1 <!doctype linuxdoc system> <!-- -*- text-mode -*- -->
4 <title>ld65 Users Guide
5 <author><url url="mailto:uz@cc65.org" name="Ullrich von Bassewitz">
8 The ld65 linker combines object files into an executable file. ld65 is highly
9 configurable and uses configuration files for high flexibility.
12 <!-- Table of contents -->
15 <!-- Begin the document -->
19 The ld65 linker combines several object modules created by the ca65
20 assembler, producing an executable file. The object modules may be read
21 from a library created by the ar65 archiver (this is somewhat faster and
22 more convenient). The linker was designed to be as flexible as possible.
23 It complements the features that are built into the ca65 macroassembler:
27 <item> Accept any number of segments to form an executable module.
29 <item> Resolve arbitrary expressions stored in the object files.
31 <item> In case of errors, use the meta information stored in the object files
32 to produce helpful error messages. In case of undefined symbols,
33 expression range errors, or symbol type mismatches, ld65 is able to
34 tell you the exact location in the original assembler source, where
35 the symbol was referenced.
37 <item> Flexible output. The output of ld65 is highly configurable by a config
38 file. Some more-common platforms are supported by default configurations
39 that may be activated by naming the target system. The output
40 generation was designed with different output formats in mind, so
41 adding other formats shouldn't be a great problem.
49 <sect1>Command-line option overview<p>
51 The linker is called as follows:
54 ---------------------------------------------------------------------------
55 Usage: ld65 [options] module ...
57 -( Start a library group
58 -) End a library group
59 -C name Use linker config file
60 -D sym=val Define a symbol
61 -L path Specify a library search path
62 -Ln name Create a VICE label file
63 -S addr Set the default start address
64 -V Print the linker version
66 -m name Create a map file
67 -o name Name the default output file
68 -t sys Set the target system
69 -u sym Force an import of symbol `sym'
74 --cfg-path path Specify a config file search path
75 --config name Use linker config file
76 --dbgfile name Generate debug information
77 --define sym=val Define a symbol
78 --end-group End a library group
79 --force-import sym Force an import of symbol `sym'
80 --help Help (this text)
81 --lib file Link this library
82 --lib-path path Specify a library search path
83 --mapfile name Create a map file
84 --module-id id Specify a module id
85 --obj file Link this object file
86 --obj-path path Specify an object file search path
87 --start-addr addr Set the default start address
88 --start-group Start a library group
89 --target sys Set the target system
90 --version Print the linker version
91 ---------------------------------------------------------------------------
95 <sect1>Command-line options in detail<p>
97 Here is a description of all of the command-line options:
101 <label id="option--start-group">
102 <tag><tt>-(, --start-group</tt></tag>
104 Start a library group. The libraries specified within a group are searched
105 multiple times to resolve crossreferences within the libraries. Normally,
106 crossreferences are resolved only within a library, that is the library is
107 searched multiple times. Libraries specified later on the command line
108 cannot reference otherwise unreferenced symbols in libraries specified
109 earlier, because the linker has already handled them. Library groups are
110 a solution for this problem, because the linker will search repeatedly
111 through all libraries specified in the group, until all possible open
112 symbol references have been satisfied.
115 <tag><tt>-), --end-group</tt></tag>
117 End a library group. See the explanation of the <tt><ref
118 id="option--start-group" name="--start-group"></tt> option.
121 <tag><tt>-h, --help</tt></tag>
123 Print the short option summary shown above.
126 <label id="option-m">
127 <tag><tt>-m name, --mapfile name</tt></tag>
129 This option (which needs an argument that will used as a filename for
130 the generated map file) will cause the linker to generate a map file.
131 The map file does contain a detailed overview over the modules used, the
132 sizes for the different segments, and a table containing exported
136 <label id="option-o">
137 <tag><tt>-o name</tt></tag>
139 The -o switch is used to give the name of the default output file.
140 Depending on your output configuration, this name <em/might not/ be used as the
141 name for the output file. However, for the default configurations, this
142 name is used for the output file name.
145 <label id="option-t">
146 <tag><tt>-t sys, --target sys</tt></tag>
148 The argument for the -t switch is the name of the target system. Since this
149 switch will activate a default configuration, it may not be used together
150 with the <tt><ref id="option-C" name="-C"></tt> option. The following target
151 systems are currently supported:
162 <item>c16 (works also for the c116 with memory up to 32K)
165 <item>cbm510 (CBM-II series with 40-column video)
166 <item>cbm610 (all CBM series-II computers with 80-column video)
172 <item>pet (all CBM PET systems except the 2001)
180 There are a few more targets defined but neither of them is actually
184 <tag><tt>-u sym[:addrsize], --force-import sym[:addrsize]</tt></tag>
186 Force an import of a symbol. While object files are always linked to the
187 output file, regardless if there are any references, object modules from
188 libraries get only linked in if an import can be satisfied by this module.
189 The <tt/--force-import/ option may be used to add a reference to a symbol and
190 as a result force linkage of the module that exports the identifier.
192 The name of the symbol may optionally be followed by a colon and an address-size
193 specifier. If no address size is specified, the default address size
194 for the target machine is used.
196 Please note that the symbol name needs to have the internal representation,
197 meaning you have to prepend an underscore for C identifiers.
200 <label id="option-v">
201 <tag><tt>-v, --verbose</tt></tag>
203 Using the -v option, you may enable more output that may help you to
204 locate problems. If an undefined symbol is encountered, -v causes the
205 linker to print a detailed list of the references (that is, source file
206 and line) for this symbol.
209 <tag><tt>-vm</tt></tag>
211 Must be used in conjunction with <tt><ref id="option-m" name="-m"></tt>
212 (generate map file). Normally the map file will not include empty segments
213 and sections, or unreferenced symbols. Using this option, you can force the
214 linker to include all that information into the map file. Also, it will
215 include a second <tt/Exports/ list. The first list is sorted by name;
216 the second one is sorted by value.
219 <label id="option-C">
220 <tag><tt>-C</tt></tag>
222 This gives the name of an output config file to use. See section 4 for more
223 information about config files. -C may not be used together with <tt><ref
224 id="option-t" name="-t"></tt>.
227 <label id="option-D">
228 <tag><tt>-D sym=value, --define sym=value</tt></tag>
230 This option allows to define an external symbol on the command line. Value
231 may start with a '$' sign or with <tt/0x/ for hexadecimal values,
232 otherwise a leading zero denotes octal values. See also <ref
233 id="SYMBOLS" name="the SYMBOLS section"> in the configuration file.
236 <label id="option--lib-path">
237 <tag><tt>-L path, --lib-path path</tt></tag>
239 Specify a library search path. This option may be used more than once. It
240 adds a directory to the search path for library files. Libraries specified
241 without a path are searched in the current directory, in the list of
242 directories specified using <tt/--lib-path/, in directories given by
243 environment variables, and in a built-in default directory.
246 <tag><tt>-Ln</tt></tag>
248 This option allows you to create a file that contains all global labels and
249 may be loaded into the VICE emulator using the <tt/ll/ (load label) command
250 or into the Oricutron emulator using the <tt/sl/ (symbols load) command. You
251 may use this to debug your code with VICE. Note: Older versions had some
252 bugs in the label code. If you have problems, please get the latest <url
253 url="http://vice-emu.sourceforge.net" name="VICE"> version.
256 <label id="option-S">
257 <tag><tt>-S addr, --start-addr addr</tt></tag>
259 Using -S you may define the default starting address. If and how this
260 address is used depends on the config file in use. For the default
261 configurations, only the "none", "apple2" and "apple2enh" systems honor an
262 explicit start address, all other default configs provide their own.
265 <tag><tt>-V, --version</tt></tag>
267 This option prints the version number of the linker. If you send any
268 suggestions or bugfixes, please include this number.
271 <label id="option--cfg-path">
272 <tag><tt>--cfg-path path</tt></tag>
274 Specify a config file search path. This option may be used more than once.
275 It adds a directory to the search path for config files. A config file given
276 with the <tt><ref id="option-C" name="-C"></tt> option that has no path in
277 its name is searched in the current directory, in the list of directories
278 specified using <tt/--cfg-path/, in directories given by environment variables,
279 and in a built-in default directory.
282 <label id="option--dbgfile">
283 <tag><tt>--dbgfile name</tt></tag>
285 Specify an output file for debug information. Available information will be
286 written to this file. Using the <tt/-g/ option for the compiler and assembler
287 will increase the amount of information available. Please note that debug
288 information generation is currently being developed, so the format of the
289 file and its contents are subject to change without further notice.
292 <tag><tt>--lib file</tt></tag>
294 Links a library to the output. Use this command-line option instead of just
295 naming the library file, if the linker is not able to determine the file
296 type because of an unusual extension.
299 <tag><tt>--obj file</tt></tag>
301 Links an object file to the output. Use this command-line option instead
302 of just naming the object file, if the linker is not able to determine the
303 file type because of an unusual extension.
306 <label id="option--obj-path">
307 <tag><tt>--obj-path path</tt></tag>
309 Specify an object file search path. This option may be used more than once.
310 It adds a directory to the search path for object files. An object file
311 passed to the linker that has no path in its name is searched in the current
312 directory, in the list of directories specified using <tt/--obj-path/, in
313 directories given by environment variables, and in a built-in default directory.
319 <sect>Search paths<p>
321 Starting with version 2.10, there are now several search-path lists for files needed
322 by the linker: one for libraries, one for object files, and one for config
326 <sect1>Library search path<p>
328 The library search-path list contains in this order:
331 <item>The current directory.
332 <item>Any directory added with the <tt><ref id="option--lib-path"
333 name="--lib-path"></tt> option on the command line.
334 <item>The value of the environment variable <tt/LD65_LIB/ if it is defined.
335 <item>A subdirectory named <tt/lib/ of the directory defined in the environment
336 variable <tt/CC65_HOME/, if it is defined.
337 <item>An optionally compiled-in library path.
341 <sect1>Object file search path<p>
343 The object file search-path list contains in this order:
346 <item>The current directory.
347 <item>Any directory added with the <tt><ref id="option--obj-path"
348 name="--obj-path"></tt> option on the command line.
349 <item>The value of the environment variable <tt/LD65_OBJ/ if it is defined.
350 <item>A subdirectory named <tt/obj/ of the directory defined in the environment
351 variable <tt/CC65_HOME/, if it is defined.
352 <item>An optionally compiled-in directory.
356 <sect1>Config file search path<p>
358 The config file search-path list contains in this order:
361 <item>The current directory.
362 <item>Any directory added with the <tt><ref id="option--cfg-path"
363 name="--cfg-path"></tt> option on the command line.
364 <item>The value of the environment variable <tt/LD65_CFG/ if it is defined.
365 <item>A subdirectory named <tt/cfg/ of the directory defined in the environment
366 variable <tt/CC65_HOME/, if it is defined.
367 <item>An optionally compiled-in directory.
372 <sect>Detailed workings<p>
374 The linker does several things when combining object modules:
376 First, the command line is parsed from left to right. For each object file
377 encountered (object files are recognized by a magic word in the header, so
378 the linker does not care about the name), imported and exported
379 identifiers are read from the file and inserted in a table. If a library
380 name is given (libraries are also recognized by a magic word, there are no
381 special naming conventions), all modules in the library are checked if an
382 export from this module would satisfy an import from other modules. All
383 modules where this is the case are marked. If duplicate identifiers are
384 found, the linker issues warnings.
386 That procedure (parsing and reading from left to right) does mean that a
387 library may only satisfy references for object modules (given directly or from
388 a library) named <em/before/ that library. With the command line
391 ld65 crt0.o clib.lib test.o
394 the module <tt/test.o/ must not contain references to modules in the library
395 <tt/clib.lib/. But, if it does, you have to change the order of the modules
399 ld65 crt0.o test.o clib.lib
402 Step two is, to read the configuration file, and assign start addresses
403 for the segments and define any linker symbols (see <ref id="config-files"
404 name="Configuration files">).
406 After that, the linker is ready to produce an output file. Before doing that,
407 it checks its data for consistency. That is, it checks for unresolved
408 externals (if the output format is not relocatable) and for symbol type
409 mismatches (for example a zero-page symbol is imported by a module as an absolute
412 Step four is, to write the actual target files. In this step, the linker will
413 resolve any expressions contained in the segment data. Circular references are
414 also detected in this step (a symbol may have a circular reference that goes
415 unnoticed if the symbol is not used).
417 Step five is to output a map file with a detailed list of all modules,
418 segments and symbols encountered.
420 And, last step, if you give the <tt><ref id="option-v" name="-v"></tt> switch
421 twice, you get a dump of the segment data. However, this may be quite
422 unreadable if you're not a developer. :-)
426 <sect>Configuration files<label id="config-files"><p>
428 Configuration files are used to describe the layout of the output file(s). Two
429 major topics are covered in a config file: The memory layout of the target
430 architecture, and the assignment of segments to memory areas. In addition,
431 several other attributes may be specified.
433 Case is ignored for keywords, that is, section or attribute names, but it is
434 <em/not/ ignored for names and strings.
438 <sect1>Memory areas<p>
440 Memory areas are specified in a <tt/MEMORY/ section. Let's have a look at an
441 example (this one describes the usable memory layout of the C64):
445 RAM1: start = $0800, size = $9800;
446 ROM1: start = $A000, size = $2000;
447 RAM2: start = $C000, size = $1000;
448 ROM2: start = $E000, size = $2000;
452 As you can see, there are two RAM areas and two ROM areas. The names
453 (before the colon) are arbitrary names that must start with a letter, with
454 the remaining characters being letters or digits. The names of the memory
455 areas are used when assigning segments. As mentioned above, case is
456 significant for those names.
458 The syntax above is used in all sections of the config file. The name
459 (<tt/ROM1/ etc.) is said to be an identifier, the remaining tokens up to the
460 semicolon specify attributes for this identifier. You may use the equal sign
461 to assign values to attributes, and you may use a comma to separate
462 attributes, you may also leave both out. But you <em/must/ use a semicolon to
463 mark the end of the attributes for one identifier. The section above may also
464 have looked like this:
467 # Start of memory section
485 There are of course more attributes for a memory section than just start and
486 size. Start and size are mandatory attributes, that means, each memory area
487 defined <em/must/ have these attributes given (the linker will check that). I
488 will cover other attributes later. As you may have noticed, I've used a
489 comment in the example above. Comments start with a hash mark (`#'), the
490 remainder of the line is ignored if this character is found.
495 Let's assume you have written a program for your trusty old C64, and you would
496 like to run it. For testing purposes, it should run in the <tt/RAM/ area. So
497 we will start to assign segments to memory sections in the <tt/SEGMENTS/
502 CODE: load = RAM1, type = ro;
503 RODATA: load = RAM1, type = ro;
504 DATA: load = RAM1, type = rw;
505 BSS: load = RAM1, type = bss, define = yes;
509 What we are doing here is telling the linker, that all segments go into the
510 <tt/RAM1/ memory area in the order specified in the <tt/SEGMENTS/ section. So
511 the linker will first write the <tt/CODE/ segment, then the <tt/RODATA/
512 segment, then the <tt/DATA/ segment - but it will not write the <tt/BSS/
513 segment. Why? Here enters the segment type: For each segment specified, you may also
514 specify a segment attribute. There are five possible segment attributes:
519 bss means that this is an uninitialized segment
520 zp a zeropage segment
521 overwrite a segment that overwrites (parts of) another one
525 So, because we specified that the segment with the name BSS is of type bss,
526 the linker knows that this is uninitialized data, and will not write it to an
527 output file. This is an important point: For the assembler, the <tt/BSS/
528 segment has no special meaning. You specify, which segments have the bss
529 attribute when linking. This approach is much more flexible than having one
530 fixed bss segment, and is a result of the design decision to supporting an
531 arbitrary segment count.
533 If you specify "<tt/type = bss/" for a segment, the linker will make sure that
534 this segment does only contain uninitialized data (that is, zeroes), and issue
535 a warning if this is not the case.
537 For a <tt/bss/ type segment to be useful, it must be cleared somehow by your
538 program (this happens usually in the startup code - for example the startup
539 code for cc65-generated programs takes care about that). But how does your
540 code know, where the segment starts, and how big it is? The linker is able to
541 give that information, but you must request it. This is, what we're doing with
542 the "<tt/define = yes/" attribute in the <tt/BSS/ definitions. For each
543 segment, where this attribute is true, the linker will export three symbols.
546 __NAME_LOAD__ This is set to the address where the
548 __NAME_RUN__ This is set to the run address of the
549 segment. We will cover run addresses
551 __NAME_SIZE__ This is set to the segment size.
554 Replace <tt/NAME/ by the name of the segment, in the example above, this would
555 be <tt/BSS/. These symbols may be accessed by your code.
557 Now, as we've configured the linker to write the first three segments and
558 create symbols for the last one, there's only one question left: Where does
559 the linker put the data? It would be very convenient to have the data in a
562 <sect1>Output files<p>
564 We don't have any files specified above, and indeed, this is not needed in a
565 simple configuration like the one above. There is an additional attribute
566 "file" that may be specified for a memory area, that gives a file name to
567 write the area data into. If there is no file name given, the linker will
568 assign the default file name. This is "a.out" or the one given with the
569 <tt><ref id="option-o" name="-o"></tt> option on the command line. Since the
570 default behaviour is OK for our purposes, I did not use the attribute in the
571 example above. Let's have a look at it now.
573 The "file" attribute (the keyword may also be written as "FILE" if you like
574 that better) takes a string enclosed in double quotes (`&dquot;') that specifies the
575 file, where the data is written. You may specify the same file several times,
576 in that case the data for all memory areas having this file name is written
577 into this file, in the order of the memory areas defined in the <tt/MEMORY/
578 section. Let's specify some file names in the <tt/MEMORY/ section used above:
582 RAM1: start = $0800, size = $9800, file = %O;
583 ROM1: start = $A000, size = $2000, file = "rom1.bin";
584 RAM2: start = $C000, size = $1000, file = %O;
585 ROM2: start = $E000, size = $2000, file = "rom2.bin";
589 The <tt/%O/ used here is a way to specify the default behaviour explicitly:
590 <tt/%O/ is replaced by a string (including the quotes) that contains the
591 default output name, that is, "a.out" or the name specified with the <tt><ref
592 id="option-o" name="-o"></tt> option on the command line. Into this file, the
593 linker will first write any segments that go into <tt/RAM1/, and will append
594 then the segments for <tt/RAM2/, because the memory areas are given in this
595 order. So, for the RAM areas, nothing has really changed.
597 We've not used the ROM areas, but we will do that below, so we give the file
598 names here. Segments that go into <tt/ROM1/ will be written to a file named
599 "rom1.bin", and segments that go into <tt/ROM2/ will be written to a file
600 named "rom2.bin". The name given on the command line is ignored in both cases.
602 Assigning an empty file name for a memory area will discard the data written
603 to it. This is useful, if the memory area has segments assigned that are empty
604 (for example because they are of type bss). In that case, the linker will
605 create an empty output file. This may be suppressed by assigning an empty file
606 name to that memory area.
608 The <tt/%O/ sequence is also allowed inside a string. So using
612 ROM1: start = $A000, size = $2000, file = "%O-1.bin";
613 ROM2: start = $E000, size = $2000, file = "%O-2.bin";
617 would write two files that start with the name of the output file specified on
618 the command line, with "-1.bin" and "-2.bin" appended respectively. Because
619 '%' is used as an escape char, the sequence "%%" has to be used if a single
620 percent sign is required.
622 <sect1>OVERWRITE segments<p>
624 There are situations when you may wish to overwrite some part (or parts) of a
625 segment with another one. Perhaps you are modifying an OS ROM that has its
626 public subroutines at fixed, well-known addresses, and you want to prevent them
627 from shifting to other locations in memory if your changed code takes less
628 space. Or you are updating a block of code available in binary-only form with
629 fixes that are scattered in various places. Generally, whenever you want to
630 minimize disturbance to an existing code brought on by your updates, OVERWRITE
631 segments are worth considering.
637 RAM: file = "", start = $6000, size = $2000, type=rw;
638 ROM: file = %O, start = $8000, size = $8000, type=ro;
642 Nothing unusual so far, just two memory blocks - one RAM, one ROM. Now let's
643 look at the segment configuration:
647 RAM: load = RAM, type = bss;
648 ORIGINAL: load = ROM, type = ro;
649 FASTCOPY: load = ROM, start=$9000, type = overwrite;
650 JMPPATCH1: load = ROM, start=$f7e8, type = overwrite;
651 DEBUG: load = ROM, start=$8000, type = overwrite;
652 VERSION: load = ROM, start=$e5b7, type = overwrite;
656 Segment named ORIGINAL contains the original code, disassembled or provided in
657 a binary form (i.e. using <tt/.INCBIN/ directive; see the <tt/ca65/ assembler
658 document). Subsequent four segments will be relocated to addresses specified
659 by their "start" attributes ("offset" can also be used) and then will overwrite
660 whatever was at these locations in the ORIGINAL segment. In the end, resulting
661 binary output file will thus contain original data with the exception of four
662 sequences starting at $9000, $f7e8, $8000 and $e5b7, which will sport code from
663 their respective segments. How long these sequences will be depends on the
664 lengths of corresponding segments - they can even overlap, so think what you're
667 Finally, note that OVERWRITE segments should be the final segments loaded to a
668 particular memory area, and that they need at least one of "start" or "offset"
669 attributes specified.
671 <sect1>LOAD and RUN addresses (ROMable code)<p>
673 Let us look now at a more complex example. Say, you've successfully tested
674 your new "Super Operating System" (SOS for short) for the C64, and you
675 will now go and replace the ROMs by your own code. When doing that, you
676 face a new problem: If the code runs in RAM, we need not to care about
677 read/write data. But now, if the code is in ROM, we must care about it.
678 Remember the default segments (you may of course specify your own):
682 RODATA read-only data
684 BSS uninitialized data, read/write
687 Since <tt/BSS/ is not initialized, we must not care about it now, but what
688 about <tt/DATA/? <tt/DATA/ contains initialized data, that is, data that was
689 explicitly assigned a value. And your program will rely on these values on
690 startup. Since there's no way to remember the contents of the data segment,
691 other than storing it into one of the ROMs, we have to put it there. But
692 unfortunately, ROM is not writable, so we have to copy it into RAM before
693 running the actual code.
695 The linker won't copy the data from ROM into RAM for you (this must be done by
696 the startup code of your program), but it has some features that will help you
699 First, you may not only specify a "<tt/load/" attribute for a segment, but
700 also a "<tt/run/" attribute. The "<tt/load/" attribute is mandatory, and, if
701 you don't specify a "<tt/run/" attribute, the linker assumes that load area
702 and run area are the same. We will use this feature for our data area:
706 CODE: load = ROM1, type = ro;
707 RODATA: load = ROM2, type = ro;
708 DATA: load = ROM2, run = RAM2, type = rw, define = yes;
709 BSS: load = RAM2, type = bss, define = yes;
713 Let's have a closer look at this <tt/SEGMENTS/ section. We specify that the
714 <tt/CODE/ segment goes into <tt/ROM1/ (the one at $A000). The readonly data
715 goes into <tt/ROM2/. Read/write data will be loaded into <tt/ROM2/ but is run
716 in <tt/RAM2/. That means that all references to labels in the <tt/DATA/
717 segment are relocated to be in <tt/RAM2/, but the segment is written to
718 <tt/ROM2/. All your startup code has to do is, to copy the data from its
719 location in <tt/ROM2/ to the final location in <tt/RAM2/.
721 So, how do you know, where the data is located? This is the second point,
722 where you get help from the linker. Remember the "<tt/define/" attribute?
723 Since we have set this attribute to true, the linker will define three
724 external symbols for the data segment that may be accessed from your code:
727 __DATA_LOAD__ This is set to the address where the segment
728 is loaded, in this case, it is an address in
730 __DATA_RUN__ This is set to the run address of the segment,
731 in this case, it is an address in RAM2.
732 __DATA_SIZE__ This is set to the segment size.
735 So, what your startup code must do, is to copy <tt/__DATA_SIZE__/ bytes from
736 <tt/__DATA_LOAD__/ to <tt/__DATA_RUN__/ before any other routines are called.
737 All references to labels in the <tt/DATA/ segment are relocated to <tt/RAM2/
738 by the linker, so things will work properly.
740 There's a library subroutine called <tt/copydata/ (in a module named
741 <tt/copydata.s/) that might be used to do actual copying. Be sure to have a
742 look at it's inner workings before using it!
745 <sect1>Other MEMORY area attributes<p>
747 There are some other attributes not covered above. Before starting the
748 reference section, I will discuss the remaining things here.
750 You may request symbols definitions also for memory areas. This may be
751 useful for things like a software stack, or an I/O area.
755 STACK: start = $C000, size = $1000, define = yes;
759 This will define some external symbols that may be used in your code:
762 __STACK_START__ This is set to the start of the memory
763 area, $C000 in this example.
764 __STACK_SIZE__ The size of the area, here $1000.
765 __STACK_LAST__ This is NOT the same as START+SIZE.
766 Instead, it is defined as the first
767 address that is not used by data. If we
768 don't define any segments for this area,
769 the value will be the same as START.
770 __STACK_FILEOFFS__ The binary offset in the output file. This
771 is not defined for relocatable output file
775 A memory section may also have a type. Valid types are
778 ro for readonly memory
779 rw for read/write memory.
782 The linker will assure, that no segment marked as read/write or bss is put
783 into a memory area that is marked as readonly.
785 Unused memory in a memory area may be filled. Use the "<tt/fill = yes/"
786 attribute to request this. The default value to fill unused space is zero. If
787 you don't like this, you may specify a byte value that is used to fill these
788 areas with the "<tt/fillval/" attribute. If there is no "<tt/fillval/"
789 attribute for the segment, the "<tt/fillval/" attribute of the memory area (or
790 its default) is used instead. This means that the value may also be used to
791 fill unfilled areas generated by the assembler's <tt/.ALIGN/ and <tt/.RES/
794 The symbol <tt/%S/ may be used to access the default start address (that is,
795 the one defined in <ref id="FEATURES" name="the FEATURES section">, or the
796 value given on the command line with the <tt><ref id="option-S" name="-S"></tt>
799 To support systems with banked memory, a special attribute named <tt/bank/ is
800 available. The attribute value is an arbitrary 32-bit integer. The assembler
801 has a builtin function named <tt/.BANK/ which may be used with an argument
802 that has a segment reference (for example a symbol). The result of this
803 function is the value of the bank attribute for the run memory area of the
807 <sect1>Other SEGMENT attributes<p>
809 Segments may be aligned to some memory boundary. Specify "<tt/align = num/" to
810 request this feature. Num must be a power of two. To align all segments on a
815 CODE: load = ROM1, type = ro, align = $100;
816 RODATA: load = ROM2, type = ro, align = $100;
817 DATA: load = ROM2, run = RAM2, type = rw, define = yes,
819 BSS: load = RAM2, type = bss, define = yes, align = $100;
823 If an alignment is requested, the linker will add enough space to the output
824 file, so that the new segment starts at an address that is dividable by the
825 given number without a remainder. All addresses are adjusted accordingly. To
826 fill the unused space, bytes of zero are used, or, if the memory area has a
827 "<tt/fillval/" attribute, that value. Alignment is always needed, if you have
828 used the <tt/.ALIGN/ command in the assembler. The alignment of a segment
829 must be equal or greater than the alignment used in the <tt/.ALIGN/ command.
830 The linker will check that, and issue a warning, if the alignment of a segment
831 is lower than the alignment requested in an <tt/.ALIGN/ command of one of the
832 modules making up this segment.
834 For a given segment you may also specify a fixed offset into a memory area or
835 a fixed start address. Use this if you want the code to run at a specific
836 address (a prominent case is the interrupt vector table which must go at
837 address $FFFA). Only one of <tt/ALIGN/ or <tt/OFFSET/ or <tt/START/ may be
838 specified. If the directive creates empty space, it will be filled with zero,
839 of with the value specified with the "<tt/fillval/" attribute if one is given.
840 The linker will warn you if it is not possible to put the code at the
841 specified offset (this may happen if other segments in this area are too
842 large). Here's an example:
846 VECTORS: load = ROM2, type = ro, start = $FFFA;
850 or (for the segment definitions from above)
854 VECTORS: load = ROM2, type = ro, offset = $1FFA;
858 The "<tt/align/", "<tt/start/" and "<tt/offset/" attributes change placement
859 of the segment in the run memory area, because this is what is usually
860 desired. If load and run memory areas are equal (which is the case if only the
861 load memory area has been specified), the attributes will also work. There is
862 also an "<tt/align_load/" attribute that may be used to align the start of the
863 segment in the load memory area, in case different load and run areas have
864 been specified. There are no special attributes to set start or offset for
865 just the load memory area.
867 A "<tt/fillval/" attribute may not only be specified for a memory area, but
868 also for a segment. The value must be an integer between 0 and 255. It is used
869 as the fill value for space reserved by the assembler's <tt/.ALIGN/ and <tt/.RES/
870 commands. It is also used as the fill value for space between sections (part of a
871 segment that comes from one object file) caused by alignment, but not for
872 space that preceeds the first section.
874 To suppress the warning, the linker issues if it encounters a segment that is
875 not found in any of the input files, use "<tt/optional=yes/" as an additional
876 segment attribute. Be careful when using this attribute, because a missing
877 segment may be a sign of a problem, and if you're suppressing the warning,
878 there is no one left to tell you about it.
880 <sect1>The FILES section<p>
882 The <tt/FILES/ section is used to support other formats than straight binary
883 (which is the default, so binary output files do not need an explicit entry
884 in the <tt/FILES/ section).
886 The <tt/FILES/ section lists output files and as only attribute the format of
887 each output file. Assigning binary format to the default output file would
896 The only other available output format is the o65 format specified by Andre
897 Fachat (see the <url url="http://www.6502.org/users/andre/o65/fileformat.html"
898 name="6502 binary relocation format specification">). It is defined like this:
906 The necessary o65 attributes are defined in a special section labeled
907 <ref id="FORMAT" name="FORMAT">.
911 <sect1>The FORMAT section<label id="FORMAT"><p>
913 The <tt/FORMAT/ section is used to describe file formats. The default (binary)
914 format has currently no attributes, so, while it may be listed in this
915 section, the attribute list is empty. The second supported format,
916 <url url="http://www.6502.org/users/andre/o65/fileformat.html" name="o65">,
917 has several attributes that may be defined here.
921 o65: os = lunix, version = 0, type = small,
922 import = LUNIXKERNEL,
929 <sect1>The FEATURES section<label id="FEATURES"><p>
931 In addition to the <tt/MEMORY/ and <tt/SEGMENTS/ sections described above, the
932 linker has features that may be enabled by an additional section labeled
936 <sect2>The CONDES feature<p>
938 <tt/CONDES/ is used to tell the linker to emit module constructor/destructor
943 CONDES: segment = RODATA,
945 label = __CONSTRUCTOR_TABLE__,
946 count = __CONSTRUCTOR_COUNT__;
950 The <tt/CONDES/ feature has several attributes:
954 <tag><tt>segment</tt></tag>
956 This attribute tells the linker into which segment the table should be
957 placed. If the segment does not exist, it is created.
960 <tag><tt>type</tt></tag>
962 Describes the type of the routines to place in the table. Type may be one of
963 the predefined types <tt/constructor/, <tt/destructor/, <tt/interruptor/, or
964 a numeric value between 0 and 6.
967 <tag><tt>label</tt></tag>
969 This specifies the label to use for the table. The label points to the start
970 of the table in memory and may be used from within user-written code.
973 <tag><tt>count</tt></tag>
975 This is an optional attribute. If specified, an additional symbol is defined
976 by the linker using the given name. The value of this symbol is the number
977 of entries (<em/not/ bytes) in the table. While this attribute is optional,
978 it is often useful to define it.
981 <tag><tt>order</tt></tag>
983 An optional attribute that takes one of the keywords <tt/increasing/ or
984 <tt/decreasing/ as an argument. Specifies the sorting order of the entries
985 within the table. The default is <tt/increasing/, which means that the
986 entries are sorted with increasing priority (the first entry has the lowest
987 priority). "Priority" is the priority specified when declaring a symbol as
988 <tt/.CONDES/ with the assembler, higher values mean higher priority. You may
989 change this behaviour by specifying <tt/decreasing/ as the argument, the
990 order of entries is reversed in this case.
992 Please note that the order of entries with equal priority is undefined.
994 <tag><tt>import</tt></tag>
996 This attribute defines a valid symbol name, that is added as an import
997 to the modules defining a constructor/destructor of the given type.
998 This can be used to force linkage of a module if this module exports the
1003 Without specifying the <tt/CONDES/ feature, the linker will not create any
1004 tables, even if there are <tt/condes/ entries in the object files.
1006 For more information see the <tt/.CONDES/ command in the <url
1007 url="ca65.html" name="ca65 manual">.
1010 <sect2>The STARTADDRESS feature<p>
1012 <tt/STARTADDRESS/ is used to set the default value for the start address,
1013 which can be referenced by the <tt/%S/ symbol. The builtin default for the
1014 linker is $200.
1018 # Default start address is $1000
1019 STARTADDRESS: default = $1000;
1023 Please note that order is important: The default start address must be defined
1024 <em/before/ the <tt/%S/ symbol is used in the config file. This does usually
1025 mean, that the <tt/FEATURES/ section has to go to the top of the config file.
1029 <sect1>The SYMBOLS section<label id="SYMBOLS"><p>
1031 The configuration file may also be used to define symbols used in the link
1032 stage or to force symbols imports. This is done in the SYMBOLS section. The
1033 symbol name is followed by a colon and symbol attributes.
1035 The following symbol attributes are supported:
1039 <tag><tt>addrsize</tt></tag>
1041 The <tt/addrsize/ attribute specifies the address size of the symbol and
1044 <item><tt/zp/, <tt/zeropage/ or <tt/direct/
1045 <item><tt/abs/, <tt/absolute/ or <tt/near/
1047 <item><tt/long/ or <tt/dword/.
1050 Without this attribute, the default address size is <tt/abs/.
1052 <tag><tt>type</tt></tag>
1054 This attribute is mandatory. Its value is one of <tt/export/, <tt/import/ or
1055 <tt/weak/. <tt/export/ means that the symbol is defined and exported from
1056 the linker config. <tt/import/ means that an import is generated for this
1057 symbol, eventually forcing a module that exports this symbol to be included
1058 in the output. <tt/weak/ is similar as <tt/export/. However, the symbol is
1059 only defined if it is not defined elsewhere.
1061 <tag><tt>value</tt></tag>
1063 This must only be given for symbols of type <tt/export/ or <tt/weak/. It
1064 defines the value of the symbol and may be an expression.
1068 The following example defines the stack size for an application, but allows
1069 the programmer to override the value by specifying <tt/--define
1070 __STACKSIZE__=xxx/ on the command line.
1074 # Define the stack size for the application
1075 __STACKSIZE__: type = weak, value = $800;
1081 <sect>Special segments<p>
1083 The builtin config files do contain segments that have a special meaning for
1084 the compiler and the libraries that come with it. If you replace the builtin
1085 config files, you will need the following information.
1089 The ONCE segment is used for initialization code run only once before
1090 execution reaches main() - provided that the program runs in RAM. You
1091 may for example add the ONCE segment to the heap in really memory
1092 constrained systems.
1096 For the LOWCODE segment, it is guaranteed that it won't be banked out, so it
1097 is reachable at any time by interrupt handlers or similar.
1101 This segment contains the startup code which initializes the C software stack
1102 and the libraries. It is placed in its own segment because it needs to be
1103 loaded at the lowest possible program address on several platforms.
1107 The ZPSAVE segment contains the original values of the zeropage locations used
1108 by the ZEROPAGE segment. It is placed in its own segment because it must not be
1115 ld65 (and all cc65 binutils) are (C) Copyright 1998-2005 Ullrich von
1116 Bassewitz. For usage of the binaries and/or sources the following
1117 conditions do apply:
1119 This software is provided 'as-is', without any expressed or implied
1120 warranty. In no event will the authors be held liable for any damages
1121 arising from the use of this software.
1123 Permission is granted to anyone to use this software for any purpose,
1124 including commercial applications, and to alter it and redistribute it
1125 freely, subject to the following restrictions:
1128 <item> The origin of this software must not be misrepresented; you must not
1129 claim that you wrote the original software. If you use this software
1130 in a product, an acknowledgment in the product documentation would be
1131 appreciated but is not required.
1132 <item> Altered source versions must be plainly marked as such, and must not
1133 be misrepresented as being the original software.
1134 <item> This notice may not be removed or altered from any source