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)
181 There are a few more targets defined but neither of them is actually
185 <tag><tt>-u sym[:addrsize], --force-import sym[:addrsize]</tt></tag>
187 Force an import of a symbol. While object files are always linked to the
188 output file, regardless if there are any references, object modules from
189 libraries get only linked in if an import can be satisfied by this module.
190 The <tt/--force-import/ option may be used to add a reference to a symbol and
191 as a result force linkage of the module that exports the identifier.
193 The name of the symbol may optionally be followed by a colon and an address-size
194 specifier. If no address size is specified, the default address size
195 for the target machine is used.
197 Please note that the symbol name needs to have the internal representation,
198 meaning you have to prepend an underscore for C identifiers.
201 <label id="option-v">
202 <tag><tt>-v, --verbose</tt></tag>
204 Using the -v option, you may enable more output that may help you to
205 locate problems. If an undefined symbol is encountered, -v causes the
206 linker to print a detailed list of the references (that is, source file
207 and line) for this symbol.
210 <tag><tt>-vm</tt></tag>
212 Must be used in conjunction with <tt><ref id="option-m" name="-m"></tt>
213 (generate map file). Normally the map file will not include empty segments
214 and sections, or unreferenced symbols. Using this option, you can force the
215 linker to include all that information into the map file. Also, it will
216 include a second <tt/Exports/ list. The first list is sorted by name;
217 the second one is sorted by value.
220 <label id="option-C">
221 <tag><tt>-C</tt></tag>
223 This gives the name of an output config file to use. See section 4 for more
224 information about config files. -C may not be used together with <tt><ref
225 id="option-t" name="-t"></tt>.
228 <label id="option-D">
229 <tag><tt>-D sym=value, --define sym=value</tt></tag>
231 This option allows to define an external symbol on the command line. Value
232 may start with a '$' sign or with <tt/0x/ for hexadecimal values,
233 otherwise a leading zero denotes octal values. See also <ref
234 id="SYMBOLS" name="the SYMBOLS section"> in the configuration file.
237 <label id="option--lib-path">
238 <tag><tt>-L path, --lib-path path</tt></tag>
240 Specify a library search path. This option may be used more than once. It
241 adds a directory to the search path for library files. Libraries specified
242 without a path are searched in the current directory, in the list of
243 directories specified using <tt/--lib-path/, in directories given by
244 environment variables, and in a built-in default directory.
247 <tag><tt>-Ln</tt></tag>
249 This option allows you to create a file that contains all global labels and
250 may be loaded into the VICE emulator using the <tt/ll/ (load label) command
251 or into the Oricutron emulator using the <tt/sl/ (symbols load) command. You
252 may use this to debug your code with VICE. Note: Older versions had some
253 bugs in the label code. If you have problems, please get the latest <url
254 url="http://vice-emu.sourceforge.net" name="VICE"> version.
257 <label id="option-S">
258 <tag><tt>-S addr, --start-addr addr</tt></tag>
260 Using -S you may define the default starting address. If and how this
261 address is used depends on the config file in use. For the default
262 configurations, only the "none", "apple2" and "apple2enh" systems honor an
263 explicit start address, all other default configs provide their own.
266 <tag><tt>-V, --version</tt></tag>
268 This option prints the version number of the linker. If you send any
269 suggestions or bugfixes, please include this number.
272 <label id="option--cfg-path">
273 <tag><tt>--cfg-path path</tt></tag>
275 Specify a config file search path. This option may be used more than once.
276 It adds a directory to the search path for config files. A config file given
277 with the <tt><ref id="option-C" name="-C"></tt> option that has no path in
278 its name is searched in the current directory, in the list of directories
279 specified using <tt/--cfg-path/, in directories given by environment variables,
280 and in a built-in default directory.
283 <label id="option--dbgfile">
284 <tag><tt>--dbgfile name</tt></tag>
286 Specify an output file for debug information. Available information will be
287 written to this file. Using the <tt/-g/ option for the compiler and assembler
288 will increase the amount of information available. Please note that debug
289 information generation is currently being developed, so the format of the
290 file and its contents are subject to change without further notice.
293 <tag><tt>--lib file</tt></tag>
295 Links a library to the output. Use this command-line option instead of just
296 naming the library file, if the linker is not able to determine the file
297 type because of an unusual extension.
300 <tag><tt>--obj file</tt></tag>
302 Links an object file to the output. Use this command-line option instead
303 of just naming the object file, if the linker is not able to determine the
304 file type because of an unusual extension.
307 <label id="option--obj-path">
308 <tag><tt>--obj-path path</tt></tag>
310 Specify an object file search path. This option may be used more than once.
311 It adds a directory to the search path for object files. An object file
312 passed to the linker that has no path in its name is searched in the current
313 directory, in the list of directories specified using <tt/--obj-path/, in
314 directories given by environment variables, and in a built-in default directory.
320 <sect>Search paths<p>
322 Starting with version 2.10, there are now several search-path lists for files needed
323 by the linker: one for libraries, one for object files, and one for config
327 <sect1>Library search path<p>
329 The library search-path list contains in this order:
332 <item>The current directory.
333 <item>Any directory added with the <tt><ref id="option--lib-path"
334 name="--lib-path"></tt> option on the command line.
335 <item>The value of the environment variable <tt/LD65_LIB/ if it is defined.
336 <item>A subdirectory named <tt/lib/ of the directory defined in the environment
337 variable <tt/CC65_HOME/, if it is defined.
338 <item>An optionally compiled-in library path.
342 <sect1>Object file search path<p>
344 The object file search-path list contains in this order:
347 <item>The current directory.
348 <item>Any directory added with the <tt><ref id="option--obj-path"
349 name="--obj-path"></tt> option on the command line.
350 <item>The value of the environment variable <tt/LD65_OBJ/ if it is defined.
351 <item>A subdirectory named <tt/obj/ of the directory defined in the environment
352 variable <tt/CC65_HOME/, if it is defined.
353 <item>An optionally compiled-in directory.
357 <sect1>Config file search path<p>
359 The config file search-path list contains in this order:
362 <item>The current directory.
363 <item>Any directory added with the <tt><ref id="option--cfg-path"
364 name="--cfg-path"></tt> option on the command line.
365 <item>The value of the environment variable <tt/LD65_CFG/ if it is defined.
366 <item>A subdirectory named <tt/cfg/ of the directory defined in the environment
367 variable <tt/CC65_HOME/, if it is defined.
368 <item>An optionally compiled-in directory.
373 <sect>Detailed workings<p>
375 The linker does several things when combining object modules:
377 First, the command line is parsed from left to right. For each object file
378 encountered (object files are recognized by a magic word in the header, so
379 the linker does not care about the name), imported and exported
380 identifiers are read from the file and inserted in a table. If a library
381 name is given (libraries are also recognized by a magic word, there are no
382 special naming conventions), all modules in the library are checked if an
383 export from this module would satisfy an import from other modules. All
384 modules where this is the case are marked. If duplicate identifiers are
385 found, the linker issues warnings.
387 That procedure (parsing and reading from left to right) does mean that a
388 library may only satisfy references for object modules (given directly or from
389 a library) named <em/before/ that library. With the command line
392 ld65 crt0.o clib.lib test.o
395 the module <tt/test.o/ must not contain references to modules in the library
396 <tt/clib.lib/. But, if it does, you have to change the order of the modules
400 ld65 crt0.o test.o clib.lib
403 Step two is, to read the configuration file, and assign start addresses
404 for the segments and define any linker symbols (see <ref id="config-files"
405 name="Configuration files">).
407 After that, the linker is ready to produce an output file. Before doing that,
408 it checks its data for consistency. That is, it checks for unresolved
409 externals (if the output format is not relocatable) and for symbol type
410 mismatches (for example a zero-page symbol is imported by a module as an absolute
413 Step four is, to write the actual target files. In this step, the linker will
414 resolve any expressions contained in the segment data. Circular references are
415 also detected in this step (a symbol may have a circular reference that goes
416 unnoticed if the symbol is not used).
418 Step five is to output a map file with a detailed list of all modules,
419 segments and symbols encountered.
421 And, last step, if you give the <tt><ref id="option-v" name="-v"></tt> switch
422 twice, you get a dump of the segment data. However, this may be quite
423 unreadable if you're not a developer. :-)
427 <sect>Configuration files<label id="config-files"><p>
429 Configuration files are used to describe the layout of the output file(s). Two
430 major topics are covered in a config file: The memory layout of the target
431 architecture, and the assignment of segments to memory areas. In addition,
432 several other attributes may be specified.
434 Case is ignored for keywords, that is, section or attribute names, but it is
435 <em/not/ ignored for names and strings.
439 <sect1>Memory areas<p>
441 Memory areas are specified in a <tt/MEMORY/ section. Let's have a look at an
442 example (this one describes the usable memory layout of the C64):
446 RAM1: start = $0800, size = $9800;
447 ROM1: start = $A000, size = $2000;
448 RAM2: start = $C000, size = $1000;
449 ROM2: start = $E000, size = $2000;
453 As you can see, there are two RAM areas and two ROM areas. The names
454 (before the colon) are arbitrary names that must start with a letter, with
455 the remaining characters being letters or digits. The names of the memory
456 areas are used when assigning segments. As mentioned above, case is
457 significant for those names.
459 The syntax above is used in all sections of the config file. The name
460 (<tt/ROM1/ etc.) is said to be an identifier, the remaining tokens up to the
461 semicolon specify attributes for this identifier. You may use the equal sign
462 to assign values to attributes, and you may use a comma to separate
463 attributes, you may also leave both out. But you <em/must/ use a semicolon to
464 mark the end of the attributes for one identifier. The section above may also
465 have looked like this:
468 # Start of memory section
486 There are of course more attributes for a memory section than just start and
487 size. Start and size are mandatory attributes, that means, each memory area
488 defined <em/must/ have these attributes given (the linker will check that). I
489 will cover other attributes later. As you may have noticed, I've used a
490 comment in the example above. Comments start with a hash mark ('#'), the
491 remainder of the line is ignored if this character is found.
496 Let's assume you have written a program for your trusty old C64, and you would
497 like to run it. For testing purposes, it should run in the <tt/RAM/ area. So
498 we will start to assign segments to memory sections in the <tt/SEGMENTS/
503 CODE: load = RAM1, type = ro;
504 RODATA: load = RAM1, type = ro;
505 DATA: load = RAM1, type = rw;
506 BSS: load = RAM1, type = bss, define = yes;
510 What we are doing here is telling the linker, that all segments go into the
511 <tt/RAM1/ memory area in the order specified in the <tt/SEGMENTS/ section. So
512 the linker will first write the <tt/CODE/ segment, then the <tt/RODATA/
513 segment, then the <tt/DATA/ segment - but it will not write the <tt/BSS/
514 segment. Why? Here enters the segment type: For each segment specified, you may also
515 specify a segment attribute. There are five possible segment attributes:
520 bss means that this is an uninitialized segment
521 zp a zeropage segment
522 overwrite a segment that overwrites (parts of) another one
526 So, because we specified that the segment with the name BSS is of type bss,
527 the linker knows that this is uninitialized data, and will not write it to an
528 output file. This is an important point: For the assembler, the <tt/BSS/
529 segment has no special meaning. You specify, which segments have the bss
530 attribute when linking. This approach is much more flexible than having one
531 fixed bss segment, and is a result of the design decision to supporting an
532 arbitrary segment count.
534 If you specify "<tt/type = bss/" for a segment, the linker will make sure that
535 this segment does only contain uninitialized data (that is, zeroes), and issue
536 a warning if this is not the case.
538 For a <tt/bss/ type segment to be useful, it must be cleared somehow by your
539 program (this happens usually in the startup code - for example the startup
540 code for cc65-generated programs takes care about that). But how does your
541 code know, where the segment starts, and how big it is? The linker is able to
542 give that information, but you must request it. This is, what we're doing with
543 the "<tt/define = yes/" attribute in the <tt/BSS/ definitions. For each
544 segment, where this attribute is true, the linker will export three symbols.
547 __NAME_LOAD__ This is set to the address where the
549 __NAME_RUN__ This is set to the run address of the
550 segment. We will cover run addresses
552 __NAME_SIZE__ This is set to the segment size.
555 Replace <tt/NAME/ by the name of the segment, in the example above, this would
556 be <tt/BSS/. These symbols may be accessed by your code.
558 Now, as we've configured the linker to write the first three segments and
559 create symbols for the last one, there's only one question left: Where does
560 the linker put the data? It would be very convenient to have the data in a
563 <sect1>Output files<p>
565 We don't have any files specified above, and indeed, this is not needed in a
566 simple configuration like the one above. There is an additional attribute
567 "file" that may be specified for a memory area, that gives a file name to
568 write the area data into. If there is no file name given, the linker will
569 assign the default file name. This is "a.out" or the one given with the
570 <tt><ref id="option-o" name="-o"></tt> option on the command line. Since the
571 default behaviour is OK for our purposes, I did not use the attribute in the
572 example above. Let's have a look at it now.
574 The "file" attribute (the keyword may also be written as "FILE" if you like
575 that better) takes a string enclosed in double quotes ('&dquot;') that specifies the
576 file, where the data is written. You may specify the same file several times,
577 in that case the data for all memory areas having this file name is written
578 into this file, in the order of the memory areas defined in the <tt/MEMORY/
579 section. Let's specify some file names in the <tt/MEMORY/ section used above:
583 RAM1: start = $0800, size = $9800, file = %O;
584 ROM1: start = $A000, size = $2000, file = "rom1.bin";
585 RAM2: start = $C000, size = $1000, file = %O;
586 ROM2: start = $E000, size = $2000, file = "rom2.bin";
590 The <tt/%O/ used here is a way to specify the default behaviour explicitly:
591 <tt/%O/ is replaced by a string (including the quotes) that contains the
592 default output name, that is, "a.out" or the name specified with the <tt><ref
593 id="option-o" name="-o"></tt> option on the command line. Into this file, the
594 linker will first write any segments that go into <tt/RAM1/, and will append
595 then the segments for <tt/RAM2/, because the memory areas are given in this
596 order. So, for the RAM areas, nothing has really changed.
598 We've not used the ROM areas, but we will do that below, so we give the file
599 names here. Segments that go into <tt/ROM1/ will be written to a file named
600 "rom1.bin", and segments that go into <tt/ROM2/ will be written to a file
601 named "rom2.bin". The name given on the command line is ignored in both cases.
603 Assigning an empty file name for a memory area will discard the data written
604 to it. This is useful, if the memory area has segments assigned that are empty
605 (for example because they are of type bss). In that case, the linker will
606 create an empty output file. This may be suppressed by assigning an empty file
607 name to that memory area.
609 The <tt/%O/ sequence is also allowed inside a string. So using
613 ROM1: start = $A000, size = $2000, file = "%O-1.bin";
614 ROM2: start = $E000, size = $2000, file = "%O-2.bin";
618 would write two files that start with the name of the output file specified on
619 the command line, with "-1.bin" and "-2.bin" appended respectively. Because
620 '%' is used as an escape char, the sequence "%%" has to be used if a single
621 percent sign is required.
623 <sect1>OVERWRITE segments<p>
625 There are situations when you may wish to overwrite some part (or parts) of a
626 segment with another one. Perhaps you are modifying an OS ROM that has its
627 public subroutines at fixed, well-known addresses, and you want to prevent them
628 from shifting to other locations in memory if your changed code takes less
629 space. Or you are updating a block of code available in binary-only form with
630 fixes that are scattered in various places. Generally, whenever you want to
631 minimize disturbance to an existing code brought on by your updates, OVERWRITE
632 segments are worth considering.
638 RAM: file = "", start = $6000, size = $2000, type=rw;
639 ROM: file = %O, start = $8000, size = $8000, type=ro;
643 Nothing unusual so far, just two memory blocks - one RAM, one ROM. Now let's
644 look at the segment configuration:
648 RAM: load = RAM, type = bss;
649 ORIGINAL: load = ROM, type = ro;
650 FASTCOPY: load = ROM, start=$9000, type = overwrite;
651 JMPPATCH1: load = ROM, start=$f7e8, type = overwrite;
652 DEBUG: load = ROM, start=$8000, type = overwrite;
653 VERSION: load = ROM, start=$e5b7, type = overwrite;
657 Segment named ORIGINAL contains the original code, disassembled or provided in
658 a binary form (i.e. using <tt/.INCBIN/ directive; see the <tt/ca65/ assembler
659 document). Subsequent four segments will be relocated to addresses specified
660 by their "start" attributes ("offset" can also be used) and then will overwrite
661 whatever was at these locations in the ORIGINAL segment. In the end, resulting
662 binary output file will thus contain original data with the exception of four
663 sequences starting at $9000, $f7e8, $8000 and $e5b7, which will sport code from
664 their respective segments. How long these sequences will be depends on the
665 lengths of corresponding segments - they can even overlap, so think what you're
668 Finally, note that OVERWRITE segments should be the final segments loaded to a
669 particular memory area, and that they need at least one of "start" or "offset"
670 attributes specified.
672 <sect1>LOAD and RUN addresses (ROMable code)<p>
674 Let us look now at a more complex example. Say, you've successfully tested
675 your new "Super Operating System" (SOS for short) for the C64, and you
676 will now go and replace the ROMs by your own code. When doing that, you
677 face a new problem: If the code runs in RAM, we need not to care about
678 read/write data. But now, if the code is in ROM, we must care about it.
679 Remember the default segments (you may of course specify your own):
683 RODATA read-only data
685 BSS uninitialized data, read/write
688 Since <tt/BSS/ is not initialized, we must not care about it now, but what
689 about <tt/DATA/? <tt/DATA/ contains initialized data, that is, data that was
690 explicitly assigned a value. And your program will rely on these values on
691 startup. Since there's no way to remember the contents of the data segment,
692 other than storing it into one of the ROMs, we have to put it there. But
693 unfortunately, ROM is not writable, so we have to copy it into RAM before
694 running the actual code.
696 The linker won't copy the data from ROM into RAM for you (this must be done by
697 the startup code of your program), but it has some features that will help you
700 First, you may not only specify a "<tt/load/" attribute for a segment, but
701 also a "<tt/run/" attribute. The "<tt/load/" attribute is mandatory, and, if
702 you don't specify a "<tt/run/" attribute, the linker assumes that load area
703 and run area are the same. We will use this feature for our data area:
707 CODE: load = ROM1, type = ro;
708 RODATA: load = ROM2, type = ro;
709 DATA: load = ROM2, run = RAM2, type = rw, define = yes;
710 BSS: load = RAM2, type = bss, define = yes;
714 Let's have a closer look at this <tt/SEGMENTS/ section. We specify that the
715 <tt/CODE/ segment goes into <tt/ROM1/ (the one at $A000). The readonly data
716 goes into <tt/ROM2/. Read/write data will be loaded into <tt/ROM2/ but is run
717 in <tt/RAM2/. That means that all references to labels in the <tt/DATA/
718 segment are relocated to be in <tt/RAM2/, but the segment is written to
719 <tt/ROM2/. All your startup code has to do is, to copy the data from its
720 location in <tt/ROM2/ to the final location in <tt/RAM2/.
722 So, how do you know, where the data is located? This is the second point,
723 where you get help from the linker. Remember the "<tt/define/" attribute?
724 Since we have set this attribute to true, the linker will define three
725 external symbols for the data segment that may be accessed from your code:
728 __DATA_LOAD__ This is set to the address where the segment
729 is loaded, in this case, it is an address in
731 __DATA_RUN__ This is set to the run address of the segment,
732 in this case, it is an address in RAM2.
733 __DATA_SIZE__ This is set to the segment size.
736 So, what your startup code must do, is to copy <tt/__DATA_SIZE__/ bytes from
737 <tt/__DATA_LOAD__/ to <tt/__DATA_RUN__/ before any other routines are called.
738 All references to labels in the <tt/DATA/ segment are relocated to <tt/RAM2/
739 by the linker, so things will work properly.
741 There's a library subroutine called <tt/copydata/ (in a module named
742 <tt/copydata.s/) that might be used to do actual copying. Be sure to have a
743 look at it's inner workings before using it!
746 <sect1>Other MEMORY area attributes<p>
748 There are some other attributes not covered above. Before starting the
749 reference section, I will discuss the remaining things here.
751 You may request symbols definitions also for memory areas. This may be
752 useful for things like a software stack, or an I/O area.
756 STACK: start = $C000, size = $1000, define = yes;
760 This will define some external symbols that may be used in your code:
763 __STACK_START__ This is set to the start of the memory
764 area, $C000 in this example.
765 __STACK_SIZE__ The size of the area, here $1000.
766 __STACK_LAST__ This is NOT the same as START+SIZE.
767 Instead, it is defined as the first
768 address that is not used by data. If we
769 don't define any segments for this area,
770 the value will be the same as START.
771 __STACK_FILEOFFS__ The binary offset in the output file. This
772 is not defined for relocatable output file
776 A memory section may also have a type. Valid types are
779 ro for readonly memory
780 rw for read/write memory.
783 The linker will assure, that no segment marked as read/write or bss is put
784 into a memory area that is marked as readonly.
786 Unused memory in a memory area may be filled. Use the "<tt/fill = yes/"
787 attribute to request this. The default value to fill unused space is zero. If
788 you don't like this, you may specify a byte value that is used to fill these
789 areas with the "<tt/fillval/" attribute. If there is no "<tt/fillval/"
790 attribute for the segment, the "<tt/fillval/" attribute of the memory area (or
791 its default) is used instead. This means that the value may also be used to
792 fill unfilled areas generated by the assembler's <tt/.ALIGN/ and <tt/.RES/
795 The symbol <tt/%S/ may be used to access the default start address (that is,
796 the one defined in <ref id="FEATURES" name="the FEATURES section">, or the
797 value given on the command line with the <tt><ref id="option-S" name="-S"></tt>
800 To support systems with banked memory, a special attribute named <tt/bank/ is
801 available. The attribute value is an arbitrary 32-bit integer. The assembler
802 has a builtin function named <tt/.BANK/ which may be used with an argument
803 that has a segment reference (for example a symbol). The result of this
804 function is the value of the bank attribute for the run memory area of the
808 <sect1>Other SEGMENT attributes<p>
810 Segments may be aligned to some memory boundary. Specify "<tt/align = num/" to
811 request this feature. Num must be a power of two. To align all segments on a
816 CODE: load = ROM1, type = ro, align = $100;
817 RODATA: load = ROM2, type = ro, align = $100;
818 DATA: load = ROM2, run = RAM2, type = rw, define = yes,
820 BSS: load = RAM2, type = bss, define = yes, align = $100;
824 If an alignment is requested, the linker will add enough space to the output
825 file, so that the new segment starts at an address that is dividable by the
826 given number without a remainder. All addresses are adjusted accordingly. To
827 fill the unused space, bytes of zero are used, or, if the memory area has a
828 "<tt/fillval/" attribute, that value. Alignment is always needed, if you have
829 used the <tt/.ALIGN/ command in the assembler. The alignment of a segment
830 must be equal or greater than the alignment used in the <tt/.ALIGN/ command.
831 The linker will check that, and issue a warning, if the alignment of a segment
832 is lower than the alignment requested in an <tt/.ALIGN/ command of one of the
833 modules making up this segment.
835 For a given segment you may also specify a fixed offset into a memory area or
836 a fixed start address. Use this if you want the code to run at a specific
837 address (a prominent case is the interrupt vector table which must go at
838 address $FFFA). Only one of <tt/ALIGN/ or <tt/OFFSET/ or <tt/START/ may be
839 specified. If the directive creates empty space, it will be filled with zero,
840 of with the value specified with the "<tt/fillval/" attribute if one is given.
841 The linker will warn you if it is not possible to put the code at the
842 specified offset (this may happen if other segments in this area are too
843 large). Here's an example:
847 VECTORS: load = ROM2, type = ro, start = $FFFA;
851 or (for the segment definitions from above)
855 VECTORS: load = ROM2, type = ro, offset = $1FFA;
859 The "<tt/align/", "<tt/start/" and "<tt/offset/" attributes change placement
860 of the segment in the run memory area, because this is what is usually
861 desired. If load and run memory areas are equal (which is the case if only the
862 load memory area has been specified), the attributes will also work. There is
863 also an "<tt/align_load/" attribute that may be used to align the start of the
864 segment in the load memory area, in case different load and run areas have
865 been specified. There are no special attributes to set start or offset for
866 just the load memory area.
868 A "<tt/fillval/" attribute may not only be specified for a memory area, but
869 also for a segment. The value must be an integer between 0 and 255. It is used
870 as the fill value for space reserved by the assembler's <tt/.ALIGN/ and <tt/.RES/
871 commands. It is also used as the fill value for space between sections (part of a
872 segment that comes from one object file) caused by alignment, but not for
873 space that preceeds the first section.
875 To suppress the warning, the linker issues if it encounters a segment that is
876 not found in any of the input files, use "<tt/optional=yes/" as an additional
877 segment attribute. Be careful when using this attribute, because a missing
878 segment may be a sign of a problem, and if you're suppressing the warning,
879 there is no one left to tell you about it.
881 <sect1>The FILES section<p>
883 The <tt/FILES/ section is used to support other formats than straight binary
884 (which is the default, so binary output files do not need an explicit entry
885 in the <tt/FILES/ section).
887 The <tt/FILES/ section lists output files and as only attribute the format of
888 each output file. Assigning binary format to the default output file would
897 There are two other available formats, one is the o65 format specified by Andre
898 Fachat (see the <url url="http://www.6502.org/users/andre/o65/fileformat.html"
899 name="6502 binary relocation format specification">). It is defined like this:
907 The other format available is the Atari (xex) segmented file format, this is
908 the standard format used by Atari DOS 2.0 and upward file managers in the Atari
909 8-bit computers, and it is defined like this:
917 In the Atari segmented file format, the linker will write each <tt/MEMORY/ area
918 as a new segment, including a header with the start and end address.
920 The necessary o65 or Atari attributes are defined in a special section labeled
921 <ref id="FORMAT" name="FORMAT">.
925 <sect1>The FORMAT section<label id="FORMAT"><p>
927 The <tt/FORMAT/ section is used to describe file formats. The default (binary)
928 format has currently no attributes, so, while it may be listed in this
929 section, the attribute list is empty. The second supported format,
930 <url url="http://www.6502.org/users/andre/o65/fileformat.html" name="o65">,
931 has several attributes that may be defined here.
935 o65: os = lunix, version = 0, type = small,
936 import = LUNIXKERNEL,
941 The Atari file format has only one attribute, <tt/RUNAD/ that allows to specify
942 a symbol as the run address of the binary. If the attribute is omiteed, no run
943 address is specified.
947 atari: runad = _start;
952 <sect1>The FEATURES section<label id="FEATURES"><p>
954 In addition to the <tt/MEMORY/ and <tt/SEGMENTS/ sections described above, the
955 linker has features that may be enabled by an additional section labeled
959 <sect2>The CONDES feature<p>
961 <tt/CONDES/ is used to tell the linker to emit module constructor/destructor
966 CONDES: segment = RODATA,
968 label = __CONSTRUCTOR_TABLE__,
969 count = __CONSTRUCTOR_COUNT__;
973 The <tt/CONDES/ feature has several attributes:
977 <tag><tt>segment</tt></tag>
979 This attribute tells the linker into which segment the table should be
980 placed. If the segment does not exist, it is created.
983 <tag><tt>type</tt></tag>
985 Describes the type of the routines to place in the table. Type may be one of
986 the predefined types <tt/constructor/, <tt/destructor/, <tt/interruptor/, or
987 a numeric value between 0 and 6.
990 <tag><tt>label</tt></tag>
992 This specifies the label to use for the table. The label points to the start
993 of the table in memory and may be used from within user-written code.
996 <tag><tt>count</tt></tag>
998 This is an optional attribute. If specified, an additional symbol is defined
999 by the linker using the given name. The value of this symbol is the number
1000 of entries (<em/not/ bytes) in the table. While this attribute is optional,
1001 it is often useful to define it.
1004 <tag><tt>order</tt></tag>
1006 An optional attribute that takes one of the keywords <tt/increasing/ or
1007 <tt/decreasing/ as an argument. Specifies the sorting order of the entries
1008 within the table. The default is <tt/increasing/, which means that the
1009 entries are sorted with increasing priority (the first entry has the lowest
1010 priority). "Priority" is the priority specified when declaring a symbol as
1011 <tt/.CONDES/ with the assembler, higher values mean higher priority. You may
1012 change this behaviour by specifying <tt/decreasing/ as the argument, the
1013 order of entries is reversed in this case.
1015 Please note that the order of entries with equal priority is undefined.
1017 <tag><tt>import</tt></tag>
1019 This attribute defines a valid symbol name, that is added as an import
1020 to the modules defining a constructor/destructor of the given type.
1021 This can be used to force linkage of a module if this module exports the
1026 Without specifying the <tt/CONDES/ feature, the linker will not create any
1027 tables, even if there are <tt/condes/ entries in the object files.
1029 For more information see the <tt/.CONDES/ command in the <url
1030 url="ca65.html" name="ca65 manual">.
1033 <sect2>The STARTADDRESS feature<p>
1035 <tt/STARTADDRESS/ is used to set the default value for the start address,
1036 which can be referenced by the <tt/%S/ symbol. The builtin default for the
1037 linker is $200.
1041 # Default start address is $1000
1042 STARTADDRESS: default = $1000;
1046 Please note that order is important: The default start address must be defined
1047 <em/before/ the <tt/%S/ symbol is used in the config file. This does usually
1048 mean, that the <tt/FEATURES/ section has to go to the top of the config file.
1052 <sect1>The SYMBOLS section<label id="SYMBOLS"><p>
1054 The configuration file may also be used to define symbols used in the link
1055 stage or to force symbols imports. This is done in the SYMBOLS section. The
1056 symbol name is followed by a colon and symbol attributes.
1058 The following symbol attributes are supported:
1062 <tag><tt>addrsize</tt></tag>
1064 The <tt/addrsize/ attribute specifies the address size of the symbol and
1067 <item><tt/zp/, <tt/zeropage/ or <tt/direct/
1068 <item><tt/abs/, <tt/absolute/ or <tt/near/
1070 <item><tt/long/ or <tt/dword/.
1073 Without this attribute, the default address size is <tt/abs/.
1075 <tag><tt>type</tt></tag>
1077 This attribute is mandatory. Its value is one of <tt/export/, <tt/import/ or
1078 <tt/weak/. <tt/export/ means that the symbol is defined and exported from
1079 the linker config. <tt/import/ means that an import is generated for this
1080 symbol, eventually forcing a module that exports this symbol to be included
1081 in the output. <tt/weak/ is similar as <tt/export/. However, the symbol is
1082 only defined if it is not defined elsewhere.
1084 <tag><tt>value</tt></tag>
1086 This must only be given for symbols of type <tt/export/ or <tt/weak/. It
1087 defines the value of the symbol and may be an expression.
1091 The following example defines the stack size for an application, but allows
1092 the programmer to override the value by specifying <tt/--define
1093 __STACKSIZE__=xxx/ on the command line.
1097 # Define the stack size for the application
1098 __STACKSIZE__: type = weak, value = $800;
1104 <sect>Special segments<p>
1106 The builtin config files do contain segments that have a special meaning for
1107 the compiler and the libraries that come with it. If you replace the builtin
1108 config files, you will need the following information.
1112 The ONCE segment is used for initialization code run only once before
1113 execution reaches main() - provided that the program runs in RAM. You
1114 may for example add the ONCE segment to the heap in really memory
1115 constrained systems.
1119 For the LOWCODE segment, it is guaranteed that it won't be banked out, so it
1120 is reachable at any time by interrupt handlers or similar.
1124 This segment contains the startup code which initializes the C software stack
1125 and the libraries. It is placed in its own segment because it needs to be
1126 loaded at the lowest possible program address on several platforms.
1130 The ZPSAVE segment contains the original values of the zeropage locations used
1131 by the ZEROPAGE segment. It is placed in its own segment because it must not be
1138 ld65 (and all cc65 binutils) are (C) Copyright 1998-2005 Ullrich von
1139 Bassewitz. For usage of the binaries and/or sources the following
1140 conditions do apply:
1142 This software is provided 'as-is', without any expressed or implied
1143 warranty. In no event will the authors be held liable for any damages
1144 arising from the use of this software.
1146 Permission is granted to anyone to use this software for any purpose,
1147 including commercial applications, and to alter it and redistribute it
1148 freely, subject to the following restrictions:
1151 <item> The origin of this software must not be misrepresented; you must not
1152 claim that you wrote the original software. If you use this software
1153 in a product, an acknowledgment in the product documentation would be
1154 appreciated but is not required.
1155 <item> Altered source versions must be plainly marked as such, and must not
1156 be misrepresented as being the original software.
1157 <item> This notice may not be removed or altered from any source