such as
395:address space layout randomization
47:because it has been split from/to
25:
564:Microsoft Dynamic Link Libraries
185:designed to be used by multiple
64:
34:
753:from the original on 9 May 2012
647:. microsoft.com. Archived from
455:. Applications written for the
75:needs additional citations for
507:, although it is disabled for
1:
698:Information Technology Digest
643:Anderson, Rick (2000-01-11).
620:How To Write Shared Libraries
459:(since 2002), also check the
405:Locating libraries at runtime
375:), built in the late 1960s.
783:Operating system technology
606:, also have a single format
799:
598:Some older systems, e.g.,
519:
316:
258:
161:
749:. Microsoft. 2012-03-06.
279:position-independent code
164:Monitor (synchronization)
715:IBM Corporation (2011).
386:prebinding or prelinking
373:Michigan Terminal System
347:; shareable image under
43:This article or section
546:uses the API functions
645:"The End of DLL Hell"
461:Global Assembly Cache
696:"A History of MTS".
505:environment variable
453:environment variable
337:dynamic-link library
84:improve this article
323:Dynamic linking or
50:Library (computing)
778:Computer libraries
678:. VSI. August 2019
497:configuration file
291:single-level store
544:Microsoft Windows
483:Unix-like systems
449:SetDllDirectory()
433:Microsoft Windows
428:Microsoft Windows
293:, as used by the
187:computer programs
160:
159:
152:
134:
58:
57:
16:(Redirected from
790:
762:
761:
759:
758:
739:
733:
732:
730:
728:
723:
712:
706:
705:
693:
687:
686:
684:
683:
677:
669:
663:
662:
657:
656:
640:
607:
596:
581:
577:
573:
561:
557:
553:
549:
542:. For instance,
450:
362:operating system
339:, or DLL, under
202:operating system
155:
148:
144:
141:
135:
133:
99:"Shared library"
92:
68:
60:
38:
37:
30:
21:
18:Shared libraries
798:
797:
793:
792:
791:
789:
788:
787:
768:
767:
766:
765:
756:
754:
741:
740:
736:
726:
724:
721:
714:
713:
709:
695:
694:
690:
681:
679:
675:
671:
670:
666:
654:
652:
642:
641:
634:
629:
616:
614:Further reading
611:
610:
597:
593:
588:
579:
575:
571:
559:
555:
551:
547:
524:
522:Dynamic loading
518:
516:Dynamic loading
501:executable file
485:
473:
448:
430:
417:dependency hell
407:
381:
331:) or executed (
321:
315:
313:Dynamic linking
263:
257:
183:executable code
167:
156:
145:
139:
136:
93:
91:
81:
69:
54:
39:
35:
28:
23:
22:
15:
12:
11:
5:
796:
794:
786:
785:
780:
770:
769:
764:
763:
734:
707:
688:
664:
631:
630:
628:
625:
624:
623:
615:
612:
609:
608:
590:
589:
587:
584:
560:GetProcAddress
520:Main article:
517:
514:
484:
481:
472:
469:
457:.NET Framework
429:
426:
406:
403:
380:
377:
319:Dynamic linker
317:Main article:
314:
311:
259:Main article:
256:
255:Memory sharing
253:
241:16-bit Windows
181:that contains
171:shared library
158:
157:
72:
70:
63:
56:
55:
42:
40:
33:
26:
24:
14:
13:
10:
9:
6:
4:
3:
2:
795:
784:
781:
779:
776:
775:
773:
752:
748:
744:
738:
735:
720:
719:
711:
708:
703:
699:
692:
689:
674:
668:
665:
661:
651:on 2001-06-05
650:
646:
639:
637:
633:
626:
621:
618:
617:
613:
605:
601:
600:Burroughs MCP
595:
592:
585:
583:
569:
565:
552:LoadLibraryEx
545:
541:
537:
532:
529:
523:
515:
513:
510:
506:
502:
498:
494:
490:
482:
480:
477:
470:
468:
466:
462:
458:
454:
446:
442:
438:
434:
427:
425:
423:
419:
418:
411:
404:
402:
400:
396:
391:
387:
379:Optimizations
378:
376:
374:
370:
365:
363:
358:
354:
350:
346:
342:
338:
334:
330:
326:
320:
312:
310:
308:
304:
298:
296:
295:IBM System/38
292:
288:
284:
280:
275:
272:
268:
262:
261:Shared memory
254:
252:
250:
246:
242:
237:
235:
231:
227:
223:
217:
213:
211:
207:
203:
198:
196:
192:
188:
184:
180:
179:computer file
176:
175:shared object
172:
165:
154:
151:
143:
132:
129:
125:
122:
118:
115:
111:
108:
104:
101: –
100:
96:
95:Find sources:
89:
85:
79:
78:
73:This article
71:
67:
62:
61:
52:
51:
46:
41:
32:
31:
19:
755:. Retrieved
746:
737:
725:. Retrieved
717:
710:
701:
697:
691:
680:. Retrieved
667:
659:
653:. Retrieved
649:the original
594:
533:
525:
486:
474:
444:
431:
415:
412:
408:
382:
366:
325:late binding
322:
299:
276:
264:
238:
222:symbol table
218:
214:
199:
174:
170:
168:
146:
137:
127:
120:
113:
106:
94:
82:Please help
77:verification
74:
48:
44:
556:FreeLibrary
548:LoadLibrary
493:directories
445:private DLL
441:COM objects
435:checks the
772:Categories
757:2012-05-20
682:2021-01-31
655:2012-01-15
627:References
110:newspapers
489:Unix-like
353:Unix-like
329:load time
267:processes
206:load time
191:libraries
189:or other
140:July 2023
751:Archived
536:run-time
476:OpenStep
471:OpenStep
465:DLL hell
437:registry
422:DLL hell
307:DLL file
303:DLL hell
281:, as in
271:OpenStep
247:for the
727:Jan 29,
604:Multics
576:dlclose
538:linker
528:runtime
369:Multics
349:OpenVMS
341:Windows
333:runtime
249:HP 3000
210:runtime
195:runtime
124:scholar
572:dlopen
509:setuid
399:64-bit
357:linker
232:, and
230:Mach-O
126:
119:
112:
105:
97:
722:(PDF)
676:(PDF)
586:Notes
580:dlsym
568:POSIX
562:with
487:Most
177:is a
131:JSTOR
117:books
729:2022
704:(5).
578:and
558:and
390:z/VM
345:OS/2
343:and
287:OS/2
283:Unix
103:news
540:API
245:MPE
243:or
226:ELF
208:or
193:at
173:or
86:by
774::
745:.
700:.
658:.
635:^
602:,
574:,
566:;
554:,
550:,
467:.
236:.
234:PE
228:,
197:.
169:A
760:.
731:.
702:5
685:.
166:.
153:)
147:(
142:)
138:(
128:·
121:·
114:·
107:·
80:.
53:.
20:)
Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.
