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 --allow-multiple-definition Allow multiple definitions
75 --cfg-path path Specify a config file search path
76 --config name Use linker config file
77 --dbgfile name Generate debug information
78 --define sym=val Define a symbol
79 --end-group End a library group
80 --force-import sym Force an import of symbol 'sym'
81 --help Help (this text)
82 --lib file Link this library
83 --lib-path path Specify a library search path
84 --mapfile name Create a map file
85 --module-id id Specify a module id
86 --obj file Link this object file
87 --obj-path path Specify an object file search path
88 --start-addr addr Set the default start address
89 --start-group Start a library group
90 --target sys Set the target system
91 --version Print the linker version
92 ---------------------------------------------------------------------------
96 <sect1>Command-line options in detail<p>
98 Here is a description of all of the command-line options:
102 <tag><tt>--allow-multiple-definition</tt></tag>
104 Normally when a global symbol is defined multiple times, ld65 will
105 issue an error and not create the output file. This option lets it
106 silently ignore this fact and continue. The first definition of a
110 <label id="option--start-group">
111 <tag><tt>-(, --start-group</tt></tag>
113 Start a library group. The libraries specified within a group are searched
114 multiple times to resolve crossreferences within the libraries. Normally,
115 crossreferences are resolved only within a library, that is the library is
116 searched multiple times. Libraries specified later on the command line
117 cannot reference otherwise unreferenced symbols in libraries specified
118 earlier, because the linker has already handled them. Library groups are
119 a solution for this problem, because the linker will search repeatedly
120 through all libraries specified in the group, until all possible open
121 symbol references have been satisfied.
124 <tag><tt>-), --end-group</tt></tag>
126 End a library group. See the explanation of the <tt><ref
127 id="option--start-group" name="--start-group"></tt> option.
130 <tag><tt>-h, --help</tt></tag>
132 Print the short option summary shown above.
135 <label id="option-m">
136 <tag><tt>-m name, --mapfile name</tt></tag>
138 This option (which needs an argument that will used as a filename for
139 the generated map file) will cause the linker to generate a map file.
140 The map file does contain a detailed overview over the modules used, the
141 sizes for the different segments, and a table containing exported
145 <label id="option-o">
146 <tag><tt>-o name</tt></tag>
148 The -o switch is used to give the name of the default output file.
149 Depending on your output configuration, this name <em/might not/ be used as the
150 name for the output file. However, for the default configurations, this
151 name is used for the output file name.
154 <label id="option-t">
155 <tag><tt>-t sys, --target sys</tt></tag>
157 The argument for the -t switch is the name of the target system. Since this
158 switch will activate a default configuration, it may not be used together
159 with the <tt><ref id="option-C" name="-C"></tt> option. The following target
160 systems are currently supported:
171 <item>c16 (works also for the c116 with memory up to 32K)
174 <item>cbm510 (CBM-II series with 40-column video)
175 <item>cbm610 (all CBM series-II computers with 80-column video)
181 <item>pet (all CBM PET systems except the 2001)
190 There are a few more targets defined but neither of them is actually
194 <tag><tt>-u sym[:addrsize], --force-import sym[:addrsize]</tt></tag>
196 Force an import of a symbol. While object files are always linked to the
197 output file, regardless if there are any references, object modules from
198 libraries get only linked in if an import can be satisfied by this module.
199 The <tt/--force-import/ option may be used to add a reference to a symbol and
200 as a result force linkage of the module that exports the identifier.
202 The name of the symbol may optionally be followed by a colon and an address-size
203 specifier. If no address size is specified, the default address size
204 for the target machine is used.
206 Please note that the symbol name needs to have the internal representation,
207 meaning you have to prepend an underscore for C identifiers.
210 <label id="option-v">
211 <tag><tt>-v, --verbose</tt></tag>
213 Using the -v option, you may enable more output that may help you to
214 locate problems. If an undefined symbol is encountered, -v causes the
215 linker to print a detailed list of the references (that is, source file
216 and line) for this symbol.
219 <tag><tt>-vm</tt></tag>
221 Must be used in conjunction with <tt><ref id="option-m" name="-m"></tt>
222 (generate map file). Normally the map file will not include empty segments
223 and sections, or unreferenced symbols. Using this option, you can force the
224 linker to include all that information into the map file. Also, it will
225 include a second <tt/Exports/ list. The first list is sorted by name;
226 the second one is sorted by value.
229 <label id="option-C">
230 <tag><tt>-C</tt></tag>
232 This gives the name of an output config file to use. See section 4 for more
233 information about config files. -C may not be used together with <tt><ref
234 id="option-t" name="-t"></tt>.
237 <label id="option-D">
238 <tag><tt>-D sym=value, --define sym=value</tt></tag>
240 This option allows to define an external symbol on the command line. Value
241 may start with a '$' sign or with <tt/0x/ for hexadecimal values,
242 otherwise a leading zero denotes octal values. See also <ref
243 id="SYMBOLS" name="the SYMBOLS section"> in the configuration file.
246 <label id="option--lib-path">
247 <tag><tt>-L path, --lib-path path</tt></tag>
249 Specify a library search path. This option may be used more than once. It
250 adds a directory to the search path for library files. Libraries specified
251 without a path are searched in the current directory, in the list of
252 directories specified using <tt/--lib-path/, in directories given by
253 environment variables, and in a built-in default directory.
256 <tag><tt>-Ln</tt></tag>
258 This option allows you to create a file that contains all global labels and
259 may be loaded into the VICE emulator using the <tt/ll/ (load label) command
260 or into the Oricutron emulator using the <tt/sl/ (symbols load) command. You
261 may use this to debug your code with VICE. Note: Older versions had some
262 bugs in the label code. If you have problems, please get the latest <url
263 url="http://vice-emu.sourceforge.net" name="VICE"> version.
266 <label id="option-S">
267 <tag><tt>-S addr, --start-addr addr</tt></tag>
269 Using -S you may define the default starting address. If and how this
270 address is used depends on the config file in use. For the default
271 configurations, only the "none", "apple2" and "apple2enh" systems honor an
272 explicit start address, all other default configs provide their own.
275 <tag><tt>-V, --version</tt></tag>
277 This option prints the version number of the linker. If you send any
278 suggestions or bugfixes, please include this number.
281 <label id="option--cfg-path">
282 <tag><tt>--cfg-path path</tt></tag>
284 Specify a config file search path. This option may be used more than once.
285 It adds a directory to the search path for config files. A config file given
286 with the <tt><ref id="option-C" name="-C"></tt> option that has no path in
287 its name is searched in the current directory, in the list of directories
288 specified using <tt/--cfg-path/, in directories given by environment variables,
289 and in a built-in default directory.
292 <label id="option--dbgfile">
293 <tag><tt>--dbgfile name</tt></tag>
295 Specify an output file for debug information. Available information will be
296 written to this file. Using the <tt/-g/ option for the compiler and assembler
297 will increase the amount of information available. Please note that debug
298 information generation is currently being developed, so the format of the
299 file and its contents are subject to change without further notice.
302 <tag><tt>--lib file</tt></tag>
304 Links a library to the output. Use this command-line option instead of just
305 naming the library file, if the linker is not able to determine the file
306 type because of an unusual extension.
309 <tag><tt>--obj file</tt></tag>
311 Links an object file to the output. Use this command-line option instead
312 of just naming the object file, if the linker is not able to determine the
313 file type because of an unusual extension.
316 <label id="option--obj-path">
317 <tag><tt>--obj-path path</tt></tag>
319 Specify an object file search path. This option may be used more than once.
320 It adds a directory to the search path for object files. An object file
321 passed to the linker that has no path in its name is searched in the current
322 directory, in the list of directories specified using <tt/--obj-path/, in
323 directories given by environment variables, and in a built-in default directory.
329 <sect>Search paths<p>
331 Starting with version 2.10, there are now several search-path lists for files needed
332 by the linker: one for libraries, one for object files, and one for config
336 <sect1>Library search path<p>
338 The library search-path list contains in this order:
341 <item>The current directory.
342 <item>Any directory added with the <tt><ref id="option--lib-path"
343 name="--lib-path"></tt> option on the command line.
344 <item>The value of the environment variable <tt/LD65_LIB/ if it is defined.
345 <item>A subdirectory named <tt/lib/ of the directory defined in the environment
346 variable <tt/CC65_HOME/, if it is defined.
347 <item>An optionally compiled-in library path.
351 <sect1>Object file search path<p>
353 The object file search-path list contains in this order:
356 <item>The current directory.
357 <item>Any directory added with the <tt><ref id="option--obj-path"
358 name="--obj-path"></tt> option on the command line.
359 <item>The value of the environment variable <tt/LD65_OBJ/ if it is defined.
360 <item>A subdirectory named <tt/obj/ of the directory defined in the environment
361 variable <tt/CC65_HOME/, if it is defined.
362 <item>An optionally compiled-in directory.
366 <sect1>Config file search path<p>
368 The config file search-path list contains in this order:
371 <item>The current directory.
372 <item>Any directory added with the <tt><ref id="option--cfg-path"
373 name="--cfg-path"></tt> option on the command line.
374 <item>The value of the environment variable <tt/LD65_CFG/ if it is defined.
375 <item>A subdirectory named <tt/cfg/ of the directory defined in the environment
376 variable <tt/CC65_HOME/, if it is defined.
377 <item>An optionally compiled-in directory.
382 <sect>Detailed workings<p>
384 The linker does several things when combining object modules:
386 First, the command line is parsed from left to right. For each object file
387 encountered (object files are recognized by a magic word in the header, so
388 the linker does not care about the name), imported and exported
389 identifiers are read from the file and inserted in a table. If a library
390 name is given (libraries are also recognized by a magic word, there are no
391 special naming conventions), all modules in the library are checked if an
392 export from this module would satisfy an import from other modules. All
393 modules where this is the case are marked. If duplicate identifiers are
394 found, the linker issues warnings.
396 That procedure (parsing and reading from left to right) does mean that a
397 library may only satisfy references for object modules (given directly or from
398 a library) named <em/before/ that library. With the command line
401 ld65 crt0.o clib.lib test.o
404 the module <tt/test.o/ must not contain references to modules in the library
405 <tt/clib.lib/. But, if it does, you have to change the order of the modules
409 ld65 crt0.o test.o clib.lib
412 Step two is, to read the configuration file, and assign start addresses
413 for the segments and define any linker symbols (see <ref id="config-files"
414 name="Configuration files">).
416 After that, the linker is ready to produce an output file. Before doing that,
417 it checks its data for consistency. That is, it checks for unresolved
418 externals (if the output format is not relocatable) and for symbol type
419 mismatches (for example a zero-page symbol is imported by a module as an absolute
422 Step four is, to write the actual target files. In this step, the linker will
423 resolve any expressions contained in the segment data. Circular references are
424 also detected in this step (a symbol may have a circular reference that goes
425 unnoticed if the symbol is not used).
427 Step five is to output a map file with a detailed list of all modules,
428 segments and symbols encountered.
430 And, last step, if you give the <tt><ref id="option-v" name="-v"></tt> switch
431 twice, you get a dump of the segment data. However, this may be quite
432 unreadable if you're not a developer. :-)
436 <sect>Configuration files<label id="config-files"><p>
438 Configuration files are used to describe the layout of the output file(s). Two
439 major topics are covered in a config file: The memory layout of the target
440 architecture, and the assignment of segments to memory areas. In addition,
441 several other attributes may be specified.
443 Case is ignored for keywords, that is, section or attribute names, but it is
444 <em/not/ ignored for names and strings.
448 <sect1>Memory areas<p>
450 Memory areas are specified in a <tt/MEMORY/ section. Let's have a look at an
451 example (this one describes the usable memory layout of the C64):
455 RAM1: start = $0800, size = $9800;
456 ROM1: start = $A000, size = $2000;
457 RAM2: start = $C000, size = $1000;
458 ROM2: start = $E000, size = $2000;
462 As you can see, there are two RAM areas and two ROM areas. The names
463 (before the colon) are arbitrary names that must start with a letter, with
464 the remaining characters being letters or digits. The names of the memory
465 areas are used when assigning segments. As mentioned above, case is
466 significant for those names.
468 The syntax above is used in all sections of the config file. The name
469 (<tt/ROM1/ etc.) is said to be an identifier, the remaining tokens up to the
470 semicolon specify attributes for this identifier. You may use the equal sign
471 to assign values to attributes, and you may use a comma to separate
472 attributes, you may also leave both out. But you <em/must/ use a semicolon to
473 mark the end of the attributes for one identifier. The section above may also
474 have looked like this:
477 # Start of memory section
495 There are of course more attributes for a memory section than just start and
496 size. Start and size are mandatory attributes, that means, each memory area
497 defined <em/must/ have these attributes given (the linker will check that). I
498 will cover other attributes later. As you may have noticed, I've used a
499 comment in the example above. Comments start with a hash mark ('#'), the
500 remainder of the line is ignored if this character is found.
505 Let's assume you have written a program for your trusty old C64, and you would
506 like to run it. For testing purposes, it should run in the <tt/RAM/ area. So
507 we will start to assign segments to memory sections in the <tt/SEGMENTS/
512 CODE: load = RAM1, type = ro;
513 RODATA: load = RAM1, type = ro;
514 DATA: load = RAM1, type = rw;
515 BSS: load = RAM1, type = bss, define = yes;
519 What we are doing here is telling the linker, that all segments go into the
520 <tt/RAM1/ memory area in the order specified in the <tt/SEGMENTS/ section. So
521 the linker will first write the <tt/CODE/ segment, then the <tt/RODATA/
522 segment, then the <tt/DATA/ segment - but it will not write the <tt/BSS/
523 segment. Why? Here enters the segment type: For each segment specified, you may also
524 specify a segment attribute. There are five possible segment attributes:
529 bss means that this is an uninitialized segment
530 zp a zeropage segment
531 overwrite a segment that overwrites (parts of) another one
535 So, because we specified that the segment with the name BSS is of type bss,
536 the linker knows that this is uninitialized data, and will not write it to an
537 output file. This is an important point: For the assembler, the <tt/BSS/
538 segment has no special meaning. You specify, which segments have the bss
539 attribute when linking. This approach is much more flexible than having one
540 fixed bss segment, and is a result of the design decision to supporting an
541 arbitrary segment count.
543 If you specify "<tt/type = bss/" for a segment, the linker will make sure that
544 this segment does only contain uninitialized data (that is, zeroes), and issue
545 a warning if this is not the case.
547 For a <tt/bss/ type segment to be useful, it must be cleared somehow by your
548 program (this happens usually in the startup code - for example the startup
549 code for cc65-generated programs takes care about that). But how does your
550 code know, where the segment starts, and how big it is? The linker is able to
551 give that information, but you must request it. This is, what we're doing with
552 the "<tt/define = yes/" attribute in the <tt/BSS/ definitions. For each
553 segment, where this attribute is true, the linker will export three symbols.
556 __NAME_LOAD__ This is set to the address where the
558 __NAME_RUN__ This is set to the run address of the
559 segment. We will cover run addresses
561 __NAME_SIZE__ This is set to the segment size.
564 Replace <tt/NAME/ by the name of the segment, in the example above, this would
565 be <tt/BSS/. These symbols may be accessed by your code.
567 Now, as we've configured the linker to write the first three segments and
568 create symbols for the last one, there's only one question left: Where does
569 the linker put the data? It would be very convenient to have the data in a
572 <sect1>Output files<p>
574 We don't have any files specified above, and indeed, this is not needed in a
575 simple configuration like the one above. There is an additional attribute
576 "file" that may be specified for a memory area, that gives a file name to
577 write the area data into. If there is no file name given, the linker will
578 assign the default file name. This is "a.out" or the one given with the
579 <tt><ref id="option-o" name="-o"></tt> option on the command line. Since the
580 default behaviour is OK for our purposes, I did not use the attribute in the
581 example above. Let's have a look at it now.
583 The "file" attribute (the keyword may also be written as "FILE" if you like
584 that better) takes a string enclosed in double quotes ('&dquot;') that specifies the
585 file, where the data is written. You may specify the same file several times,
586 in that case the data for all memory areas having this file name is written
587 into this file, in the order of the memory areas defined in the <tt/MEMORY/
588 section. Let's specify some file names in the <tt/MEMORY/ section used above:
592 RAM1: start = $0800, size = $9800, file = %O;
593 ROM1: start = $A000, size = $2000, file = "rom1.bin";
594 RAM2: start = $C000, size = $1000, file = %O;
595 ROM2: start = $E000, size = $2000, file = "rom2.bin";
599 The <tt/%O/ used here is a way to specify the default behaviour explicitly:
600 <tt/%O/ is replaced by a string (including the quotes) that contains the
601 default output name, that is, "a.out" or the name specified with the <tt><ref
602 id="option-o" name="-o"></tt> option on the command line. Into this file, the
603 linker will first write any segments that go into <tt/RAM1/, and will append
604 then the segments for <tt/RAM2/, because the memory areas are given in this
605 order. So, for the RAM areas, nothing has really changed.
607 We've not used the ROM areas, but we will do that below, so we give the file
608 names here. Segments that go into <tt/ROM1/ will be written to a file named
609 "rom1.bin", and segments that go into <tt/ROM2/ will be written to a file
610 named "rom2.bin". The name given on the command line is ignored in both cases.
612 Assigning an empty file name for a memory area will discard the data written
613 to it. This is useful, if the memory area has segments assigned that are empty
614 (for example because they are of type bss). In that case, the linker will
615 create an empty output file. This may be suppressed by assigning an empty file
616 name to that memory area.
618 The <tt/%O/ sequence is also allowed inside a string. So using
622 ROM1: start = $A000, size = $2000, file = "%O-1.bin";
623 ROM2: start = $E000, size = $2000, file = "%O-2.bin";
627 would write two files that start with the name of the output file specified on
628 the command line, with "-1.bin" and "-2.bin" appended respectively. Because
629 '%' is used as an escape char, the sequence "%%" has to be used if a single
630 percent sign is required.
632 <sect1>OVERWRITE segments<p>
634 There are situations when you may wish to overwrite some part (or parts) of a
635 segment with another one. Perhaps you are modifying an OS ROM that has its
636 public subroutines at fixed, well-known addresses, and you want to prevent them
637 from shifting to other locations in memory if your changed code takes less
638 space. Or you are updating a block of code available in binary-only form with
639 fixes that are scattered in various places. Generally, whenever you want to
640 minimize disturbance to an existing code brought on by your updates, OVERWRITE
641 segments are worth considering.
647 RAM: file = "", start = $6000, size = $2000, type=rw;
648 ROM: file = %O, start = $8000, size = $8000, type=ro;
652 Nothing unusual so far, just two memory blocks - one RAM, one ROM. Now let's
653 look at the segment configuration:
657 RAM: load = RAM, type = bss;
658 ORIGINAL: load = ROM, type = ro;
659 FASTCOPY: load = ROM, start=$9000, type = overwrite;
660 JMPPATCH1: load = ROM, start=$f7e8, type = overwrite;
661 DEBUG: load = ROM, start=$8000, type = overwrite;
662 VERSION: load = ROM, start=$e5b7, type = overwrite;
666 Segment named ORIGINAL contains the original code, disassembled or provided in
667 a binary form (i.e. using <tt/.INCBIN/ directive; see the <tt/ca65/ assembler
668 document). Subsequent four segments will be relocated to addresses specified
669 by their "start" attributes ("offset" can also be used) and then will overwrite
670 whatever was at these locations in the ORIGINAL segment. In the end, resulting
671 binary output file will thus contain original data with the exception of four
672 sequences starting at $9000, $f7e8, $8000 and $e5b7, which will sport code from
673 their respective segments. How long these sequences will be depends on the
674 lengths of corresponding segments - they can even overlap, so think what you're
677 Finally, note that OVERWRITE segments should be the final segments loaded to a
678 particular memory area, and that they need at least one of "start" or "offset"
679 attributes specified.
681 <sect1>LOAD and RUN addresses (ROMable code)<p>
683 Let us look now at a more complex example. Say, you've successfully tested
684 your new "Super Operating System" (SOS for short) for the C64, and you
685 will now go and replace the ROMs by your own code. When doing that, you
686 face a new problem: If the code runs in RAM, we need not to care about
687 read/write data. But now, if the code is in ROM, we must care about it.
688 Remember the default segments (you may of course specify your own):
692 RODATA read-only data
694 BSS uninitialized data, read/write
697 Since <tt/BSS/ is not initialized, we must not care about it now, but what
698 about <tt/DATA/? <tt/DATA/ contains initialized data, that is, data that was
699 explicitly assigned a value. And your program will rely on these values on
700 startup. Since there's no way to remember the contents of the data segment,
701 other than storing it into one of the ROMs, we have to put it there. But
702 unfortunately, ROM is not writable, so we have to copy it into RAM before
703 running the actual code.
705 The linker won't copy the data from ROM into RAM for you (this must be done by
706 the startup code of your program), but it has some features that will help you
709 First, you may not only specify a "<tt/load/" attribute for a segment, but
710 also a "<tt/run/" attribute. The "<tt/load/" attribute is mandatory, and, if
711 you don't specify a "<tt/run/" attribute, the linker assumes that load area
712 and run area are the same. We will use this feature for our data area:
716 CODE: load = ROM1, type = ro;
717 RODATA: load = ROM2, type = ro;
718 DATA: load = ROM2, run = RAM2, type = rw, define = yes;
719 BSS: load = RAM2, type = bss, define = yes;
723 Let's have a closer look at this <tt/SEGMENTS/ section. We specify that the
724 <tt/CODE/ segment goes into <tt/ROM1/ (the one at $A000). The readonly data
725 goes into <tt/ROM2/. Read/write data will be loaded into <tt/ROM2/ but is run
726 in <tt/RAM2/. That means that all references to labels in the <tt/DATA/
727 segment are relocated to be in <tt/RAM2/, but the segment is written to
728 <tt/ROM2/. All your startup code has to do is, to copy the data from its
729 location in <tt/ROM2/ to the final location in <tt/RAM2/.
731 So, how do you know, where the data is located? This is the second point,
732 where you get help from the linker. Remember the "<tt/define/" attribute?
733 Since we have set this attribute to true, the linker will define three
734 external symbols for the data segment that may be accessed from your code:
737 __DATA_LOAD__ This is set to the address where the segment
738 is loaded, in this case, it is an address in
740 __DATA_RUN__ This is set to the run address of the segment,
741 in this case, it is an address in RAM2.
742 __DATA_SIZE__ This is set to the segment size.
745 So, what your startup code must do, is to copy <tt/__DATA_SIZE__/ bytes from
746 <tt/__DATA_LOAD__/ to <tt/__DATA_RUN__/ before any other routines are called.
747 All references to labels in the <tt/DATA/ segment are relocated to <tt/RAM2/
748 by the linker, so things will work properly.
750 There's a library subroutine called <tt/copydata/ (in a module named
751 <tt/copydata.s/) that might be used to do actual copying. Be sure to have a
752 look at it's inner workings before using it!
755 <sect1>Other MEMORY area attributes<p>
757 There are some other attributes not covered above. Before starting the
758 reference section, I will discuss the remaining things here.
760 You may request symbols definitions also for memory areas. This may be
761 useful for things like a software stack, or an I/O area.
765 STACK: start = $C000, size = $1000, define = yes;
769 This will define some external symbols that may be used in your code:
772 __STACK_START__ This is set to the start of the memory
773 area, $C000 in this example.
774 __STACK_SIZE__ The size of the area, here $1000.
775 __STACK_LAST__ This is NOT the same as START+SIZE.
776 Instead, it is defined as the first
777 address that is not used by data. If we
778 don't define any segments for this area,
779 the value will be the same as START.
780 __STACK_FILEOFFS__ The binary offset in the output file. This
781 is not defined for relocatable output file
785 A memory section may also have a type. Valid types are
788 ro for readonly memory
789 rw for read/write memory.
792 The linker will assure, that no segment marked as read/write or bss is put
793 into a memory area that is marked as readonly.
795 Unused memory in a memory area may be filled. Use the "<tt/fill = yes/"
796 attribute to request this. The default value to fill unused space is zero. If
797 you don't like this, you may specify a byte value that is used to fill these
798 areas with the "<tt/fillval/" attribute. If there is no "<tt/fillval/"
799 attribute for the segment, the "<tt/fillval/" attribute of the memory area (or
800 its default) is used instead. This means that the value may also be used to
801 fill unfilled areas generated by the assembler's <tt/.ALIGN/ and <tt/.RES/
804 The symbol <tt/%S/ may be used to access the default start address (that is,
805 the one defined in <ref id="FEATURES" name="the FEATURES section">, or the
806 value given on the command line with the <tt><ref id="option-S" name="-S"></tt>
809 To support systems with banked memory, a special attribute named <tt/bank/ is
810 available. The attribute value is an arbitrary 32-bit integer. The assembler
811 has a builtin function named <tt/.BANK/ which may be used with an argument
812 that has a segment reference (for example a symbol). The result of this
813 function is the value of the bank attribute for the run memory area of the
817 <sect1>Other SEGMENT attributes<p>
819 Segments may be aligned to some memory boundary. Specify "<tt/align = num/" to
820 request this feature. To align all segments on a page boundary, use
824 CODE: load = ROM1, type = ro, align = $100;
825 RODATA: load = ROM2, type = ro, align = $100;
826 DATA: load = ROM2, run = RAM2, type = rw, define = yes,
828 BSS: load = RAM2, type = bss, define = yes, align = $100;
832 If an alignment is requested, the linker will add enough space to the output
833 file, so that the new segment starts at an address that is dividable by the
834 given number without a remainder. All addresses are adjusted accordingly. To
835 fill the unused space, bytes of zero are used, or, if the memory area has a
836 "<tt/fillval/" attribute, that value. Alignment is always needed, if you have
837 used the <tt/.ALIGN/ command in the assembler. The alignment of a segment
838 must be equal or greater than the alignment used in the <tt/.ALIGN/ command.
839 The linker will check that, and issue a warning, if the alignment of a segment
840 is lower than the alignment requested in an <tt/.ALIGN/ command of one of the
841 modules making up this segment.
843 For a given segment you may also specify a fixed offset into a memory area or
844 a fixed start address. Use this if you want the code to run at a specific
845 address (a prominent case is the interrupt vector table which must go at
846 address $FFFA). Only one of <tt/ALIGN/ or <tt/OFFSET/ or <tt/START/ may be
847 specified. If the directive creates empty space, it will be filled with zero,
848 of with the value specified with the "<tt/fillval/" attribute if one is given.
849 The linker will warn you if it is not possible to put the code at the
850 specified offset (this may happen if other segments in this area are too
851 large). Here's an example:
855 VECTORS: load = ROM2, type = ro, start = $FFFA;
859 or (for the segment definitions from above)
863 VECTORS: load = ROM2, type = ro, offset = $1FFA;
867 The "<tt/align/", "<tt/start/" and "<tt/offset/" attributes change placement
868 of the segment in the run memory area, because this is what is usually
869 desired. If load and run memory areas are equal (which is the case if only the
870 load memory area has been specified), the attributes will also work. There is
871 also an "<tt/align_load/" attribute that may be used to align the start of the
872 segment in the load memory area, in case different load and run areas have
873 been specified. There are no special attributes to set start or offset for
874 just the load memory area.
876 A "<tt/fillval/" attribute may not only be specified for a memory area, but
877 also for a segment. The value must be an integer between 0 and 255. It is used
878 as the fill value for space reserved by the assembler's <tt/.ALIGN/ and <tt/.RES/
879 commands. It is also used as the fill value for space between sections (part of a
880 segment that comes from one object file) caused by alignment, but not for
881 space that preceeds the first section.
883 To suppress the warning, the linker issues if it encounters a segment that is
884 not found in any of the input files, use "<tt/optional=yes/" as an additional
885 segment attribute. Be careful when using this attribute, because a missing
886 segment may be a sign of a problem, and if you're suppressing the warning,
887 there is no one left to tell you about it.
889 <sect1>The FILES section<p>
891 The <tt/FILES/ section is used to support other formats than straight binary
892 (which is the default, so binary output files do not need an explicit entry
893 in the <tt/FILES/ section).
895 The <tt/FILES/ section lists output files and as only attribute the format of
896 each output file. Assigning binary format to the default output file would
905 There are two other available formats, one is the o65 format specified by Andre
906 Fachat (see the <url url="http://www.6502.org/users/andre/o65/fileformat.html"
907 name="6502 binary relocation format specification">). It is defined like this:
915 The other format available is the Atari (xex) segmented file format, this is
916 the standard format used by Atari DOS 2.0 and upward file managers in the Atari
917 8-bit computers, and it is defined like this:
925 In the Atari segmented file format, the linker will write each <tt/MEMORY/ area
926 as a new segment, including a header with the start and end address.
928 The necessary o65 or Atari attributes are defined in a special section labeled
929 <ref id="FORMAT" name="FORMAT">.
933 <sect1>The FORMAT section<label id="FORMAT"><p>
935 The <tt/FORMAT/ section is used to describe file formats. The default (binary)
936 format has currently no attributes, so, while it may be listed in this
937 section, the attribute list is empty. The second supported format,
938 <url url="http://www.6502.org/users/andre/o65/fileformat.html" name="o65">,
939 has several attributes that may be defined here.
943 o65: os = lunix, version = 0, type = small,
944 import = LUNIXKERNEL,
949 The Atari file format has two attributes:
953 <tag><tt>RUNAD = symbol</tt></tag>
955 Specify a symbol as the run address of the binary, the loader will call this
956 address after all the file is loaded in memory. If the attribute is omitted,
957 no run address is included in the file.
959 <tag><tt>INITAD = memory_area : symbol</tt></tag>
961 Specify a symbol as the initialization address for the given memory area.
962 The binary loader will call this address just after the memory area is loaded
963 into memory, before continuing loading the rest of the file.
970 atari: runad = _start;
975 <sect1>The FEATURES section<label id="FEATURES"><p>
977 In addition to the <tt/MEMORY/ and <tt/SEGMENTS/ sections described above, the
978 linker has features that may be enabled by an additional section labeled
982 <sect2>The CONDES feature<p>
984 <tt/CONDES/ is used to tell the linker to emit module constructor/destructor
989 CONDES: segment = RODATA,
991 label = __CONSTRUCTOR_TABLE__,
992 count = __CONSTRUCTOR_COUNT__;
996 The <tt/CONDES/ feature has several attributes:
1000 <tag><tt>segment</tt></tag>
1002 This attribute tells the linker into which segment the table should be
1003 placed. If the segment does not exist, it is created.
1006 <tag><tt>type</tt></tag>
1008 Describes the type of the routines to place in the table. Type may be one of
1009 the predefined types <tt/constructor/, <tt/destructor/, <tt/interruptor/, or
1010 a numeric value between 0 and 6.
1013 <tag><tt>label</tt></tag>
1015 This specifies the label to use for the table. The label points to the start
1016 of the table in memory and may be used from within user-written code.
1019 <tag><tt>count</tt></tag>
1021 This is an optional attribute. If specified, an additional symbol is defined
1022 by the linker using the given name. The value of this symbol is the number
1023 of entries (<em/not/ bytes) in the table. While this attribute is optional,
1024 it is often useful to define it.
1027 <tag><tt>order</tt></tag>
1029 An optional attribute that takes one of the keywords <tt/increasing/ or
1030 <tt/decreasing/ as an argument. Specifies the sorting order of the entries
1031 within the table. The default is <tt/increasing/, which means that the
1032 entries are sorted with increasing priority (the first entry has the lowest
1033 priority). "Priority" is the priority specified when declaring a symbol as
1034 <tt/.CONDES/ with the assembler, higher values mean higher priority. You may
1035 change this behaviour by specifying <tt/decreasing/ as the argument, the
1036 order of entries is reversed in this case.
1038 Please note that the order of entries with equal priority is undefined.
1040 <tag><tt>import</tt></tag>
1042 This attribute defines a valid symbol name, that is added as an import
1043 to the modules defining a constructor/destructor of the given type.
1044 This can be used to force linkage of a module if this module exports the
1049 Without specifying the <tt/CONDES/ feature, the linker will not create any
1050 tables, even if there are <tt/condes/ entries in the object files.
1052 For more information see the <tt/.CONDES/ command in the <url
1053 url="ca65.html" name="ca65 manual">.
1056 <sect2>The STARTADDRESS feature<p>
1058 <tt/STARTADDRESS/ is used to set the default value for the start address,
1059 which can be referenced by the <tt/%S/ symbol. The builtin default for the
1060 linker is $200.
1064 # Default start address is $1000
1065 STARTADDRESS: default = $1000;
1069 Please note that order is important: The default start address must be defined
1070 <em/before/ the <tt/%S/ symbol is used in the config file. This does usually
1071 mean, that the <tt/FEATURES/ section has to go to the top of the config file.
1075 <sect1>The SYMBOLS section<label id="SYMBOLS"><p>
1077 The configuration file may also be used to define symbols used in the link
1078 stage or to force symbols imports. This is done in the SYMBOLS section. The
1079 symbol name is followed by a colon and symbol attributes.
1081 The following symbol attributes are supported:
1085 <tag><tt>addrsize</tt></tag>
1087 The <tt/addrsize/ attribute specifies the address size of the symbol and
1090 <item><tt/zp/, <tt/zeropage/ or <tt/direct/
1091 <item><tt/abs/, <tt/absolute/ or <tt/near/
1093 <item><tt/long/ or <tt/dword/.
1096 Without this attribute, the default address size is <tt/abs/.
1098 <tag><tt>type</tt></tag>
1100 This attribute is mandatory. Its value is one of <tt/export/, <tt/import/ or
1101 <tt/weak/. <tt/export/ means that the symbol is defined and exported from
1102 the linker config. <tt/import/ means that an import is generated for this
1103 symbol, eventually forcing a module that exports this symbol to be included
1104 in the output. <tt/weak/ is similar as <tt/export/. However, the symbol is
1105 only defined if it is not defined elsewhere.
1107 <tag><tt>value</tt></tag>
1109 This must only be given for symbols of type <tt/export/ or <tt/weak/. It
1110 defines the value of the symbol and may be an expression.
1114 The following example defines the stack size for an application, but allows
1115 the programmer to override the value by specifying <tt/--define
1116 __STACKSIZE__=xxx/ on the command line.
1120 # Define the stack size for the application
1121 __STACKSIZE__: type = weak, value = $800;
1127 <sect>Special segments<p>
1129 The builtin config files do contain segments that have a special meaning for
1130 the compiler and the libraries that come with it. If you replace the builtin
1131 config files, you will need the following information.
1135 The ONCE segment is used for initialization code run only once before
1136 execution reaches main() - provided that the program runs in RAM. You
1137 may for example add the ONCE segment to the heap in really memory
1138 constrained systems.
1142 For the LOWCODE segment, it is guaranteed that it won't be banked out, so it
1143 is reachable at any time by interrupt handlers or similar.
1147 This segment contains the startup code which initializes the C software stack
1148 and the libraries. It is placed in its own segment because it needs to be
1149 loaded at the lowest possible program address on several platforms.
1153 The ZPSAVE segment contains the original values of the zeropage locations used
1154 by the ZEROPAGE segment. It is placed in its own segment because it must not be
1161 ld65 (and all cc65 binutils) are (C) Copyright 1998-2005 Ullrich von
1162 Bassewitz. For usage of the binaries and/or sources the following
1163 conditions do apply:
1165 This software is provided 'as-is', without any expressed or implied
1166 warranty. In no event will the authors be held liable for any damages
1167 arising from the use of this software.
1169 Permission is granted to anyone to use this software for any purpose,
1170 including commercial applications, and to alter it and redistribute it
1171 freely, subject to the following restrictions:
1174 <item> The origin of this software must not be misrepresented; you must not
1175 claim that you wrote the original software. If you use this software
1176 in a product, an acknowledgment in the product documentation would be
1177 appreciated but is not required.
1178 <item> Altered source versions must be plainly marked as such, and must not
1179 be misrepresented as being the original software.
1180 <item> This notice may not be removed or altered from any source