<article>
<title>ld65 Users Guide
<author><url url="mailto:uz@cc65.org" name="Ullrich von Bassewitz">
-<date>2014-04-20
<abstract>
The ld65 linker combines object files into an executable file. ld65 is highly
-m name Create a map file
-o name Name the default output file
-t sys Set the target system
- -u sym Force an import of symbol `sym'
+ -u sym Force an import of symbol 'sym'
-v Verbose mode
-vm Verbose map file
--dbgfile name Generate debug information
--define sym=val Define a symbol
--end-group End a library group
- --force-import sym Force an import of symbol `sym'
+ --force-import sym Force an import of symbol 'sym'
--help Help (this text)
--lib file Link this library
--lib-path path Specify a library search path
<item>sim6502
<item>sim65c02
<item>supervision
+ <item>telestrat
<item>vic20
</itemize>
size. Start and size are mandatory attributes, that means, each memory area
defined <em/must/ have these attributes given (the linker will check that). I
will cover other attributes later. As you may have noticed, I've used a
-comment in the example above. Comments start with a hash mark (`#'), the
+comment in the example above. Comments start with a hash mark ('#'), the
remainder of the line is ignored if this character is found.
the linker will first write the <tt/CODE/ segment, then the <tt/RODATA/
segment, then the <tt/DATA/ segment - but it will not write the <tt/BSS/
segment. Why? Here enters the segment type: For each segment specified, you may also
-specify a segment attribute. There are four possible segment attributes:
+specify a segment attribute. There are five possible segment attributes:
<tscreen><verb>
- ro means readonly
- rw means read/write
- bss means that this is an uninitialized segment
- zp a zeropage segment
+ ro means readonly
+ rw means read/write
+ bss means that this is an uninitialized segment
+ zp a zeropage segment
+ overwrite a segment that overwrites (parts of) another one
+
</verb></tscreen>
So, because we specified that the segment with the name BSS is of type bss,
example above. Let's have a look at it now.
The "file" attribute (the keyword may also be written as "FILE" if you like
-that better) takes a string enclosed in double quotes (`&dquot;') that specifies the
+that better) takes a string enclosed in double quotes ('&dquot;') that specifies the
file, where the data is written. You may specify the same file several times,
in that case the data for all memory areas having this file name is written
into this file, in the order of the memory areas defined in the <tt/MEMORY/
'%' is used as an escape char, the sequence "%%" has to be used if a single
percent sign is required.
+<sect1>OVERWRITE segments<p>
+
+There are situations when you may wish to overwrite some part (or parts) of a
+segment with another one. Perhaps you are modifying an OS ROM that has its
+public subroutines at fixed, well-known addresses, and you want to prevent them
+from shifting to other locations in memory if your changed code takes less
+space. Or you are updating a block of code available in binary-only form with
+fixes that are scattered in various places. Generally, whenever you want to
+minimize disturbance to an existing code brought on by your updates, OVERWRITE
+segments are worth considering.
+
+Here is an example:
+
+<tscreen><verb>
+MEMORY {
+ RAM: file = "", start = $6000, size = $2000, type=rw;
+ ROM: file = %O, start = $8000, size = $8000, type=ro;
+}
+</verb></tscreen>
+
+Nothing unusual so far, just two memory blocks - one RAM, one ROM. Now let's
+look at the segment configuration:
+
+<tscreen><verb>
+SEGMENTS {
+ RAM: load = RAM, type = bss;
+ ORIGINAL: load = ROM, type = ro;
+ FASTCOPY: load = ROM, start=$9000, type = overwrite;
+ JMPPATCH1: load = ROM, start=$f7e8, type = overwrite;
+ DEBUG: load = ROM, start=$8000, type = overwrite;
+ VERSION: load = ROM, start=$e5b7, type = overwrite;
+}
+</verb></tscreen>
+
+Segment named ORIGINAL contains the original code, disassembled or provided in
+a binary form (i.e. using <tt/.INCBIN/ directive; see the <tt/ca65/ assembler
+document). Subsequent four segments will be relocated to addresses specified
+by their "start" attributes ("offset" can also be used) and then will overwrite
+whatever was at these locations in the ORIGINAL segment. In the end, resulting
+binary output file will thus contain original data with the exception of four
+sequences starting at $9000, $f7e8, $8000 and $e5b7, which will sport code from
+their respective segments. How long these sequences will be depends on the
+lengths of corresponding segments - they can even overlap, so think what you're
+doing.
+
+Finally, note that OVERWRITE segments should be the final segments loaded to a
+particular memory area, and that they need at least one of "start" or "offset"
+attributes specified.
+
<sect1>LOAD and RUN addresses (ROMable code)<p>
Let us look now at a more complex example. Say, you've successfully tested
}
</verb></tscreen>
-The only other available output format is the o65 format specified by Andre
+There are two other available formats, one is the o65 format specified by Andre
Fachat (see the <url url="http://www.6502.org/users/andre/o65/fileformat.html"
name="6502 binary relocation format specification">). It is defined like this:
}
</verb></tscreen>
-The necessary o65 attributes are defined in a special section labeled
+The other format available is the Atari (xex) segmented file format, this is
+the standard format used by Atari DOS 2.0 and upward file managers in the Atari
+8-bit computers, and it is defined like this:
+
+<tscreen><verb>
+ FILES {
+ %O: format = atari;
+ }
+</verb></tscreen>
+
+In the Atari segmented file format, the linker will write each <tt/MEMORY/ area
+as a new segment, including a header with the start and end address.
+
+The necessary o65 or Atari attributes are defined in a special section labeled
<ref id="FORMAT" name="FORMAT">.
}
</verb></tscreen>
+The Atari file format has only one attribute, <tt/RUNAD/ that allows to specify
+a symbol as the run address of the binary. If the attribute is omiteed, no run
+address is specified.
+
+<tscreen><verb>
+ FORMATS {
+ atari: runad = _start;
+ }
+</verb></tscreen>
<sect1>The FEATURES section<label id="FEATURES"><p>
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