6 .Nd GNU Linker Internals
8 This file documents the internals of the GNU linker
10 It is a collection of miscellaneous information with little form at this point.
11 Mostly, it is a repository into which you can put information about GNU
13 as you discover it (or as you design changes to
16 This document is distributed under the terms of the GNU Free Documentation
17 License. A copy of the license is included in the section entitled "GNU Free
18 Documentation License".
20 .Sh The Pa README File
23 file; it often has useful information that does not appear anywhere else in
26 .Sh How linker emulations are generated
27 Each linker target has an
29 The emulation includes the default linker script, and certain emulations also
30 modify certain types of linker behaviour.
32 Emulations are created during the build process by the shell script
37 script starts by reading a file in the
39 directory. This is a shell script which sets various shell variables used
42 and the other shell scripts it invokes.
46 script will invoke a shell script in the
48 directory in order to create default linker scripts written in the linker
51 script will be invoked 5 (or, in some cases, 6) times, with different assignments
52 to shell variables, to create different default scripts. The choice of script
53 is made based on the command line options.
55 After creating the scripts,
57 will invoke yet another shell script, this time in the
59 directory. That shell script will create the emulation source file, which
60 contains C code. This C code permits the linker emulation to override various
61 linker behaviours. Most targets use the generic emulation code, which is in
62 .Pa emultempl/generic.em .
66 reads three shell scripts: an emulation parameters script in the
68 directory, a linker script generation script in the
70 directory, and an emulation source file generation script in the
74 For example, the Sun 4 linker sets up variables in
75 .Pa emulparams/sun4.sh ,
76 creates linker scripts using
77 .Pa scripttempl/aout.sc ,
78 and creates the emulation code using
79 .Pa emultempl/sunos.em .
81 Note that the linker can support several emulations simultaneously, depending
82 upon how it is configured. An emulation can be selected with the
86 option will list all supported emulations.
88 .Ss Pa emulparams scripts
89 Each target selects a particular file in the
91 directory by setting the shell variable
95 This shell variable is used by the
97 script to control building an emulation source file.
99 Certain conventions are enforced. Suppose the
105 The name of the emulation shell script will be
106 .Pa emulparams/ Va emul.sh .
109 must have a target named
111 this target must depend upon
112 .Pa emulparams/ Va emul.sh ,
113 as well as the appropriate scripts in the
123 and the value of the make variable
125 The value of the latter variable will be set by the
127 script, and is used to set the default target directory to search.
130 .Pa emulparams/ Va emul.sh
131 shell script should only set shell variables. It may set shell variables which
132 are to be interpreted by the
136 scripts. Certain shell variables are interpreted directly by the
140 Here is a list of shell variables interpreted by
142 as well as some conventional shell variables interpreted by the
150 This is the name of the
158 .Pa scripttempl/ Va script.sc .
161 This is the name of the
169 .Pa emultempl/ Va template.em .
170 If this variable is not set, the default value is
173 .It GENERATE_SHLIB_SCRIPT
174 If this is set to a nonempty string,
178 script an extra time to create a shared library script. linker scripts.
181 This is normally set to indicate the BFD output format use (e.g.,
182 .Li "a.out-sunos-big" .
185 script will normally use it in an
187 expression in the linker script.
190 This is normally set to indicate the architecture to use (e.g.,
194 script will normally use it in an
196 expression in the linker script.
201 scripts use this to set the entry address, in an
203 expression in the linker script.
208 scripts use this to set the start address of the
212 .It NONPAGED_TEXT_START_ADDR
213 If this is defined, the
217 to its value before running the
224 .Dq linker scripts ) .
229 script uses this to set the default value of
240 script uses this to define it.
245 scripts set this to a number to pass to
247 to set the required alignment for the
252 .Ss Pa scripttempl scripts
253 Each linker target uses a
255 script to generate the default linker scripts. The name of the
267 .Pa scripttempl/ Va script.sc .
271 script will invoke the
273 script 5 to 8 times. Each time it will set the shell variable
275 to a different value. When the linker is run, the options used will direct
276 it to select a particular script. (Script selection is controlled by the
278 emulation entry point; this describes the conventional behaviour).
282 script should just write a linker script, written in the linker command language,
283 to standard output. If the emulation name--the name of the
289 then the output will be directed to
290 .Pa ldscripts/ Va emul. Va extension
291 in the build directory, where
293 changes each time the
297 Here is the list of values assigned to
302 The script generated is used by default (when none of the following cases
303 apply). The output has an extension of
306 The script generated is used when the linker is invoked with the
308 option. The output has an extension of
311 The script generated is used when the linker is invoked with the
313 option. The output has an extension of
316 The script generated is used when the linker is invoked with the
318 option. The output has an extension of
321 The script generated is used when the linker is invoked with the
323 option. The output has an extension of
328 script is only invoked with
331 .Li GENERATE_SHLIB_SCRIPT
336 script must arrange to use this script at the appropriate time, normally when
337 the linker is invoked with the
339 option. The output has an extension of
344 script is only invoked with
347 .Li GENERATE_COMBRELOC_SCRIPT
356 script must arrange to use this script at the appropriate time, normally when
357 the linker is invoked with the
359 option. The output has an extension of
364 script is only invoked with
367 .Li GENERATE_COMBRELOC_SCRIPT
375 .Li GENERATE_SHLIB_SCRIPT
380 script must arrange to use this script at the appropriate time, normally when
381 the linker is invoked with the
382 .Li -shared -z combreloc
383 option. The output has an extension of
387 Besides the shell variables set by the
393 script will set certain variables for each run of the
399 This will be set to a non-empty string when the linker is doing a final relocation
400 (e.g., all scripts other than
406 This will be set to a non-empty string when the linker is building global
407 constructor and destructor tables (e.g., all scripts other than
411 This will be set to an
413 expression when the output should be page aligned, or to
420 This will be set to a non-empty string when generating a
425 This will be set to a non-empty string when generating
427 scripts to a temporary file name which can be used during script generation.
430 The conventional way to write a
432 script is to first set a few shell variables, and then write out a linker
435 with a here document. The linker script will use variable substitutions, based
436 on the above variables and those set in the
438 script, to control its behaviour.
440 When there are parts of the
442 script which should only be run when doing a final relocation, they should
443 be enclosed within a variable substitution based on
445 For example, on many targets special symbols such as
447 should be defined when doing a final link. Naturally, those symbols should
448 not be defined when doing a relocatable link using
452 script could use a construct like this to define those symbols:
453 .Bd -literal -offset indent
454 ${RELOCATING+ _end = .;}
456 This will do the symbol assignment only if the
460 The basic job of the linker script is to put the sections in the correct order,
461 and at the correct memory addresses. For some targets, the linker script may
462 have to do some other operations.
464 For example, on most MIPS platforms, the linker is responsible for defining
467 used to initialize the
469 register. It must be set to the start of the small data section plus
471 Naturally, it should only be defined when doing a final relocation. This will
472 typically be done like this:
473 .Bd -literal -offset indent
474 ${RELOCATING+ _gp = ALIGN(16) + 0x8000;}
476 This line would appear just before the sections which compose the small data
480 All those sections would be contiguous in memory.
482 Many COFF systems build constructor tables in the linker script. The compiler
483 will arrange to output the address of each global constructor in a
485 section, and the address of each global destructor in a
487 section (this is done by defining
488 .Li ASM_OUTPUT_CONSTRUCTOR
490 .Li ASM_OUTPUT_DESTRUCTOR
493 configuration files). The
495 runtime support routines expect the constructor table to be named
497 They expect it to be a list of words, with the first word being the count
498 of the number of entries. There should be a trailing zero word. (Actually,
499 the count may be -1 if the trailing word is present, and the trailing word
500 may be omitted if the count is correct, but, as the
502 behaviour has changed slightly over the years, it is safest to provide both).
503 Here is a typical way that might be handled in a
506 .Bd -literal -offset indent
507 ${CONSTRUCTING+ __CTOR_LIST__ = .;}
508 ${CONSTRUCTING+ LONG((__CTOR_END__ - __CTOR_LIST__) / 4 - 2)}
509 ${CONSTRUCTING+ *(.ctors)}
510 ${CONSTRUCTING+ LONG(0)}
511 ${CONSTRUCTING+ __CTOR_END__ = .;}
512 ${CONSTRUCTING+ __DTOR_LIST__ = .;}
513 ${CONSTRUCTING+ LONG((__DTOR_END__ - __DTOR_LIST__) / 4 - 2)}
514 ${CONSTRUCTING+ *(.dtors)}
515 ${CONSTRUCTING+ LONG(0)}
516 ${CONSTRUCTING+ __DTOR_END__ = .;}
520 ensures that these linker script commands will only appear when the linker
521 is supposed to be building the constructor and destructor tables. This example
522 is written for a target which uses 4 byte pointers.
524 Embedded systems often need to set a stack address. This is normally best
527 construct with a default stack address. This permits the user to easily override
528 the stack address using the
530 option. Here is an example:
531 .Bd -literal -offset indent
532 ${RELOCATING+ PROVIDE (__stack = 0x80000000);}
534 The value of the symbol
536 would then be used in the startup code to initialize the stack pointer.
538 .Ss Pa emultempl scripts
539 Each linker target uses an
541 script to generate the emulation code. The name of the
549 variable is not set, the default is
557 .Pa emultempl/ Va template.em .
559 Most targets use the generic
562 .Pa emultempl/generic.em .
565 script is only needed if the linker must support unusual actions, such as
566 linking against shared libraries.
570 script is normally written as a simple invocation of
572 with a here document. The document will use a few variable substitutions.
573 Typically each function names uses a substitution involving
575 for ease of debugging when the linker supports multiple emulations.
577 Every function and variable in the emitted file should be static. The only
578 globally visible object must be named
579 .Li ld_ Va EMULATION_NAME_emulation ,
582 is the name of the emulation set in
584 (this is also the name of the
590 script will set the shell variable
597 .Li ld_ Va EMULATION_NAME_emulation
599 .Li struct ld_emulation_xfer_struct ,
602 It defines a set of function pointers which are invoked by the linker, as
603 well as strings for the emulation name (normally set from the shell variable
605 and the default BFD target name (normally set from the shell variable
607 which is normally set by the
613 script will set the shell variable
617 script for the default emulation. In this case, the
619 script should include the linker scripts directly, and return them from the
621 entry point. When the emulation is not the default, the
623 entry point should just return a file name. See
624 .Pa emultempl/generic.em
625 for an example of how this is done.
627 At some point, the linker emulation entry points should be documented.
629 .Sh A Walkthrough of a Typical Emulation
630 This chapter is to help people who are new to the way emulations interact
631 with the linker, or who are suddenly thrust into the position of having to
632 work with existing emulations. It will discuss the files you need to be aware
633 of. It will tell you when the given "hooks" in the emulation will be called.
634 It will, hopefully, give you enough information about when and how things
635 happen that you'll be able to get by. As always, the source is the definitive
638 The starting point for the linker is in
642 is defined. The bulk of the code that's emulation specific will initially
644 .Li emultempl/ Va emulation.em
647 when the build is done. Most of the work to select and interface with emulations
655 .Li ld_emulation_xfer_struct
656 structure your emulation exports.
658 Your emulation file exports a symbol
659 .Li ld_ Va EMULATION_NAME_emulation .
660 If your emulation is selected (it usually is, since usually there's only one),
666 also defines a number of API functions that interface to your emulation, like
667 .Li ldemul_after_parse
668 which simply calls your
669 .Li ld_ Va EMULATION_emulation.after_parse
670 function. For the rest of this section, the functions will be mentioned, but
671 you should assume the indirect reference to your emulation also.
673 We will also skip or gloss over parts of the link process that don't relate
674 to emulations, like setting up internationalization.
676 After initialization,
678 selects an emulation by pre-scanning the command line arguments. It calls
679 .Li ldemul_choose_target
680 to choose a target. If you set
683 .Li ldemul_default_target ,
690 .Li ldemul_before_parse ,
695 .Li ldemul_parse_args
696 for each arg, which must update the
698 globals if it recognizes the argument. If the emulation doesn't recognize
699 it, then parse_args checks to see if it recognizes it.
701 Now that the emulation has had access to all its command-line options,
704 .Li ldemul_set_symbols .
705 This can be used for any initialization that may be affected by options. It
706 is also supposed to set up any variables needed by the emulation script.
710 .Li ldemul_get_script
711 to get the emulation script to use (based on arguments, no doubt,see Section
713 and runs it. While parsing,
723 commands. It may call
724 .Li ldemul_unrecognized_file
725 if you asked the linker to link a file it doesn't recognize. It will call
726 .Li ldemul_recognized_file
727 for each file it does recognize, in case the emulation wants to handle some
728 files specially. All the while, it's loading the files (possibly calling
729 .Li ldemul_open_dynamic_archive )
730 and symbols and stuff. After it's done reading the script,
733 .Li ldemul_after_parse .
734 Use the after-parse hook to set up anything that depends on stuff the script
735 might have set up, like the entry point.
742 This appears to be the main core of the linking itself, as far as emulation
743 hooks are concerned(*). It first opens the output file's BFD, calling
744 .Li ldemul_set_output_arch ,
746 .Li ldemul_create_output_section_statements
747 in case you need to use other means to find or create object files (i.e. shared
748 libraries found on a path, or fake stub objects). Despite the name, nobody
749 creates output sections here.
751 (*) In most cases, the BFD library does the bulk of the actual linking, handling
752 symbol tables, symbol resolution, relocations, and building the final output
753 file. See the BFD reference for all the details. Your emulation is usually
754 concerned more with managing things at the file and section level, like "put
755 this here, add this section", etc.
757 Next, the objects to be linked are opened and BFDs created for them, and
758 .Li ldemul_after_open
759 is called. At this point, you have all the objects and symbols loaded, but
760 none of the data has been placed yet.
762 Next comes the Big Linking Thingy (except for the parts BFD does). All input
763 sections are mapped to output sections according to the script. If a section
764 doesn't get mapped by default,
765 .Li ldemul_place_orphan
766 will get called to figure out where it goes. Next it figures out the offsets
767 for each section, calling
768 .Li ldemul_before_allocation
770 .Li ldemul_after_allocation
771 after deciding where each input section ends up in the output sections.
775 is to figure out all the symbols' values. After assigning final values to
778 is called, and after that, any undefined symbols are turned into fatal errors.
787 calls BFD's final_link, which does all the relocation fixups and writes the
788 output bfd to disk, and we're done.
798 .Pa emultempl/ Va EMULATION.em
801 .Li ldemul_choose_target
805 .Li ldemul_before_parse
808 .Li ldemul_parse_args
811 .Li ldemul_set_symbols
813 .Li ldemul_get_script
825 .Li ldemul_open_dynamic_archive
829 .Li ldemul_after_parse
840 .Li ldemul_set_output_arch
842 .Li ldemul_create_output_section_statements
844 read objects, create input bfds - all symbols exist, but have no values
847 .Li ldemul_unrecognized_file
850 .Li ldemul_recognized_file
852 .Li ldemul_after_open
854 map input sections to output sections
857 .Li ldemul_place_orphan
858 for remaining sections
860 .Li ldemul_before_allocation
862 gives input sections offsets into output sections, places output sections
864 .Li ldemul_after_allocation
865 - section addresses valid
867 assigns values to symbols
870 - symbol values valid
874 output bfd is written to disk
877 .Sh Some Architecture Specific Notes
878 This is the place for notes on the behavior of
880 on specific platforms. Currently, only Intel x86 is documented (and of that,
881 only the auto-import behavior for DLLs).
886 can create DLLs that operate with various runtimes available on a common x86
887 operating system. These runtimes include native (using the mingw "platform"),
890 .It auto-import from DLLs
893 With this feature on, DLL clients can import variables from DLL without any
894 concern from their side (for example, without any source code modifications).
895 Auto-import can be enabled using the
896 .Li --enable-auto-import
897 flag, or disabled via the
898 .Li --disable-auto-import
899 flag. Auto-import is disabled by default.
902 This is done completely in bounds of the PE specification (to be fair, there's
903 a minor violation of the spec at one point, but in practice auto-import works
904 on all known variants of that common x86 operating system) So, the resulting
905 DLL can be used with any other PE compiler/linker.
908 Auto-import is fully compatible with standard import method, in which variables
909 are decorated using attribute modifiers. Libraries of either type may be mixed
913 Overhead (space): 8 bytes per imported symbol, plus 20 for each reference
914 to it; Overhead (load time): negligible; Overhead (virtual/physical memory):
915 should be less than effect of DLL relocation.
920 The obvious and only way to get rid of dllimport insanity is to make client
921 access variable directly in the DLL, bypassing the extra dereference imposed
922 by ordinary DLL runtime linking. I.e., whenever client contains something
925 .Li mov dll_var,%eax,
927 address of dll_var in the command should be relocated to point into loaded
928 DLL. The aim is to make OS loader do so, and than make ld help with that.
929 Import section of PE made following way: there's a vector of structures each
930 describing imports from particular DLL. Each such structure points to two
931 other parallel vectors: one holding imported names, and one which will hold
932 address of corresponding imported name. So, the solution is de-vectorize these
933 structures, making import locations be sparse and pointing directly into code.
937 For each reference of data symbol to be imported from DLL (to set of which
938 belong symbols with name <sym>, if __imp_<sym> is found in implib), the import
939 fixup entry is generated. That entry is of type IMAGE_IMPORT_DESCRIPTOR and
940 stored in .idata$3 subsection. Each fixup entry contains pointer to symbol's
941 address within .text section (marked with __fuN_<sym> symbol, where N is integer),
942 pointer to DLL name (so, DLL name is referenced by multiple entries), and
943 pointer to symbol name thunk. Symbol name thunk is singleton vector (__nm_th_<symbol>)
944 pointing to IMAGE_IMPORT_BY_NAME structure (__nm_<symbol>) directly containing
945 imported name. Here comes that "om the edge" problem mentioned above: PE specification
946 rambles that name vector (OriginalFirstThunk) should run in parallel with
947 addresses vector (FirstThunk), i.e. that they should have same number of elements
948 and terminated with zero. We violate this, since FirstThunk points directly
949 into machine code. But in practice, OS loader implemented the sane way: it
950 goes thru OriginalFirstThunk and puts addresses to FirstThunk, not something
951 else. It once again should be noted that dll and symbol name structures are
952 reused across fixup entries and should be there anyway to support standard
953 import stuff, so sustained overhead is 20 bytes per reference. Other question
954 is whether having several IMAGE_IMPORT_DESCRIPTORS for the same DLL is possible.
955 Answer is yes, it is done even by native compiler/linker (libth32's functions
956 are in fact resident in windows9x kernel32.dll, so if you use it, you have
957 two IMAGE_IMPORT_DESCRIPTORS for kernel32.dll). Yet other question is whether
958 referencing the same PE structures several times is valid. The answer is why
959 not, prohibiting that (detecting violation) would require more work on behalf
960 of loader than not doing it.
963 .Sh GNU Free Documentation License
964 GNU Free Documentation License Version 1.1, March 2000
966 Copyright (C) 2000 Free Software Foundation, Inc. 51 Franklin Street, Fifth
967 Floor, Boston, MA 02110-1301 USA Everyone is permitted to copy and distribute
968 verbatim copies of this license document, but changing it is not allowed.
972 The purpose of this License is to make a manual, textbook, or other written
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974 freedom to copy and redistribute it, with or without modifying it, either
975 commercially or noncommercially. Secondarily, this License preserves for the
976 author and publisher a way to get credit for their work, while not being considered
977 responsible for modifications made by others.
979 This License is a kind of "copyleft", which means that derivative works of
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984 We have designed this License in order to use it for manuals for free software,
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1121 If there is no section entitled "History" in the Document, create one stating
1122 the title, year, authors, and publisher of the Document as given on its Title
1123 Page, then add an item describing the Modified Version as stated in the previous
1124 sentence. J. Preserve the network location, if any, given in the Document
1125 for public access to a Transparent copy of the Document, and likewise the
1126 network locations given in the Document for previous versions it was based
1127 on. These may be placed in the "History" section. You may omit a network location
1128 for a work that was published at least four years before the Document itself,
1129 or if the original publisher of the version it refers to gives permission.
1130 K. In any section entitled "Acknowledgements" or "Dedications", preserve the
1131 section's title, and preserve in the section all the substance and tone of
1132 each of the contributor acknowledgements and/or dedications given therein.
1133 L. Preserve all the Invariant Sections of the Document, unaltered in their
1134 text and in their titles. Section numbers or the equivalent are not considered
1135 part of the section titles. M. Delete any section entitled "Endorsements".
1136 Such a section may not be included in the Modified Version. N. Do not retitle
1137 any existing section as "Endorsements" or to conflict in title with any Invariant
1140 If the Modified Version includes new front-matter sections or appendices that
1141 qualify as Secondary Sections and contain no material copied from the Document,
1142 you may at your option designate some or all of these sections as invariant.
1143 To do this, add their titles to the list of Invariant Sections in the Modified
1144 Version's license notice. These titles must be distinct from any other section
1147 You may add a section entitled "Endorsements", provided it contains nothing
1148 but endorsements of your Modified Version by various parties--for example,
1149 statements of peer review or that the text has been approved by an organization
1150 as the authoritative definition of a standard.
1152 You may add a passage of up to five words as a Front-Cover Text, and a passage
1153 of up to 25 words as a Back-Cover Text, to the end of the list of Cover Texts
1154 in the Modified Version. Only one passage of Front-Cover Text and one of Back-Cover
1155 Text may be added by (or through arrangements made by) any one entity. If
1156 the Document already includes a cover text for the same cover, previously
1157 added by you or by arrangement made by the same entity you are acting on behalf
1158 of, you may not add another; but you may replace the old one, on explicit
1159 permission from the previous publisher that added the old one.
1161 The author(s) and publisher(s) of the Document do not by this License give
1162 permission to use their names for publicity for or to assert or imply endorsement
1163 of any Modified Version.
1165 5. COMBINING DOCUMENTS
1167 You may combine the Document with other documents released under this License,
1168 under the terms defined in section 4 above for modified versions, provided
1169 that you include in the combination all of the Invariant Sections of all of
1170 the original documents, unmodified, and list them all as Invariant Sections
1171 of your combined work in its license notice.
1173 The combined work need only contain one copy of this License, and multiple
1174 identical Invariant Sections may be replaced with a single copy. If there
1175 are multiple Invariant Sections with the same name but different contents,
1176 make the title of each such section unique by adding at the end of it, in
1177 parentheses, the name of the original author or publisher of that section
1178 if known, or else a unique number. Make the same adjustment to the section
1179 titles in the list of Invariant Sections in the license notice of the combined
1182 In the combination, you must combine any sections entitled "History" in the
1183 various original documents, forming one section entitled "History"; likewise
1184 combine any sections entitled "Acknowledgements", and any sections entitled
1185 "Dedications". You must delete all sections entitled "Endorsements."
1187 6. COLLECTIONS OF DOCUMENTS
1189 You may make a collection consisting of the Document and other documents released
1190 under this License, and replace the individual copies of this License in the
1191 various documents with a single copy that is included in the collection, provided
1192 that you follow the rules of this License for verbatim copying of each of
1193 the documents in all other respects.
1195 You may extract a single document from such a collection, and distribute it
1196 individually under this License, provided you insert a copy of this License
1197 into the extracted document, and follow this License in all other respects
1198 regarding verbatim copying of that document.
1200 7. AGGREGATION WITH INDEPENDENT WORKS
1202 A compilation of the Document or its derivatives with other separate and independent
1203 documents or works, in or on a volume of a storage or distribution medium,
1204 does not as a whole count as a Modified Version of the Document, provided
1205 no compilation copyright is claimed for the compilation. Such a compilation
1206 is called an "aggregate", and this License does not apply to the other self-contained
1207 works thus compiled with the Document, on account of their being thus compiled,
1208 if they are not themselves derivative works of the Document.
1210 If the Cover Text requirement of section 3 is applicable to these copies of
1211 the Document, then if the Document is less than one quarter of the entire
1212 aggregate, the Document's Cover Texts may be placed on covers that surround
1213 only the Document within the aggregate. Otherwise they must appear on covers
1214 around the whole aggregate.
1218 Translation is considered a kind of modification, so you may distribute translations
1219 of the Document under the terms of section 4. Replacing Invariant Sections
1220 with translations requires special permission from their copyright holders,
1221 but you may include translations of some or all Invariant Sections in addition
1222 to the original versions of these Invariant Sections. You may include a translation
1223 of this License provided that you also include the original English version
1224 of this License. In case of a disagreement between the translation and the
1225 original English version of this License, the original English version will
1230 You may not copy, modify, sublicense, or distribute the Document except as
1231 expressly provided for under this License. Any other attempt to copy, modify,
1232 sublicense or distribute the Document is void, and will automatically terminate
1233 your rights under this License. However, parties who have received copies,
1234 or rights, from you under this License will not have their licenses terminated
1235 so long as such parties remain in full compliance.
1237 10. FUTURE REVISIONS OF THIS LICENSE
1239 The Free Software Foundation may publish new, revised versions of the GNU
1240 Free Documentation License from time to time. Such new versions will be similar
1241 in spirit to the present version, but may differ in detail to address new
1242 problems or concerns. See http://www.gnu.org/copyleft/.
1244 Each version of the License is given a distinguishing version number. If the
1245 Document specifies that a particular numbered version of this License "or
1246 any later version" applies to it, you have the option of following the terms
1247 and conditions either of that specified version or of any later version that
1248 has been published (not as a draft) by the Free Software Foundation. If the
1249 Document does not specify a version number of this License, you may choose
1250 any version ever published (not as a draft) by the Free Software Foundation.
1252 ADDENDUM: How to use this License for your documents
1254 To use this License in a document you have written, include a copy of the
1255 License in the document and put the following copyright and license notices
1256 just after the title page:
1258 .Bd -literal -offset indent
1259 Copyright (c) YEAR YOUR NAME.
1260 Permission is granted to copy, distribute and/or modify this document
1261 under the terms of the GNU Free Documentation License, Version 1.1
1262 or any later version published by the Free Software Foundation;
1263 with the Invariant Sections being LIST THEIR TITLES, with the
1264 Front-Cover Texts being LIST, and with the Back-Cover Texts being LIST.
1265 A copy of the license is included in the section entitled "GNU
1266 Free Documentation License".
1269 If you have no Invariant Sections, write "with no Invariant Sections" instead
1270 of saying which ones are invariant. If you have no Front-Cover Texts, write
1271 "no Front-Cover Texts" instead of "Front-Cover Texts being LIST"; likewise
1272 for Back-Cover Texts.
1274 If your document contains nontrivial examples of program code, we recommend
1275 releasing these examples in parallel under your choice of free software license,
1276 such as the GNU General Public License, to permit their use in free software.
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