1 <!doctype linuxdoc system>
4 <title>ld65 Users Guide
5 <author>Ullrich von Bassewitz, <htmlurl url="mailto:uz@cc65.org" name="uz@cc65.org">
6 <date>02.12.2000, 02.10.2001
9 The ld65 linker combines object files into an executable file. ld65 is highly
10 configurable and uses configuration files for high flexibility.
13 <!-- Table of contents -->
16 <!-- Begin the document -->
20 The ld65 linker combines several object modules created by the ca65
21 assembler, producing an executable file. The object modules may be read
22 from a library created by the ar65 archiver (this is somewhat faster and
23 more convenient). The linker was designed to be as flexible as possible.
24 It complements the features that are built into the ca65 macroassembler:
28 <item> Accept any number of segments to form an executable module.
30 <item> Resolve arbitrary expressions stored in the object files.
32 <item> In case of errors, use the meta information stored in the object files
33 to produce helpful error messages. In case of undefined symbols,
34 expression range errors, or symbol type mismatches, ld65 is able to
35 tell you the exact location in the original assembler source, where
36 the symbol was referenced.
38 <item> Flexible output. The output of ld65 is highly configurable by a config
39 file. More common platforms are supported by builtin configurations
40 that may be activated by naming the target system. The output
41 generation was designed with different output formats in mind, so
42 adding other formats shouldn't be a great problem.
50 <sect1>Command line option overview<p>
52 The linker is called as follows:
55 ---------------------------------------------------------------------------
56 Usage: ld65 [options] module ...
58 -C name Use linker config file
59 -L path Specify a library search path
60 -Ln name Create a VICE label file
61 -S addr Set the default start address
62 -V Print the linker version
64 -m name Create a map file
65 -o name Name the default output file
66 -t sys Set the target system
71 --cfg-path path Specify a config file search path
72 --config name Use linker config file
73 --dbgfile name Generate debug information
74 --dump-config name Dump a builtin configuration
75 --help Help (this text)
76 --lib file Link this library
77 --lib-path path Specify a library search path
78 --mapfile name Create a map file
79 --module-id id Specify a module id
80 --obj file Link this object file
81 --obj-path path Specify an object file search path
82 --start-addr addr Set the default start address
83 --target sys Set the target system
84 --version Print the linker version
85 ---------------------------------------------------------------------------
89 <sect1>Command line options in detail<p>
91 Here is a description of all the command line options:
95 <label id="option--start-group">
96 <tag><tt>-(, --start-group</tt></tag>
98 Start a library group. The libraries specified within a group are searched
99 multiple times to resolve crossreferences within the libraries. Normally,
100 crossreferences are only resolved within a library, that is the library is
101 searched multiple times. Libraries specified later on the command line
102 cannot reference otherwise unreferenced symbols in libraries specified
103 earlier, because the linker has already handled them. Library groups are
104 a solution for this problem, because the linker will search repeatedly
105 through all libraries specified in the group, until all possible open
106 symbol references have been satisfied.
109 <tag><tt>-), --end-group</tt></tag>
111 End a library group. See the explanation of the <tt><ref
112 id="option--start-group" name="--start-group"></tt> option.
115 <tag><tt>-h, --help</tt></tag>
117 Print the short option summary shown above.
120 <label id="option-m">
121 <tag><tt>-m name, --mapfile name</tt></tag>
123 This option (which needs an argument that will used as a filename for
124 the generated map file) will cause the linker to generate a map file.
125 The map file does contain a detailed overview over the modules used, the
126 sizes for the different segments, and a table containing exported
130 <label id="option-o">
131 <tag><tt>-o name</tt></tag>
133 The -o switch is used to give the name of the default output file.
134 Depending on your output configuration, this name may NOT be used as
135 name for the output file. However, for the builtin configurations, this
136 name is used for the output file name.
139 <label id="option-t">
140 <tag><tt>-t sys, --target sys</tt></tag>
142 The argument for the -t switch is the name of the target system. Since this
143 switch will activate a builtin configuration, it may not be used together
144 with the <tt><ref id="option-C" name="-C"></tt> option. The following target
145 systems are currently supported:
152 <item>c16 (works also for the c116 with memory up to 32K)
156 <item>cbm510 (CBM-II series with 40 column video)
157 <item>cbm610 (all CBM series-II computers with 80 column video)
158 <item>pet (all CBM PET systems except the 2001)
165 There are a few more targets defined but neither of them is actually
169 <label id="option-v">
170 <tag><tt>-v, --verbose</tt></tag>
172 Using the -v option, you may enable more output that may help you to
173 locate problems. If an undefined symbol is encountered, -v causes the
174 linker to print a detailed list of the references (that is, source file
175 and line) for this symbol.
178 <tag><tt>-vm</tt></tag>
180 Must be used in conjunction with <tt><ref id="option-m" name="-m"></tt>
181 (generate map file). Normally the map file will not include empty segments
182 and sections, or unreferenced symbols. Using this option, you can force the
183 linker to include all this information into the map file.
186 <label id="option-C">
187 <tag><tt>-C</tt></tag>
189 This gives the name of an output config file to use. See section 4 for more
190 information about config files. -C may not be used together with <tt><ref
191 id="option-t" name="-t"></tt>.
194 <label id="option--lib-path">
195 <tag><tt>-L path, --lib-path path</tt></tag>
197 Specify a library search path. This option may be used more than once. It
198 adds a directory to the search path for library files. Libraries specified
199 without a path are searched in current directory, in the directory given in
200 the <tt/LD65_LIB/ environment variable, and in the list of directories
201 specified using <tt/--lib-path/.
204 <tag><tt>-Ln</tt></tag>
206 This option allows you to create a file that contains all global labels and
207 may be loaded into VICE emulator using the <tt/ll/ (load label) command. You
208 may use this to debug your code with VICE. Note: Older versions had some
209 bugs in the label code. If you have problems, please get the latest VICE
213 <label id="option-S">
214 <tag><tt>-S addr, --start-addr addr</tt></tag>
216 Using -S you may define the default starting address. If and how this
217 address is used depends on the config file in use. For the builtin
218 configurations, only the "none" system honors an explicit start address,
219 all other builtin config provide their own.
222 <tag><tt>-V, --version</tt></tag>
224 This option print the version number of the linker. If you send any
225 suggestions or bugfixes, please include this number.
228 <label id="option--cfg-path">
229 <tag><tt>--cfg-path path</tt></tag>
231 Specify a config file search path. This option may be used more than once.
232 It adds a directory to the search path for config files. A config file given
233 with the <tt><ref id="option-C" name="-C"></tt> option that has no path in
234 its name is searched in the current directory, in the directory given in the
235 <tt/LD65_CFG/ environment variable, and in the list of directories specified
236 using <tt/--cfg-path/.
239 <label id="option--dbgfile">
240 <tag><tt>--dbgfile name</tt></tag>
242 Specify an output file for debug information. Available information will be
243 written to this file. Using the <tt/-g/ option for the compiler and assembler
244 will increase the amount of information available. Please note that debug
245 information generation is currently being developed, so the format of the
246 file and it's contents are subject to change without further notice.
249 <tag><tt>--lib file</tt></tag>
251 Links a library to the output. Use this command line option instead of just
252 naming the library file, if the linker is not able to determine the file
253 type because of an unusual extension.
256 <tag><tt>--obj file</tt></tag>
258 Links an object file to the output. Use this command line option instead
259 of just naming the object file, if the linker is not able to determine the
260 file type because of an unusual extension.
263 <label id="option--obj-path">
264 <tag><tt>--obj-path path</tt></tag>
266 Specify an object file search path. This option may be used more than once.
267 It adds a directory to the search path for object files. An object file
268 passed to the linker that has no path in its name is searched in current
269 directory, in the directory given in the <tt/LD65_OBJ/ environment variable,
270 and in the list of directories specified using <tt/--obj-path/.
276 <sect>Search paths<p>
278 Starting with version 2.10 there are now several search paths for files needed
279 by the linker: One for libraries, one for object files and one for config
283 <sect1>Library search path<p>
285 The library search path contains in this order:
288 <item>The current directory.
289 <item>A compiled in library path which is often <tt>/usr/lib/cc65/lib</tt> on
291 <item>The value of the environment variable <tt/LD65_LIB/ if it is defined.
292 <item>The value of the environment variable <tt/CC65_LIB/ if it is defined.
293 Please note that use of this environment variable is obsolete and may
294 get removed in future versions.
295 <item>Any directory added with the <tt><ref id="option--lib-path"
296 name="--lib-path"></tt> option on the command line.
300 <sect1>Object file search path<p>
302 The object file search path contains in this order:
305 <item>The current directory.
306 <item>A compiled in directory which is often <tt>/usr/lib/cc65/lib</tt> on
308 <item>The value of the environment variable <tt/LD65_OBJ/ if it is defined.
309 <item>The value of the environment variable <tt/CC65_LIB/ if it is defined.
310 Please note that use of this environment variable is obsolete and may
311 get removed in future versions.
312 <item>Any directory added with the <tt><ref id="option--obj-path"
313 name="--obj-path"></tt> option on the command line.
317 <sect1>Config file search path<p>
319 The config file search path contains in this order:
322 <item>The current directory.
323 <item>A compiled in directory which is often <tt>/usr/lib/cc65/lib</tt> on
325 <item>The value of the environment variable <tt/LD65_CFG/ if it is defined.
326 <item>Any directory added with the <tt><ref id="option--cfg-path"
327 name="--cfg-path"></tt> option on the command line.
332 <sect>Detailed workings<p>
334 The linker does several things when combining object modules:
336 First, the command line is parsed from left to right. For each object file
337 encountered (object files are recognized by a magic word in the header, so
338 the linker does not care about the name), imported and exported
339 identifiers are read from the file and inserted in a table. If a library
340 name is given (libraries are also recognized by a magic word, there are no
341 special naming conventions), all modules in the library are checked if an
342 export from this module would satisfy an import from other modules. All
343 modules where this is the case are marked. If duplicate identifiers are
344 found, the linker issues a warning.
346 This procedure (parsing and reading from left to right) does mean, that a
347 library may only satisfy references for object modules (given directly or from
348 a library) named <em/before/ that library. With the command line
351 ld65 crt0.o clib.lib test.o
354 the module test.o may not contain references to modules in the library
355 clib.lib. If this is the case, you have to change the order of the modules
359 ld65 crt0.o test.o clib.lib
362 Step two is, to read the configuration file, and assign start addresses
363 for the segments and define any linker symbols (see <ref id="config-files"
364 name="Configuration files">).
366 After that, the linker is ready to produce an output file. Before doing that,
367 it checks it's data for consistency. That is, it checks for unresolved
368 externals (if the output format is not relocatable) and for symbol type
369 mismatches (for example a zero page symbol is imported by a module as absolute
372 Step four is, to write the actual target files. In this step, the linker will
373 resolve any expressions contained in the segment data. Circular references are
374 also detected in this step (a symbol may have a circular reference that goes
375 unnoticed if the symbol is not used).
377 Step five is to output a map file with a detailed list of all modules,
378 segments and symbols encountered.
380 And, last step, if you give the <tt><ref id="option-v" name="-v"></tt> switch
381 twice, you get a dump of the segment data. However, this may be quite
382 unreadable if you're not a developer:-)
386 <sect>Configuration files<label id="config-files"><p>
388 Configuration files are used to describe the layout of the output file(s). Two
389 major topics are covered in a config file: The memory layout of the target
390 architecture, and the assignment of segments to memory areas. In addition,
391 several other attributes may be specified.
393 Case is ignored for keywords, that is, section or attribute names, but it is
394 <em/not/ ignored for names and strings.
398 <sect1>Memory areas<p>
400 Memory areas are specified in a <tt/MEMORY/ section. Lets have a look at an
401 example (this one describes the usable memory layout of the C64):
405 RAM1: start = $0800, size = $9800;
406 ROM1: start = $A000, size = $2000;
407 RAM2: start = $C000, size = $1000;
408 ROM2: start = $E000, size = $2000;
412 As you can see, there are two ram areas and two rom areas. The names
413 (before the colon) are arbitrary names that must start with a letter, with
414 the remaining characters being letters or digits. The names of the memory
415 areas are used when assigning segments. As mentioned above, case is
416 significant for these names.
418 The syntax above is used in all sections of the config file. The name
419 (<tt/ROM1/ etc.) is said to be an identifier, the remaining tokens up to the
420 semicolon specify attributes for this identifier. You may use the equal sign
421 to assign values to attributes, and you may use a comma to separate
422 attributes, you may also leave both out. But you <em/must/ use a semicolon to
423 mark the end of the attributes for one identifier. The section above may also
424 have looked like this:
427 # Start of memory section
445 There are of course more attributes for a memory section than just start and
446 size. Start and size are mandatory attributes, that means, each memory area
447 defined <em/must/ have these attributes given (the linker will check that). I
448 will cover other attributes later. As you may have noticed, I've used a
449 comment in the example above. Comments start with a hash mark (`#'), the
450 remainder of the line is ignored if this character is found.
455 Let's assume you have written a program for your trusty old C64, and you would
456 like to run it. For testing purposes, it should run in the <tt/RAM/ area. So
457 we will start to assign segments to memory sections in the <tt/SEGMENTS/
462 CODE: load = RAM1, type = ro;
463 RODATA: load = RAM1, type = ro;
464 DATA: load = RAM1, type = rw;
465 BSS: load = RAM1, type = bss, define = yes;
469 What we are doing here is telling the linker, that all segments go into the
470 <tt/RAM1/ memory area in the order specified in the <tt/SEGMENTS/ section. So
471 the linker will first write the <tt/CODE/ segment, then the <tt/RODATA/
472 segment, then the <tt/DATA/ segment - but it will not write the <tt/BSS/
473 segment. Why? Enter the segment type: For each segment specified, you may also
474 specify a segment attribute. There are five possible segment attributes:
478 wprot same as ro but will be marked as write protected in
479 the VICE label file if -Lp is given
481 bss means that this is an uninitialized segment
482 zp a zeropage segment
485 So, because we specified that the segment with the name BSS is of type bss,
486 the linker knows that this is uninitialized data, and will not write it to an
487 output file. This is an important point: For the assembler, the <tt/BSS/
488 segment has no special meaning. You specify, which segments have the bss
489 attribute when linking. This approach is much more flexible than having one
490 fixed bss segment, and is a result of the design decision to supporting an
491 arbitrary segment count.
493 If you specify "<tt/type = bss/" for a segment, the linker will make sure that
494 this segment does only contain uninitialized data (that is, zeroes), and issue
495 a warning if this is not the case.
497 For a <tt/bss/ type segment to be useful, it must be cleared somehow by your
498 program (this happens usually in the startup code - for example the startup
499 code for cc65 generated programs takes care about that). But how does your
500 code know, where the segment starts, and how big it is? The linker is able to
501 give that information, but you must request it. This is, what we're doing with
502 the "<tt/define = yes/" attribute in the <tt/BSS/ definitions. For each
503 segment, where this attribute is true, the linker will export three symbols.
506 __NAME_LOAD__ This is set to the address where the
508 __NAME_RUN__ This is set to the run address of the
509 segment. We will cover run addresses
511 __NAME_SIZE__ This is set to the segment size.
514 Replace <tt/NAME/ by the name of the segment, in the example above, this would
515 be <tt/BSS/. These symbols may be accessed by your code.
517 Now, as we've configured the linker to write the first three segments and
518 create symbols for the last one, there's only one question left: Where does
519 the linker put the data? It would be very convenient to have the data in a
522 <sect1>Output files<p>
524 We don't have any files specified above, and indeed, this is not needed in a
525 simple configuration like the one above. There is an additional attribute
526 "file" that may be specified for a memory area, that gives a file name to
527 write the area data into. If there is no file name given, the linker will
528 assign the default file name. This is "a.out" or the one given with the
529 <tt><ref id="option-o" name="-o"></tt> option on the command line. Since the
530 default behaviour is ok for our purposes, I did not use the attribute in the
531 example above. Let's have a look at it now.
533 The "file" attribute (the keyword may also be written as "FILE" if you like
534 that better) takes a string enclosed in double quotes (`"') that specifies the
535 file, where the data is written. You may specifiy the same file several times,
536 in that case the data for all memory areas having this file name is written
537 into this file, in the order of the memory areas defined in the <tt/MEMORY/
538 section. Let's specify some file names in the <tt/MEMORY/ section used above:
542 RAM1: start = $0800, size = $9800, file = %O;
543 ROM1: start = $A000, size = $2000, file = "rom1.bin";
544 RAM2: start = $C000, size = $1000, file = %O;
545 ROM2: start = $E000, size = $2000, file = "rom2.bin";
549 The <tt/%O/ used here is a way to specify the default behaviour explicitly:
550 <tt/%O/ is replaced by a string (including the quotes) that contains the
551 default output name, that is, "a.out" or the name specified with the <tt><ref
552 id="option-o" name="-o"></tt> option on the command line. Into this file, the
553 linker will first write any segments that go into <tt/RAM1/, and will append
554 then the segments for <tt/RAM2/, because the memory areas are given in this
555 order. So, for the RAM areas, nothing has really changed.
557 We've not used the ROM areas, but we will do that below, so we give the file
558 names here. Segments that go into <tt/ROM1/ will be written to a file named
559 "rom1.bin", and segments that go into <tt/ROM2/ will be written to a file
560 named "rom2.bin". The name given on the command line is ignored in both cases.
562 Assigning an empty file name for a memory area will discard the data written
563 to it. This is useful, if the a memory area has segments assigned that are
564 empty (for example because they are of type bss). In that case, the linker
565 will create an empty output file. This may be suppressed by assigning an empty
566 file name to that memory area.
569 <sect1>LOAD and RUN addresses (ROMable code)<p>
571 Let us look now at a more complex example. Say, you've successfully tested
572 your new "Super Operating System" (SOS for short) for the C64, and you
573 will now go and replace the ROMs by your own code. When doing that, you
574 face a new problem: If the code runs in RAM, we need not to care about
575 read/write data. But now, if the code is in ROM, we must care about it.
576 Remember the default segments (you may of course specify your own):
580 RODATA read only data
582 BSS uninitialized data, read/write
585 Since <tt/BSS/ is not initialized, we must not care about it now, but what
586 about <tt/DATA/? <tt/DATA/ contains initialized data, that is, data that was
587 explicitly assigned a value. And your program will rely on these values on
588 startup. Since there's no other way to remember the contents of the data
589 segment, than storing it into one of the ROMs, we have to put it there. But
590 unfortunately, ROM is not writeable, so we have to copy it into RAM before
591 running the actual code.
593 The linker cannot help you copying the data from ROM into RAM (this must be
594 done by the startup code of your program), but it has some features that will
595 help you in this process.
597 First, you may not only specify a "<tt/load/" attribute for a segment, but
598 also a "<tt/run/" attribute. The "<tt/load/" attribute is mandatory, and, if
599 you don't specify a "<tt/run/" attribute, the linker assumes that load area
600 and run area are the same. We will use this feature for our data area:
604 CODE: load = ROM1, type = ro;
605 RODATA: load = ROM2, type = ro;
606 DATA: load = ROM2, run = RAM2, type = rw, define = yes;
607 BSS: load = RAM2, type = bss, define = yes;
611 Let's have a closer look at this <tt/SEGMENTS/ section. We specify that the
612 <tt/CODE/ segment goes into <tt/ROM1/ (the one at $A000). The readonly data
613 goes into <tt/ROM2/. Read/write data will be loaded into <tt/ROM2/ but is run
614 in <tt/RAM2/. That means that all references to labels in the <tt/DATA/
615 segment are relocated to be in <tt/RAM2/, but the segment is written to
616 <tt/ROM2/. All your startup code has to do is, to copy the data from it's
617 location in <tt/ROM2/ to the final location in <tt/RAM2/.
619 So, how do you know, where the data is located? This is the second point,
620 where you get help from the linker. Remember the "<tt/define/" attribute?
621 Since we have set this attribute to true, the linker will define three
622 external symbols for the data segment that may be accessed from your code:
625 __DATA_LOAD__ This is set to the address where the segment
626 is loaded, in this case, it is an address in
628 __DATA_RUN__ This is set to the run address of the segment,
629 in this case, it is an address in RAM2.
630 __DATA_SIZE__ This is set to the segment size.
633 So, what your startup code must do, is to copy <tt/__DATA_SIZE__/ bytes from
634 <tt/__DATA_LOAD__/ to <tt/__DATA_RUN__/ before any other routines are called.
635 All references to labels in the <tt/DATA/ segment are relocated to <tt/RAM2/
636 by the linker, so things will work properly.
639 <sect1>Other MEMORY area attributes<p>
641 There are some other attributes not covered above. Before starting the
642 reference section, I will discuss the remaining things here.
644 You may request symbols definitions also for memory areas. This may be
645 useful for things like a software stack, or an i/o area.
649 STACK: start = $C000, size = $1000, define = yes;
653 This will define three external symbols that may be used in your code:
656 __STACK_START__ This is set to the start of the memory
657 area, $C000 in this example.
658 __STACK_SIZE__ The size of the area, here $1000.
659 __STACK_LAST__ This is NOT the same as START+SIZE.
660 Instead, it it defined as the first
661 address that is not used by data. If we
662 don't define any segments for this area,
663 the value will be the same as START.
666 A memory section may also have a type. Valid types are
669 ro for readonly memory
670 rw for read/write memory.
673 The linker will assure, that no segment marked as read/write or bss is put
674 into a memory area that is marked as readonly.
676 Unused memory in a memory area may be filled. Use the "<tt/fill = yes/"
677 attribute to request this. The default value to fill unused space is zero. If
678 you don't like this, you may specify a byte value that is used to fill these
679 areas with the "<tt/fillval/" attribute. This value is also used to fill unfilled
680 areas generated by the assemblers <tt/.ALIGN/ and <tt/.RES/ directives.
682 The symbol <tt/%S/ may be used to access the default start address (that is,
683 the one defined in the <ref id="FEATURES" name="FEATURES"> section, or the
684 value given on the command line with the <tt><ref id="option-S" name="-S"></tt>
688 <sect1>Other SEGMENT attributes<p>
690 Segments may be aligned to some memory boundary. Specify "<tt/align = num/" to
691 request this feature. Num must be a power of two. To align all segments on a
696 CODE: load = ROM1, type = ro, align = $100;
697 RODATA: load = ROM2, type = ro, align = $100;
698 DATA: load = ROM2, run = RAM2, type = rw, define = yes,
700 BSS: load = RAM2, type = bss, define = yes, align = $100;
704 If an alignment is requested, the linker will add enough space to the output
705 file, so that the new segment starts at an address that is divideable by the
706 given number without a remainder. All addresses are adjusted accordingly. To
707 fill the unused space, bytes of zero are used, or, if the memory area has a
708 "<tt/fillval/" attribute, that value. Alignment is always needed, if you have
709 the used the <tt/.ALIGN/ command in the assembler. The alignment of a segment
710 must be equal or greater than the alignment used in the <tt/.ALIGN/ command.
711 The linker will check that, and issue a warning, if the alignment of a segment
712 is lower than the alignment requested in a <tt/.ALIGN/ command of one of the
713 modules making up this segment.
715 For a given segment you may also specify a fixed offset into a memory area or
716 a fixed start address. Use this if you want the code to run at a specific
717 address (a prominent case is the interrupt vector table which must go at
718 address $FFFA). Only one of <tt/ALIGN/ or <tt/OFFSET/ or <tt/START/ may be
719 specified. If the directive creates empty space, it will be filled with zero,
720 of with the value specified with the "<tt/fillval/" attribute if one is given.
721 The linker will warn you if it is not possible to put the code at the
722 specified offset (this may happen if other segments in this area are too
723 large). Here's an example:
727 VECTORS: load = ROM2, type = ro, start = $FFFA;
731 or (for the segment definitions from above)
735 VECTORS: load = ROM2, type = ro, offset = $1FFA;
739 The "<tt/align/", "<tt/start/" and "<tt/offset/" attributes change placement
740 of the segment in the run memory area, because this is what is usually
741 desired. If load and run memory areas are equal (which is the case if only the
742 load memory area has been specified), the attributes will also work. There is
743 also a "<tt/align_load/" attribute that may be used to align the start of the
744 segment in the load memory area, in case different load and run areas have
745 been specified. There are no special attributes to set start or offset for
746 just the load memory area.
748 To suppress the warning, the linker issues if it encounters a segment that is
749 not found in any of the input files, use "<tt/optional=yes/" as additional
750 segment attribute. Be careful when using this attribute, because a missing
751 segment may be a sign of a problem, and if you're suppressing the warning,
752 there is no one left to tell you about it.
754 <sect1>The FILES section<p>
756 The <tt/FILES/ section is used to support other formats than straight binary
757 (which is the default, so binary output files do not need an explicit entry
758 in the <tt/FILES/ section).
760 The <tt/FILES/ section lists output files and as only attribute the format of
761 each output file. Assigning binary format to the default output file would
770 The only other available output format is the o65 format specified by Andre
771 Fachat. It is defined like this:
779 The necessary o65 attributes are defined in a special section labeled
784 <sect1>The FORMAT section<p>
786 The <tt/FORMAT/ section is used to describe file formats. The default (binary)
787 format has currently no attributes, so, while it may be listed in this
788 section, the attribute list is empty. The second supported format, o65, has
789 several attributes that may be defined here.
793 o65: os = lunix, version = 0, type = small,
794 import = LUNIXKERNEL,
803 <sect1>Features<label id="FEATURES"><p>
805 In addition to the <tt/MEMORY/ and <tt/SEGMENTS/ sections described above, the
806 linker has features that may be enabled by an additional section labeled
810 <sect2>The CONDES feature<p>
812 <tt/CONDES/ is used to tell the linker to emit module constructor/destructor
817 CONDES: segment = RODATA,
819 label = __CONSTRUCTOR_TABLE__,
820 count = __CONSTRUCTOR_COUNT__;
824 The <tt/CONDES/ feature has several attributes:
828 <tag><tt>segment</tt></tag>
830 This attribute tells the linker into which segment the table should be
831 placed. If the segment does not exist, it is created.
834 <tag><tt>type</tt></tag>
836 Describes the type of the routines to place in the table. Type may be one of
837 the predefined types <tt/constructor/, <tt/destructor/, <tt/interruptor/, or
838 a numeric value between 0 and 6.
841 <tag><tt>label</tt></tag>
843 This specifies the label to use for the table. The label points to the start
844 of the table in memory and may be used from within user written code.
847 <tag><tt>count</tt></tag>
849 This is an optional attribute. If specified, an additional symbol is defined
850 by the linker using the given name. The value of this symbol is the number
851 of entries (<em/not/ bytes) in the table. While this attribute is optional,
852 it is often useful to define it.
855 <tag><tt>order</tt></tag>
857 Optional attribute that takes one of the keywords <tt/increasing/ or
858 <tt/decreasing/ as an argument. Specifies the sorting order of the entries
859 within the table. The default is <tt/increasing/, which means that the
860 entries are sorted with increasing priority (the first entry has the lowest
861 priority). "Priority" is the priority specified when declaring a symbol as
862 <tt/.CONDES/ with the assembler, higher values mean higher priority. You may
863 change this behaviour by specifying <tt/decreasing/ as the argument, the
864 order of entries is reversed in this case.
866 Please note that the order of entries with equal priority is undefined.
870 Without specifying the <tt/CONDES/ feature, the linker will not create any
871 tables, even if there are <tt/condes/ entries in the object files.
873 For more information see the <tt/.CONDES/ command in the <htmlurl
874 url="ca65.html" name="ca65 manual">.
877 <sect2>The STARTADDRESS feature<p>
879 <tt/STARTADDRESS/ is used to set the default value for the start address,
880 which can be referenced by the <tt/%S/ symbol. The builtin default for the
881 linker is $200.
885 # Default start address is $1000
886 STARTADDRESS: default = $1000;
890 Please note that order is important: The default start address must be defined
891 <em/before/ the <tt/%S/ symbol is used in the config file. This does usually
892 mean, that the <tt/FEATURES/ section has to go to the top of the config file.
896 <sect1>Builtin configurations<p>
898 The builtin configurations are part of the linker source. They are also
899 distributed together with the machine specific binary packages (usually in the
900 doc directory) and don't have a special format. So if you need a special
901 configuration, it's a good idea to start with the builtin configuration for
902 your system. In a first step, just replace <tt/-t target/ by <tt/-C
903 configfile/. The go on and modify the config file to suit your needs.
907 <sect>Bugs/Feedback<p>
909 If you have problems using the linker, if you find any bugs, or if you're
910 doing something interesting with it, I would be glad to hear from you. Feel
911 free to contact me by email (<htmlurl url="mailto:uz@cc65.org"
912 name="uz@cc65.org">).
918 ld65 (and all cc65 binutils) are (C) Copyright 1998-2001 Ullrich von
919 Bassewitz. For usage of the binaries and/or sources the following
922 This software is provided 'as-is', without any expressed or implied
923 warranty. In no event will the authors be held liable for any damages
924 arising from the use of this software.
926 Permission is granted to anyone to use this software for any purpose,
927 including commercial applications, and to alter it and redistribute it
928 freely, subject to the following restrictions:
931 <item> The origin of this software must not be misrepresented; you must not
932 claim that you wrote the original software. If you use this software
933 in a product, an acknowledgment in the product documentation would be
934 appreciated but is not required.
935 <item> Altered source versions must be plainly marked as such, and must not
936 be misrepresented as being the original software.
937 <item> This notice may not be removed or altered from any source